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Glossary |
This page provides explanations of many terms and acronyms used throughout the website. Select the beginning letter of the word or acronym to go to that portion of the glossary.
The content of the glossary is based on Newton's Telecom Dictionary.
The explanations in this glossary are for reference only. No warranty is given by PCCW Global on the content.
The term access minutes or access minutes of use is used by NECA (the National Exchange Carrier Association) and the FCC (the Federal Communications Commission) in measuring traffic between LATA (Local Access and Transport Area) service providers (CLECs, competitive local exchange carriers, or ILECs, incumbent local exchange carriers) and IXCs (IntereXchange Carriers). The formal definition is "Access Minutes or Access Minutes of Use is that usage of exchange facilities in interstate or foreign service for the purpose of calculating chargeable usage. On the originating end of an interstate or foreign call, usage is to be measured from the time the originating end user's call is delivered by the telephone company and acknowledged as received by the interexchange carrier's facilities connected with the originating exchange. On the terminating end of an interstate or foreign call, usage is to be measured from the time the call is received by the end user in the terminating exchange. Timing of usage at both the originating and terminating end of an interstate or foreign call shall terminate when the calling or called party disconnects, whichever event is recognized first in the originating or terminating end exchanges, as applicable." This comes from the FCC's 69.2 definitions.
A Local Exchange Carrier (LEC) switching system that provides concentration and distribution for originating and/or terminating traffic between a LEC end office network and IXC (interexchange carriers) POPs (point of presences). In short, a distinct type of local phone company switching system specifically designed to provide access between the local exchange network and the interexchange networks for long-distance carriers in that area. The access tandem provides the interexchange carrier with access to multiple end offices within the LATA. More than one access tandem may be needed to provide access to all end offices within any given LATA (Local Access and Transport Area). Currently, the access tandem function may be in the form of a physical and logical partition of a LEC Central Office switch, which also serves end users for purposes of satisfying local calling requirements. Additionally, the IXC may extend the reach of the POP (point of presence) through a high-speed channel extension via dedicated circuits, thereby achieving interconnection with the LEC though collocation of termination facilities in the LEC CO (central office). In short, the access tandem is the switching system that provides distribution for originating or terminating traffic between end offices and the interexchange carrier's point-of-termination. An access tandem is also used to distribute originating or terminating traffic between a CLEC (competitive local exchange carrier) end office and an intraLATA toll point or an interexchange carrier's point of termination.
To make something active. To make it work. The process of enabling a subscriber device for network access and privileges on behalf of a registered account -- e.g. a customer or an internal user. The word "activation" is commonly heard in reference to cell phones, also called mobiles. For a cellular phone to be "activated," the cell phone carrier's system must be informed of the combination of the subscriber's telephone number and the mobile's phone's Electronic Serial Number (ESN). This information is usually entered into the cellular provider's operations computer system. Once this information has been entered, the phone can place and receive calls.
Advanced Encryption Standard. An ultra-strong standard for encryption adopted by the U.S. Government in 2001. AES is replacing the older DES (Data Encryption Standard), a standard developed by IBM in 1977 and thought to be virtually uncrackable until 1997. The AES standard specifies the Rijndael algorithm, a symmetric block cipher that can process data blocks of 128 bits using cipher keys with lengths of 128, 192 and 256 bits. AES is explained in this document http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf. See also Block Cipher, DES, Encryption, and Private Key.
Air interface is a cellular industry term. It refers to the system that ensures compatibility between subscriber terminal equipment (i.e. cell phones and PDAs) and base stations. It involves the specification of channel frequencies and widths, modulation, power and power sensitivity levels, and data framing. The system also selects which radio channels are employed during a call. Air interface is the standard operating system of a mobile network. A four-layer protocol stack which ensures compatibility between terminal equipment and base stations, or hubs, through the development of a standard. In terms of the OSI Reference Model, the layers include the Physical (PHY), the Media Access Control (MAC) layer, the Data Link Control (DLC) layer, and the Network layer. The PHY layer specifies radio characteristics such as channel frequencies and widths, modulation schemes, power and power sensitivity levels, and data framing. The MAC layer, which cuts across the PHY and DLC layers, specifies the procedures by which the wireless terminal and the base station negotiate selection of the radio channel to be employed. The DLC layer specifies the manner in which the frames are sequenced, and the mechanism used to ensure their integrity during transmission. The Network layer specifies the mechanism used to identify and authenticate the wireless terminal to the base station. Air interfaces are specified for technologies such as AMPS (Advanced Mobile Phone System), CDMA (Code Division Multiple Access), DECT (Digital European Cordless Telecommunications), GSM (Global System for Mobile Communications), PCS (Personal Telecommunications Services), and PWT (Personal Wireless Telecommunications), and TDMA (Time Division Multiple Access). See also AMPS, CDMA, DECT, GSM, OSI Reference Model, PCS, PWT and TDMA.
A way of sending signals -- voice, video, data -- in which the transmitted signal is analogous to the original signal. In other words, if you spoke into a microphone and saw your voice on an oscilloscope and you took the same voice as it was transmitted on the phone line and displayed that signal onto the oscilloscope, the two signals would look essentially the same. The only difference would be that the electrically transmitted signal would be at a higher frequency. Most transmission is now done digitally. In some countries (e.g. the U.S.), analogue is spelled analog.
Automatic Number Identification. A calls B. When B's phone rings, he sees A's phone displayed on his telephone's screen (assuming his phone has a screen). ANI sends the number through the network. The number sent is the caller's billing number (BN), not necessarily the exact phone line. An example: Someone calls me from behind a PBX. The number I'll see on my screen will most likely be the company's main number, not the line the caller is on. For example, I might see 515-219-5000 (the main number), not 515-219-5345 the actual line the caller used. This sometimes makes it hard to figure who from the company called me. ANI originally was intended exclusively for the use of the long distance and local phone carriers for billing purposes. ANI information is sent through the network, from the originating central office, through all intermediate tandem offices, to the terminating central office. The information originally was sent over analog trunks in the form of DTMF (Dual Tone MultiFrequency) signals. Now networks pass the information through the digital SS7 (Signaling System 7) network. For some years, ANI has been available to end users. In order to gain access to ANI data, you must have a "trunk side" connection, which carries an additional charge. Much like CLID (Calling Line IDentification), ANI delivers the number of the calling party. Unlike CLID, ANI does not depend on the presence of SS7 throughout the entire network. Also unlike CLID, ANI information cannot be blocked by the calling party. So, let's pretend that you are running a large call center. A customer calls you. Before the call is even connected to your ACD (Automatic Call Distributor), ANI presents the BN of the calling party to the ACD. Your ACD captures the BN, dips into a computer database and matches that number with the profile of the caller. As your telephone agent answers the call, he gets a "screen pop" with information about the caller, and he answers the call with "Good morning, Mr. Newton. This is Ray. I read about ANI in your Dictionary. Isn't it wonderful!" Some large users say they save as much as 30 seconds on the average IN-WATS call by knowing the phone number of the person calling them and being able to use that information to access information about them in the company database. They avoid asking regular customers for routine identification information (like their address and phone number) since it is all there in the database. See also Caller ID, CLASS, Common Channel Signaling, DNIS, Flex ANI, ISDN and ISUP.
Additional Point Of Termination. The significance of APOT is that in the CLEC (competitive local exchange) environment APOT is a requirement to submit LSR (line service request) orders for collocation. These are some requirements that apply to APOT from Bell's point of view: APOT= Location "A" tie down information; CFA= Location "Z" tie down information; ACTL= Location "A" CLLI; LST= Location "Z" CLLI. (Common Language Location Identifier).
A software program that carries out some useful task. Database managers, spreadsheets, communications packages, graphics programs and word processors are all applications. Applications run on top of operating systems like Windows, Linux, Unix, or the Mac OS.
Autonomous System Boundary Router. ABR located between an OSPF (Open Shortest Path First) autonomous system and a non-OSPF network. ASBRs run both OSPF and another routing protocol, such as RIP. ASBRs must reside in a nonstub OSPF area. See also ABR, nonstub area, and OSPF.
Three or more people speaking to each other over some form of telecommunications circuit or circuits. There are a million ways of doing an audioconference, beginning with something simple like several people huddled around a speakerphone, to using sophisticated pricey conferencing devices that amplify, balance and remove static and allow thousands of people to listen and (God forbid) talk at the same time. An audioconference used to be called a teleconference, but now that word tends to include video.
The process whereby a user, information source, or simply information proves they are who they claim to be. In other words, the process of determining the identify of a user attempting to access a network and/or computer system. I believed that defining authentication was pretty simple until I came across the following definition in a book on cryptography. Here it is: Authentication is any technique enabling the receiver to automatically identify and reject messages that have been altered deliberately or by channel errors. Also, can be used to provide positive identification of the sender of a message although secret (symmetric) key algorithms may be used for some authentication without the prior sharing of any secrets between the messaging parties. See Authentication Token
Light reflected from the cleaved or polished end of a fiber caused by the difference of refractive indices of air and glass. Typically 4% of the incident light. Expressed in dB relative to incident power. See also narcissus.
The backbone is that part of the communications network which carries the heaviest traffic. The backbone is also that part of a network which joins LANs (local area networks) together -- either inside a building or across a city or the country. LANs are connected to the backbone via bridges and/or routers and the backbone serves as a communications highway for LAN-to-LAN traffic. The backbone is one basis for design of the overall network service. The backbone may be the more permanent part of the network. A backbone in a LAN, a WAN, or a combination of both is dedicated to providing connectivity between subnetworks in an enterprise-wide network.
Backhaul is a verb. A communications channel is back hauling when it takes traffic beyond its destination and back. There are many reasons it might do this. The first is that it may be cheaper to go that route instead of going directly. You might, for example, have a full-time private line from New York to Dallas. You might find it cheaper to reach Nashville by going to Dallas first, then going back to Nashville. The economics of backhauling may change from one moment to another as the line to Dallas is empty, close to full or full. Another reason for backhauling is that you may do it to accommodate changes in your calling or staffing patterns. You may have an automatic call distributor in Omaha and one in Chicago. A call from New York may come into your Omaha ACD, but when it gets there you may discover that there are no agents available to handle the call. So it may now make sense to backhaul the call to the Chicago ACD, where an agent is available. In fiber networks, backhauling is a traffic management technique used to reduce the expense of multiplexing/demultiplexing.
A copy of computer data on an external storage medium, such as a CD, DVD, tape, hard drive or array of hard drives. Computers and telephone systems (which are computers) are unreliable. They glitch and lose data for all sorts of unusual and impossible-to-predict reasons. Hence, the necessity for backups. The theory is that when, not if, a glitch occurs, the computer data (e.g. the PBX's database) will disappear off the face of the earth. If this happens, and you have a backup, simply retrieve it, load it up and, presto, you're back live. Only information changed since the backup was made is lost. But you lose less information, the more often you backup. Backups save time in restoring the system after a loss. Most PBXs work with a database and other extensive customized instructions the user loads in. Most PBX users forget to make and keep backups of their PBX data. They expect their vendor to make backups, but he rarely does. This carelessness costs weeks of aggravation, as the PBX's database and instruction set is manually (and painfully) put back together.
The method by which backups are maintained is also important. The medium should clearly be reliable, i.e. the best quality magnetic medium. The method of backing up is also important. For example, a streaming tape backup is less reliable than a file-by-file backup. In a streaming backup, the backup medium simply captures the original data one bit after another in one long stream. In a file-by-file backup, the data moves over in logical segments -- command files, data files, etc. Streaming backups will work if their data is placed back on the same precise device from which they were originally taken. But, if they are placed on a different device (even though the same model number, etc.), they may barf because the tape assumes bad sectors are in the same place. This will probably not be true. Streaming tape backup devices are less expensive to buy and much faster to use. Avoid them. These days I prefer to back everything up on multiple hard drives. They're cheap and ultra-reliable.
A term for a Quality of Service (QoS) class with no specified parameters and with no assurances that the traffic will be delivered across the network to the target device. ATM's ABR (Available Bit Rate) and UBR (Unspecified Bit Rate) are both best-effort service examples.
Broadband Global Area Network. Think of a satellite providing 432,000 bits per second access to the Internet anywhere in the world. That's a broadband global area network. Inmarsat has such a service. You can send and receive voice, video and text pretty well to and from anywhere in the world. Industries like oil and gas, mining, disaster aid services are candidates for BGAN.
Broadband Passive Optical Network. BPON standards were set by the ITU-T as G.983.3 for a local loop technology running the ATM protocol over single mode fiber. Synonymous with APON (ATM PON) BPON runs at 155 Mbps or 622 Mbps downstream at a wavelength of 1490nm (nanometer) for voice and data and 1550nm for video transmission. The upstream speed is 155 Mbps at 1310nm for voice and data. The maximum logical reach of BPON is 20km, and the split ratio is 32:1. See also APON, EPON, GPON and PON.
Back reflection.
Basic Rate Interface. There are two subscriber "interfaces" in ISDN. This one and PRI (Primary Rate Interface). In BRI, you get two bearer B-channels at 64 kilobits per second and a data D-channel at 16 kilobits per second. The bearer B-channels are designed for PCM voice, slow-scan video conferencing, group 4 facsimile machines, or whatever you can squeeze into 64,000 bits per second full duplex. The data (or D) channel is for bringing in information about incoming calls and taking out information about outgoing calls. It is also for access to slow-speed data networks, like videotex, packet switched networks, etc.
An ATM term. Beginning Tag: A one octet field of the CPCS_PDU used in conjunction with the etag octet to form an association between the beginning of message and end of message. See ATM.
A term that describes network hardware or software designed for telecommunications service providers. Carrier-grade components have the performance, robustness, scalability and reliability to support continuous network availability in a service provider environment. The term carrier-grade is fairly loose. It should not be considered a technical standard. It reminds me a little of corporate documents in which the management team is "world-class."
Calling Card & Third Number Settlement. An telephone company system for ICS (intercompany settlements) processed through CMDS (Centralized Message Distribution System). Similar to BEARS.
Customer edge router. A router that is part of a customer network and that interfaces to a provider edge (PE) router.
Centrex is a contraction of Central Exchange. Centrex is a business telephone service offered by a local telephone company from a local central office (also called a public exchange). Centrex is basically normal single line telephone service with "bells and whistles," added. Those "bells and whistles" include intercom, call forwarding, call transfer, toll restrict, least cost routing and call hold (on single line phones). Think about your home phone. You can often get "Custom Calling" features. These features are typically fourfold: Call forwarding, Call Waiting, Call Conferencing and Speed Calling. Centrex is basically Custom Calling, but instead of four features, it has as many as 19 features. Like Custom Calling, Centrex features are provided by the local phone company's central office.
Phone companies peddle Centrex which is leased to businesses as a substitute for that business buying or leasing its own on-premises telephone system -- its own PBX, key system or ACD. Before Divestiture in 1984, Centrex was presumed dead. AT&T was, at that time, intent on becoming a major PBX and key system supplier. Then Divestiture came, and the operating phone companies recognized they were no longer part of AT&T, no longer had factories to support, but did have a huge number of Centrex installations providing large monthly revenues. As a result, the local operating companies injected new life into Centrex, making the service more attractive in features, price, service and attitude. Here are the main reasons businesses go with Centrex as opposed to going with a stand-alone telephone system:
The above arguments are pro-Centrex. There are also anti-Centrex arguments. Central offices often run out of capacity. Centrex is also cable-intensive. A PBX with 20 trunks and 100 phones only needs 20 cable pairs from the user's office to the telephone company. A Centrex installation with the same configuration needs 100 pairs. Every time someone new joins your company, the phone company needs to install another cable pair from the central office to your new employee's desk. Sometimes, they have it. Sometimes, they don't. Delays can get extensive. What with the explosion of telecom demand in recent years -- individual fax machines, the Internet, etc. --there just isn't enough copper in the ground, and a typical telco won't plow in the cable unless they receive a pay-off in three years.
The "big" key to Centrex traditionally comes down to price. In some cities the price of Centrex lines is lower than "normal" PBX lines. Of course, you can buy Centrex lines and attach your own PBX or key system to those Centrex lines. The big disadvantage of Centrex is that there are very few specialized Centrex phones able to take better advantage of Centrex central office features the way electronic PBX phones take advantage of PBX features.
Centrex is known by many names among operating phone companies, including Centron and Cenpac. Centrex comes in two variations -- CO and CU. CO means the Centrex service is provided by the Central Office. CU means the central office is on the customer's premises.
A circuit is a connection or line between two points. The connection can be made through various media, including copper, coaxial cable, fiber, or microwave or satellite radio wave. From a customer's point of view, a "circuit" could be dedicated to the customer or shared among many customers. A dedicated circuit is, as it sounds, a link that is dedicated to the systems at either end. Dedication is expensive because it does not use the network as efficiently as it could. If A, B, C, and D all need to be connected with dedicated lines, then a total of six separate links are needed to connect them. Instead, a central switch to which each is connected reduces the number of links required to four. This difference in efficiency increases exponentially as the number of users increases.
See COS.
Central Office. Pronounced "See-Oh". In North America, a CO is that location which houses a switch to serve local telephone subscribers. Sometimes the words "central office" are confused with the switch itself. In Europe and abroad, the words "central office" are not known. The more common words are "public exchange." But those words tend to refer more to the switch itself, rather than the site, as in North America. See also Central Office or Public Exchange.
Colocation occurs when a competing local phone company (often called a CLEC, Competitive Local Exchange Carrier or an Other Common Carrier) locates (i.e. puts) its switches within an incumbent local exchange carrier's (ILEC) central office. An ILEC is the dominant phone carrier within a geographic area as determined by the FCC. Section 252 of the Telecommunications Act 1996 defined Incumbent Local Exchange Carrier as a carrier that, as of the date of enactment of the Act, provided local exchange service to a specific area. The Act provided that the Commission may treat "comparable carriers as incumbents" if they either "occupy a position in the market for telephone exchange service within an area that is comparable to the position occupied by the ILEC or such a "carrier that has substantially replaced an ILEC...." or if "such treatment is consistent with the public interest..."
There are basically two types of colocation -- adjacent / physical, and virtual. Adjacent and physical are the same. They mean that your equipment sits in the same building as the ILEC's switching and cable termination equipment. Typically it sits in a locked cage. Only the CLEC and its personnel have the key. Access to that equipment is negotiated between the ILEC and the CLEC through an interconnection agreement. The CLEC will have 24x7 access to it because they have to maintain it for customers who expect service 24 hours a day seven days a week. The concept of colocation -- at this stage a peculiarly North American idea -- came about through the Telecommunications Act of 1996. U.S. It was a federal bill signed into law on February 8, 1996 "to promote competition and reduce regulation in order to secure lower prices and higher quality services for American telecommunications consumers and encourage rapid deployment of new telecommunications technologies." The Act required local service providers in the 100 largest metropolitan areas of the United States, the Baby Bells, to implement Local Number Portability by the end of 1998. The Act also allowed the local regional Bell operating phone companies into long distance once they had met certain conditions about allowing competition in their local monopoly areas -- thus the concept of colocation. That's what the word colocation means. OK, now to the real stuff -- how to spell it. Several readers have complained that in previous editions of this dictionary it was spelled "colocation." They point out that their non-technical English language dictionaries spell it collocation -- with two "l"s. Random House Dictionary says that back in 1505-15 the word collocation appeared and was based on the Latin collocatus, which derives from collocare. But Random House also includes a spelling from the era of 1965-1970, which it spells colocate and defines as to locate or be located in jointly or together, as two or more groups, military units, or the like; share or designate to share the same place. My preference is colocation, since it seems to me a logical shortening of co-location. But I'm not arguing. Choose which spelling you'd like. See also Carrier Hotel, CLEC, ELEC, ILEC, and Virtual Colocation.
Colocation also refers to the sharing of an antenna tower by two or more wireless operators. See tower colocation.
A condition that arises when a communications link, path, or network experiences an offered load (i.e. the amount of traffic offered) that exceeds its capacity. For example, consider a T-1 link connected to the outgoing port of a switch. If the switch attempts to offer a traffic load in excess of 1.544 Mbps, a congestion condition arises, and can be resolved in one of several ways. First, the switch can simply discard the excess data. Discard Eligible (DE) data applications generally will not suffer beyond their expectations unless the congestion condition becomes extreme. Second, the switch can buffer the excess data until such time as the congestion condition eases; this process is known as "congestion control," and is limited to the maximum capacity of the buffers involved. If the congestion condition persists and the switch discards no data, eventually the congestion backs up all the way to the user terminal, and the application ceases to function in an acceptable manner. See also Utilization.
A domain of connected components that adhere to a defined set of connection rules. The set of rules is termed Connectivity Architecture. Connectivity is the property of a network that allows dissimilar devices to communicate with each other. See also Connectivity Law.
Class of service. Think quality. A Rolls Royce costs more than a Mercedes. Think service. A closer theater seat costs more than one further back. Same thing in telecommunications. Class of service is simply a fancy way of saying you pay more, you get more. Class of service means different things, depending on where you and which facilities you are using.
Customer Proprietary Network Information. Information which is available to a telephone company by virtue of the telephone company's basic service customer relationship. This information may include the quantity, location, type and amount of use of local telephone service subscribed to, and information contained on telephone company bills. This is the definition of CPNI that the independent voice mail and live telephone answering industry uses.
Optical fiber through which no light is transmitted and which, therefore, no signal is being carried. Generally speaking, a dark fiber is one of many fibers contained within a bundle of fibers. Carriers commonly deploy a large number of fibers (432 is a common number) at any given time, since the incremental cost of laying a big bundle is modest compared to pulling them one at a time as the need arises. In fact, a carrier often has little choice, as the right of way may be granted once, and only once. The fibers the carrier is using immediately are "lit," and those that currently are unused are left "dark." The dark fiber is available for future use. Sometimes dark fiber is sold by a carrier without the accompanying transmission electronics. The customer, which may be an end user organization or another carrier, is expected to light it up that strand of fiber with his own electronics. See also dark copper, dark current, dim fiber and lit fiber.
A centralized location where computing resources (e.g. host computers, peripherals, applications, databases, and network access) critical to an organization are maintained in a highly controlled physical environment (temperature, humidity, etc.). A data center is manned by trained professionals, many of whom are specialized in fields such as programming, security management, system repair, and technical support. The facility is secure with both physical and network security. All systems are provided clean power, with backup power supplies (i.e. both battery power and diesel generators) on-line in the event of the failure of the commercial power source. Application software is carefully controlled in order to ensure that software licenses are not violated, no software conflicts arise, versions are released in a controlled fashion, and software bugs are screened out through extensive testing. System backups are done regularly, with copies of backed-up data stored both on-site and off-site. This definition lists some of the characteristics of an ideal data center. Note that even the ideal data center should have a backup in the form of a hot, warm, or cold standby. A hot standby is the ultimate, and the most expensive. It consists of an exact, up-to-the-second duplicate of the primary data center, including not only the host computers and peripherals, but also the applications and databases, and the network configuration. A hot standby is ready to take over instantaneously in the event of a catastrophic failure -- and often that hot, standby data center will be located elsewhere -- in essence a duplicate data center that can takeover instantly in the event of a catastrophe -- fire, flood, earthquake, etc. A warm standby is much the same, but takes a bit longer to take over, as it must be activated, the most recent updates data must be loaded, etc. A cold standby takes longer still, as equipment might need to be reconfigured, applications loaded, entire databases loaded, etc.
A way of putting redundancy into a network, with the result being greater protection from failure. In its English language definition, diversity means varied. In common parlance it means different peoples -- black, white, Chinese, etc. Diversity in a network actually is the complete opposite. The best diversity would be a second, identical network, but located elsewhere -- a network taking a completely different route and using completely different telecom facilities but beginning and ending at the same place as the one it's protecting. There are levels of diversity:
A ground-based antenna and associated equipment used to receive and/or transmit telecommunications signals via satellite. Earth stations come in all sizes, shapes and purposes. For example, most earth stations used by cable television operators are receive-only. Other terms used synonymously with "earth station" include downlink, ground station, and TVRO ("Television Receive Only").
Equal Cost Multipath Routing. ECMP distributes traffic across multiple high-bandwidth links to increase performance. One company's OSPF implementation supports multiple equal-cost paths between points and divides traffic evenly among the available paths. As many as four links may be involved in an ECMP link and traffic is shared on an IP source/destination address session basis.
Emulated Local Area Network: A logical network initiated by using the mechanisms defined by LANE (LAN Emulation). This could include ATM and legacy attached end stations. See also LANE.
A Local Area Network (LAN) standard officially known as IEEE 802.3 (1980)/ Ethernet, and other LAN technologies are used for connecting computers, printers, workstations, terminals, servers, etc. typically within the same building or campus. That was Ethernet's original intent, but now the Ethernet standard is embraced and used in long distance and internationally. Ethernet operates over twisted wire, coaxial cable, optical fiber and through the air (where it's known as Wi-Fi) at speeds beginning at 10 Mbps. For LAN interconnection, Ethernet is a physical link and data link protocol reflecting the two lowest layers of the OSI Reference Model. The theoretical limit of 10-Mbps Ethernet, measured in the smallest 64-byte packets, is 14,800 pps (packets per second). By comparison, Token Ring is 30,000 and FDDI is 170,000.
Ethernet specifies a CSMA/CD (Carrier Sense Multiple Access with Collision Detection) MAC (Media Access Control) mechanism. CSMA/CD is a technique of sharing a common medium (e.g. twisted pair, or coaxial cable) among several devices. As Byte Magazine explained in its January, 1991 issue, Ethernet is based on the same etiquette that makes for a polite conversation: "Listen before talking." Of course, even when people are trying not to interrupt each other, there are those embarrassing moments when two people accidentally start talking at the same time. This is essentially what happens in Ethernet networks, where such a situation is called a "collision." If a node on the network detects a collision, it alerts the other nodes by jamming the network with a collision "notification." Then, after a random pause, the sending nodes try again. The messages are called frames (see the diagram).
Ethernet transmits variable length frames from 72 to 1518 bytes in length, each containing a header with the addresses of the source and destination stations and a trailer that contains error correction data. The preamble is 8 bytes, the destination is 6 bytes, the source is 6 bytes, the type is 2 bytes. Data is up to 1500 bytes. The final part of the Ethernet frame is the frame check sequence of 4 bytes.
│ │
│ Preamble │ Destination │ Source │ Type │ Data │ Frame check │
│ │ │ │ │ │ sequence │
│ │ │ │ │ │ │
│ 8 bytes │ address │ address │2 bytes │ up to 1500 │ 4 bytes │
│ │ 6 bytes │ 6 bytes │ │ bytes │(contains a │
│ │ │ │ │ │ CRC check) │
│ │ │ │ │ │ │
The first personal computer Ethernet LAN adapter was shipped by 3Com on September 29, 1982 using the first Ethernet silicon chip from SEEQ Technology. Bob Metcalfe created the original Ethernet specification at Xerox PARC and later went on to found 3Com. In the October 31, 1994 issue of the magazine InfoWorld, Bob Metcalfe explained that Ethernet got its name "when I was writing a memo at the Xerox Palo Alto Research Center on May 22, 1973. Until then I had been calling our proposed multimegabit LAN the Alto Aloha Network. The purpose of the Alto Aloha Network was to connect experimental personal computers called Altos. And it used randomized retransmission ideas from the University of Hawaii's Aloha System packet radio network, circa 1970. The word ether came from luminiferous ether -- the omnipresent passive medium once theorized to carry electromagnetic waves through space, in particular light from the Sun to the Earth. Around the time of Einstein's Theory of Relativity, the light-bearing ether was proven not to exist. So, in naming our LAN's omnipresent passive medium, then a coaxial cable, which would propagate electromagnetic waves, namely data packets, I chose to recycle ether. Hence, Ethernet."
According to Metcalfe, "Ethernet has been renamed repeatedly since 1973. In 1976, when Xerox began turning Ethernet into a product at 20 million bits per second (Mbps), we called it The Xerox Wire. When Digital, Intel, and Xerox decided in 1979 to make it a LAN standard at 10 Mbps, they went back to Ethernet. IEEE tried calling its Ethernet standard 802.3 CSMA/CD -- carrier sense multiple access with collision detection. And as the 802.3 standard evolved, it picked up such names as Thick Ethernet (IEEE 10Base-5), Thin Ethernet (10Base-2), Twisted Ethernet (10Base-T), and now Fast Ethernet (100Base-T)."
Originally, the way computers joined to an Ethernet LAN was through cards that got dropped into the computer's bus. But quickly, with its increasing popularity, Ethernet connectivity simply got built onto the computer's motherboard. Most computers -- especially laptops, notebooks and netbooks -- have at least two ways of joining to a wireless network -- an RJ-45 receptacle (also called an Ethernet plug) and Wi-Fi.
The May 22, 2003 issue of my favorite magazine, the Economist, had an article on Ethernet. I excerpt it because it's so good: "When Ethernet, now by far the most popular way of distributing data around local networks, was devised by Bob Metcalfe in a memo on May 22, 1973, at Xerox's celebrated Palo Alto Research Centre (PARC), it was designed to send data at about three megabits per second. Today, one gigabit per second Ethernet is common and speeds of 100 gigabits per second are being developed. The vast majority of the Internet's traffic begins and ends its journey on Ethernet networks, which are found in nearly every office network and home broadband connection. It was not supposed to be this way. Few imagined that this particular networking protocol would last as long as it has. Indeed, the landscape is littered with better-financed, better-backed rival protocols that failed against Ethernet. IBM's Token Ring system is one famous casualty. Asynchronous Transfer Mode, supported by the telephone industry, is another. So the case of Ethernet is worth examining: the reasons for its longevity may offer lessons to the information-technology industry. Keep it simple, stupid. The first reason is simplicity. Ethernet never presupposed what sort of medium the data would travel over, be it coaxial cable or radio waves (hence the term "ether" to describe some undefined path). That made it flexible, able to incorporate improvements without challenging its fundamental design.
Second, it rapidly became an open standard at a time when most data-networking protocols were proprietary. That openness has made for a better business model. It enabled a horde of engineers from around the world to improve the technology as they competed to build inter-operable products. That competition lowered the price. What is more, the open standard meant that engineers in different organisations had to agree with each other on revised specifications, in order to avoid being cut out of the game. This ensured that the technology never became too complex or over-designed. As Charles Spurgeon, author of "Ethernet: The Definitive Guide" puts it, "It always stayed close to the ground. It addressed problems customers came up against, not problems that networking specialists thought needed to be addressed." That, coupled with the economies of scale that come from being the entrenched technology, meant that Ethernet was faster, less expensive and less complicated to deploy than rival systems.
Third, Ethernet is based on decentralisation. It lets smart "end-devices", such as PCs, do the work of plucking the data out of the ether, rather than relying on a central unit to control the way those data are routed. In this way, Ethernet evolved in tandem with improvements in computing power-a factor that was largely overlooked by both critics and proponents when Ethernet was being pooh-poohed in the 1980s and early 1990s.
Beyond the technology, there is even a lesson for companies investing in research, albeit one learned through tears rather than triumph. Xerox failed to commercialise Ethernet, as it similarly missed exploiting other inventions created at PARC, such as the mouse and the graphical user interface. To develop Ethernet fully, Dr Metcalfe had to leave PARC and found 3Com, now a big telecommunications-component firm. The lesson may have sunk in. In January 2002 PARC was carved out as an independent subsidiary of Xerox. That allows it to explore partnerships, spin-offs and licensing agreements without having to get its parent's permission.
And the future? Over the years, as technology hardware has improved, Ethernet's speed has risen. It jumped from 10 megabits per second to 100 and now to a 1,000. It's clearly going higher. And more of it will be delivered wirelessly, as in Wi-Fi and WiMAX.
A shortened way of saying "fiber optic." Fiber is made of very pure glass. In Bill Gates' book called "the Road Ahead," he says that optical fiber is so clear and pure that if you looked through a wall of it 70 miles thick, you'd be able to see a candle burning on the other side." Digital signals, in the form of modulated light, travel on strands of fiber for long distances. The big advantage that fiber has over copper is that it can carry far, far more information over much, much longer distances. The short history of fiber optics for communications is that scientists keep discovering more and more ways of putting more and more information down the same one single strand of fiber. Based on my own personal researches, no one has any idea what the eventual capacity limit of a strand of fiber optic might be. I have personally asked many scientists (including one Nobel Physics prize winner) and all seem to think there must be a theoretical limit. But they don't know what it is, or when we'll reach that limit. And they believe we have many, many years of breakthroughs in fiber still to go. As of the time of this writing, SONET OC-192 (Synchronous Optical NETwork Optical Carrier Level 192) systems are being deployed fairly routinely by a number of major long distance carriers. Each OC-192 strand supports approximately 10 Gbps. With DWDM (Dense Wavelength Division Multiplexing), as many as 32 "windows," or wavelengths of light, can be overlaid into a single strand at OC-192, yielding a total of approximately 320 Gbps. Fiber is the American spelling. The spelling in England, Europe, Canada, Australia and New Zealand is fibre.
A firewall is a piece of hardware or software, or hardware and software that prevents unauthorized people from gaining access to your computer or computer network. That's its main function. Its secondary function is to check on information to and from your PC and/or your network to make sure the information is kosher, i.e. non-damaging. Basically, a firewall will protect against two threats from outside the firewall:
Firewalls -- whether hardware or software, or both -- do not protect against computer viruses and spam emails. For that you need other protection. In short, a firewall is a system or combination of systems that enforce a boundary between two or more networks, one of which is likely to be the Internet and the other your own computer and/or your own network, whether local or wide area. There are several types of firewalls -- packet filter, circuit gateway, application gateway or trusted gateway. A network-level firewall, or packet filter, examines traffic at the network protocol packet level. An application-level firewall examines traffic at the application level -- for example, FTP, E-mail, or Telenet. An application-level firewall also often readdresses outgoing traffic so it appears to have originated from the firewall rather than the internal host. How does a firewall know if someone or some program is trying to deliberately break in.
Firewalls -- named after the flame-blocking structures designed to keep fires from spreading -- are programmed to analyze the network traffic flowing between your computer and the Internet. The firewall compares the information it monitors with a set of rules in its database. If it sees something not conforming to the rules or to normal traffic, say, another computer trying to connect directly to one of the machines on your network, the firewall should block that access. Most firewall programs let you adjust the rules to allow certain types of data to flow freely back and forth without interference, in cases where you want to do things like stream music or share files with another computer on your network, e.g. over FTP. Both Windows and Mac OS include basic firewall programs as part of their operating systems. There are also more complex third-party firewall programs available from independent software companies. Makers of antivirus software often have a combination package that includes a firewall program and other security software as well, which can help protect your computer from a variety of Internet threats.
FR or FRS. What goes around comes around. Flat rate service was originally the way you paid for local phone calls in North America. The concept was that for a fixed amount of money -- say $10 a month -- you received a plain old desk telephone and were able to make and receive an unlimited number of local calls that month. For years, most residential and most business phones were on a flat rate service. But that changed for reasons I've never figured. The first thing to go was the phone instrument. You had to pay a dollar or so a month to continue renting it, or you could send it back and buy your own. Second to go was the size of the local calling area you could call as part of you flat rate plan. The area got smaller. Third to go were the phone calls themselves. This happened first with businesses and now increasingly with residential service. Under this new "pay-per-call" you get charged a "message unit" for each local calls. A message unit could be eight to ten cents. Psychologically, "message units" sound better than dollars and cents. Calls which years ago were free (i.e. on flat rate service) have now become long distance calls. You can witness this phenomenon of changing local pricing in California, New York and Jersey. In other states, especially those with rural areas, it's taking a little longer. That was the story until the year 2000 or so. At that point, VoIP (Voice over Internet Protocol) was introduced with a flat monthly rates for calls all over the country -- local and long distance. The carriers providing the VoIP service were varied -- from cable TV providers to independents who provided you with a magic box -- one side of which connected to your broadband access service and the other to your phone instrument or phone system. To counter this new competition, some telephone companies began to introduce flat rate phone for calling all around North America. Cellphone service in North America is a combination of flat rate service – as many hours in your plan -- and so much per call for every minute or so over your plan.
Fixed Mobile Convergence. This is an evolving concept. In its simplest terms it means you have one phone, which is portable and you carry wherever you go. You use that phone when you're at home or in your office or on the road. When you're at home or in your office that phone would connect to your wireless Wi-Fi network or something called a femtocell and dial through the Internet as a VoIP call. When you're outside of your home or office, you would use that phone as a cell phone. The theory of FMC is that you can be talking on your phone in your house then walk outside and be seamlessly switched to the local cellular network. See also IP multimedia subsystem.
Frame relay was once a popular telecommunications service, but has now been replaced by various forms of the now, much more popular Ethernet. Frame relay, technically speaking, is an access standard defined by the ITU-T in the I.122 recommendation, "Framework for Providing Additional Packet Mode Bearer Services." Frame relay services, as delivered by the telecommunications carriers, employ a form of packet switching analogous to a streamlined version of X.25 networks. The packets are in the form of "frames," which are variable in length, with the payload being anywhere between 0 and 4,096 octets. The key advantage to this approach is that a frame relay network can accommodate data packets of various sizes associated with virtually any native data protocol. In other words, a X.25 packet of 128 bytes or 256 bytes can be switched and transported over the network just as can an Ethernet frame of 1,500 bytes. The native Protocol Data Unit (PDU) is encapsulated in a Frame Relay frame, which involves header and trailer information specific to the operation of the Frame Relay network.
Further, a Frame Relay network is completely protocol independent. Not only can any set of data be accepted, switched and transported across the network, but the specific control data associated with the payload is undisturbed in the process of encapsulation. Additionally, and unlike an X.25 network, a Frame Relay network assumes no responsibility for protocol conversion; rather, such conversions are the responsibility of the user. While this may seem like a step down from X.25, the data neither require segmentation into fixed-length packets nor does the network have to undertake processor-intensive and time-consuming protocol conversion. The yield is faster and less expensive switching.
A Frame Relay network also assumes no responsibility for errors created in the processes of transport and switching. Rather, the user also must accept full responsibility for the detection and correction of such errors. The user also must accept responsibility for the detection of lost packets (frames), as well for the recovery of them through retransmission. Again, this may seem like a step down from X.25 networks, which correct for errors at each network node, and which detect and recover from lost packets. Once again, however, the yield is faster and less expensive switching. In fact, it is unlikely that frames will be damaged, as the switches and transmission facilities are fully digital and offer excellent error performance.
Much like X.25, Frame Relay employs the concept of a shared network. In other words, the network switches accept frames of data, buffer them as required, read the target address and forward them one-by-one as the next transmission link becomes available. In this fashion, the efficiency of transmission bandwidth is maximized, yielding much improved cost of service. The downside is that some level of congestion is ensured during times of peak usage. The level of congestion will vary from time-to-time and frame-to-frame, resulting in latency (delay) which is unpredictable and variable in length. This is especially true in a Frame Relay network, as the length of the frames is variable -- the switches never quite know what to expect.
Access to a Frame Relay is over a dedicated, digital circuit which typically is 56/64 Kbps, Nx56/64 Kbps, T-1 or T-3. The device which interfaces the user to the network is in the form of a Frame Relay Access Device (FRAD) which serves to encapsulate the native PDU before presenting it to the network. The FRAD at the destination address unframes the data before presenting it to the target device, with the two FRADs working together much as do PADs in a X.25 environment. Further, it generally is the responsibility of the FRAD to accomplish the error detection and correction process, although this responsibility may be that of the eventual target device. Across the digital local loop, the FRADs connect functionally to Frame Relay Network Devices (FRNDs, pronounced "friends"), proving once again that the carriers want to be your friends (especially as Frame Relay users tend to be large organizations with lots of $$$ to spend).
Frame Relay is intended for data communications applications, most especially LAN-to-LAN internetworking, which is bursty in nature. Frame Relay is very good at efficiently handling high-speed, bursty data over wide area networks. It offers lower costs and higher performance for those applications in contrast to the traditional point-to-point services (leased lines). Additionally, Frame Relay offers a highly cost-effective alternative to meshed private line networks. As the Frame Relay network is a shared, switched network, there is no need for dedicated private lines, although special-purpose local loops connect each customer location to a frame switch.
Frame Relay is a connection-oriented protocol, as transmission of frames between the user sites generally is on the basis of Permanent Virtual Circuits (PVCs), which are pre-determined paths specifically defined in the Frame Relay routing logic. All frames transmitted between any two sites always follow the same PVC path, ensuring that the frames will not arrive out of sequence. Backup PVCs, generally offered by the carrier at trivial cost, provide redundancy and, therefore, network resiliency in the event of a catastrophic network failure. Switched Virtual Circuits (SVCs) are VCs selected on a call-by-call basis. SVCs are advantageous as they result in automatic load balancing, which improves overall service. As SVC logic is more costly, however, not all carriers offer it; those that do impose a surcharge on SVC users.
With Frame Relay, a pool of bandwidth is made instantly available to any of the concurrent data sessions sharing the access circuit whenever a burst of data occurs. An addressed frame is sent into the network, which in turn interprets the address and sends the information to its destination over broadband facilities. Those facilities may be as "slow" as 45 Mbps, but more often are SONET fiber optics in nature and operating at much higher speeds. Like traditional X.25 packet networks, frame relay networks use bandwidth only when there is traffic to send.
Frame Relay, while intended for data communications, also supports compressed and packetized voice and video. While such isochronous data is highly sensitive to the variable latency characteristic of packet networks, improved voice compression algorithms such as ACELP provide quite acceptable support for Voice over Frame Relay (VoFR), subject to the level of congestion in the network. For voice to be supported satisfactorily in a packet network, the receiving end compensates for delay and delay variation.
In addition to public network services, Frame Relay can also be implemented in a private network environment consisting of unchannelized T-Carrier circuits. Such an implementation offers exceptional data communications performance over an existing leased line network. Additionally, framed voice and video can ride over such a network, essentially for "free" when the circuits are not being used for data communications purposes. Thereby, the usage of the circuits is maximized, with little concern for poor quality due to network congestion.
A Frame Relay frame consists of a header, information field, and trailer. The header comprises a Flag denoting the beginning of the frame, and an Address Field used for routing of the frame, as well as for purposes of congestion notification. The Information Field is of variable length, from 0 to 4,096 Bytes. The trailer consists of a Frame Check Sequence (FCS) for detection and correction of errors in the Address Field, and an ending Flag denoting the end of the frame.
The American National Standards Institute (ANSI) describes frame relay service in the following documents:
ANSI T1.602 -- Telecommunications -- ISDN -- Data Link Layer Signaling Specification for Application at the User Network Interface.
ANSI T1.606 -- Frame Relaying Bearer Service -- Architectural Framework and Service Description.
ANSI T1S1/90 - 175 - Addendum to T1.606 - Frame Relaying Bearer Service -- Architectural Framework and Service Description.
T1.607-1990 ISDN Layer 3 Signaling Specification for Circuit-Switched Bearer Service for DSS-1.
T1.618 DSS-1 Core aspects of Frame Protocol for use with frame relay bearer service, ANSI, 1991.
ANSI T1.617a, Signaling specification for Frame Relay bearer service for DSS-1, 1994.
Frame relay access makes use of the LAP-D signaling protocol developed for ISDN. Frame relay, technically speaking again, does not address the operation of the network switches, multiplexers or other elements. Both the ITU-T and ANSI were highly active in the development of Frame Relay standards, as was ETSI in Europe. See the next three definitions and also LAP-D, FRAD, FRND, PVC, SVC, VoFR, and X.25.
Generic Attribute Registration Protocol. An IEEE standard for a generic method by which various devices (e.g., clients, servers, and bridges) can automatically disseminate attribute information across a bridged LAN. GARP is a Layer 2 (i.e. Data Link Layer) protocol used extensively in VLANs (Virtual LANs). A GARP participant consists of a GARP application software component, and a GARP Information Declaration (GID) component which is associated with each port of the bridge. GARP participants in a given application disseminate their attribute information through the use of the GARP Information Propagation (GIP) component. Relying on GARP services is GMRP (GARP Multicast Registration Protocol), which provides a mechanism by which bridges and end stations can automatically and dynamically register their membership in a group with the MAC bridges by which a physical LAN segment attaches to the larger logical LAN. Once the bridges receive that registration information, they propagate it to all other bridges that support extended filtering services. The GARP VLAN Registration Protocol (GVRP) is a GARP application that provides registration services in a VLAN context. See also GVRP and VLAN.
A gateway is what it sounds like. It's an entrance and exit into a communications network. That "communications network" may be huge, for example, at the point where AT&T Communications ends and Comsat begins -- for taking my satellite call overseas. Gateways may be small -- between one LAN and another LAN. Technically, a gateway is an electronic repeater and signal regeneration device that intercepts and steers electrical signals from one network to another. Generally, the gateway includes a signal conditioner which filters out unwanted noise and controls characters. In data networks, gateways are typically a node on both two networks that connects two otherwise incompatible networks. For example, PC users on a local area network may need a gateway to gain access to a mainframe computer since the mainframe does not speak the same language (protocols) as the PCs on the LAN. Thus, gateways on data networks often perform code and protocol conversion processes. Gateways also eliminate duplicate wiring by giving all users on the network access to the mainframe without each having a direct, hard-wired connection. Gateways also connect compatible networks owned by different entities, such as X.25 networks linked by X.75 gateways. Gateways are commonly used to connect people on one network, say a token ring network, with those on a long distance network. According to the OSI model, a gateway is a device that provides mapping at all seven layers of the model. A gateway may be used to interface between two incompatible electronic mail systems or for transferring data files from one system to another.
A gateway is an optional element in an H.323 conference. Gateways bridge H.323 conferences to other networks, communications protocols, and multimedia formats. Gateways are not required if connections to other networks or non-H.323 compliant terminals are not needed. Gatekeepers perform two important functions which help maintain the robustness of the network -- address translation and bandwidth management. Gatekeepers map LAN aliases to IP addresses and provide address lookups when needed. Gatekeepers also exercise call control functions to limit the number of H.323 connections, and the total bandwidth used by these connections, in an H.323 "zone." A gatekeeper is not required in an H.323 system-however, if a gatekeeper is present, terminals must make use of its services.
Generalized Multiprotocol Label (Lambda) Switching. GMPLS represents a natural extension of MPLS to allow MPLS to be used as the control mechanism for configuring not only packet-based paths, but also paths in non-packet based devices such as optical switches, TDM muxes, and SONET/ADMs." In short, all of the mechanisms that allow MPLS to be used as a viable solution for traffic engineering
Generic Routing Encapsulation. An Internet term. GRE is one of the basic operations performed by tunnel servers when tunneling through the Internet in order to provide a secure VPN (Virtual Private Network). GRE simply provides for the encapsulation of one data packet inside another data packet. The original packet becomes the payload (i.e. data field, or content) for the final packet, which also includes a new header and trailer. Tunnel servers also encrypt the payload, and continuously authenticate the identity of the communicating machines on a packet-by-packet basis. GRE for IPX tunneling is defined by the IETF (Internet Engineering Task Force) in RFC 1701, and for IP-in-IP or bridge tunneling in RFC 1702. See also IETF, IP, IPX, Packet, and VPN.
GSM is the most common cell phone service in the world. It's in most countries of the world. The major difference between the GSM networks worldwide is that they often work on different radio frequencies, of which there are four major ones. That means that if you carry a so-called quad-band GSM phone, you will be able to receive and make GSM cell phone calls in most countries of the world, including North America. GSM originally stood for Groupe Speciale Mobile. Now it's known as Global System for Mobile Communications. GSM is the standard digital cellular (also called mobile) phone service you will find in Europe, Japan, Australia and elsewhere -- at least 133 countries -- and two U.S. carriers -- AT&T and T-Mobile. Most countries decided to pick a single, standard wireless phone technology years ago, and they settled on GSM. The U.S. refused to settle on a standard and that has resulted in a patchwork of multiple, incompatible cellphone technologies. GSM actually is a set of ETSI standards specifying the infrastructure for a digital cellular service. To ensure interoperability between countries, these ETSI standards address much of the network wireless infrastructure, including the radio interface, switching, signaling, and intelligent network. Since GSM is limited to technical standards, an association of GSM operators called the Memorandum of Understanding (MoU) ensures service interoperability, allowing subscribers to roam across networks and countries. There are essentially two parts to a GSM "phone". There's the physical phone, which can be a simple phone or it can be a PDA (personal digital assistant, e.g. BlackBerry or iPhone. Second, all GSM phones -- whether phones or PDAs -- have something called a SIM card (called a Subscriber Identity Module). First the phone. It's a two-way radio. It works on a radio frequency. There are now four frequency flavors of GSM: 450 MHz (upgrade of old NMT systems in Scandinavia), 900 MHz (original flavor everywhere except North America and most countries in South America), 1800 MHz (new flavor everywhere except North and South America -- brought in to add capacity and competition), and 1900 MHz (North America and much of South America), In the United States, the GSM frequencies are 1850-1910 MHz and 1930-1990 MHz. The frequency defines the phone. Some carriers sell phones that work only on their frequencies. Hence they're not useful for traveling. You can also buy quad-band GSM phones that will work on basically any GSM network. That's the phone to get, if you plan on traveling. But it's typically more expensive. Data on the GSM subscriber data is carried on a Subscriber Identity Module (SIM) or "smartcard" which is inserted into the phone to get it going. The SIM card basically identifies the subscriber to the cell carrier. GSM cell phones come in locked and unlocked varieties. An unlocked GSM phone will accept pretty well any GSM card and become the phone number and account of the SIM card -- perhaps one purchased from a local tobacconist. A locked GSM phone will only work with the carrier who locked the phone. Locking is done to prevent a customer leaving the carrier for a cheaper one. Most locked phones can be unlocked with software and techniques you'll find on the Internet. Unlocking a locked phone usually destroys its warranty.
Here's a brief discussion of the technology of GSM: Access method: mixed TDMA and FDMA with optional frequency hopping. Security: Optional radio interface encryption. Carrier frequency division: 200 KHz. Users per carrier frequency: 8. Speech bit rate (transfer rate): full rate (13 Kbps) or half rate. Total bit rate: 21 Kbps. Bandwidth per channel: 25 KHz. The audio encoding subset of the GSM standard is best known to computer users because its data compression and decompression techniques are also being used for Web phone communication and encoding .wav and .aiff files. The best book on GSM is "The GSM System for Mobile Communications" by Michel Mouly and Marie-Bernadette Pautet, both of France. The authors contributed to the development of GSM. See also BSS, which stands for Base Station System and SIM Card.
The GARP VLAN Registration Protocol (GVRP) is a GARP (Generic Attribute Registration Protocol) application that provides registration services in a VLAN context. See GARP for more information.
High level Data Link Control. A link layer protocol (Layer 2 of the OSI Reference Model) standard for point-to-point and point-to-multipoint communications. HDLC was based on IBM's SDLC (Synchronous Data Link Control) and ANSI's ADCCP (Advanced Data Communication Control Procedure). HDLC encapsulates packet data in a frame (i.e. yet another packet), with the frame header and trailer including various control information such as an error control mechanism. Variants on HDLC include Frame Relay, LAP-B (Link Access Procedure-Balanced), Link Access Procedure-Data channel), PPP (Point-To-Point Protocol), and SDLC (Synchronous Data Link Control).
Someone else owns my PBX and rents me space, time and telecommunications services on it. That PBX is typically away from my office. It's joined to me by various types of phone lines, including T-1. Essentially hosted PBX is a fancy new name for what we used to call Centrex, when the phone company owned the PBX (actually it was a big central office, also called or pubic exchange) and rented me space, time and telephone services on it. There are advantages and disadvantages to being a customer of a hosted PBX. The arguments are similar to the age-old question: Should I buy or rent my house? See also Centrex.
I have several web sites. One is www.InSearchOfThePerfectInvestment.com. For my friends to be able to read it, my web site has to be connected full-time to the Internet. I can do that myself if I have a full-time high-speed connection to the Internet and if I have the computing equipment and if I have the full-time people to make sure my web site is working 24/7, i.e. 100% of the time. Most of us can't afford that. We're not in our offices at 3 AM checking that my web site is working. As a result, a whole bunch of businesses have sprung up to run web sites for other people. These businesses are called web site hosters, web hosters, or just hosters. The service they provide is called hosting. Typically, they offer four types of hosting services:
Web sites hosted on shared servers. This is what I have. I'm one web site on a server which also hosts other peoples' web sites. Clearly, this is an economical solution for people like me who have simple or moderately accessed sites. In other words, I'm not the New York Times.
Let's say my web site was larger and accessed more frequently by more people. Then clearly I'd want a computer server dedicated to me. This way I could have more people coming to my site and they'd get faster service. With dedicated hosting, I get my own server dedicated to me. This solution provides greater server and network resources than shared hosting and allows for a hardware configuration to optimize my site's performance and/or to accommodate to my various strange and wonderful needs -- like tieing into a remote database for customer delivery services.
Let's say that I don't want the computer my hoster provides. Let's say that I want to use my to use own special computer and special software (for whatever reason). But I want my computer to be on the web hoster's site for two reasons: First, the hoster can connect my computer (i.e. my Web site server) to much faster telecom lines than I can. Most often, hosters site themselves at major Internet switching sites on T-3 rings. See MAE. Second, the hoster will have people on duty 24-hours a day, 365 days a year. So, if my server goes down, he can have someone look at it quickly -- even in the middle of the night. People who like this service tend to have "sophisticated mission-critical applications," for example ecommerce.
In the three services above, the hoster has no responsibility for what the customer has actually put on his web site. Whether it's ecommerce, a gossip site or porn, he doesn't care. With application hosting, the web hoster cares. He takes your application and works with you, sort of a combination web hoster / consultant/ webmaster. He might help you get an ecommerce site up, or a corporate email system, or a Lotus Notes collaboration system.
A hub is a shortened way of saying network hub or repeater hub. A hub connects Ethernet devices together, allowing them to communicate with each other. Those devices -- PCs, printers, hard drives, network servers etc. -- may be connected via twisted pair or fiber optic. A network hub is an unsophisticated broadcast device. Hubs do not manage any of the traffic that comes through them, and any packet entering any port is broadcast out on all the other ports. Since every packet is being sent out through all other ports, packet collisions result. This can impede the flow of traffic. The need for hosts to be able to detect collisions limits the number of hubs and the total size of the network. Hubs work at the physical layer (layer 1) of the OSI model. The device is thus a form of multiport repeater. Repeater hubs also participate in collision detection, forwarding a jam signal to all ports if it detects a collision. As I write this, Ethernet 5-port hubs which connect five RJ-45 connected devices cost as little as $20. I find them most useful in a simple home or small office environment. I might install hubs towards the periphery of a LAN -- for example to allow a user to connect his printer, his laptop and his desktop to the main network, and then to the Internet. There'd be little chance of continuing collisions since the user is likely to do his tasks serially -- one task after another -- not simultaneously (unless he's as talented as my wife). Historically, the main reason for buying hubs rather than switches was their low price. This has largely been eliminated by reductions in the price of switches, To be clear: Hubs are not sophisticated devices. Hubs do not read any of the data passing through them and are not aware of the data's source or destination. Essentially, a hub simply receives incoming packets, possibly amplifies the electrical signal, and broadcasts these packets out to all devices attached to the hub -- including the one that originally sent the packet.
There are three different types of hubs:
Interexchange Carrier Interface. The interface between carrier networks that support SMDS (Switched Multimegabit Data Service).
Interior Gateway Protocol. The protocol used to exchange routing information between collaborating routers in the Internet. RIP and OSPF are examples of IGPs.
A collection of all those telecommunications components that together provide the distribution of all information within a building and campus. Originally infrastructure was a local term. But increasingly, it means all the telecom equipment and networks that serve the entire organization.
The word interconnect means the same as connect, i.e. to join. In telecommunications you interconnect equipment to equipment, and equipment to telecom lines and networks. The word came because many people prefer big words to smaller words. Using bigger words appears to make them feel more important. A prime example is the word utilize versus use. They both mean the same thing. But utilize seems more formal, more authoritative to some people (not to me). Words can also acquire bad feelings. In 1968 the FCC's Carterfone's decision forced telephone companies to connect telephone equipment they didn't make to their networks. Now equipment could be made by startups like Rolm and Mitel and installed and maintained by one of their new distributors. The phone companies had fought these interlopers before the FCC on mostly technical grounds -- their equipment would destroy the phone companies' precious networks. When they lost this argument and the FCC ruled in favor of the interlopers, the telephone companies (especially AT&T) tried a different tack. They tried psychology. They called the equipment "interconnect equipment" and they called the distributors "interconnect dealers." The idea was to make these new companies second class citizens, to call into question the quality of their equipment and their service skills. They called them "interconnect companies" and their equipment was called "foreign equipment" -- even though virtually all of it was made in the U.S. or Canada. In reality, the new companies displayed far more innovation and did a better job installing and maintaining equipment like -- PBXs and key systems -- and today, the irony is, all telephone companies simply don't make or install phone systems, or voice mail or automatic call distributors, etc. See interconnect companies.
1. Noun. A mechanical or electrical link connecting two or more pieces of equipment together. 2. Noun. A shared boundary. A physical point of demarcation between two devices where the electrical signals, connectors, timing and handshaking are defined. The procedures, codes and protocols that enable two entities to interact for a meaningful exchange of information. 3. Verb. To bring two things or people together to allow them to talk, either in English or in some technical way. 4. Verb. A poorly-defined word often used when the speaker is incapable of figuring precisely what he means. No one would ever invite a pretty young lady to lunch by asking her to "interface" with you. See also Interface Device.
The Internet Protocol. IP is the most important of the software protocols on which the Internet is based. The IP Protocol keeps track of the Internet's addresses for different nodes, routes outgoing messages, and recognizes incoming messages. It allows a packet to traverse multiple networks on the way to its final destination. It was originally developed by the Department of Defense to support interworking of dissimilar computers across a network. While its roots are in the ARPAnet development, IP was first standardized in RFC 791, published in 1981, and updated in RFC 1349. This protocol works in conjunction with TCP (Transmission Control Protocol) and is usually identified as TCP/IP. It is a connectionless protocol that operates at the network layer (layer 3) of the OSI model. See IP Address, IPv4, IPv5, IPv6, the Internet, and TAPI 3.0. 2. Intelligent Peripheral. A device in an IN (Intelligent Network) or AIN (Advanced IN) that provides capabilities such as voice announcements, voice recognition, voice printing and help guidance. By way of example, MCI's 1-800-COLLECT makes use of IPs, which are specialized voice processing systems. The IP prompts the caller to enter the target telephone number and speak his or her name. The system then instructs the network to connect the call. Based on a spoken acceptance of the call by the called party, the system authorizes call completion. 3. Information Provider. A customer that offers recorded information on its listed numbers. 4. Intellectual Property. A legal term that refers to original creative work (a book, a movie, software code, etc.) manifested in a tangible form that can be legally protected, for example, by a patent, trademark, or copyright. 5. Illustrative Paragraph. A term dictionary writers (also called lexicogrphers) use to explain the meaning of a term. Often they use their friends.
International private leased or international private line circuit.
Internet Protocol Security (IPsec) is a collection of protocols designed to secure Internet Protocol (IP) communications. IPsec authenticates and encrypts each IP packet of a stream of data. IPsec includes protocols for establishing mutual authentication between agents at the beginning of the session and negotiation of cryptographic keys to be used during the session. IPsec can be used to protect data flows between a pair of hosts (e.g. computer users or servers), between a pair of security gateways (e.g. routers or firewalls), or between a security gateway and a host. IPsec is a dual mode, end-to-end, security scheme operating at the Internet Layer of the Internet Protocol Suite or OSI model Layer 3. Some other Internet security systems in widespread use, such as Secure Sockets Layer (SSL), Transport Layer Security (TLS) and Secure Shell (SSH), operate in the upper layers of these models. Hence, IPsec can be used for protecting any application traffic across the Internet. Applications need not be specifically designed to use IPsec. IPsec is a successor of the ISO standard Network Layer Security Protocol (NLSP). NLSP was based on the SP3 protocol that was published by NIST, but designed by the Secure Data Network System project of the National Security Agency (NSA). IPsec supports authentication through an "authentication header" which is used to verify the validity of the originating address in the header of every packet of a packet stream. An "encapsulating security payload" header encrypts the entire datagram, based on the encryption algorithm chosen by the implementer.
Internet Protocol version 4 (IPv4) is the fourth revision in the development of the Internet Protocol (IP). It is the first version of the protocol to be widely deployed. It is the protocol most commonly used today. Although its roots are in the initial development work for ARPAnet, IPv4 was first formalized as a standard in 1981. Since that time, it has been widely deployed in all variety of data networks, including LANs, LAN internetworks and the Internet. While IPv4 has served its purpose for some 25 years, it has lately proved to be inadequate, largely in terms of security and limitations of the address field, i.e. the numbering system that the Internet uses to find its various sites. The address field is limited to 32 bits; although 2 to the 32nd power is a very large number, we are running out of IP addresses just as we have run out of 800 numbers and traditional area codes. Hence, the development of IPv6. IPv4 is described in IETF publication RFC 791 (September 1981). The United States Department of Defense also standardized it as MIL-STD-1777. IPv4 is a connection-less protocol to be used on packet-switched Link Layer networks (e.g., Ethernet). It operates on a best effort delivery model, in that it does not guarantee delivery, nor does it assure proper sequencing, or avoid duplicate delivery. These aspects, including data integrity, are addressed by an upper layer transport protocol (e.g., Transmission Control Protocol). IPv4 provides only header integrity achieved with a checksum. All this is why you see TCP/IP as the primary protocol of the Internet.
Internet Protocol Version 6. This new Internet Protocol designed to replace and enhance the present protocol which is called TCP/IP, or officially IPv4. IPv6 has 128-bit addressing, auto configuration, new security features and supports real-time communications and multicasting. IPv6 is described in RFC 1752, The Recommendation for IP Next Generation Protocol, including the strengths and weaknesses of each of the proposed protocols which were blended to form the final proposed solution. At the time of this writing, IPv6 is standardized, but not widely deployed. It requires upgrades that are expensive. They will be fork-lift upgrades in many cases. Therefore, IPv6 is being deployed pretty much only in the NextGen carrier networks, which are being built from the ground up. IPv6 offers 128-bit addressing, auto configiuration, new security features and supports real-time communications and multicasting. The 128-bit addressing scheme will relieve pressure on the current 32-bit scheme, which is nearly exhausted due to widespread use of IP in the Internet and a wide variety of LAN, MAN and WAN networks. Clearly, 2 to the 128th power is a huge number, yielding a staggering number of IP addresses. According to Mark Miller of Diginet Corporation, it equates to approximately 1,500 addresses per square angstrom, with an angstrom being one ten-millionth of a millimeter. Another way of looking at this is that IPv6 yields about 32 addresses per square inch of dry land on the earth's surface – in other words, we are not likely to run out of IPv6 addresses. (Don't be surprised to see your telephone assigned an IP address in the future). Autoconfiguration Protocol, an intrinsic part of IPv6, allows a device to assign itself a unique IP address without the intervention of a server. The self-assigned address is based in part on the unique LAN MAC (Media Access Control) address of the device, which might be in the form of laptop computer. This feature allows the user the same full IPv6 capability when on the road as he might enjoy in the office when the laptop is inserted into a LAN-attached docking station. IPv6 security is provided in several ways. Data integrity and user authentication are provided by any of a number of authentication schemes. Second, the Encapsulating Security Payload feature provides for confidentiality of data through encryption algorithms such as DES (Data Encryption Standard). Several different types of IPv6 addresses support various types of communications. Unicast supports point-to-point transmission, Anycast allows communications with the closest member of a device group, and Multicast supports communications with multiple members of a device group.
Internet Packet eXchange. Novell NetWare's native LAN communications protocol, used to move data between server and/or workstation programs running on different network nodes. IPX packets are encapsulated and carried by the packets used in Ethernet and the similar frames used in Token-Ring networks. IPX supports packet sizes up to 64 bytes. Novell's NCP and SPX both use IPX. See also IPX.COM.
Indefeasible Right of Use (or User). A term used in the underseas cable and fiber optic carrier business. Someone owning an IRU means he has the right to use the circuit for the time and bandwidth the IRU applies to. An IRU is to a submarine or fiber optic cable what a lease is to a building.
Integrated Services Digital Network. ISDN services were the telephone industry's first attempt at providing data connection speeds for you and I at speeds faster than dial-up phone lines. With the exception of the ISDN version of T-1 (more about that in a moment), ISDN has essentially flopped at the hand of DSL, cable modems, Ethernet and the Internet. ISDN equipment cost too much, was far too difficult to connect and far too difficult to keep running. ISDN standards were set by the ITU-T (International Telecommunications Union-Telecommunications Services Sector). Those ISDN standards cover a circuit-switched digital network that supports access to any type of service (e.g. voice, data, and video) over a single, integrated local loop from the customer premises to the network edge. ISDN requires that all network elements (e.g. local loops, PBXs, and COs) be ISDN-compatible, and that the SS7 (Signaling System 7) be in place throughout the entire network. ISDN also specifies two standard interfaces -- BRI and PRI.
BRI (Basic Rate Interface) is the North American term for the low speed version known internationally as BRA (Basic Rate Access). It delivers a total of 144,000 bits per second and is designed for the desktop. (That speed is one-hundredth of what many users receive today through broadband access channels like cable modems.) BRI is known also as 2B+D. The two B (Bearer) channels are information-bearing; that is to say that they support end user data (and voice) transfer. The B channels support "clear channel" communications at 64 Kbps each. The D (Data or Delta) channel is intended primarily for signaling and control (e.g. on-hook and off-hook signaling, performance monitoring, synchronization, and error control) at 16 Kbps. The D channel also will support end user packet data transfer at speeds up to 9.6 Kbps. BRI is intended primarily for consumer and small business applications. As ISDN-compatible terminal equipment generally is too expensive, most end users had opted for a relatively inexpensive Terminal Adapter (TA) that serves as the interface between the ISDN local loop and the non-ISDN terminal equipment.
PRI (Primary Rate Interface) is the North American term for an ISDN T-1 circuit. PRI runs at a total signaling speed of 1,544,000 bits per second and supports up to 24 channels. Also known as 23B+D, PRI supports 23 Bearer channels and one D channel. Multiple PRIs can be linked to share a single D channel, as the signaling and control bandwidth requirements are relatively light; however, a backup D channel is recommended in such implementations in order to ensure that the PRI links continue to function should a D channel fail. ITU-T specifications allow as many as five PRIs to be so linked, although some manufacturers support as many as eight. The European/International version is PRA (Primary Rate Access). Also known as 30B+D, PRA supports 30 B channels and one D channel, and is the ISDN equivalent of E-1. PRI and PRA are intended for application in connecting PBXs, ACDs, and data switches, routers and concentrators to the network. All of these various switching and concentrating devices must be ISDN-compatible. A PRI/T-1 is often installed on two unloaded copper pairs, or more commonly, on fiber.
As ISDN essentially is a highly sophisticated enhancement of the traditional circuit-switched PSTN (Public Switched Telephone Network), it offers the advantage of some flexibility. As long as IDSN is supported by all network elements at all end user locations and throughout the service provider networks, ISDN vendors pushed ISDN's pluses thus: First, a single local loop connecting to a single service provider can support any mix of voice, data and video -- channel-by-channel. Second, multiple channels can be linked together in what is known as "bonding" or "rate adaption." For example, rate adaption allows you to link together two 64-Kbps B channels to form a 128 Kbps chunk of bandwidth for a videoconference or, perhaps, a single symmetric (i.e. equal speed in each direction) Internet access experience at 128 Kbps. Third, ISDN is standardized worldwide (or was), so connectivity generally is not an issue. That is not to say that there are not differences from country to country or region to region, but most of those differences are relatively inconsequential at the basic level.
ISDN has "enjoyed" many "meanings," including "I Still Don't kNow what it means," referring to the fact that ISDN was not well explained by the service providers; "It Still Does Nothing," referring to the fact that ISDN does relatively little of significance (It took so long for the service provider to make it available that technologies like Frame Relay, DSL, cable modems made it obsolete; and "I Smell Dollars Now," referring to the fact that the service providers tried charge a lot for ISDN service.
ISDN was designed originally to be a totally new concept of what the world's telephone system would eventually become. (Remember this "Vision" came long before the Internet.) According to AT&T one of the original ISDN pushers, the public switched phone network had limitations: 1. Each voice line is only 4 KHz, which is very narrow, which limits also the speed you can send data across. 2. Most signaling is in-band signaling, which is very consuming of bandwidth (i.e. it's expensive and inefficient). 3. The little out-of-band signaling that exists today runs on lines separate to the network. This includes signaling for PBX attendants, hotel/motel, Centrex and PBX calling information. 4. Most users have separate voice and data networks, which is inefficient, expensive and limiting. (The Internet solved that one. Now everything, including voice runs on the Internet.) 5. Premises telephone and data equipment must be separately administered from the network it runs on. 6. There is a wide and growing variety of voice, data and digital interface standards, many of which are incompatible. ISDN's "vision" was to overcome these deficiencies in four ways: 1. By providing an internationally accepted standard for voice, data and signaling. That standard has pretty well achieved, though don't try and take North American ISDN equipment to Europe. 2. By making all transmission circuits end-to-end digital. 3. By adopting a standard out-of-band signaling system. 4. By bringing significantly more bandwidth to the desktop. One of the best features of ISDN is the speed of dialing. Instead of 20 seconds for a call to go through on today's still partially analog network, with ISDN it takes less than a second. Also ISDN expanded the range of phone services. Here are some sample ISDN services (some of which are now available on non-ISDN phone lines): Call waiting; Citywide Centrex; Central management of all ISDN terminals; Credit card calling: Automatic billing of certain or all calls into accounts independent of the calling line/s. Calling line identification presentation: Provides the calling party the ISDN "phone" number, possibly with additional address information, of the called party. Such information may flash across the screen of an ISDN phone or be announced by a synthesized voice. The called party can then accept, reject or transfer the call. If the called party is not there, then his/her phone will automatically record the incoming call's phone number and allow automatic callbacks when he/she returns or calls back in from elsewhere. Calling line identification restriction; Closed user group: Restricts conversations to or among a select group of phone numbers, local, long distance or international; Collaborative Computing. Work on the same document or drawing or design with someone 10,000 miles away. Desktop videoconferencing; ISDN can carry information to and from unattended phones as long as they're equipped with proper hardware and software. Internet Access at 128 Kbps instead of 53.3 Kbps which is the fastest you can get on a dial-up phone line; Simultaneous Data Calls: Two users can talk and exchange information over the D packet and/or the B circuit or packet switched channel.
There were three major problems to the widespread acceptance of ISDN: First, the cost of ISDN terminal equipment was too high. Second, the cost of upgrading central office hardware and software to ISDN was too high. Third, Ethernet and the Internet came along. They came out of the "open" computer industry, not the "closed" telephone industry. For more on ISDN, see also AO/DI, Euro-ISDN, Intel Blue, ISDN 2, ISDN 30, ISDN Standards, ISDN Telephone, ISUP, NT1, NT2, Q.931, Robbed Bit Signaling, S Interface, SS7, SPID, T Interface, TCAP, Terminal Adapter, and U Interface.
1. An Internet service provider is a company that offers its customers access to the Internet, and then some. That "some" might be email, voice over IP, a portal into the Internet, news of the world and/or web hosting. In the old days, you connected to an ISP via a dial-up phone line. These days you connect to the Internet via a broadband access line, such as a cable modem or a DSL line. Companies which provide these services are communications carriers. They don't think of themselves as ISPs. At one stage there were dozens of ISPs -- the biggest being CompuServe and AOL. They got rich on monthly subscription fees and advertising featured on their portals -- the page a subscriber received initially when they dialed in. These days users don't access the Internet through ISPs. ISPs have become anachronisms.
2. Information Service Provider. A company which provides information over the phone in response to touchtones punched in by a subscriber. That information may be weather, stock prices, etc. Often it is provided over 900 number, in which a phone company (local or long distance) bills the end user for calls to the ISP (Information Service Provider), paying part of the revenue collected to the ISP and keeping some of it as its collection billing and network fee. In many states, ISPs also use special local numbers, like those in New York beginning with 970 and 976. Most information service providers have moved to the Internet. 3. Integrated Service Provider. This is a term for a company that delivers all of the different data and voice services including: normal dialup phone service, voice over IP, and Internet service. The term is pretty well obsolete today. 4. ISDN Signal Processor. 5. Information Services Platform.
The ITU, an organization based in Geneva, Switzerland, is the most important telecom standards-setting body in the world. In actual fact, it has no power to set standards. But if its members -- virtually every country in the world -- agree on a standard, that effectively becomes a world standard. ITU stands for the International Telecommunication Union, a name that the organization adopted in 1934. The ITU presently consists of three major sectors that were established in 1992: the Radiocommunication Sector (ITU-R), the Telecommunication Development Sector (ITU-D), and the Telecommunication Standardization Sector (ITU-T). When it was created, the ITU-T took over the work formerly done by the CCITT (Comite Consultatif Internationale de Telegraphique et Telephonique or, in English, International Telegraph and Telephone Consultative Committee, which until 1992 had been the most influential telecom standards organization. Even one of the ITU's own acronyms databases lists "Telecommunications Standardization Sector" as the meaning of the "-T" in "ITU-T." However, the official names of the organizations are International Telecommunication Union" and International Telecommunication Union-Telecommunication Standardization Sector. The scope of the ITU's work is now much broader than just telegraphy and telephony. It now also includes IP voice, telematics, data, new services, systems and networks (like ISDN). The ITU is a United Nations Agency and all UN members may also belong to the ITU, represented by their governments. In most cases, the governments hand their rights on their national telecom standards to their telecommunications administrations (PTTs). But other national bodies (in the US, for example, the State Department) may additionally authorize Recognized Private Operating Agencies (RPOAs) to participate in the work of the ITU. After approval from their relevant national governmental body, manufacturers and scientific organizations may also be admitted, as well as other international organizations. This means, says the ITU, that participants are drawn from the broad arena. The activities of the ITU-T divide into three areas: Study Groups (at present 15) to set up standard ("recommendations") for telecommunications equipment, systems, networks and services. Plan Committees (World Plan Committee and Regional Plan Committee) for developing general plans for a harmonized evolution of networks and services. Specialized Autonomous Groups (GAS, at present three) to produce handbooks, strategies and case studies for support mainly of developing countries.
Jitter is variability in latency, or delay. If a network provides varying levels of latency (i.e. different waiting times) for different packets or cells, it introduces jitter, which is particularly disruptive to audio communications because it can cause audible pops and clicks. Jitter is also the tendency towards lack of synchronization caused by mechanical or electrical changes. Technically, jitter is the phase shift of digital pulses over a transmission medium. Three forms of jitter exist: Data Dependent Jitter (DDJ), Duty Cycle Distortion (DCD), and Random Jitter (RJ). Data Dependent Jitter is caused by limited bandwidth characteristics and imperfections in the optical channel components as it relates to the transmitted symbol sequence. This jitter results from less than ideal individual pulse responses and from variation in the average value of the encoded pulse sequence which may cause baseline wander and may change the sampling threshold level in the receiver. DCD Jitter is caused by propagation delay differences between low-to-high and high-to-low transitions. DCD is manifested as a pulse width distortion of the nominal baud time. RJ is the result of thermal noise.
Layer 2 Tunneling Protocol. An IETF (Internet Engineering Task Force) standard tunneling protocol for VPNs (Virtual Private Networks). L2TP evolved from a combination of PPTP (Point-to-Point Tunneling Protocol) and the proprietary Layer 2 Forwarding (L2F) protocol from Cisco. L2TP is used to provide secure, node-to-node communications in support of multiple, simultaneous tunnels in the core of the Internet or other IP-based network. End user access to the ISP is on an insecure basis. The network provider assumes responsibility for encryption at the network edge. See also IETF, L2F, PPTP, Tunneling, and VPN.
A set of symbols used to identify or describe an item, record, message or file. It can also be the same as the address in storage.
Local Area Network. A fancy name for a communications network connecting personal computers, workstations, printers, file servers, scanners, and other devices inside a home, an office, a home, a factory, a building or a campus. Devices on a LAN can connect to each other, either over cables or through the air. A PC can send another a file. One PC can print to any printer connected to the LAN -- high-speed ones, expensive color printers, etc. Devices on one LAN can transmit to the outside world if the LAN is connected to a telecommunications link. That link might be the Internet. It may be a link into a corporate network, which would let the LAN connect to a LAN across the country. LANs come in many flavors. But by far the most popular is Ethernet. LANs have come a long way. LAN software used to be difficult to install and expensive to buy. Now all Windows and Apple computers have built-in LAN software. And virtually all computers have Ethernet LAN hardware built in. (It wasn't always so.) LANs come in wired and wireless versions. A simple hub you buy at your local electronics store will connect your LAN with your cable modem or DSL line to the Internet and allow your computer and your various stuff to connect together to each other and to the Internet. See also AppleTalk, Ethernet, local area network, LocalTalk, network and how to set up a home or small office network in the Introduction.
The last mile is an imprecise term that typically means the link between an end-user and the telephone company central office -- local, long distance or Internet. Of course, it doesn't mean a "mile," since that "mile" could be less than a mile or several miles. The term has entered the language referring to the problems of your telecommunications service making it that last mile at a price you can afford, for the quality you deserve and achieving a decent speed. Let's take price first. Competition in telecom has been heavily concentrated on long distance and international. Carriers in long distance and international have relied on local phone companies to deliver their customers' communications. Since there was little competition, the price for the last mile has often been very high. Second, there's the issue of the technology and quality of that last mile. Often that last mile runs over old, limited bandwidth copper wire that has been in the ground or on telephone poles for eons and is supplied by a sleepy phone company wnich doesn't have any competition and has little incentive to provide its competitors with a competitve edge. The "solution" to the local loop issue has often been to introduce competition in the form of a cable company or have the long distance company build local facilities.
The OSI (Open Systems Interconnection) Reference Model, organizes the communications process into seven separate and distinct, interrelated categories in a layered sequence. Layer 2 is the Data Link Layer (DLL). It is concerned with procedures and protocols for operating the communications lines, including the detection and correction of message errors. X.25 and Frame Relay are examples of Layer 2 protocols. See also OSI Reference Model.
In the widely-adopted OSI (Open Standards Interconnection) model, there are seven levels defined of interconnection. Layer 3 is the Network layer. It determines how data is transferred between computers. It also addresses routing within and between individual networks.
1. A software-based telephone system feature that automatically chooses the lowest cost phone line to the destination. What actually is the "lowest cost" is determined by algorithms, equations and decision trees programmed into the PBX. Least Cost Routing typically works with "look-up" tables in the PBX's memory. These tables are put into the PBX by the user. The PBX does not automatically know how to route each call. It must be told so by the user. That "telling" might be as simple as saying "all 312 area codes will go via the company FX (foreign exchange) line." Or it might be as complex as actually listing which exchanges in the 312 area code go by which method. Least cost routing tells the calls to go over the lines which are perceived by the user to be the least cost way of getting the call from point A to point B. There are typically two types of "least cost routing" translation -- that which examines the first three digits of the phone number (i.e. just the area code) and the first six digits of the phone number (i.e. the area code and the three digits of the local central office). Six digit translation is preferred because it allows you more flexibility in routing -- particularly to big area codes, like 213 in LA, where there are long distance calls within the area code. These days, least cost routing can virtually be "no cost" routing. For example, a company might choose to ship its voice calls via VoIP over its own internal data network. If there's unused capacity on that network the voice calls are essentially going for free. Least cost routing can also be done in stages. For a New York to LA call, a company might choose to use the company's data network as a VoIP call and then to hop off the end as a local call. Least cost routing was a huge advance in telephony when coast to coast calls in the U.S. were 35 cents a minute. Now they're one cent a minute for big companies, least cost routing is less significant.. 2. Line Concentration Ratio. A CO (Central Office) design and engineering term for the optimization of system capacity through the classic act of balancing cost and performance. LCR is used to determine central office switching equipment quantities and configurations based upon line usage. It is neither necessary nor economical to equip every outside line with a dedicated path through the switch. With the possible exceptions of Mother's Day or when George Straitconcert tickets go on sale, not every line goes off hook at the same time. The higher ratios have been predominantly used in rural areas while the lower, more equipment intensive ratios have been the standard in urban and suburban areas. An LCR of xx:1 indicates that there exists one predetermined dial tone path for any given number (xx) of lines at a given time; in other words, an LCR of 6:1 means that six lines would have access to one dial tone path through the switch.
While the specific architecture of the central office switch manufacturer impacts the LCR calculations, in the AT&T 5ESS switch, the following calculations show the maximum allowable lines per line unit when assuming an average holding time. Exceeding the maximum allowed lines would require load balancing of line units, deloading line units, or extra line unit equipment. The following is based on the relatively short holding times characteristic of voice communications.
4:1 concentration ratio, 256 lines/unit, 5.74 ccs/line, 1470 ccs/unit
6:1 concentration ratio, 384 lines/unit, 4.30 ccs/line, 1650 ccs/unit
8:1 concentration ratio, 512 lines/unit, 3.32 ccs/line, 1700 ccs/unit
Note that there are 64 voice-grade channels of 64 Kbps per unit. Also note that "ccs" means "centum call seconds," which translates to "100 call seconds." A voice-grade channel supports up to 36 ccs, which is 3600 seconds (60 seconds x 60 minutes = 3600 seconds per hour) of traffic capacity.
At one stage the Internet forced the re-evaluation of the LCR and equipment capacities, as circuit-switched connections through the CO to an ISP tended to last a very long time compared to voice conversations. But that has changed once again, as dial-up Internet calls have switched to broadband access lines, like cable and DSL.
1. Local Exchange Carrier. The local phone companies, which can be either a Bell Operating Company (BOC) or an independent which traditionally had the exclusive, franchised right and responsibility to provide local transmission and switching services. Prior to divestiture, the LECs were called telephone companies or telcos. With the advent of deregulation and competition, LECs now are known as ILECs (Incumbent LECs). This terminology separates them from CLECs (Competitive LECs). CLECs were invented in 1996 as a phone companies which would use the local phone companies'(LECs') facilities. 2. LAN Emulation Client: An ATM term for a router capable of supporting LANE (LAN Emulation). It works like this: A LAN-attached device, typically in the form of a PC, addresses another LAN-attached device-of course, the originating device hasn't a clue where the other device is physically located. When the router receives the data packets, it exercises its LEC capability, establishing a connection to an edge ATM switch, mapping the native LAN MAC addresses to ATM addresses. Through the ATM network, a matching connection is established to a matching LEC. MPOA (MultiProtocol Over ATM) is much better, but less mature. See also LANE and MPOA.
1. As a noun, it's all the stuff you have on hand -- equipment, software, files and paperwork. Everything of a computer/telecommunications nature in your business today. The use of the word legacy suggests that you've inherited all this stuff. And it's old stuff and now sadly, obsolete. Hence bad. Most English dictionaries define the word legacy as anything handed down from the past. And many vendors use the word legacy pejoratively. If you own legacy equipment it must be obsolete and hence in need of being replaced with expensive new equipment which the vendor will happily sell you. Of course, the new stuff is not inexpensive and potentially problematical. It's often a toss-up between two aphorisms, the first being -- don't mess with something that works -- and the second being -- take advantage of the efficiencies of new technologies. 2. Microsoft defines legacy as hardware and devices cards that don't conform to its Plug and Play standard. 3. As an adjective, you'll find the word in legacy system, legacy media, legacy bank. In this case, it's often referred to as pre-Internet way of the doing things.
Label Edge Router: Converts IP packets into MPLS packets, and MPLS packets into IP packets. On the ingress side, the LER examines the incoming packet to determine whether the packet should be labeled. A special database in the LER matches the destination address to the label. An MPLS shim header is attached and the packet is sent on its way. The LER adds and/or removes (pops or pushes) labels. See MPLS.
Local Loop Unbundling. This term is used in England where British Telecom (BT), the pre-eminent British telecom company, encourages other telecom companies to rent the copper wire in its local loops for applications such as broadband Internet access such as DSL. Local loop unbundling hapened in the U.S. after the Telecommunications Act of 1996. Because the main renters tended to be companies who wanted to use the phone companies' own cables to compete against the phone companies, the risk of success was small. And predictably, most CLECs, as they were called in the U.S. (competitive local exchange carriers), failed. In the melee that followed, the good news was that the price of DSL lines fell worldwide
The physical or wireless connection from the subscriber's premise to the carrier's POP (Point of Presence), also called central office or pubic exchange. The local loop can be provided over any suitable transmission medium, including twisted pair, fiber optic, coaxial cable, microwave or radio of some kind. Traditionally and most commonly, the local loop is a twisted pair or pairs between the telephone set, PBX or key telephone system, and the LEC (Local Exchange Carrier) CO (Central Office). As a result of the deregulation of inside wire and cable worldwide, the local loop typically goes from the demarc (demarcation point) in the phone room closet, in the basement or garage, or on the outside of the house, to the CO. The subscriber or building owner is responsible for extending the connection from the demarc to the phone, PBX, key system, router, local area network, computer or other CPE device.
Trunks between Class 5 local central offices, also called switching centers.
Multipoint Control Unit. A bridging or switching device used in support of multipoint videoconferencing and supporting as many as 28 conferenced sites. The devices may be in the form of CPE or may be embedded in the WAN in support of carrier-based videoconferencing services. MCU standards are defined in ITU-T H.231, with T.120 describing generic conference control functions.
Imagine a bunch of network nodes -- where users get on and off a network. The nodes are perhaps buildings, perhaps towers on mountain tops, perhaps antennas on telephone poles, or perhaps just wireless devices on various floors of a building. Imagine now that basically each of the nodes are joined together by telecom "lines" -- wireless or wired. Now you have a mesh network. The advantage of a mesh networks include:
The disadvantages of a full mesh network include high costs, difficulty of configuration and reconfiguration, and lead times associated with carrier provisioning. Mesh networks are relatively easy and inexpensive to configure where four or fewer sites must be interconnected; the cost and complexity increase significantly where more than four sites are involved. As a result, large organizations increasingly tend to favor alternative solutions for voice and data. Such alternatives as fiber ring networks, Virtual Private Networks (VPNs), Frame Relay, SMDS and ATM.
The switchover from one system to another, for example, from one network to another, or from one switch to another, or from one email system to another.
Modified Modified Read data compression method used in Group 3 facsimile machines.
Acronym for Modulator/DEModulator. A modem converts digital signals to analog signals and vice versa. Modems are used to send digital data signals over analog phone lines, e.g. a local dial-up phone line. Modems work like this. Your PC outputs data in the form of "1's" and "0's" which are represented by varying levels of voltage. The modem converts the digital data signal into variations of the analog sine wave so the data can be transmitted over analog phone lines. A matching modem on the other end reverses the process in order to present the target device with a digital bit stream. The modulation techniques include some combination of Amplitude Modulation (AM), Frequency Modulation (FM) and Phase Modulation (PM), also known as Phase Shift Keying (PSK). Used in combination, these techniques allow multiple bits to be represented with a single (or single set) of sine waves. In this fashion, compression is accomplished, which allows more data to be transmitted in the same period of time and which therefore reduces the connect time and the associated cost of the data transfer. Contemporary, conventional modems are standardized by the ITU-T as part of the "V" series of standards. Such modems are characterized by error detection and correction mechanisms, adaptive equalization, internal dialing, and numerous other capabilities. 56 Kbps modems are the latest development in the world of conventional modems and are about the fastest able to be used on conventional dialup phone lines. The term "modem" also is applied (and correctly so, in the purely technical sense) to ISDN TAs (Terminal Adapters), ADSL TUs (Terminating Units), line drivers and short-haul modems. The last two, in fact, are voltage converters.
Modems have progressed. Now there are cable modems which support high-speed (now called broadband) data communications over the coaxial cable owned by a local cable TV company. There are also DSL modems which support high-speed broadband data communications over phone lines that have been conditioned to support broadband service.
1. Memorandum Of Understanding. In the old days, we called MOUs "Letters of Understanding." We've become more fancy. We now call them "Memorandum of Understandings." Whatever you call them, they're basically bits of paper which detail the essence of a legal agreement -- what you will do and what I will do and how much money will change hands. An MOU is not a legally-binding contract or agreement. Once we've agreed and detailed our agreement in a MOU, the MOU goes to a lawyer, who quadruples its size and its complexity, and makes it into a legal Agreement. Don't tell the lawyers, however: If two of us had signed the MOU and changed its name to an "Agreement," it would be a legally binding agreement. And half the world's lawyers would be out of a job. 2. Minutes Of Use.
Multiprotocol Label Switching (MPLS) is a way for high-performance telecommunications networks to direct and carry data from one network node to the next. MPLS lets you create "virtual links" between distant nodes. It can encapsulate packets of various network protocols. In an MPLS network, data packets are assigned labels. Packet-forwarding decisions are made solely on the contents of this label, without the need to examine the packet itself. This allows you to create end-to-end circuits across any type of transport medium, using any protocol. The primary benefit is to remove dependence on a particular Data Link Layer technology, such as ATM, frame relay, SONET or Ethernet, and eliminate the need for multiple Layer 2 networks to satisfy different types of traffic. MPLS belongs to the family of packet-switched networks. MPLS operates at an OSI Model layer. It is often referred to as a "Layer 2.5" protocol.
It can be used to carry many different kinds of traffic, including IP packets, as well as native ATM, SONET, and Ethernet frames. MPLS works by prefixing packets with an MPLS header, containing one or more 'labels'. This is called a label stack. Each label stack entry contains four fields:
+ A 20-bit label value.
+ A 3-bit Traffic Class field for QoS (Quality of Service) priority (experimental) and ECN (Explicit Congestion Notification).
+ A 1-bit bottom of stack flag. If this is set, it signifies that the current label is the last in the stack.
+ An 8-bit TTL (time to live) field.
These MPLS-labeled packets are switched after a Label Lookup/Switch. The entry and exit points of an MPLS network are called Label Edge Routers (LER), which push an MPLS label onto an incoming packet and pop it off the outgoing packet. Routers that perform routing based only on the label are called Label Switch Routers (LSR). In some applications, the packet presented to the LER already may have a label, so that the new LSR pushes a second label onto the packet.
MPLS is family of IETF standards in which Internet Protocol networks can make forwarding decisions based on a pre-allocated label to set up a Label Switched Path (LSP). MPLS grew out of Cisco's proprietary TAG Switching protocol. MPLS has faster forwarding performance than IPv4 networks due to its ability to make decisions based on the pre-allocation of a 20-bit label through the IPv4 routing protocols. MPLS works like this: As an IP data stream enters the edge of the network, the ingress Label Edge Router (LER) reads the destination address of the first data packet and attaches a 32-bit shim header "label" in between the layer 2 and layer 3 headers of the packet The label is mapped to a Forwarding Equivalency Class (FEC) based on the destination network and the MPLS EXP value which signified the QoS level. The Label Switch Router (LSR) in the core of the network examine the 20-bit label, and switches the packet with greater speed than if the device had to interrogate the IP routing table of the device. The router swaps the label with the new label that the next router needs to assist in the completion of the LSP. There are two flavors of MPLS available: Frame-based and cell-based. Cell-based MPLS is used in ATM networks, while frame-based MPLS is used in packet-based networks like Ethernet and Frame-Relay. Although MPLS offers slight performance increases, the richness of MPLS comes from the MPLS Applications. The two MPLS applications most widely deployed are MPLS VPNs (IETF RFC2547) and MPLS Traffic Engineering.
Mobile Switching Center. A switch providing services and coordination between mobile users in a network and external networks.
MultiService Provisioning Platform. A marketing term for a network of devices (e.g. switches and multiplexers) that can support multiple protocols (e.g. ATM, Ethernet and IP) and multiple services such as voice, data and video in a variety of formats.
Electronic equipment which allows two or more signals to pass over one communications circuit. That "circuit" may be a phone line, a microwave circuit, a through-the-air TV signal. That circuit may be analog or digital. There are many multiplexing techniques. When spelled "multiplexor," it refers only to optical units. Some multiplexing methods include Frequency Division Multiplexing, Time Division Multiplexing and Pulse Code Modulation. See also packet switching and the Internet.
See multiplexer.
A defect in infrared systems that appears as a dark circular area on a displayed image, caused by radiation reflecting into a detector. It can be reduced by low-reflective coatings or by altering the lens surface.
Networks are common in our lives. Think about trains and phones. A network ties things together. Computer networks connect all types of computers and computer related things -- terminals, printers, modems, door entry sensors, databases, temperature monitors, etc. The networks we're most familiar with are long distance ones, like phones, trains and the internet. But there are also Local Area Networks (LANs) which exist within a limited geographic area -- like the few hundred feet of a small office, an entire building or even a "campus," such as a university or industrial park. There are also Metropolitan Area Networks (MANs). There's a network law: the more things (including people) connected to the network, the more useful the network. A phone network with only 20 phones is not as useful as one with 5,000. See also LAN and MAN.
Next generation networking is a marketing term designed to entice you, the customer. NGN describes an all-IP network to be deployed sometime over the next 5-10 years. The general idea behind NGN is that one network transports all information and services (voice, data, and all sorts of media such as video) by encapsulating these into packets, like it is on the Internet. (Maybe that's what the Internet already is.) NGNs are commonly built around the Internet Protocol, An NGN is meant to be the ultimate network -- able to provide any network service, including broadband, quality of service-enabled transport technologies and in which service-related functions are independent of the underlying transport-related technologies. See also Carrier Ethernet Transport.
Network to Network Interface is an protocol interface which specifies signaling and management functions between two networks. An NNI circuit can be used for interconnection of either signaling (e.g. SS7), IP (e.g. MPLS) or ATM networks. Basically NNI is used for interconnection of P (class 4 or higher provider core) routers in signaling or GMPLS networks. NNI can be used for interconnection of two VoIP nodes. In GMPLS case that could be Back-to-Back or eBGP or mixed NNI connection scenarios depends on what type of VRF exchange is used for interconnection. In case of Back-to-Back VRF it is necessary to create VLANs and subsequently sub-interfaces (VLAN headers and DLCI headers for Ethernet and Frame Relay network packets) on the each interface used for the NNI circuit. In case of eBGP NNI interconnection P routers are taught how to dynamically exchange VRF records without VLAN creation. In cases of mixed or full-mesh scenarios, other NNI types are possible. Note that there could be different encapsulation types for NNI interconnection, but Ethernet (GigE) and Frame Relay are basically used. Network-Network Interface (in Telecommunication). NNI is defined by the Frame Relay Forum and the ATM forum to govern how ATM switches establish connection and how ATM signaling requests are routed through an ATM network. Equivalent to a routing protocol in a router environment. There are two types of network interfaces specified by frame relay standards. The first is a user-to-network (UNI) interface and the second is a network-to-network interface (NNI). The NNI describes the connection between two public frame relay services, and includes elements such as bidirectional polling, to assist the network services providers with gaining information on the status of the public networks being interconnected.
A network operations center (or NOC, pronounced "knock") is one or more locations from which control is exercised over a computer, television broadcast, utility, and/ or telecommunications network. NOCs are responsible for monitoring a network for everything that can go right and wrong with it -- from power failures, to line problems, to alarms, to circuit overloads, to major and minor disasters, like earthquakes, fires, etc. NOCs analyze problems, perform troubleshooting, communicate with site technicians and other NOCs, and track problems through resolution. NOCs escalate problems. Large organizations may operate more than one NOC, either to manage different networks or to provide geographic redundancy in the event of one site being unavailable or offline. Many NOCs are large and have their own management hierarchy. A newly-hired NOC technician might be considered a "tier 1", whereas a technician that has been there for several years may be considered a "tier 3" or "tier 4". NOCs tend to look the same. They have many people sitting in front of computer screens, often in tiered rows and al facing forward to what might be a collection of immense screens, keeping tabs on the network's metrics. Also called NCC for Network Control Center and Network Operations Control Center.
A point of entry into a network or a point of connection in the network. That's it. After that you can add complexity. For example, you can define it by the network and protocol layer referred to. You can define it by whether it's an active electronic device and capable of sending, receiving, or forwarding information over a communications channel. Or it can be a passive distribution point such as a hub. When you graph a network, the node refers to the point at which lines intersect or branch.
Operations, Administration, Maintenance and Provisioning. This term refers to the specifics of managing a telecommunications network. In simple terms that means everything relating to keeping it running and providing services to customers from it. It is typically a group of network management functions that provide everything from network fault indication, performance information, and data and diagnosis functions. Some switches have computers devoted to OAM&P.
Phone call which is carried in part on a network but are destined for a phone not on the network, i.e. some part of the conversation's journey will be over the public switched network or over someone else's network. The concept of off-net calling is important for billing.
Operations Support System. Methods and procedures (computerized or not) which directly support the daily operation of the telecommunications infrastructure. The average LEC (Local Exchange Carrier) has hundreds of OSSs, including automated systems supporting order negotiation, order processing, line assignment, line testing and billing.
Private Automatic Branch eXchange. Originally, PBX was the word for a switch inside a business, government office or college campus, (as against one owned by the phone company and serving the public). PBX means a Private Branch Exchange. Such "PBX" was typically a manual device, requiring operator assistance to complete a call. Then the PBX went "modern" (i.e. automatic) and no operator was needed any longer to complete outgoing calls. You could dial "9," reach an outside line and dial whatever number you wanted. Thus it became a "PABX." Now all PABXs are modern. And a PABX is now commonly referred to as a PBX, or just a business telephone switch.
Term for a bundle of data organized in a specific way for transmission. A packet consists of the user data to be transmitted and control information. The packet has the user data (the payload) plus administrative information in one or more headers (a header and possibly a trailer). The specific native protocol of the data network may call the packet a packet, block, frame or cell. The three principal elements of a packet include: 1. Header -- control information such as synchronizing bits, address of the destination or target device, address of originating device, length of packet, etc. 2. Text or payload -- the data to be transmitted. The payload may be fixed in length (e.g. X.25 packets and ATM cells), or variable in length (e.g. Ethernet and Frame Relay frames). 3. Trailer -- end of packet, and error detection and correction bits. See also ATM, Block, Cell, CRC, Ethernet, Frame Relay, Packet Assembler/Disassembler (PAD) and X.25.
Sending data of any kind -- voice, video, images -- in packets through a network to a remote location. The data to be sent is assembled by the PAD (Packet Assembler/Disassembler) into individual packets of data, involving segmenting or subdividing larger sets of data as specified by the native protocol of the transmitting device. Each packet has a unique identification and each packet carries its own destination address. Thereby, each packet is independent, with multiple packets in a stream of packets often traversing the network from originating to destination packet switch by different routes. Since the packets may follow different physical paths of varying lengths, they may experience varying levels of propagation delay, also known as latency. Additionally, they may encounter varying levels of delay as they are held in packet buffers awaiting the availability of a subsequent circuit. Finally, they may be acted upon by varying numbers of packet switches in their journeys through the network, with each switch accomplishing the process of error detection and correction. As a result, the packets may also arrive in a different order than they were presented to the network. The packet sequence number allows the destination node to reassemble the packet data in the proper sequence before presenting it to the target device. Originally developed to support interactive communications between asynchronous computers for time-share applications, packet switched networks are shared networks, based on the assumption of varying levels of latency and, thereby, yielding a high level of efficiency for digital data networking. Isochronous data such as realtime voice and video, on the other hand, are stream-oriented and highly intolerant of latency. As a result, packet switched networks were originally considered to be inappropriate for such applications. Recent development of certain software and making use of complex compression algorithms, however, has introduced packetized voice and video to corporate intranets and the Internet, which was the first public packet-switched data network and remains by far the most heavily used. Here is another way of explaining packet switching: There are two basic ways of making a call. First, the one everyone's familiar with -- the common phone call. You dial. Your local switch finds an unused path to the person you called and joins you. While you are speaking, the circuit is 100% all yours. It's dedicated to your conversation. This is called circuit switching. Packet switching is different. In packet switching, the "conversation" (which may be voice, video, images, data, etc.) is sliced into small packets of information. Each packet is given a unique identification and each packet carries its own destination address -- i.e. where it's going. Each packet may go by a different route. The packets may also arrive in a different order than how they were shipped. The identification and sequencing information on each packet lets the data be reassembled in proper sequence. Packet switching is the way the Internet works. Circuit switching is the way the worldwide phone system basically works, also called the PSTN (Public Switched Telephone Network). Packet and Circuit Switching each have their own significant advantages. Packet switching for example does a wonderful job getting oodles of data into circuits. Think about a voice conversation. When you are talking, he's listening. Therefore half the circuit is dead. There are pauses between your voice. Packet switching takes advantage of those pauses to send data. Packet switching has been used primarily for data. But with the growth of the Internet, it has been used also for voice and video. Because of the need to re-assemble packets and other reasons, there used to be up to a half second delay between talking and the person at the other end hearing anything. But equipment and speed has improved and now package voice on the Internet or on corporate Intranets (also called VoIP -- voice over IP) means Internet voice is typically as clear as circuit switched voice. And the quality of VoIP is getting better and better as the packets come faster and the technology improves. See Internet, IP Telephony and TAPI 3.0
Peering is connecting two or more communications and networks thus carrying each other's traffic, and figuring out how to pay each other for the traffic each carries. The phone industry figured interconnection out eons ago and used complex rules originally established by AT&T. The term peering came about with the Internet. Carriers of Internet traffic called ISPs (Internet Service Providers) had to figure out how to charge for their services. Traditional Internet architecture (to the extent that there is a "traditional architecture") calls for ISPs and regional carriers to exchange traffic at Network Access Points (NAPs), using carrier-class switches and routers, of which there currently are a dozen or so around the world. Traditionally, that traffic has been exchanged between one ISP and another at no cost, although that no longer is true. In order to avoid the headaches and expenses of figuring who should get paid and for how much, many of the larger ISPs have developed peering relationships which allow them to exchange traffic directly over dedicated circuits. In some geographical regions, mostly in North America, several ISPs have formed "private peering points." These packet switching centers allow them to exchange traffic on a switched basis, once again avoiding the cost of doing so through a NAP. Peering requires the exchange and updating of router information between the peered ISPs, typically using the border gateway protocol (BGP). Initially, peering arrangements did not include an exchange of money. More recently, some larger lSPs have charged smaller lSPs for peering. Each major ISP generally develops a peering policy that states the terms and conditions under which it will peer with other networks for various types of traffic.
1. Personal Handy Phone. Japan's standard for digital cordless phones.
2. PHP is a widely-used, general-purpose scripting language that is especially suited for web development. PHP generally runs on a web server. Any PHP code in a requested file is executed by the PHP runtime, usually to create dynamic web page content. It can also be used for command-line scripting and client-side GUI applications. Initially known as Personal Home Page Tools and now officially called PHP: Hypertext Preprocessor, PHP was developed in late 1994 by Rasmus Lerdorf. Its aim is to make it easy to write dynamic Web pages. PHP code is embedded into standard HTML Web pages. I use PHP on my main web site, www.TechnologyInvestor.com.
Platform is a loosely-defined word for a software operating system and/or open hardware, which an outsider could write software for. Windows, Linux, Unix and the Mac OS are platforms. If every phone system were a platform, every owner of that phone system could write software for his phone system or buy outside-produced software and have his phone system work more to his liking. That's the objective of creating a "platform."
Passive Optical Network is a fiber optic network without active electronics, such as repeaters you plug into the wall or a battery. A PON uses passive splitters to deliver signals to multiple terminal devices. Passive optical networking (PON) technology allows a fiber optic network to be built without the costly, active electronics found in all other types of networks. Rather, a PON network relies on inexpensive optical splitters and couplers, which are placed at each fiber "junction," or connection, throughout the network, providing a tremendous fan-out of fiber to a large number of end points. By eliminating the dependence on expensive active network elements -- and the ongoing powering and maintenance costs associated with them -- carriers can realize significant cost savings. PON technology generally is used in the local loop to connect customer premises to an all-fiber network. A PON is a tree-like structure consisting of several branches, called Optical Distribution Networks. These run from the central office to the customer premises using a mix of passive branching components, passive optical attenuators and splices. Three active devices can be used in a PON. An Optical Line Terminal (OLT) either generates light signals on its own or takes in SONET signals from a collocated SONET crossconnect. The OLT then broadcasts this traffic to either an Optical Network Unit ONU or an Optical Network Termination, which receives the signal and converts it into an electrical signal for use in the customer premises. The speed of operation depends on whether the PON is symmetrical or asymmetrical. Symmetrical PONs operate at OC-3 speeds (155.52Mbit/sec), for asymmetrical PONs the upstream transmission is also 155.52Mbit/sec from the Optical Network Termination to the customer premises; downstream transmission can range between 155.52 to 622.08Mbit/sec. Depending on where the PON terminates, the system can be described as fiber-to-the-curb (FTTC), fiber-to-the-building (FTTB), or fiber-to-the-home (FTTH). Most PON approaches start with the specifications developed by the Full Service Access Network (FSAN) initiative. Variations on the PON theme include APON (ATM over PON) and TPON (Telephony over PON).
1. Point Of Presence. An Internet point of presence is an access point to the Internet. It is a physical location that houses servers, routers, ATM switches and digital/analog call aggregators. It may be either part of the facilities of a telecommunications provider that the Internet service provider (ISP) rents or a location separate from the telecommunications provider. ISPs typically have multiple POPs, sometimes numbering in the thousands. POPs are also located at Internet exchange points and colocation centers. The telephone industry's Point Of Presence is the interexchange carrier's equivalent of a local phone company's central office. The POP is a long distance carrier's office in your local community (defined as your LATA). A POP is the place your long distance carrier, called an IntereXchange Carrier (IXC), terminates your long distance lines just before those lines are connected to your local phone company's lines or to your own direct hookup. Each IXC can have multiple POPs within one LATA. All long distance phone connections go through the POPs. 2. Post Office Protocol. An e-mail server protocol used in the Internet. You use POP to get your mail and download it to your PC, using SMTP (Simple Mail Transfer Protocol). POP3 is the current version, as defined in RFC 1725. POP is increasingly being replaced by IMAP.
1. noun. The physical interface between a device and a circuit. The device may be a system (e.g. a mainframe, PC, or other host computer), a switch (e.g. PBX, Central Office, or ATM switch) or router, a hub or bridge, a buffer, a printer or other peripheral, or virtually any other type of device. The port and circuit may be either digital or analog, and either electrical (e.g. twisted pair or coaxial cable) or optical (e.g. optical fiber). The port and circuit connect through some sort of plug and socket arrangement. For example, your PC typically has one or more serial ports, a parallel port, a USB port and maybe a firewire port. 2. noun. A logical point of connection, most especially in the context of TCP (Transmission Control Protocol, which is part of the TCP/IP protocol suite developed for what we now know as the Internet. Port numbers are 16-bit values which range from 0 to 65,536. "Well-known ports" are numbered 0 to 1,023, and assigned by the IANA (Internet Assigned Numbers Authority) for the use of system (root) processes or by programs executed by "privileged users." Examples of well-known ports include 25 for SMTP (Simple Mail Transfer Protocol), 80 for HTTP (HyperText Transport Protocol), and 107 for Remote Telnet Service). In the Internet TCP/IP-based client/server environment the ports are assigned by the server in consideration of the application-level protocol being exercised at the client level. In Internet terms, it is the identifier (16-bit unsigned integer) used by Internet transport protocols to distinguish among multiple simultaneous connections to a single destination host. "Ephemeral ports" are short-lived ports assigned randomly to the source port of the sender, or client. Ephemeral port numbers usually have a value between 1,024 and 5,000. Their short life is due to the fact that the client normally stops using the randomly selected port number once the transaction or session is completed. 3. verb. To move a process, program or subroutine from one processor, controller, or operating system to another. For example, a software developer might "port" an application software system from UNIX to Windows. 4. verb. To transfer a customer's phone number from one carrier to another.
Also called web portal. The classic definition of a portal is a door, gate, or entrance, especially one of imposing appearance, as to a palace. In the Internet / World Wide Web, a portal is a site, which the owner positions (through marketing and heavy promotion) as an entrance to all the other web sites on the Internet. In the old days, you had no choice. You dialed your ISP (Internet Service Provider). As the ISP answered you landed on the ISP's portal. You would then savor the advertising on his site (an important way of his making money). In those days, a portal typically had, at minimum, some news, a search engine, free email, instant messaging and chat. In the past, companies like America Online and CompuServe would have been called portals. Many browsers then (e.g. Netscape Navigator and Internet Explorer) pointed you to a Web site -- their own Web site, which they were endeavoring to position as a "portal." Once there, you might then want to use a search engine. You would then be taken to their Web site. These sites would be your secondary portal, or point of entry, into the Web. Each of these first and secondary portals had advertisements. The concept of a web portal is now dead, or almost dead. Few people reach the Internet any longer using a dial-up ISP. Most people access it via permanent broadband access line -- DSL, cable or T-1. They launch their browser and it takes them typically to a web site of their choice, or often the last one they visited). In short, web portals no longer really exist, though the once-greatest of them all, AOL, tries to hang on.
Point-to-Point Protocol. PPP is a data link protocol used to establish a direct connection between two networking nodes. It can provide connection authentication, transmission encryption privacy, and compression. It is a Layer 2, or Data Link Layer (DLL), protocol that allows two peer devices (e.g. two host computers, or a host computer and a bridge or router) to transport packets over a simple link. PPP commonly is used to support TCP/IP traffic between an asynchronous PC and an access router for Internet access over a dialup serial link. This generally is the way that you connect across the PSTN (public switched telephone network) from your PC at home to your ISP (Internet Service Provider). PPP is a connection-oriented protocol that encapsulates packet data using a variation on the HDLC (High level Data Link Control) protocol. PPP, which largely has replaced the less robust predecessor SLIP (Serial Line Internet Protocol), supports full-duplex data transmission, both synchronous and asynchronous. PPP includes error detection and data protection features, unlike SLIP. See also HDLC, Link Control Protocol, Multilink PPP, PPPoA, PPPoE, and SLIP.
Taking the initiative. Doing it before someone (most likely your competition) forces you to do it. The word is currently in vogue among those people who believe the telephone companies should do all the positive, forward-looking actions before the competition does them, wins the customers and gets the public kudos. The word has no real meaning, but serves a purpose as a cry to action. The word actually is grammatically incorrect. The real word is "active." It is the opposite of reactive.
Protocols define the rules by which devices talk with each other, or more formally, a protocol is a set of rules governing the format of messages that are exchanged between computers and people. Imagine making a phone call. You pick up the phone, listen for dial tone, then punch out some buttons on your phone, then listen for ringing and for an answer. The person says "Hello." You say "Hello." Then you talk... What you're doing is following a protocol to make a call. When computers make calls between themselves -- to transfer data, for example -- they follow a protocol. They aren't smart, like you and I. They can't distinguish between dial tone and fast busies, unless those sounds and signals are specifically defined. A protocol defines the procedure for adding order to the exchange of data (i.e. a "conversation.") A protocol is a specific set of rules, procedures or conventions relating to format and timing of data transmission between two devices. It is a standard procedure that two data devices must accept and use to be able to understand each other. The protocols for data communications cover such things as framing, error handling, transparency and line control. There are three basic types of protocol: character-oriented, byte-oriented and bit-oriented.
Protocols break a file into equal parts called blocks or packets. These packets are sent and the receiving computer checks the arriving packet and sends an acknowledgement (ACK) back to the sending computer. Because modems use phone lines to transfer data, noise or interference on the line will often mess up the block. When a block is damaged in transit, an error occurs. The purpose of a protocol is to set up a mathematical way of measuring if the block came through accurately. And if it didn't, ask the distant end to re-transmit the block until it gets it right. See PROTOCOLS for a list of the more common protocols. See the following protocol definitions. See also Handshaking and Line Discipline.
The act of supplying telecommunications service to a user, including all associated transmission, wiring, and equipment. The telephone industry defines provisioning as an engineering term referring to the act of providing sufficient quantities of switching equipment to meet established service standards. In NS/EP telecommunication services, "provisioning" and "initiation" are synonymous and include altering the state of an existing priority service or capability.
Also called pseudo tandem. It is an end-office switch in a remote geographical area to which other end offices in the area are connected instead of their being connected to the LEC's access tandem. When a long-distance call originates in one of these distant end offices, the originating end-office switch sends it to the pseudo tandem, and then the pseudo tandem routes the call to the LEC's access tandem for routing to the IXC's POP. It's more economical to have a pseudo access tandem in such a geographical situation rather than having each distant end office directly connect to the LEC's access tandem.
A mechanism that generalizes the pseudowire concept introduced in the Martini Draft. Pseudowire Emulation Edge-to-Edge defines encapsulations for ATM, Frame Relay, TDM, Ethernet and other services over a packet-switched network, such as an IP network.
Public Switched Telephone Network. PSTN is an abbreviation used by the ITU-T. PSTN simply refers to the local, long distance and international phone system which we use every day. In some countries it's only one phone company. In countries with competition, e.g. the United States, PSTN refers to the entire interconnected collection of local, long distance and international phone companies, which could be thousands.
Quality of Service. Essentially how good the service you get from your circuits and your vendor. My feeling is that the service you get from any vendor depends heavily on how well the vendor communicates with you -- talks to you, returns your phone calls and emails, and tells you of problems, dropouts, delays and progress. No one denies that delays and screwups are inevitable. But all you as a customer demand is being kept informed. Note to vendors: One of the benefits of cell phones, BlackBerries and iPhones is they keep you in touch with your customers. Please use them. Since quality of service is a perceived emotion, your customers will perceive you give better service if you actually use these communications gadgets. Various vendors and their customers have tried to quantify QoS in service level agreements. They go part way. See SLA and diversity.
1. Rate Demarcation Point. 2. Remote Desktop Protocol. Invented by Microsoft, this tool allows you to remotely access one computer from another. You can see the desktop, control the mouse and open files. It debuted in 1998 as a feature of Windows NT 4.0 Terminal Server and has been gradually refined since. Remote Assistance is a similar program that allows you to request help from a remote user. It first appeared in Windows XP. RDP is useful for accessing files on remote servers and for technical support.
1. Rate Demarcation Point. 2. Remote Desktop Protocol. Invented by Microsoft, this tool allows you to remotely access one computer from another. You can see the desktop, control the mouse and open files. It debuted in 1998 as a feature of Windows NT 4.0 Terminal Server and has been gradually refined since. Remote Assistance is a similar program that allows you to request help from a remote user. It first appeared in Windows XP. RDP is useful for accessing files on remote servers and for technical support.
See Diversity.
Physical device that runs one or more network layer routing protocols and uses route query protocol to provide network layer routing forwarding descriptions to clients.
A router is a device that forwards information. It can be tiny, fitting on a desk, or huge, occupying a central office. It can switch information around an office. It can switch information around the world. Routers can be simple or immensely complex, including tasks like quality of service for different conversations. Routers are bought by everybody -- from backbone service providers to local Internet Service Providers (ISPs), from corporations to Universities. Routers can be highly intelligent devices which connect like and unlike LANs (Local Area Networks). They connect to MANs (Metropolitan Area Networks) and WANs (Wide Area Networks), such as X.25, Frame Relay and ATM. Routers are protocol-insensitive, typically supporting multiple protocols. Routers most commonly operate at the bottom 3 layers of the OSI model, using the Physical, Link and Network Layers to provide addressing and switching. Routers also may operate at Layer 4, the Transport Layer, in order to ensure end-to-end reliability of data transfer. Routers send their traffic based on a high level of intelligence inside themselves. This intelligence allows them to consider the network as a whole. How they route (also called routing considerations) might include destination address, packet priority level, least-cost route, minimum route delay, minimum route distance, route congestion level, and community of interest. Routers are unique in their ability to consider an enterprise network as comprising multiple physical and logical subnets (subnetworks). Thereby, they are quite capable of confining data traffic within a subnet, on the basis of privilege as defined in a policy-based routing table. In a traditional router topology, each router port defines a physical subnet, and each subnet is a broadcast domain. Within that domain, all connected devices share broadcast traffic; devices outside of that domain can neither see that traffic, nor can they respond to it. Contemporary routers have the ability to define subnets on a logical basis, based on logical address (e.g. MAC or IP address) information contained within the packet header, and acted upon through consultation with a programmed routing table.
A router is a device that forwards information. It can be tiny, fitting on a desk, or huge, occupying a central office. It can switch information around an office. It can switch information around the world. Routers can be simple or immensely complex, including tasks like quality of service for different conversations. Routers are bought by everybody -- from backbone service providers to local Internet Service Providers (ISPs), from corporations to Universities. Routers can be highly intelligent devices which connect like and unlike LANs (Local Area Networks). They connect to MANs (Metropolitan Area Networks) and WANs (Wide Area Networks), such as X.25, Frame Relay and ATM. Routers are protocol-insensitive, typically supporting multiple protocols. Routers most commonly operate at the bottom 3 layers of the OSI model, using the Physical, Link and Network Layers to provide addressing and switching. Routers also may operate at Layer 4, the Transport Layer, in order to ensure end-to-end reliability of data transfer. Routers send their traffic based on a high level of intelligence inside themselves. This intelligence allows them to consider the network as a whole. How they route (also called routing considerations) might include destination address, packet priority level, least-cost route, minimum route delay, minimum route distance, route congestion level, and community of interest. Routers are unique in their ability to consider an enterprise network as comprising multiple physical and logical subnets (subnetworks). Thereby, they are quite capable of confining data traffic within a subnet, on the basis of privilege as defined in a policy-based routing table. In a traditional router topology, each router port defines a physical subnet, and each subnet is a broadcast domain. Within that domain, all connected devices share broadcast traffic; devices outside of that domain can neither see that traffic, nor can they respond to it. Contemporary routers have the ability to define subnets on a logical basis, based on logical address (e.g. MAC or IP address) information contained within the packet header, and acted upon through consultation with a programmed routing table.
The process of selecting the circuit path for a message.
Resilient packet ring. The IEEE 802.17 technological specification to deliver packet-based services over SONET rings. RPR is an OSI-Rm (OSI Reference Model) Layer 2 technology with framing very similar to that of Ethernet. The RPR offers the same sub 50ms (millisecond) restoration times offered by SONET without the inefficient allocation of SONET time slots. for leased line services. RPR can be oversubscribed in ways similar to that of Ethernet. (Oversubscribed means too subscribers for great service.) Quality of Service (QoS) is important in RPR networks to ensure that customer traffic within the CIR defined in the SLA is not dropped during periods of congestion. See 802.17, Ethernet and SONET.
The Resource Reservation Protocol (RSVP) is an IETF standard designed to support resource (for example, bandwidth) reservations through networks of varying topologies and media. Through RSVP, a user's quality of service requests are propagated to all routers along the data path, allowing the network to reconfigure itself (at all network levels) to meet the desired level of service. The RSVP protocol engages network resources by establishing flows throughout the network. A flow is a network path associated with one or more senders, one or more receivers, and a certain quality of service. A sending host wishing to send data that requires a certain QoS will broadcast, via an RSVP-enabled Winsock Service Provider, "path" messages toward the intended recipients. These path messages, which describe the bandwidth requirements and relevant parameters of the data to be sent, are propagated to all intermediate routers along the path. A receiving host, interested in this particular data, will confirm the flow (and the network path) by sending "reserve" messages through the network, describing the bandwidth characteristics of data it wishes to receive from the sender. As these reserve messages propagate back toward the sender, intermediate routers, based on bandwidth capacity, decide whether or not to accept the proposed reservation and commit resources. If an affirmative decision is made, the resources are committed and reserve messages are propagated to the next hop on the path from source to destination. The idea is that for presumably a premium price, RSVP will enable certain traffic, such as videoconferences, to be delivered before e-mail. Today, all traffic on IP networks moves on a first-come-first-served basis and is charged at a flat rate. "In some ways RSVP will change what the Internet is all about, because you'll start to have different qualities of service and differential prices which are new," said Abel Weinrib, a key Internet strategist for Intel Corp. Virtually unknown among the general Internet community, RSVP has been quietly pushing ahead towards becoming acceptable and popular. It is now part of Microsoft's TAPI 3.0. It is being pushed also by Cisco Systems Inc., which makes the routers that direct most Internet traffic, and by Intel, which wants to spur demand for microprocessors by making computers and IP networks more useful for uses like phone calls and video conferencing. In an article I read, Cisco marketing manager Peter Long said RSVP technology would be included in new network software Cisco is delivering. That software controls the routers that direct Internet traffic. Cisco sells more than 80 percent of the routers used in commercial and corporate Internets. Long expects Cisco customers to start using RSVP technology to create what he calls "diamond lanes" on the Internet. "Right now, if there is congestion on the Internet, your traffic sits there, like a car stuck on an onramp," Long said. He said RSVP would act like "a big crane that picks you up and puts you over the other cars," onto these so-called diamond lanes that bypass congested parts of the Net.
Realtime Transport Protocol. An IETF standard for streaming realtime multimedia over IP in packets. Supports transport of real-time data like interactive voice and video over packet switched networks. A thin protocol providing support for content identification, timing reconstruction, loss detection and security. The ARPA DARTnet transcontinental IP network experiments lead to RTPs popularity. Now championed by the Audio/Video Transport (AVT) Working Group. AVT is part of the IETF (Internet Engineering Task Force). RTP does not do resource reservation or quality of service control. It relies on resource reservation protocols like RSVP.
1. Radio Transmission Technologies. See G3. 2. Round-Trip Time. Time required for a network communication to travel from the source to the destination and back. RTT includes the time required for the destination to process the message from the source and to generate a reply. RTT is used by some routing algorithms to aid in calculating optimal routes.
1. A microwave receiver, repeater, regenerator in orbit above the earth. Think of a mirror. You shine a signal on it. It reflects back. Same thing as a satellite except that it grabs the signals, cleans it up, amplifies it and sends it back down to earth. Traditional communications satellites -- the ones that give us TV programming from all around the globe -- are known as GEOs, as they are in Geosynchronous Earth Orbit, which is an equatorial orbit with the satellites at altitudes of approximately 22,300 miles. In such an orbital slot and at that altitude, they maintain their position relative to the earth's surface. This means that the earth antenna you use to transmit a signal to a satellite or the earth antenna you use to receive a signal from a satellite can be fixed, i.e. it doesn't have to move. More recently developed satellites are placed in Low or Middle Earth Orbits, hence the terms LEO and MEO. LEOs and MEOs vary widely in terms of orbital paths and altitudes; therefore, they are not synchronized with the earth's rotation. And ground antenna to reach them have to move. See GEO, MEO and LEO. See also Satellite Transmission. 2. Something distant to the main something. See Main Distribution Frame, Satellite Cabinet and Satellite Distribution Frame.
Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) are standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber using lasers or light-emitting diodes (LEDs). SDH is a set of international fiber-optic transmission standards. SDH was based on the North American SONET standards, which now are considered to be a subset of SDH.
The word seamless means "perfectly smooth, without awkward transitions." In software, it means that what takes place between the user and the application or applications accessed by the user is perfectly smooth to the user and the software being used by the user will work easily with other software the user is using. On a network accessing "seamless" applications, the user doesn't perceive he's on a network because his programs run as though they were on his personal computer. In actual fact, the word "seamless" is very vague. No one has a technical definition of seamless. Originally, in years past, the word meant "without the stitches showing." This 15-century word got a boost from the phrase seamless stockings which filled a brief period between silk stockings -- which had seams that always needed straightening -- and most panty hose that doesn't, sadly. In short, when any vendor says they offer "seamless integration" with something else, be markedly wary. Follow the fundamental rule in this dictionary: Check.
A way of insuring data on a network is protected from unauthorized use. Network security measures can be software-based, where passwords restrict users' access to certain data files or directories. This kind of security is usually implemented by the network operating system. Audit trails are another software-based security measure, where an ongoing journal of what users did what with what files is maintained. Security can also be hardware-based, using the more traditional lock and key.
Subscriber Identity Module, also called Smart Card. Every mobile phone and PDA (e.g. BlackBerry or iPhone) that works on GSM (global system for mobile communications) have a SIM card. It's either postage-stamp size or credit-card sized, usually the former. A SIM card has two basic functions --first, it tells the network who you are. That way the network can process your call (voice or data), and bill for it. Second, the SIM card makes your cellular device (phone or PDA) more useful to you. For example, it may contain your personal address book names and numbers, and allow you to speed dial, etc. Basically the SIM card takes a standard, off-the-shelf GSM phone (i.e. any GSM phone) and makes it yours. A GSM phone won't basically work without a valid SIM card, i.e. one which tells the network you have enough prepaid minutes to use the network or have a valid account the network can bill your call to. Each SIM card contains a microchip that houses a microprocessor with eight kilobytes of memory. The card stores a mathematical algorithm that encrypts voice and data transmissions and makes it nearly impossible to listen in on GSM calls. In most countries with a GSM cellphone system, you can buy a SIM card with prepaid minutes on it at local newsagents or convenience stores. You can then pop that card into any GSM phone and it will be yours. "Any" is not quite true. Many GSM carriers sell phones that are locked to their service. Putting someone else's SIM card in their phone will physically fit. But the phone won't work. The carrier locks their phones in the hope you'll use their phones everywhere and they can bill handsomely for it. The solution is to unlock their phone. Typically this is done through software and is often a complex task. But the Internet is full of solutions -- typically a different solution per phone. Even one for Apple's iPhone. Of course, you can buy an unlocked phone. EBay sells them. Your local non-carrier, dedicated wireless store will also sell you an unlocked phone (including an unlocked iPhone). But that phone will cost you more than buying the same phone locked from the carrier. The main reason you'd want an unlocked phone is to save money, typically for travel. As a rule of thumb, GSM calls are cheaper from a local carrier. Making calls in Europe on a U.S. phone with a U.S. carrier is expensive. Using a prepaid GSM from the local newsagent can easily save you 95% on the call. And that includes calling back to the U.S.
Session Initiation Protocol. SIP is the most important standard for setting up telephone calls, multimedia conferencing, instant messaging and other types of real-time communications on the Internet. SIP can establish sessions for features such as audio/videoconferencing, interactive gaming, and call forwarding to be deployed over IP networks, thus enabling service providers to integrate basic IP telephony services with Web, email, and chat services. SIP is much faster, more scalable and easier to implement than H.323. An array of network gear including IP phones, IP PBXs, servers, media gateways and softswitches support SIP. SIP is the Application Layer (Layer 7 of the OSI Reference Model) protocol for the establishment, modification and termination of conferencing and telephony sessions over an IP-based networks. SIP uses text-based messages, much like HTTP. SIP was developed within the IETF MMUSIC (Multiparty Multimedia Session Control) working group, and is defined in the IETF's RFC 2543. SIP is touted as being much faster, more scalable and easier to implement than H.323.SIP addressing built around either a telephone number or a Web host name. In the latter case, for example, the SIP address would be based on a URL (Uniform Resource Locator), and might look something like SIP:firstname.lastname@example.com, which makes it very easy to guess a SIP URL based on an e-mail address. The URL is translated into an IP address through a DNS (Domain Name Server). SIP also negotiates the features and capabilities of the session at the time the session is established. For example, a caller might wish to establish a call using G.711 audio and H.261 video. The codecs embedded in the two endpoints (i.e. originating and terminating multimedia terminals) negotiate a common set of voice and video compression algorithms (which might not include G.711 and H.261), prior to establishing the session. This advance negotiation process, which relies on the Session Description Protocol (SDP), is touted as greatly reducing the call setup time required for H.323 sessions. If the called party is not available, or does not wish to accept the call, it can be redirected (e.g. to voice mail or to an administrative assistant), with the negotiation process taking place in consideration of that endpoint. Once the session is established, the designated capabilities can be modified during the course of the call. For example, whiteboarding can be added if both terminals are capable and can negotiate a common compression algorithm. In addition to the unicast (i.e. one-to-one) session described above, SIP supports multicast (i.e. one-to-many) communications.
Service Level Agreement. An agreement between a user and a service provider, defining the nature of the service provided and establishing a set of metrics (fancy word for measurements) to be used to measure the level of service provided measured against the agreed level of service. Such service levels might include provisioning (when the service is meant to be up and running), average availability, restoration times for outages, availability, average and maximum periods of outage, average and maximum response times, latency, delivery rates (e.g. average and minimum throughput). The SLA also typically establishes trouble-reporting procedures, escalation procedures, penalties for not meeting the level of service demanded -- typically refunds to the users. Typical SLAs include statements about:
+ System/service availability.
+ Time to identify the cause of a customer related malfunction.
+ Time to repair a customer related malfunction.
+ Service provisioning time.
+ Quality of service targets.
Service Level Agreement. An agreement between a user and a service provider, defining the nature of the service provided and establishing a set of metrics (fancy word for measurements) to be used to measure the level of service provided measured against the agreed level of service. Such service levels might include provisioning (when the service is meant to be up and running), average availability, restoration times for outages, availability, average and maximum periods of outage, average and maximum response times, latency, delivery rates (e.g. average and minimum throughput). The SLA also typically establishes trouble-reporting procedures, escalation procedures, penalties for not meeting the level of service demanded -- typically refunds to the users. Typical SLAs include statements about:
+ System/service availability.
+ Time to identify the cause of a customer related malfunction.
+ Time to repair a customer related malfunction.
+ Service provisioning time.
+ Quality of service targets.
Short Messaging Service Center. On a wireless network, SMSC allows short text messages to be exchanged between mobile cell telephones and other networks. Sample message: "Honey, I'll be home late tonight." It is the entity that stores and forwards Short Message Service (SMS) messages. SMSC supports message storage, point-to-point, mobile terminated short message service (SMS-PP/MT). SMSC is being enhanced to support mobile originated messages also. The product can be interfaced with multi-vendor mobile switching centers (MSCs) over an SS7 link; it can work with Gateway as well as non-Gateway MSCs.
1. Signaling Network Management Protocol. 2. Simple Network Management Protocol. SNMP is the most common method by which network management applications can query a management agent using a supported MIB (Management Information Base). SNMP operates at the OSI Application layer. The IP-based SNMP is the basis of most network management software, to the extent that today the phrase "managed device" implies SNMP compliance. RMON and RMON-2 use SNMP as their method of accessing device MIB information. In 1988, the Department of Defense and commercial TCP/IP implementors designed a network management architecture for the needs of the average Internet (a collection of disparate networks joined together with bridges or routers). Although SNMP was designed as the TCP's stack network management protocol, it can now manage virtually any network type and has been extended to include non-TCP devices such as 802.1 Ethernet bridges. SNMP is widely deployed in TCP/IP (Transmission Control Protocol/Internet Protocol) networks, but actual transport independence means it is not limited to TCP/IP. SNMP has been implemented over Ethernet as well as OSI transports. SNMP became a TCP/IP standard protocol in May 1990. SNMP operates on top of the Internet Protocol, and is similar in concept to IBM's NetView and ISO's CMIP. In 1991, Microsoft started referring to SNMP as SubNetwork Access Protocol. In November of 1993 Cisco Systems announced that its internetwork routers will support version 2 of the Simple Network Management Protocol (SMNP) and it has licensed SNMP v2 developed by SNMP Research, Inc. of Knoxville, TN. See CMIP, MIB, RMON, RMON-2 SNMP-2.
1. Signaling Network Management Protocol. 2. Simple Network Management Protocol. SNMP is the most common method by which network management applications can query a management agent using a supported MIB (Management Information Base). SNMP operates at the OSI Application layer. The IP-based SNMP is the basis of most network management software, to the extent that today the phrase "managed device" implies SNMP compliance. RMON and RMON-2 use SNMP as their method of accessing device MIB information. In 1988, the Department of Defense and commercial TCP/IP implementors designed a network management architecture for the needs of the average Internet (a collection of disparate networks joined together with bridges or routers). Although SNMP was designed as the TCP's stack network management protocol, it can now manage virtually any network type and has been extended to include non-TCP devices such as 802.1 Ethernet bridges. SNMP is widely deployed in TCP/IP (Transmission Control Protocol/Internet Protocol) networks, but actual transport independence means it is not limited to TCP/IP. SNMP has been implemented over Ethernet as well as OSI transports. SNMP became a TCP/IP standard protocol in May 1990. SNMP operates on top of the Internet Protocol, and is similar in concept to IBM's NetView and ISO's CMIP. In 1991, Microsoft started referring to SNMP as SubNetwork Access Protocol. In November of 1993 Cisco Systems announced that its internetwork routers will support version 2 of the Simple Network Management Protocol (SMNP) and it has licensed SNMP v2 developed by SNMP Research, Inc. of Knoxville, TN. See CMIP, MIB, RMON, RMON-2 SNMP-2.
Someone described a "softswitch" as basically anything you want it to be. But it's not. See media gateway, media gateway controller and SoftSwitch Consortium.
Synchronous Optical NETwork. A family of fiber optic transmission rates from 51.84 million bits per second to 39.812 gigabits (billion, or thousand million) per second (and going higher, as we speak), created to provide the flexibility needed to transport many digital signals with different capacities, and to provide a design standard for manufacturers. SONET is an optical interface standard that allows interworking of transmission products from multiple vendors (i.e. mid-span meets). It defines a physical interface, optical line rates known as Optical Carrier (OC) signals, frame format and an OAM&P protocol (Operations, Administration, Maintenance, and Provisioning). The OC signals have their origins in electrical equivalents known as Synchronous Transport Signals (STSs). The base rate is 51.84 Mbps (OC-1/STS-1), which is a DS-3 (specifically, a T-3) payload of 44.736 Mbps, plus a considerable amount of overhead for network management (largely signaling and control) purposes. Higher rates are direct multiples of the base rate. Note that SONET is based in large part on T-carrier. SONET is a TDM (Time Division Multiplexed) technology, therefore, just as is T-carrier.
Signaling Point Of Interface. The demarcation point on the SS7 signaling link between a LEC network and a Wireless Services Provider (WSP) network. The point established the technical interface and can designate the test point and operational division of responsibility for the signaling.
Signaling System 7 is the latest iteration of the phone industry's way of carrying and controlling phone conversations. SS7 typically employs a dedicated 64 kilobit data circuit to carry packetized machine language messages about each call connected between and among machines of a network to achieve connection control. International equivalent of Bell DNHR. Permits many ISDN services such as CNID or Random RCF. The SS7 protocol consists of four basic sub-protocols: * Message Transfer Part (MTP), which provides functions for basic routing of signaling messages between signaling points. * Signaling Connection Control Part (SCCP), which provides additional routing and management functions for transfer of messages other than call setup between signaling points. * Integrated Services Digital Network User Part (ISUP), which provides for transfer of call setup signaling information between signaling points. * Transaction Capabilities Application Part (TCAP), which provides for transfer of non-circuit related information between signaling points.
Signaling System 7 provides two major capabilities:
A cable designed to be laid underwater.
A mechanical, electrical or electronic device which opens or closes circuits, completes or breaks an electrical path, or selects paths or circuits. Switches work at Layers 1 (Physical) and 2 (Data Link) of the OSI Reference Model, with emphasis on Layer 2. A switch looks at incoming data (voice data, or data data) to determine the destination address. Based on that address, a transmission path is set up through the switching matrix between the incoming and outgoing physical communications ports and links. Data switches (e.g. LAN switches and packet switches) also typically contain buffers, which can hold data packets in temporary memory until the necessary resources are available to allow the data packets to be forwarded. Voice switches, of course, don't, because you can't delay voice. Switches work link-by-link, with multiple switches typically being involved in complex networks; each switch forwards the data on a link-by-link (hop-by-hop) basis. Routers are highly intelligent data switches which are capable of setting up paths from end-to-end, perhaps in consideration of the level of privilege of the user and application. Routers commonly are used at the edges of complex data networks, where intelligence is required to set up appropriate network paths. Although such intelligent decisions impose some delay on the packet traffic, they are made only at the ingress and egress edges of the network. The routers often instruct switches in the core of the network, where speed is of the essence -- switches aren't as intelligent as routers, but they are faster and less expensive. See also Ethernet Switch, OSI Reference Model, Router and Switching Fabric.
All residential and most businesses use this type of telephone access. It refers to the connection between your phone and the long distance companies' switch (POP -- point of presence) when you make a regular local or long distance telephone call over standard phone lines.
TAR is the UNIX standard program for combining and compressing files. It's like a UNIX Winzip program. I believe it stands for "Tape Archiver". The UNIX System V manual lists the command description as "tape file archiver". One no longer uses it just for tape archiving, but that was its initial usage.
Offering space, security, and environmental controls for equipment owned by various carriers. This allows a company to rent space to friends and competitors in their Network Access Points and other similar facilities. Also called a carrier hotel.
A teleport is a high density communications hub, often consisting a collection of adjacent satellite antennas and a bunch of customers who want to receive their transmissions. Some teleport companies also provide local phone, data and video service around their local service area. The term has fallen into disrepair.
The word terminal is very loose. Some people call any piece of communicating equipment a terminal. Some people simply refer to any wall jack or wall plug as a terminal, as in "We need to connect these wires to the terminal." Some people believe it's the point at which a telephone line ends, or is connected to other circuits of a network. There are many ways of enhancing the word terminal by adding another word, e.g. terminal adapter or terminal block. See the following definitions.
A loosely-defined high speed VPN (Virtual Private Network) service offering of various LECs (Local Exchange Carriers), IXCs IntereXchange Carriers) and MSPs (Metropolitan Service Providers), TLS provides for the interconnection of LANs over the MAN or WAN public data network (PDN). In other words, a TLS customer can establish direct Ethernet-to-Ethernet or Token Ring-to-Token Ring connectivity through a PDN without either the trouble or expense associated with a private leased-line network, or even a Frame Relay or ATM network. Internally, the carrier may provision the network through a variety of methods. Transmission facilities may be in the form of optical fiber or xDSL (e.g. ADSL, HDSL, or SDSL) for access, and will be optical fiber in the backbone. At Layer 1, the optical fiber may run the SONET protocol, although it may be DWDM. At Layer 2 and 3, various combinations of GbE (Gigabit Ethernet) and 10GbE, IP, Frame Relay, ATM, MPLS, and other protocols may be employed. In any event, all of these protocol issues are transparent to the end user organization. TLS generally is provisioned as a managed service, with the service provider retaining full ownership of and taking full responsibility for all of the technical issues, including the CPE (Customer Premises Equipment). It looks like straight Ethernet to you, although generally at a slower speed. See 10GbE, ADSL ATM, CAP, CPE, DWDM, Ethernet, Frame Relay, GbE, HDSL, IP, IXC, LEC, MPLS, MSP, SDSL, SONET, Token Ring, VPN, and xDSL.
Bellcore's definition: A flow of attempts, calls, and messages. My definition: The amount of activity during a given period of time over a circuit, line or group of lines, or the number of messages handled by a communications switch. There are many measures of "traffic." Typically it's so many minutes of voice conversation, or so many bits of data conversation. Note that Bellcore includes attempts in its definition of traffic. I don't. The decision is yours. But you should be aware of what you include in your calculations. See also Traffic Engineering and Queuing Theory.
Sending electrical signals carrying information over a line to a destination. Bellcore says that transmission has the following definitions: (a) Designates a field work, such as equipment development, system design, planning, or engineering, in which electrical communication technology is used to create systems to carry information over a distance. (b) Refers to the process of sending information from one point to another. (c) Used with a modifier to describe the quality of a telephone connection: good, fair, or poor transmission. (d) refers to the transfer characteristic of a channel or network in general or, more specifically, to the amplitude transfer characteristic. You may sometimes hear the phrase, "transmission as a function of frequency." 1. transferred back out on a trunk over the same physical path on which it arrived. Suppose a call is placed from location A through the telephone network and arrives at location B. If the call is forwarded to location C, the call turns on itself and returns to the telephone network on its way to location C. The call is said to be "tromboned". The name derives from the suggestion of the curve in the picture similar to the U-shaped slide on a trombone musical instrument. The trombone condition results in two trunks being tied up when the optimal connection would use no trunks at location B. The cure for the tromboning condition is "anti-tromboning". In the situation described by the figure, the edge telephony switch at location B detects that transferring the call to location C will result in a tromboned trunk, and signals the transfer to the telephony switch in the telephone network to transfer the call. The call will then be set up over a more optimal path, and the trunk at location B will be released. There are at least two common signaling methods for anti-tromboning 1) Centrex flash hook and 2) QSIG path replacement. Tromboning sometimes is known as hairpinning. See also Hairpinning, Path Replacement, and QSIG. 2. A form of regulatory arbitrage used in telecommunications, and particularly in the cellular world, tromboning is used by some carriers to increase revenues
A condition when a call comes in a trunk and is or decrease costs. Tromboning involves a call from country A to country B first going through an international gateway in country C. The termination costs for traffic from C to B may be much less than from A to B. Stupid regulations developed by stupid regulators cause carriers to have to jump through such hoops. The term "tromboning" comes from the unique U-shaped section of the slide trombone. As the slide is pushed out and back in, it creates the tones between the fundamentals and the harmonics. See also Arbitrage and Broker.
Form used to report problems. Often incorrectly filled-in. Check. Check. Check.
A communication line between two switching systems.
Text-To-Speech. A term used in voice processing. The computer "reads" the text out aloud. The technology is used extensively for blind people. It's also used in diverse applications, such as having a computer read a car driver email messages. This allows him to concentrate on the road. See Text-to-Speech.
User Interface, as in GUI, or Graphical User Interface. A vague term that has come to mean how the user communicates with his computer or computer-like device.
Unbundling is the term used to describe the access provided by local exchange carriers so that other service providers (often called CLECs -- competitive exchange carriers) may buy or lease portions of its network elements, such as local loops to serve subscribers. Unbundling was an idea from the U.S. Congress as part of the Telecommunications Act of 1996 -- one of the worst pieces of legislation in the history of the world. Unbundling has not proven overly successful.
User Network Interface. Specifications for the procedures and protocols between user equipment and either an ATM or Frame Relay network. The UNI is the physical, electrical and functional demarcation point between the user and the public network service provider. By way of example, the Frame Relay UNI involves both the user's FRAD (Frame Relay Access Device) and the carrier's FRND (Frame Relay Network Device) across a dedicated link. The ATM (Asynchronous Transfer Mode) UNI was developed and is promoted by the ATM Forum; the Frame Relay UNI, by the Frame Relay Forum.
A fancy way of saying we'll sell, or rarely, give you another service on top of what we're already sold you. Every vendor has their own definition as to what a value added service might be. For example, call forwarding, call waiting, 3-way calling, and voicemail are "value-added services" offered by most local phone companies for a fee to their voice landline subscribers. In contrast, many of the "value added services" are part of standard monthly cellphone service. See also also Value Added Network.
Using communications facilities, two or more people talk to each other and see each other. Many years ago, decent video conferences required pricey equipment and pricey high bandwidth. Hence videoconferences were limited to big corporations. These days videoconferences are available to every grandparent to talk to their grandchildren wherever they are. All you need these days are a laptop equipped with a camera, speakers and a microphone and broadband access to the Internet. Most laptops now come so equipped. A videoconference that used to cost thousands ten years ago is now free when you use Skype. My nephew, Andrew, is a lawyer in Australia. He routinely conferences many of his clients on one Skype videoconference. Some of his clients are in Australia. Some are in America. It makes no difference -- so long as they all have the necessary equipment and broadband access to the Internet. He says it's a great business tool. To my brain, there's really only one technical key to successful videoconference and that's a decent microphone which you can speak directly into. That means you should probably wear a headset or have a standup microphone. See Videoconferencing Standards.
Virtual local area network. A VLAN is a private closed network (typically used by a corporation) within a larger network (typically the Internet). VLANs allow anyone (also called an administrator) to create networks based on parameters beyond the standard Internet network address -- hence the name "virtual." The virtual aspect of VLANs refers to the fact that devices in a VLAN behave as though they are on the same wire, even though they may be physically located on different segments of the LAN. In fact, a VLAN can even extend across a WAN, a wide area network. The reason to create a VLAN is to segment a large subnet. This simplifies user mobility and provides broadcast controls. Switches are configured with policies (or rules) that limit which device can access which VLAN. These rules are set on a switch port or range of ports. The most secure rules combine two or more characteristics of the connecting device, such as some combination of port, MAC address, IP address, and/or routing protocol. These rules can be statically configured or dynamically learned. If a rule is violated, that device is not allowed to access the network and alarms and/or trouble logs are generated. This provides an extra level of security for non-mobile devices such as printers and servers, especially when they are deployed in semi-public spaces. See VLAN Assignment Methods and VPN (Virtual Private Network).
Virtual Memory System.
VoIP. Voice over Internet Protocol. The technology used to transmit voice conversations over a data network using the Internet Protocol. Such data network may be the Internet or a corporate intranet. The "Internet Protocol" in this term is a catch-all for the protocols and technology of encoding a voice call into digital packets and then allow the voice call to be slotted in between data calls on a packet-switched data network. Such data network may be the public Internet, a corporate Intranet, or a managed network used by long, distance and international communications providers. VoIP phone calls, if properly engineered, sound as good as a circuit switched TDM phone call -- the ones we make and receive every day. There are three main benefits to VoIP phone calls:
First, they may potentially be cheaper. Since the data network is typically charged on a flat rate and thus the marginal cost of making a VoIP is zero, how cheaper depends on 1. The cost of terminating the VoIP call into the traditional phone network. Figure a penny a minute, or less. 2. The price of a standard circuit switched TDM call. They've been getting cheaper over the years. 3. How much tax is levied on both. Taxes are horrendous on traditional circuit switched long distance calls. They aren't so big, yet, on VoIP calls, which are classified by some regulatory agencies as "information services," not voice phone calls. And therefore they escape taxes.
Second, you may achieve benefits of managing a voice and data network as one network. With IP phones, moves, adds and changes will be easier and cheaper. IP phones are basically networkable computers, each with their own addresses. The characteristic of each phone -- their individual phone numbers, with their memories, their user profiles - are easily stored in a central database. Their software and their service are typically managed using standard computing systems. In short, they're "user friendly" to manage and can be managed remotely.
Third, -- and the key attraction of IP telephony -- is added (and integrated) new services, including integrated messaging, voice emails, number portability, caller ID with name, call waiting, call forwarding, take your area code with you, plug into the Internet anywhere and make free calls from anywhere in the world. And best of all you can typically manage your phone via a Web site on the Internet, which will tell you which calls you made and received, etc. A VoIP phone is typically a much better animal (though also more expensive) than today's circuit switched phone.
VoIP phones come in two flavors: first, a device that looks like a conventional phone -- most often a multiline phone found in offices; second, a small "black box" which contains all the electronics to create a standard analog phone line or two out of a broadband DSL or cable modem broadband access hookup to the Internet. A residential phone user receives such a device when he subscribes to a VoIP service, for example, one costing $19.95 a month. To make phone calls, he'll need to plug a normal analog single or multiline line phone into. In fact, that's how I make my VoIP phone calls.
VPLS is a class of VPN (virtual private network) that allows the connection of multiple sites in a single bridged domain over a service provider managed MPLS network. It's commonly called a Layer 2 VPN. From a customer's perspective, it looks as if all sites are connected to a single switched VLAN. To service providers, VPLS enables the MPLS infrastructure to offer secure any-to-any switched multiple services and to expand the portfolio beyond IP VPN. Customers access the service provider VPLS service using Ethernet. VPLS enhances the value of WAN Ethernet services by enabling Ethernet to flow natively across service providers' MPLS networks while providing strict security. When combined with Ethernet access, VPLS transforms the WAN into a large Ethernet switch, even across national and global distances.
Virtual Private Network. With a VPN, employees can log into a distant corporate local area network, server or corporate intranet over the Internet. A VPN has the look and feel of a private network to a user. But it's really part of the Internet with heavy security -- so no one on the Internet can see what's going on in the VPN. There are several definitions for VPN, and we'll go through them in some detail. But first, we need to explain the overall concept. A VPN is not a private network, but is virtually so, which means it's almost so. That is to say that it exhibits at least some of the characteristics of a private network, even though it uses the resources of a public switched network. True private networks absolutely guarantee access to network resources, and security is perfect -- after all, the network is a private one, comprising dedicated leased lines. Those lines (or, more commonly today, the equivalent bandwidth) have been taken out of shared public use and dedicated to the private use of an end user organization on the basis of a lease arrangement. Those dedicated leased lines often go through various switching centers (e.g. COs or POPs), but go around, rather than through, the switches. As far as the private network is concerned, it's a wire center, rather than a switching center. The dedicated leased lines most commonly are T-carrier or even SONET in nature, directly interconnect two or more end user sites, and can be used for any purposes the end user desires. The end user can run any higher-layer protocol it chooses -- after all, it's a private network. Sounds great, doesn't it? Sure, it does, but the costs are high, and the complexities of designing and implementing such a network can be way out of proportion to the benefits. Virtual Private Networks don't exhibit exactly the same characteristics and, therefore, don't perform as well as true private networks, but can come pretty close...and at much lower cost. For example, a VPN might offer priority access to bandwidth and other network resources, whereas a true private network offers guaranteed access at all times. A VPN might offer relatively tight security mechanisms, whereas a private network is totally secure. Now, let's examine the specific definitions.
The applications scenarios for IP VPNs include remote access, intranets, and extranets. Remote access VPNs are highly effective in support of telecommuters, mobile workers, and virtual employees. Intranets are used to link branch, regional, and corporate offices. Extranets link vendors, affiliates, distributors, agents, affiliates, and strategic partners into the main corporate office, with the level of access afforded being sensitive to the level of privilege indicated by a combination of password and user ID, as properly authenticated. This definition is courtesy of Ray Horak's book, "Communications Systems and Networks." See also Authentication, Encryption, Extranet, Firewall, Internet, Intranet, IP VPN, Tunneling and VPN concentrator.
Very Small Aperture Terminal. A relatively small satellite antenna, typically 1.5 to 3.0 meters in diameter, used for satellite-based point-to-multipoint data communications applications. While VSAT earth stations traditionally supported data rates of as much as 56 Kbps, contemporary systems can operate at rates of 1.544 Mbps. You see VSATs on top of retail stores which use them for transmitting the day's receipts and receiving instructions for sales, etc. Consider the VSAT dishes you see on the roofs of gas stations. Large numbers of gas stations share access to a single satellite which, in turn, provides connection to a centralized data processing center. At those gas stations are intelligent gas pumps equipped with credit card readers, monitors, and limited computer memory. You swipe your credit card through the card reader, with the credit card number being transmitted through the VAST dish to the satellite to the data processing center. Once the credit is verified (i.e. the card has not been reported lost or stolen, and the balance is not overdue), the transaction is authorized in return. Once the desired amount of gas has been pumped, that information is transmitted to the data processing center, with the transaction being noted in the accounts receivable system for billing purposes. Additionally, the level of inventory (i.e. gas in the tank) is noted as having been decreased. In other words, the VSAT network supports credit verification, transaction authorization, billing and inventory management.
VoIP Service Provider. See VoIP.
Wide Area Network. First there was the local area network which is a network confined within a building or a campus. It typically is owned and operated by one organization -- a company, a hospital, a factory, a college. Then came the WAN -- a wide area network that is basically any network bigger than a LAN. A WAN might cover a metropolitan area. It may cover the country. It may cover the world. There are more terms. A network that covers a metropolitan area might be called a MAN -- metropolitan area network. Someone has even coined GAN -- as in Global Area Network. But this is getting silly. These days most everything is the Internet.
The length of a wave measured from any point on one wave, to the corresponding point on the next wave, such as from crest-to-crest, or trough-to-trough. In other words, a wavelength is the distance an electromagnetic wave travels as it oscillates through a complete cycle.
Same as portal. See Portal.
Wireless Fidelity. Wi-Fi is now the most common way people access the Internet. Whether at their homes, in coffee shops, in Internet cafes, in hotels, in airports, or in their offices, people open their laptops, turn on their wireless access and attach to a nearby Wi-Fi service. Wi-Fi is a low power wireless system with a range of no more than 300 feet from the transmitter. Hence the closer you are to a transmitter, the more chance you have of connecting and the faster your Wi-Fi transmit/receive will be. You can improve you connection chances and "extend" the distance with a device called a range extender or signal booster. In my house, I have one installed 50 feet from my main Wi-Fi transmitter/receiver. It allows me to move farther from my main transmitter and still get a stronger signal. I use it for surfing the Internet in bed -- an activity my wife tolerates. Wi-Fi is defined in the IEEE's standard 802.11b. That standard specifies a simple low power (tops 1 WATT), unlicensed radio frequency service which actually operates on the same frequency as some cordless phones, garage door openers, walkie-talkies, etc. An 802.11b Wi-Fi base station is typically attached to a local area network, which is then attached to the Internet and/or the corporate network through a cable modem, a DSL router, or T-1 line. 802.11b defines both the Physical (PHY) and Medium Access Control (MAC) protocols. Specifically, the PHY spec includes three transmission options -- one Ir (Infrared), and two RF (Radio Frequency). Most Wi-Fi systems work in the 2.4 GHz range (2.4-2.483 GHz).
An old packet switched protocol now largely replaced by TCP/IP and the Internet. Originally the term X.25 represented a common reference point by which mainframe computers, word processors, mini-computers, VDUs, microcomputers and a wide variety of specialized terminal equipment from many manufacturers can be made to work together over a packet switched data network.