lephone numbers more efficiently. Without addresses, and vice versa. Carriers and enter- pooling, a single local telephone company prises use different internal and external IP has rights to the entire 10,000 block of tele- addresses to conserve public addresses and to phone numbers, but it might only use a por- shield IP addresses from outside sources. tion of the block. Glossary OSS (Operation and Support Service) frequencies. PCS (or DCS in Europe) is now Hardware and software that carriers use for used in the industry to refer to all 2G cellular billing, maintenance, and changes to cus- access technologies. tomer features. peer-to-peer network packet switching Distributes intelligence over devices in the A network technique that routes data in units network instead of relying on central com- called packets. Each packet contains address- puters. Peer-to-peer networks are often used ing and error-checking bits as well as trans- to download free music and movies from mitted user data. Packets from a transmission the Internet. In addition, companies such as can be routed individually through a network Skype use the technology for voice calls and such as the Internet and be assembled at the other services. end destination. photonics PAN (Personal Area Network) All of the elements of optical communica- Operates over small areas within rooms and tions. This includes fiber, lasers, and optical buildings. Bluetooth and RFID are examples switches and all elements involved in trans- of PANs. mitting light over fiber. Petabyte (PB) ping (Packet Internetwork Groper) A unit of measurement. One petabyte equals A software protocol used to test communica- 1,000,000,000,000,000 bytes or 1,000 giga- tions between devices. To "ping" means to bytes. A byte equals eight bits. send a packet to another device or host to see if the device sends back a response. The ping PBX (Private Branch Exchange) also tests round-trip delay, the time it takes to Computerized, onsite telephone system send a message to another device. located at an 