, and Frame Relay are often called a service, but in reality they are simply a technology or methodology. For example, ISDN is an access method; ATM and Frame Relay are transport methods or technologies. Standards Standards are documents containing processes, guide- lines, and recommended practices established accredited stand- ards bodies such as AES, ANSI, ETSI, IEEE, IETF, ITU, MPEG, and SMPTE. The use of standards is voluntary, not mandatory, although they can and are often used as references in contracts and other legal documents. Quite often, a Special Interest Group (SIG) or their work output is mistakenly referred to as a standard. The ATM Forum, Video GLOSSARY Services Forum, and SONET Interoperability Group are all special interest groups dedicated to promoting and advancing their col- lective and common interests. SIGs typically publish documents and support development of standards, many of which would not likely exist without SIG effort and resources. Less common is use of the term de-facto standard, which is simply another way of referring to a proprietary product or service. SONET Synchronous Optical Network SDH Synchronous Digital Hierarchy SDN Software Defined Network SNMP Simple Network Management Protocol Stratum Clock The stratum clock is a network clock reference ori- ginally arranged from 1 through 5 levels, in which level 1 is the most precise level and 5 is the least precise level. Transmission Channel A fixed amount of bandwidth usually ex- pressed in megabits per second is called a transmission channel. For example, a DTV Transmission channel runs at a precise rate of 19.392685Mbs. A T1 runs at 1.544Mbs and a DS3 at 44.736Mbs. TCP Transmission Control Protocol TCP/IP Transmission Control Protocol (over) IP (Transport) Virtual Private Network This page intentionally left blank BIBLIOGRAPHY Author Unknown. Digital Satellite Technology. Revision 1, Washington, DC: INTEL- SAT, 1992. Author Unknown. The Book: More Engineering Guidance for the Digital Transition. NVISION, Inc., 1999. Brinkley,