Synchronous Code Division Multiple Access (S-CDMA)
A multiple access physical layer technology in which different transmitters can share a channel simultaneously. The individual transmissions are kept distinct by assigning each transmission an orthogonal “code.” Orthogonality is maintained by all transmitters being precisely synchronized with one another. S-CDMA is one of the physical layer technologies included in DOCSIS® 2.0.
Synchronous Digital Hierarchy (SDH)
SDH and SONET are standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber using lasers or light-emitting diodes (LEDs). Lower data rates can also be transferred via an electrical interface. The method was developed to replace the Plesiochronous Digital Hierarchy (PDH) system for transporting larger amounts of telephone calls and data traffic over the same fiber without synchronization problems. SONET generic criteria are detailed in Telcordia Technologies Generic Requirements document GR-253-CORE. Generic criteria applicable to SONET and other transmission systems (e.g., asynchronous fiber optic systems or digital radio systems) are found in Telcordia GR-499-CORE.SONET and SDH, which are essentially the same, were originally designed to transport circuit mode communications (e.g., DS1, DS3) from a variety of different sources, but they were primarily designed to support real-time, uncompressed, circuit-switched voice encoded in PCM format. The primary difficulty in doing this prior to SONET/SDH was that the synchronization sources of these various circuits were different. This meant that each circuit was actually operating at a slightly different rate and with different phase. SONET/SDH allowed for the simultaneous transport of many different circuits of differing origin within a single framing protocol. SONET/SDH is not itself a communications protocol per se, but a transport protocol. Due to SONET/SDH's essential protocol neutrality and transport-oriented features, SONET/SDH was the obvious choice for transporting Asynchronous Transfer Mode (ATM) frames. It quickly evolved mapping structures and concatenated payload containers to transport ATM connections. In other words, for ATM (and eventually other protocols such as Ethernet), the internal complex structure previously used to transport circuit-oriented connections was removed and replaced with a large and concatenated frame (such as OC-3c) into which ATM cells, IP packets, or Ethernet frames are placed. [Wik112]
ITU-T recommendation G.707: Network Node Interface for the Synchronous Digital Hierarchy (SDH)
ITU-T recommendation G.783: Characteristics of synchronous digital hierarchy (SDH) equipment functional blocks
ITU-T recommendation G.803: Architecture of Transport Networks Based on the Synchronous Digital Hierarchy (SDH)
^ ab Telcordia GR-253-CORE, Synchronous Optical Network (SONET) Transport Systems: Common Generic Criteria (October 2009). Issue 5.
^ Telcordia GR-499-CORE, Transport Systems Generic Requirements (TSGR): Common Requirements (November 2009). Issue 4.
^ abc Horak, Ray (2007). Telecommunications and Data Communications Handbook. Wiley-Interscience. p. 476. ISBN 9780470041413.
Synchronous Optical NETwork (SONET)
SONET is an optical interface standard to transport digital signals that allows inter- working of transmission products from multiple vendors. Among other things, it defines optical line rates known as optical carrier (OC) signals; the base rate is 51.84Mbps (OC-1), with higher rates being direct multiples of the base rate. (For example, OC-3 runs at 155.52 Mbps, or three times the rate of OC-1.)
Synchronous Transmission Protocol
A method of encoding a data transmission that does not use start and stop bits at the beginning and end of each byte to synchronize the data time clocks at each end of a connection. Instead it sets its timing signal at the beginning and end of each connection, and corrects discrepancies that arise over time by using the changing values each device on the connection sends and receives to keep their clocks “in sync.” Eliminating the start and stop bits reduces the “overhead” required to transmit each byte, and allows for increased throughput.
Requirement by which cable systems must black out significant portions of their distant signals in order to protect syndicated programming offered by local television broadcasters under an exclusive contract. The FCC eliminated this requirement in 1980 and re-imposed it in 1990.
System Integrators (SI)
Companies that provide installation of networking equipment and possibly other services such as training or network management.
The level of signal in a cable television system at the output of each amplifier. Must be carefully chosen and maintained for least distortion and noise.
Cable TV distribution systems are designed to compensate the cable and device losses. The spacing between cable amplifiers can increase as system losses are minimized through the proper choice of connectors, cable and related hardware. System losses are referred to as a “dB of cable” without reference to specific cable size or device losses. Generally these losses are understood to be at the highest operating frequency of the system.
Refers to the random energy generated by thermal and shot effects in the system. It is specified in terms of its rms level as measured in a 4-MHz bandwidth centered within a 6-MHz cable television channel.
The individual, organization, company or other entity that operates a cable TV system.
System Test Plan (STP)
A plan or policy for verifying system function, performance and/or compliance to a specification.
Functions in the application layer related to the management of various Open Systems Interconnection (OSI) resources and their status across all layers of the OSI architecture.
Systems Network Architecture (SNA)
IBM's layered protocols for mainframe communications.
A type of high-speed digital data connection that operates at 1.54Mbps and requires a two-pair (four-wire) connection between the telephone company Central Office and the customer premises. See also Fractional T-1.
T-1 Carrier System
A 24-channel, time-division, pulse-code modulation, voice carrier used on exchange cable to provide short-haul trunks. Uses two pairs, in one or two cables, pulse repeaters at 6000 foot intervals. [Arr11] Take Rate
The ratio of homes that pay for a cable service to homes passed.
A tap is a device which splits off a portion of the feeder line signal for the subscriber.
In a fiber optic directional coupler, the ratio of power at the tap port to the power at the input port. [Fib111] Tap Port
In a directional coupler where the splitting ratio between output ports is not equal, the output port containing the lesser power. [Fib111]
Tap Port Diagram courtesy of Fiber Optics Info, http://www.fiber-optics.info/fiber_optic_glossary/t
TAR Total Activity Report Tariff
A set rate and service schedule established by agreement between the phone company and a government-run regulatory agency, called the Public Utilities Commission.
Generic designator for any of several digitally multiplexed telecommunications carrier systems. [Fib111] T-carrier System
A digital transmission system that takes analog voice circuits and converts them to digital form for transmission using time division multiplexing. The T-carrier system was designed to operate at different rates, known as T1 (1.544 Mbps, equivalent to 24 channels); T2 (6.312 Mbps, equivalent to 96 channels); T3 (44.736 Mbps, equivalent to 672 channels); and T4 (274.176 Mbps, equivalent to 4,032 channels). (Without compression, a 64-Kpbs channel carries a single voice conversation). Carrier systems are not always channelized; the entire system can be used to carry high-bandwidth communications. T-Commerce
Television commerce, an interactive television application which enables electronic transactions between businesses and consumers via television.
Transmission Control Protocol
TCP/IP Transmission Control Protocol/Internet Protocol; two interrelated protocols that are part of the Internet protocol suite. TCP operates on the OSI transport layer and breaks data into packets. IP operates on the OSI network layer and routes packets. Originally developed by the U.S. Department of Defense. [Fib111]
TDD Time Division Duplex
Time Division Multiplexing; a type of multiplexing where two or more channels of information are transmitted over the same link by allocating a different time interval ("slot" or "slice") for the transmission of each channel, i.e., the channels take turns to use the link. Some kind of periodic synchronizing signal or distinguishing identifier is usually required so that the receiver can tell which channel is which. TDM becomes inefficient when traffic is intermittent because the time slot is still allocated even when the channel has no data to transmit. Statistical time division multiplexing was developed to overcome this problem. [Dic01]
Time Division Multiplexing Access
Time Domain Reflectometer; a device that uses a principle similar to radar to detect faults in metallic pair cables. A pulse of energy is directed into the cable. If the pulse encounters a discontinuity (break, pinch, bad connection) in the cable, a certain amount of the pulse energy is reflected to the TDR. By calculating the time difference between the original pulse launch and the receipt of the reflected pulse, the TDR can determine where the discontinuity is located. Some units use a digital numeric readout as an indicator. Others display the pulse information graphically on a viewing screen. Also referred to as a Cable Fault Locator. [Arr11] Tearing
A term used to describe a picture condition in which groups of horizontal lines are displaced in an irregular manner. Caused by lack of horizontal synchronization.
Thermoelectric Cooler; a device used to dissipate heat in electronic assemblies. [Fib111]