SECAM - Sequential Colour Avec Memoire. Television format for countries such as France, Russia and Madagascar.

SG3 - PictureTel's proprietary software generation 3. Audio and video compression and transmission format, provides encryption. Uses proprietary packet protocol, and provides better than standards video quality.

SG4 - PictureTel's proprietary software generation 4. Based on SG3; improvements include: transmission over standard H.221 multiplex, better motion coding, and contrast enhancement.

Sideband - The frequencies the modulated carrier wave occupies. Upper sideband transmissions occupy the relevant frequencies above the carrier

Sidetone - The transmission of the speaker's input into the microphone section of the headset into the speaker's receiver.

Signal transfer point (STP) - Node in the interoffice (CCS7) network that communicates with central offices to assist in routing.

Signaling - Method of communication between network components to provide control management and performance monitoring.

Signaling point (SP) - Processor designed for handling the signaling function of a switch in a common channel signaling network.

SMDS - Switched Multimegabit Data Service. A connectionless high-speed data transmission service that transmits information in fixed cell lengths at speeds from 56kbps to 34Mbps.

S/T-interface - An ISDN NT-1 drives an S/T-bus which is usually 4 wires, but in some cases it may be 6 or 8 wires. In these optional cases, the extra wires are used to provide power to operate telephones when normal power fails (In North America there is no provision for emergency mode operation). Point T refers to the connection between the NT1 device and customer supplied equipment. Terminals can connect directly to NT1 at point T. When a PBX is present, point S refers to the connection between the PBX and the terminal.

SNMP - Simple Network Management Protocol. Standard for retrieving and transmitting management information ( configuration, control, performance monitoring, etc.) Information is formatted according to MIBs.

SPID - Service Profile Identifier.

SQCIF - Sub-QCIF 128X96 pixels.

Streaming Video - A sequence of "moving images" that are sent in compressed form over the Internet and displayed by the viewer as they arrive. 

Switched-56 - AT&T network providing connections at multiples of 56 kbps.

Synchronization -  In serial data transmission, a method of ensuring that the receiving end can recognize characters in the order in which the transmitting end sent them, and can know where one character ends and the next begins. Without synchronization, the receiving end would perceive data simply as a series of binary digits with no relation to one another. Synchronous communication relies on a clocking mechanism to synchronize the signals between the sending and receiving machines. 

TA - Terminal adapter. A DCE that connects to the ISDN S-interface and enables non-ISDN terminal equipment to communicate over the ISDN.

TCP/IP - Transmission Control Protocol/Internet Protocol. A set of protocols developed by the Department of Defense to link dissimilar computers across networks. TCP/IP is the standard upon which the Internet is based. Protocol layer that guarantees delivery of information across IP.

TDM - (Time Division Multiplex) is a scheme in which numerous signals are combined for transmission on a single communications line or channel. Each signal is broken up into many segments, each having very short duration.  

TDMA - Time Division Multiple Access.

Telecommuter - A work-at-home computer user who connects to the corporate  backbone using remote access technologies.

Token ring - A platform for transmitting information across a LAN. Token ring networks are configured so that data flows in one direction over twisted pair wires at speeds from 4 Mbps to 16 Mbps.

Trunk - A single transmission path connecting two switching system. Trunks can be shared by many users, but serve only one call at a time.

Twisted pair - Traditional copper wiring well suited for short distance transmission of information. It consists of two insulated copper conducters twisted around each other and surrounded by a plastic coating.

Two-wire circuit - A transmission circuit composed of two wires, signal and ground, used to both send and receive information. In contrast, a 4-wire circuit consists of two pairs. One pair is used to send. One pair is used to receive. All trunk circuits (long distance) are 4-wire. A 4-wire circuit delivers better reception, but also cost more. All local loop circuits (those coming from class 5 central office to the subscriber's phone system) are 2-wire, unless a 4-wire circuit is requested.

T1 - A digital transmission link with a capacity of 1.544 Mbps. T1 uses two pairs of normal twisted wires. T1 normally can handle 24 voice conversations with each conversation being digitized at 64 kbps. With more advanced digital voice encoding techniques, it can handle more voice channels. T1 is a standard for digital transmission in North America (1.536 kbps).

T3 - A connection capable of carrying data at 45,000,000 bits-per-second or 45MBPs.

T.RES - T.120 conference reservation protocol.

T.Share - Now T.128.

T.120 - Standard for data conferencing and conference control for interactive multimedia communication both multipoint and point-to-point.

T.121 - Specifies T.120 general application protocols.

T.122 - Specifies T.120 service interface for multipoint operation.

T.123 - Transport stack of T.120. Carries out functions such as specifying connection protocols between devices and providing network-independent interface for rest of T.120.

T.124 - Generic Conference Control (GCC) for T.120. Provides control of a conference (joining, locating, scheduling, etc.) and supports application protocols.

T.125 - Specifies T.120 protocol for multipoint operation.

T.126 - T.120 still image transfer and annotation protocol.

T.127 - T.120 binary file transfer protocol.

T.128 - T.120 application sharing protocol.

T.133 - Audio and video control protocol within T.120.

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