S
Designation for the ISDN subscriber interface.
SDH
Synchronous Digital Hierarchy.
SDU
Service Data Unit.
SDSL
A form of Digital Subscriber Line similar to HDSL but providing T1 or E1 connections over a single twisted-pair copper line. The technique offers a symmetric bandwidth for up and downstream.
SECAM
Sequential Couleur Avec Memoire. An alternative format for video transmission in 50 Hz mains based countries.
SHDSL
Symmetric High Bit-Rate Digital Subscriber Line and is defined by the ITU global standard G991.2. One of the latest generation additions to the DSL technology family, the benefit of G. SHDSL is not only does it support symmetrical connections at speeds up to 2.3Mbps, it also is designated to operate over a single copper pair, whereas previous generations were limited to slower speeds and mutiple pair connections. With this in mind, SHDSL is expected to supercede older generation technologies, such as HDSL, SDSL and IDSL for the provision of high-speed symmetric data services over copper, such as T1/E1 class leased circuits.
Serial Interface
A communications link for transporting data bit by bit.
Serial interface
See RS-232C.
Serial port
Socket at the back of your computer that you connect your mouse, modem or scanner to.
Server
The business end of a client/server setup, a server is usually a computer that provides the information, files, Web pages, and other services to the client that logs on to it. (The word server is also used to describe the software and operating system designed to run server hardware.) The client/server setup is analogous to a restaurant with waiters and customers. Some Internet servers take this analogy to extremes and become inattentive, or even refuse to serve you.
Signaling point
This element enables the Voice over IP network to communicate with the SS7 (Signaling System 7) network.
SIM (Subscriber Identification Module)
A small, removable plastic card embedded with a metal-coated microprocessor chip. The SIM card chip securely stores user information, and provides authentication and connection to mobile networks.
SIMD
Single Instruction Multiple Data. Computer architecture that performs one operation on more than one set of data.
SIP
Session Initiation Protocol. IP telephony protocol similar to H.323 but less feature rich.
SIP-T
Session Initiation Protocol for Telephony provides SIP communications between communication servers.
SLIP
Serial Line Internet protocol. SLIP is a standard for connecting Internet with a modem over a phone line. It has serious trouble with noisy dial-up lines and other error-prone connections, so look to higher-level protocols like PPP for error correction.
SMS
Short message service. Method for sending short text messages (typically 140-160 characters) over GSM and other mobile communication systems.
SMTP
Simple Mail Transfer Protocol. Standard email protocol on the internet.
SNMP
Simple Network Management Protocol. A common agent based network monitoring and control protocol.
SNR
Signal to Noise Ratio. The ratio of the amplitude of a signal to the amount of noise present.
Soft PBX
Term used to describe a software application that provides computer server based telephony similar to that of a traditional hardware based PBX.
Software application
Computer programs that allow you to create documents, send and receive mail over the Internet, and so on. Microsoft Word is an example of a software application.
Sonet
Synchronous Optical NETwork. A high-speed digital fibre optic network.
SPID
Service Profiles ID. Used for defining which ISDN services some ISDN terminals can access. Used mostly in North America.
SQCIF
Sub QCIF. 128 by 96 resolution.
SRP
Simple Retransmission Protocol.
Streaming
Data is streaming when it's moving quickly from one chunk of hardware to another and doesn't have to be all in one place for the destination device to do something with it. When your hard disk's data is being written to a tape backup device, it's streaming. When you're watching a QuickTime movie on the Internet, it's not streaming, because the movie must be fully downloaded before you can play it.
Subscriber Identification CLIP
To enable the caller's number (CLIP) to be displayed on the terminal of the destination subscriber of an outgoing connection, the PBX can send the number into the network.
S-video
A video signal where the chrominance and luminance components of an image are each represented as separate signals. Better quality than composite video.
Switch on (via PIN)
Allows you to switch on your answering machine remotely by using a security number (either pre-set or programmable, depending on the product).
