A physical interface in an ISDN Basic Rate service which uses two copper pairs.

Systems Application Architecture

An IBM blueprint for letting software applications written for one IBM processor run on all IBM processors.

Single-Attached Concentrator

FDDI or CDDI concentrator that connects to the network by being cascaded from the master port of another FDDI or CDDI concentrator.

Service Access Point

Field defined by the IEEE 802.2 specification that is part of an address specification. Thus, the destination plus the DSAP define the recipient of a packet. The same applies to the SSAP.

Service Advertising Protocol

IPX protocol that provides a means of informing network clients, via routers and servers, of available network resources and services.

Segmentation and Reassembly

Sublayer of 53-byte cells

Single Attachment Station

Device attached only to the primary ring of an FDDI ring.

Statically Assigned Socket

Socket that is permanently reserved for use by a designated process. In an AppleTalk network, SASs are numbered 1 to 127; they are reserved for use by specific socket clients and for low-level built-in network services.

The submarine fibre-optic cable linking Sesimbra (Portugal) with Penang (Malaysia). It is formed of two main parts SAT3/WASC (South Atlantic Telecommunications cable no.3 / West African Submarine Cable) and SAT3/SAFE which extends the cable via the South Africa Far East link. The cable measures 28,800 km and connects from Portugal (Sesimbra) to Spain (Chipiona & Altavista), Senegal (Dakar), Côte d’Ivoire (Abidjan), Ghana (Accra), Benin (Cotonou), Nigeria (Lagos), Cameroon (Douala), Gabon (Libraville), Angola (Cacuaco), South Africa (Melkbosstrand & Mtunzini), La Reunion (St. Paul), Mauritius, (Baie Jacotet), India (Cochin), ending in Malaysia(Penang).

Service Creation Environment

A key goal of IN developers is an SCE, which makes it easy for telecoms operators, third-party service providers and, perhaps, users to build services.

Service Control Point

A computer database that holds information on IN services and subscribers and is separated from the switch, making it easier to introduce new services on the network.

Sustainable Cell Rate

Parameter defined by the ATM Forum for ATM traffic management. For VBR connections, SCR determines the long-term average cell rate that can be transmitted.

Synchronous Digital Hierarchy

European standard that defines a set of rate and format standards that are transmitted using optical signals over fibre. SDH is similar to SONET, with a basic SDH rate of 155.52 Mbps, designated at STM-1.

Synchronous Data Link Control

SNA data link layer communications protocol. SDLC is a bit-oriented, full-duplex serial protocol that has spawned numerous similar protocols, including HDLC and LAPB.

Single-Line Digital Subscriber Line

One of four DSL technologies. SDSL delivers1.544 Mbps both downstream and upstream over a single copper twisted pair. The use of a single twisted pair limits the operating range of SDSL to 10,000 feet (3048.8 meters).

Symmetric DSL

Similar to HDSL with a single twisted-pair line, carrying 1.544 Mbps (U.S. and Canada) or 2.048 Mbps (Europe) each direction on a duplex line.

Service Data Unit

Unit of information from an upper-layer protocol that defines a service request to a lower-layer protocol.

A fibre optic cable to run between Singapore and Europe, through the Middle East.

In a LAN using a bus topology, a segment is a continuous electrical circuit that is often connected to other such segments with repeaters. Section of a network that is bounded by bridges, routers, or switches. (2) Term used in the TCP specification to describe a single transport layer unit of information.

Serializer/Deserializer

Secure Electronic Transaction

Automates the authorisation, verification, fraud detection and settlement processes of credit card transactions over the Internet.

Super Frame

Common framing type used on T1 circuits. SF consists of 12 frames of 192 bits each, with the 193rd bit providing error checking and other functions. SF is superseded by ESF, but is still widely used.

Simple Gateway Control Protocol

Controls Voice over IP gateways by an external call control element (called a call-agent). This has been adapted to allow SGCP to control switch ATM Circuit Emulation Service circuits (called endpoints in SGCP). The resulting system (call-agents and gateways) allows for the call-agent to engage in Common Channel Signalling (CCS) over a 64-Kbps CES circuit, governing the interconnection of bearer channels on the CES interface.

Standard Generalised Mark-up Language

International standard for the definition of system-independent, device-independent methods of representing text in electronic form.

Simple Gateway Monitoring Protocol

Network management protocol that was considered for Internet standardization and later evolved into SNMP.

Serving GPRS Support Node

Service Independent Building Blocks

Creation of SIBs will in theory make it easier for non-software specialists to create new services by mixing and matching SIBs.

Generated by an ATM-connected device that wants to establish a connection with another such device. The signalling packet contains the ATM NSAP address of the desired ATM endpoint, as well as any QoS parameters required for the connection. If the endpoint can support the desired QoS, it responds with an accept message, and the connection is opened.

Subscriber Identification Module

A plastic card which is placed in the back of a mobile phone and allows you to store information on your phone.

Subscriber Identity Module Application Toolkit

Extends the customisation of the SIM card through the development of mobile phone resident applications, such as menu structures.

Capability for transmission in only one direction between a sending station and a receiving station. Broadcast television is an example of a simplex technology.

Service Level Agreement

The minimum quality of service the provider is committed to providing and should include the CIR, response time in case of problems, and other details outlining what minimum you are agreeing to accept.

Serial Line Internet Protocol

Standard protocol for point-to-point serial connections using a variation of TCP/IP

LAN architecture based on a ring topology in which the ring is divided into slots that circulate continuously. Slots can be either empty or full, and transmissions must start at the beginning of a slot.

Service Management Architecture

Server Message Block

File-system protocol used in LAN manager and similar NOSs to package data and exchange information with other systems.

Switched Multimegabit Data Service

A high-speed data service developed by Bellcore (Bell Communications Research Inc.).

Structure of Management Information

Symmetric Multiprocessing

Simple Multicast Routing Protocol

Specialized multicast network protocol for routing multimedia data streams on enterprise networks. SMRP works in conjunction with multicast extensions to the AppleTalk protocol.

Short Messaging Service

A service that allows text messages to be sent and received via a wireless network and viewed on any number of WAP-enabled devices.

Service Management System

The SMS allows provision and updating of information on subscribers and services in near-real time for billing and administrative purposes.

Simple Mail Transfer Protocol

A protocol that regulates what goes on between the mail servers.

Service Node

Used to refer generally to an element in an advanced public networking architecture at which service requests, including service switching, are processed.

Systems Network Architecture

IBM's master plan for communications among its computer systems. The plan is implemented in IBM hardware and software products.

Sub-network Access Protocol

Internet protocol that operates between a network entity in the sub-network and a network entity in the end system. SNAP specifies a standard method of encapsulating IP datagrams and ARP messages on IEEE networks. The SNAP entity in the end system makes use of the services of the sub-network and performs three key functions: data transfer, connection management, and QoS selection.

A program to capture data from a computer network.

Simple Network Management Protocol

An application-layer protocol that facilitates the exchange of management information between network devices. It is part of the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol suite. SNMP enables network administrators to manage network performance, find and solve network problems, and plan for network growth.

Sub-network Point of Attachment

Data link layer address (such as an Ethernet address, X.25 address, or Frame Relay DLCI address). SNPA addresses are used to configure a CLNS route for an interface.

System on a Chip

Occurs when two or more logical connections on a packet pipe are utilized by the same selector.

Section Overhead

First nine bytes of an STM-1 transmission frame

Synchronous Optical Network

A building block for the forthcoming broadband integrated services digital network, Sonet is the first global transmission standard. It allows for the multiplexing of a range of signals from asynchronous data and voice, high or low-speed data or voice, and on-demand services such as videoconferencing. It also provides for sophisticated network management techniques and increased customer control. Developed by Bell Communications Research Inc. Also known as Synchronous Digital Hierarchy

Shortest Path First Algorithm

Routing algorithm that iterates on length of path to determine a shortest-path spanning tree. Commonly used in link-state routing algorithms. Sometimes called Dijkstra's algorithm.

Service Profile Identifier

Number that some service providers use to define the services to which an ISDN device subscribes. The ISDN device uses the SPID when accessing the switch that initializes the connection to a service provider.

Scheme used by routers to cause a host to treat an interface as if it were up and supporting a session. The router spoofs replies to keepalive messages from the host in order to convince that host that the session still exists. Spoofing is useful in routing environments such as DDR, in which a circuit-switched link is taken down when there is no traffic to be sent across it in order to save toll charges. (2) The act of a packet illegally claiming to be from an address from which it was not actually sent. Spoofing is designed to foil network security mechanisms such as filters and access lists.

Sequenced Packet Protocol

Provides reliable, connection-based, flow-controlled packet transmission on behalf of client processes. Part of the XNS protocol suite.

Signal Quality Error

Transmission sent by a transceiver back to the controller to let the controller know whether the collision circuitry is functional.

Structured Query Language

A type of programming language used to construct database queries and perform updates and other maintenance of relational databases, SQL is not a full-fledged language that can create standalone applications--but it is strong enough to create interactive routines in other database programs.

Source-Route Translational Bridging

Method of bridging where source-route stations can communicate with transparent bridge stations with the help of an intermediate bridge that translates between the two bridge protocols.

Type of RAM that retains its contents for as long as power is supplied. SRAM does not require constant refreshing, like DRAM.

Source-Route Bridging

Method of bridging originated by IBM and popular in Token Ring networks. In an SRB network, the entire route to a destination is predetermined, in real time, prior to the sending of data to the destination.

Source-Route Transparent Bridging

IBM bridging scheme that merges the two most prevalent bridging strategies: SRB and transparent bridging. SRT employs both technologies in one device to satisfy the needs of all ENs. No translation between bridging protocols is necessary.

Signalling System 7

The industry standard that lets telephone company switches, database servers, other equipment and switching software pass commands and data for advanced network services. (A protocol that uses out-of-band signalling to give the user greater control of high-speed digital data links.)

Service Specific Convergence Sublayer

Service Set Identifier

Wireless network name.

Secure Socket Layer

Encryption technology for the Web used to provide secure transactions such as the transmission of credit card numbers for e-commerce.

Service Switching Point

A switch that can recognise IN calls and route and connect them under the direction of an SCP.

Specialised Satellite Services Operator

Spread Spectrum Technology

This technique sends a message as a series of computer codes. However, since the signal is stretched out over a broad frequency band, the receiver only needs to receive a part of the transmitted signal to reconstruct the original message.

Synchronous Transfer Mode

B-ISDN communications method that transmits a group of different data streams synchronized to a single reference clock.

Synchronous Transport Module level 1

One of a number of SDH formats that specifies the frame structure for the 155.52-Mbps lines used to carry ATM cells.

Shielded Twisted Pair

Cable type

Signal Transfer Points

Synchronous Transport Signal

Module, Sonet hierarchy types

Portion of an SNA network that consists of a subarea node and any attached links and peripheral nodes.

SNA communication controller or host that handles complete network addresses.

In IP networks, a network sharing a particular subnet address. Sub-networks are networks arbitrarily segmented by a network administrator in order to provide a multilevel, hierarchical routing structure while shielding the sub-network from the addressing complexity of attached networks. Sometimes called a subnet. (2) In OSI networks, a collection of ESs and ISs under the control of a single administrative domain and using a single network access protocol.

A single microkernal operating system that blends NetWare and UnixWare.

Switched Virtual Circuit

A connection in a connection-oriented network which is established dynamically, rather than through network configuration. An SVC is set up through a protocol which operates between a switch and an end station, and between switches.