S

SAA (Systems Application Architecture) An IBM architecture designed to allow all of IBM products to communicate and function together.

SAAL Signaling AAL

SAC (Single-Attached Concentrator; also Security Access Control) See DAC.

SAM serial asynchronous module

SAP Service Advertisement Protocol

SAP Service Access Point

SAR Segmentation And Reassembly. One of two sublayers in an AAL.

SAS (Single-Attached Station) See DAS.

SDH Synchronous Digital Hierachy, the ITU-T version of SONET. The basic SDH rate (STM-1) is 155.52 Mbps (mostly equivalent to SONETs STS-3/OC-3).

SDDI Shielded Data Distributed Interface (FDDI over STP)

SDLC (Synchronous Data Link Control (IBM version of HDLC)) IBM communications line discipline or protocol associated with SNA, SDLC provides for control of a single communications line or link, accommodates a number of network arrangements and operates in half- or full-duplex over private or switched facilities.

SDU Service Data Unit

Secure logging A method whereby an audit trail of system activity is received from a bastion host and placed in a secure location.

Segmentation Splitting an overloaded ring into two or more separate rings, linked by a bridge/router or multipurpose hub.

Serial interface Interface which requires serial transmission, or the transfer of information in which the bits composing a character are sent sequentially. Implies only a single transmission channel.

Server In the context of the client-server model is the software (and sometimes the physical machine) that supplies the requested resources to the client.

Server clustering Placing all the servers on one or more rings in a central location.

Server Farm A cluster of servers in a centralized location serving a wide user population.

Session Layer OSI layer that provides means for dialogue control between end systems.

SGML Standard Generalized Markup Language. A generic language for representing documents.

Shared Ethernet Conventional CSMA/CD Ethernet configuration, where all stations are attached to a hub sharing 10 Mbps of bandwidth; only one station can transmit at a time.

Simplex transmission Data transmission that can occur in only one direction on a given line. Compare half duplex and full duplex.

Single mode fiber Fiber with a relatively narrow diameter, through which only one mode will propagate. Carries higher bandwidth than multimode fiber, but requires a light source with a narrow spectral width.

SIPS Software Investment Protection Service

SLIP (Serial Line Interface Protocol) Internet protocol used to run IP over serial lines such as telephone circuits or RS-232 cables interconnecting two systems. SLIP is now being replaced by PPP.

SmartAgent Intelligent management agents in devices and logical connectivity systems that reduce the computational load on the network management station and reduce management-oriented traffic on the network.

SMDS Switched Multimegabit Data Service. A standard for very high-speed data transfer.

SMI Structure of Management Information

SMM system management module

SMS Specific Multicast Server

SMT (Station Management) That part of the FDDI specification that manages stations on the ring, as defined by the X3T9.5 specification.

SMTP (Simple Mail Transfer Protocol) Protocol governing mail transmissions; defined in RFC 821, with associated message format descriptions in RFC 822.

SNA (Systems Network Architecture) IBM's proprietary network architecture.

SNAP (Sub Network Access Protocol) Internet protocol that operates between a network entity in the subnetwork and a network entity in the end system and specifies a standard method of incapsulating IP datagrams and ARP messages on IEEE networks.

SNMP (Simple Network Management Protocol) Preferred network management system for TCP/IP-based internets.

SNP (Subnetwork Protocol) (TCP/IP) Protocol residing in the subnetwork layer below IP that provides data transfer through the local subnet. In some systems, an adapter module must be inserted between IP and the Subnetwork Protocol to reconcile their dissimilar interfaces.

SONET (Synchronous Optical Network) Standard for digital transmission at rates from 51.84 Mbps to beyond 2.4 Gbps (gigabits per second).

Spam or Spamming A term used to refer to the inappropriate use of a mailing list or Usenet. Usually meaning the message has been sent to a large number of newsgroups many of which the message will not be relevent to. It's been suggested that the term comes from a Monty Python sketch where the word Spam is repeated over and over. (Spam is a Registered Trademark of Hormel Corporation, for it's processed meat product).

Spanning tree A technique that detects loops in a network and logically blocks the redundant paths, ensuring that only one route exists between any two LANs; used in an IEEE 802.1d bridged network.

SPID Service Profile ID, uniquely identifies a B channel on the ISDN network. The SPID must be stored in any device accessing the ISDN.

Split horizon Routing technique where information about routes is prevented from exiting router interfaces through which that information was received. Useful in preventing routing loops.

Spoofing The use of a forged IP source address to circumvent a firewall. The packet appears to have come from inside the protected network, and to be eligible for forwarding into the network.

SQE (Signal Quality Error) Transmission sent by a transceiver back to the controller to let the controller know whether the collision circuitry is functional.

SR Source Routing

SRT (source routing transparent) Bridge Proposed IEEE 802.1 bridge to combine source routing (in which the source end system provides routing information) with transparent bridging (in which the bridge makes independent message handling choices and therefore is transparent to the message source and destination).

SSCOP Service-Specific Connection-Oriented Protocol.

SSCS Service Specific Convergence Sublayer

SS7 The signaling system number 7 (SS7) protocol is used in the public networks to establish connections between switches. ISDN connections to switches that support SS7 have access to true 64 K bit connections between public switches. ISDN connections to switches that do not support SS7 (such as those in the Pacific Bell region) are limited to 56 kbps on each B channel as the switch signaling must be accommodated in-band.

S/T Interface An S/T interface is a four wire BRI interface presented to the customer by the PTTs in non-US markets.

STA (Spanning Tree Algorithm) Function of managed bridges which allows redundant bridges to be used for network resilience, without the broadcast storms associated with looping. If a bridge fails, a new path to a redundant bridge is opened.

Stack A group of network devices that are logically integrated into a single system.

Star topology Network configuration where all the nodes are connected to a central point via individual cables.

Static routing System in which routing information is manually entered into the routing table.

STE Spanning Tree Explorer

STM Synchronous Transport Module. Specifies the electrical and optical transmission over SDH. Transmission rates are based on 155.52 Mbps (STM-1, equivalent to SONETs OC-3).

STP (Shielded Twisted Pair) Common transmission medium which consists of a Receive (RX) and a Transmit (TX) wire twisted together to reduce crosstalk. The twisted pair is shielded by a braided outer sheath.

STS Synchronous Transport Signal. The logical signal specification for SONET frame structure. This specifies electrical transmission rates based on 51.84 Mbps (STS-1). OC-3 is 155.52 Mbps.

Subnetwork Collection of OSI end systems and intermediate systems under the control of one administrative domain and using a single network access protocol. For example, private X.25 networks, a series of bridged LANs. Compare Autonomous System.

SuperJANET The broadband upgrade to JANET.

SVC (Switched Virtual Circuit) Virtual circuit that can be dynamically established on demand.

Switched 56 Switched data transmission service at 56 Kbps (as opposed to service on dedicated leased lines).

Switched Ethernet An Ethernet hub with integrated MAC layer bridging or switching capability to provide each port with 10 Mbps of bandwidth; separate transmissions can occur on each port of the switching hub, and the switch filters traffic based on destination MAC address.

Switched Virtual LAN A logical network consisting of several different LAN Emulation domains controlled through and intelligent network management application.

Switching hubs Hubs that use intelligent Ethernet switching technology to interconnect multiple Ethernet LANs and higher-speed LANs such as FDDI.

Synchronous transmission Form of usually high-speed data communication that uses synchronization bytes instead of start or stop bits to tell the receiving device about the coming transmission. More complex that asynchronous.