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Glossary

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RTS

Request To Send: An EIA/TIA-232 control signal requesting permis-

sion to transmit data on a communication line.

S reference point

ISDN reference point that works with a T reference

point to convert a four-wire ISDN network to the two-wire ISDN network
needed to communicate with the ISDN switches at the network provider.

sampling rate

The rate at which samples of a specific waveform ampli-

tude are collected within a specified period of time.

SAP

1) Service Access Point: A field specified by IEEE 802.2 that is part of

an address specification. 2) Service Advertising Protocol: The Novell NetWare
protocol that supplies a way to inform network clients of resources and ser-
vices availability on network, using routers and servers. See also: IPX.

SCR

sustainable cell rate: An ATM Forum parameter used for traffic man-

agement, it is the long-term average cell rate for VBR connections that can
be transmitted.

SDH

Synchronous Digital Hierarchy: One of the standards developed for

Fiberoptic Transmission Systems (FOTS).

SDLC

Synchronous Data Link Control: A protocol used in SNA Data Link

layer communications. SDLC is a bit-oriented, full-duplex serial protocol
that is the basis for several similar protocols, including HDLC and LAPB.
See also: HDLC and LAPB.

seed router

In an AppleTalk network, the router that is equipped with the

network number or cable range in its port descriptor. The seed router spec-
ifies the network number or cable range for other routers in that network
section and answers to configuration requests from nonseed routers on its
connected AppleTalk network, permitting those routers to affirm or modify
their configurations accordingly. Every AppleTalk network needs at least
one seed router physically connected to each network segment.

sequencing

Used in virtual circuits and segmentation to number segments

so they can be put back together again in the correct order.

server

Hardware and software that provide network services to clients.

set-based

Set-based routers and switches use the set command to con-

figure devices. Cisco is moving away from set-based commands and is using
the command-line interface (CLI) on all new devices.

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