Page 492

460

Glossary

distribution lists

Access lists used to filter incoming and outgoing route

table entries on a router.

DLCI

Data-Link Connection Identifier: Used to identify virtual circuits in a

Frame Relay network.

DNS

Domain Name System: Used to resolve host names to IP addresses.

DSAP

Destination Service Access Point: The service access point of a net-

work node, specified in the destination field of a packet. See also: SSAP and SAP.

DSL

Digital Subscriber Line: DSL technologies are used to provide broad-

band services over a single copper pair, typically to residential customers.
Most vendors are providing DSL services at up to 6Mbps downstream, but
the technology can support 52Mbps service.

DSR

Data Set Ready: When a DCE is powered up and ready to run, this

EIA/TIA-232 interface circuit is also engaged.

DSU

Data Service Unit: This device is used to adapt the physical interface

on a data terminal equipment (DTE) mechanism to a transmission facility
such as T1 or E1 and is also responsible for signal timing. It is commonly
grouped with the Channel Service Unit and referred to as the CSU/DSU.
See also: CSU.

DTE

data terminal equipment: Any device located at the user end of a user-

network interface serving as a destination, a source, or both. DTE includes
devices such as multiplexers, protocol translators, and computers. The con-
nection to a data network is made through data communications equipment
(DCE) such as a modem, using the clocking signals generated by that device.
See also: DCE.

DTR

data terminal ready: An activated EIA/TIA-232 circuit communi-

cating to the DCE the state of preparedness of the DTE to transmit or
receive data.

DUAL

Diffusing Update Algorithm: Used in Enhanced IGRP, this conver-

gence algorithm provides loop-free operation throughout an entire route's
computation. DUAL grants routers involved in a topology revision the
ability to synchronize simultaneously, while routers unaffected by this
change are not involved. See also: Enhanced IGRP.

www.sybex.com