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Glossary

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 channel 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.

DVMRP

Distance Vector Multicast Routing Protocol: Based primarily on

the Routing Information Protocol (RIP), this Internet gateway protocol
implements a common, condensed-mode IP multicast scheme, using IGMP
to transfer routing datagrams between its neighbors. See also: IGMP.

DXI

Data Exchange Interface: Described in RFC 1482, DXI defines the

effectiveness of a network device such as a router, bridge, or hub to act as an
FEP to an ATM network by using a special DSU that accomplishes packet
encapsulation.

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