Glossary
693
DCE
data communications equipment (as defined by the EIA) or data
circuit-terminating equipment (as defined by the ITU-T): The mechanisms and
links of a communications network that make up the network portion of the
user-to-network interface, such as modems. The DCE supplies the physical
connection to the network, forwards traffic, and provides a clocking signal
to synchronize data transmission between DTE and DCE devices. Compare
with: DTE.
D channel
1) data channel: A full-duplex, 16Kbps (BRI) or 64Kbps (PRI)
ISDN channel. Compare with: B channel, E channel, and H channel. 2) In
SNA, anything that provides a connection between the processor and main
storage with any peripherals.
DDP
Datagram Delivery Protocol: Used in the AppleTalk suite of protocols
as a connectionless protocol that is responsible for sending datagrams
through an internetwork.
DDR
dial-on-demand routing: A technique that allows a router to auto-
matically initiate and end a circuit-switched session per the requirements of
the sending station. By mimicking keepalives, the router fools the end station
into treating the session as active. DDR permits routing over ISDN or tele-
phone lines via a modem or external ISDN terminal adapter.
DE
Discard Eligibility: Used in Frame Relay networks to tell a switch that
a frame can be discarded if the switch is too busy. The DE is a field in the
frame that is turned on by transmitting routers if the committed information
rate (CIR) is oversubscribed or set to 0.
dedicated line
Point-to-point connection that does not share any
bandwidth.
de-encapsulation
The technique used by layered protocols in which a
layer removes header information from the Protocol Data Unit (PDU) from
the layer below. See: encapsulation.
default route
The static routing table entry used to direct frames whose
next hop is not spelled out in the dynamic routing table.
delay
The time elapsed between a sender's initiation of a transaction and
the first response they receive. Also, the time needed to move a packet from
its source to its destination over a path. See also: latency.
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