CSU/DSU: channel service unit /data service unit.The CSU component is a disital interface device that connects end-user equipment to the local digital telephone loop.the DSU component is a device used in digital transmission that adapts the physical interface on a data terminal equipment (DTE) device to a transmission facility,such as T1 or E1.TheDSU also is responsible for functions such as a signal timing.
DCE : data communications equipment.From a physical layer perspective,the device providing the clocking on a WAN link,typically a CSU/DSU ,is the DCE.From a packet switching perspective,the service provider’s switch,to switch,to which a rputer might connect,is considered the DCE.
DDR: dial-on-demand routing.A technique where by a router can automatically initiate and close a circuit-switchedsession as transmitting stations demand.The router spoofs keepalives so that end stations treat the session as active.DDR permits routing over ISDN or telephone lines.
DE: discard eligible.The bit in the frame relay header that,if frames must be discarded,signals a switch to choose this frame to discard instead of another frame without the DE bit set.
deny: An action taken with an ACL that implies that the packet is discarded.
Designated port: The port (interface) on a bridge or switch that advertises the best spanning tree BPDU (hello message ) onto a LAN segment.
Directed broadcast address: The same as a broadcast address.
Discarding state: A Rapid Spanning Tree Protocol state that is used instead of the blocking ,listening,and disabled states in STP.
Distance vector: The logic behind the behavior of some interior routing protocols,such as RIP and IGRP.distance vector routing algorithms call for each router to send its entire routing table in each update,but only to its neighbors.Distance vector routingalgorithms can be phone to routing loops but are computationally simpler than link-state routing algorithms.Also called Bellman-Ford routing algorithm.
DLCI: data link connection identifier.A Frame Relay address used in Frame Relay headers to identify the VC.
DTE: data terminal equipment.from a layer 1 perspective,the DTE synchronizes its clock based on the clock sent by the DCE.From a packet switching perspective,the DTE is the device outside the Service Provider’s network,typically a router.
DUAL : Disffusing Update Algorithm.A convergence algorithm used in EIGRP that provides loop-free operation at every instant throughout a route computation.Allows routers involved in a topology change to synchronize at the same time,while not involving routers that are unaffected by the change.
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