Appendix C: WAN Terms and Acronyms
C-2
WPIM-S/T User’s Guide
CRC
Cyclic Redundancy Check, an algorithm or process used
to identify corrupted packets in the transmission link.
CSU
Channel Service Unit, a device that terminates the local
loop/digital channel on a customer’s (DSU) premises.
The CSU connects to a DSX-1 interface on the CPE.
DCE
Data Communications Equipment, a device such as a
modem that connects the communications circuit with
the end device (see DTE).
data (D)
channel
A full-duplex 16 Kbps channel used with BRI and PRI
services for signaling and control.
D4
D4 Framing, a popular framing format in T-1. Uses 12
T-1 Frames to identify both the channel and the signaling
bit.
DN
Directory Number, the telephone number for an ISDN
line assigned by the telephone company.
DLCI
Data Link Connection Identifier, a unique virtual circuit
identifier used in Frame Relay. Identifies a given frame as
being from a particular logical link. The DLCI has only
local significance.
DN
Directory Number, addresses assigned by the service
provider for each device operating on the line.
DoD
Dial on Demand.
DSU
Digital Service Unit, converts RS-232 or other terminal
interfaces to DSX-1 (T-1) interface.
DS-0
Digital Signal, level 0, a standard 64,000 bit/second
channel. Synonymous with “Timeslot.”
DTE
Data Terminal Equipment, equipment that originates and
terminates data transmission such as a computer or
printer (see DCE).
