APPENDIX B: WAN TERMS AND ACRONYMS
B-2
WPIM-SY LOCAL MANAGEMENT GUIDE
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 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.
DLCI
Data Link Connection Identifier, a unique virtual circuit identi-
fier used in Frame Relay. Identifies a given frame as being
from a particular logical link. The DLCI has only local signifi-
cance.
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).
E-1
European digital signal level 1. Similar to T-1 but provides 32
channels (2.048 Mbps) instead of 24 channels (1.544 Mbps).
ESF
Extended Super Frame. A new T-1 framing standard (see D4
framing) that uses 24 T-1 frames, thus allowing individual
identification of the channel and signaling bits.
Fractional T-1
Use of a portion (less than the full 24 channels) of a T-1 line.
Frame Relay
A network protocol that allows for many point-to-point virtual
connections over a single access channel.
HDB3
High Density Bipolar 3, used with E-1, a bipolar coding
method that does not allow more than 3 consecutive zeros.
HDLC
High-Level Data Link Control, layer 2 (link layer) full-duplex
protocol derived from SDLC.
INV. HDLC
A form of zero suppression in which all zeros in the HDLC
packet are changed to ones and all ones are changed to zeros.
