ADTRAN Express 5210 User Manual page 183

channel bank, or directly to another device producing a digital signal; for exam-
ple, a digital PBX, a PC, or data communications device. A CSU performs cer-
tain line-conditioning and equalization functions, and responds to loopback
commands sent from the central office. A CSU regenerates digital signals. It
monitors them for problems, and provides a way of testing the digital circuit.
CTS
clear to send. A signal on the DTE interface indicating that the DCE is clear to
send data.
dB
decibel. A unit of measure of signal strength, usually the relation between a
transmitted signal and a standard signal source.
DCE
data communications equipment. Device that provides all the functions required
for connection to telephone company lines and for converting signals between
telephone lines and DTE. Also see DTE.
DDS
digital data service. A private line digital service, for transmitting data end-to-end
at speeds of 2.4, 4.8, 9.6, and 56 kbps and in some cases 19.2, 38.4, or 64 kbps.
The systems can use central hub offices for obtaining test access, bridging legs of
multipoint circuits, and cross connecting equipment. DDS is offered on an inter-
LATA basis by AT&T and on an intra-LATA basis by the Bell operating compa-
nies.
DE
discard eligibility. A user-set bit indicating that a frame may be discarded in pref-
erence to other frames if congestion occurs, to maintain the committed quality of
service within the network. Frames with the DE bit set are considered Be excess
data.
DLCI
data link connection identifier. A unique number assigned to a PVC end point in a
frame relay network. Identifies a particular PVC endpoint within a user's access
channel in a frame relay network and has local significance only to that channel.
DSU
data service unit. A device designed to transmit and receive digital data on digital
transmission facilities.
61200208L1-1 Express 5210 User Manual
Appendix D. Glossary
D-3