ADTRAN Express 5210 User Manual page 182

Appendix D. Glossary
the frame relay frame off each LAN frame, and passes the LAN frame on to the
end device. Bridges are generally used to connect LAN segments to other LAN
segments or to a WAN. They route traffic on the Level 2 LAN protocol (e.g. the
Media Access Control address), which occupies the lower sub-layer of the LAN
OSI data link layer. See also router.
CCITT
Consultive Committee for International Telephony and Telegraphy. A standards orga-
nization that devises and proposes recommendations for international commu-
nications. See also ANSI.
CD
carrier detect. A signal generated by a modem or DSU/CSU. CD indicates the
presence of a carrier signal on a communications link.
clocking
An oscillator-generated signal that provides a timing reference for a transmis-
sion link. A clock provides signals used in a transmission system to control the
timing of certain functions. The clock has two functions, (1) to generate periodic
signals for synchronization and (2) to provide a time base.
CPE
customer premises equipment. All telecommunications terminal equipment
located on the customer premises, including telephone sets, private branch
exchanges (PBXs), data terminals, and customer-owned coin-operated tele-
phones.
CRC
cyclic redundancy check. A computational means to ensure the accuracy of frames
transmitted between devices in a frame relay network. The mathematical func-
tion is computed, before the frame is transmitted, at the originating device. Its
numerical value is computed based on the content of the frame. This value is
compared with a recomputed value of the function at the destination device. See
also FCS.
CS
See CTS.
CSU
channel service unit. A device used to connect a digital phone line (T1 or
Switched 56 line) coming in from the phone company to either a multiplexer,
D-2 Express 5210 User Manual 61200208L1-1