TSW200E1
9 - Glossary of Technical Terms
2-wire
Communication in which two modems are interconnected by only a wire pair. See full-
duplex.
4-wire
Communication in which two modems are interconnected by two wire pairs. See full-
duplex.
AIS (Alarm Indication Signal)
Alarm Indication Signal: signal that gets active when any alarm condition arises.
BPS (Bits per second) or bits/s
Number of bits transmitted or received per second
CAS (Channel Associated Signalling)
Used for 2 Mbps PCM30 and PCM30C.
CCITT
Abbreviation of Comité Consultatif International Téléphonique et Télégraphique, an
organization that sets international communications standards. CCITT, now known as ITU (the
parent organization) has defined many important standards for data communications.
CPE
(Pronounced as separate letters) Short for customer premises equipment, communications
equipment that resides on the customer's premises (i.e., it is owned or leased by the customer).
Client-owned equipment.
CRC (Cyclic Redundancy Check)
CRC-4 consists in an error detection method used for 2 Mbps frames, where for each
transmitted data block a set of bits is added, which allows error detection within the block. A CRC-4
(C1 C2 C3 C4) word, placed at the N sub-multiframe, is the remainder of the operation:
multiplication by x
4
and division by the generated polynomial x
4
+ x + 1, of the polynomial
representing the N-1 sub-multiframe. In this process, the C1 bit is defined as the most significant bit
of the remainder and C4 is the least significant bit.
DCE (Data Communications Equipment)
A device that communicates with a Data Terminal Equipment (DTE) device in RS-232C
communications. Usually a modem.
DTE (Data Terminal Equipment)
Wise Telecommunications Industry 68
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