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Interphase Tech iSPAN 5535 PRI User Manual

Page 155

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Glossary

iSPAN PRI PCI ISDN Users Guide

135

CRC (Cyclic Redundancy Check)

A bit errors detection technique

that employs an algorithm to calculate a value for the information bits

in a packet. The receiver, using the same algorithm, recalculates that

value and compares it to the value received. If the two values do not
agree, the transmitted packet is considered to be in error.

CS (Controlled Slip)

A CS is the replication or deletion of the pay-

load bits of the DS1 frame. A Controlled Slip may be performed when
there is a difference between the timing of a synchronous receiving ter-
minal and the received signal.

CSD (Circuit Switched Data)

A dial-up data communications chan-

nel which, once established, looks like a transparent data pipe. Also,
the type of ISDN service required to utilize this capability of an ISDN
circuit. Contrast with CSV.

CSU/DSU (Channel Service Unit/ Data Service Unit)

A device

which incorporates the functions of a CSU and a DSU and interfaces
between a Switched-56 (or Dedicated Digital Service) line and a user’s
data equipment.

CSV (Circuit Switched Voice)

A dial-up communications circuit for

voice grade communication. Also, the type of ISDN service required
to use this capability of an ISDN circuit. Contrast with CSD.

D channel

One of the three standard channels on a BRI line. At 16

Kbps, a D channel carries all signaling information and can carry low-
speed packet data such as X.25 packet switching.

demarc (demarcation point)

The point on a customer’s premises

where the line from the telephone company meets the customer’s wir-
ing at the customer’s premises.

Directory Number

Your seven digit telephone number (without the

area code), as found in the telephone directory. Each BRI connection
can have up to two directory numbers, one for each B channel.

DMA (Direct Memory Access)

A fast method of moving data

between two subsystems without processor intervention.

DMS/DMS100

The name of a central office switch manufactured by

Northern Telecom. These switches use Custom (proprietary) or
National ISDN-1 (NI-1) software.

DSU

See CSU/DSU.

ETS (European Telecommunications Standard)

ETSI

ETSI is the European Telecommunications Standards Insti-

tute.