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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.