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Glossary

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CPCS

Common Part Convergence Sublayer: One of two AAL sublayers

that are service-dependent, it is further segmented into the CS and SAR sub-
layers. The CPCS prepares data for transmission across the ATM network;
it creates the 48-byte payload cells that are sent to the ATM layer. See also:
AAL and ATM layer.

CPE

Customer Premises Equipment: Items such as telephones, modems,

and terminals installed at customer locations and connected to the telephone
company network.

crankback

In ATM, a correction technique used when a node somewhere

on a chosen path cannot accept a connection setup request, blocking the
request. The path is rolled back to an intermediate node, which then uses
GCAC to attempt to find an alternate path to the final destination.

CRC

Cyclic Redundancy Check: A methodology that detects errors,

whereby the frame recipient makes a calculation by dividing frame contents
with a prime binary divisor and compares the remainder to a value stored in
the frame by the sending node. Contrast with: checksum.

CSMA/CD

Carrier Sense Multiple Access Collision Detect: A technology

defined by the Ethernet IEEE 802.3 committee. Each device senses the cable
for a digital signal before transmitting. Also, CSMA/CD allows all devices on
the network to share the same cable, but one at a time. If two devices
transmit at the same time, a frame collision will occur and a jamming pattern
will be sent; the devices will stop transmitting, wait a predetermined amount
of time, and then try to transmit again.

CST

Common Spanning Tree: The IEEE uses what is called Common

Spanning Tree (CST), which is defined with IEEE 802.1q. The IEEE 802.1q
defines one spanning tree instance for all VLANs.

CSU

Channel Service Unit: A digital mechanism that connects end-user

equipment to the local digital telephone loop. Frequently referred to along
with the Data Service Unit as CSU/DSU. See also: DSU.

CTD

Cell Transfer Delay: For a given connection in ATM, the time period

between a cell exit event at the source user-network interface (UNI) and the
corresponding cell entry event at the destination. The CTD between these
points is the sum of the total inter-ATM transmission delay and the total
ATM processing delay.

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