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Glossary

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cell payload scrambling

The method by which an ATM switch maintains

framing on some medium-speed edge and trunk interfaces (T3 or E3 cir-
cuits). Cell payload scrambling rearranges the data portion of a cell to main-
tain the line synchronization with certain common bit patterns.

cell relay

A technology that uses small packets of fixed size, known as

cells. Their fixed length enables cells to be processed and switched in hard-
ware at high speeds, making this technology the foundation for ATM and
other high-speed network protocols. See also: cell.

Centrex

A local exchange carrier service, providing local switching that

resembles that of an on-site PBX. Centrex has no on-site switching capa-
bility. Therefore, all customer connections return to the CO. See also: CO.

CER

Cell Error Ratio: In ATM the ratio of the number of transmitted cells

having errors to the total number of cells sent in a transmission within a cer-
tain span of time.

CGMP

Cisco Group Management Protocol: A proprietary protocol devel-

oped by Cisco. The router uses CGMP to send multicast membership com-
mands to Catalyst switches.

Challenge

Used to provide authentication in Challenge Handshake

Authentication Protocol (CHAP) as part of the handshake process. This
numerically unique query is sent to authenticate the user without sending the
password unencrypted across the wire. See also: CHAP.

channelized E1

Operating at 2.048Mpbs, an access link that is sectioned

into 29 B channels and one D channel, supporting DDR, Frame Relay, and
X.25. Compare with: channelized T1.

channelized T1

Operating at 1.544Mbps, an access link that is sectioned

into 23 B channels and one D channel of 64Kbps each, where individual
channels or groups of channels connect to various destinations, supporting
DDR, Frame Relay, and X.25. Compare with: channelized E1.

CHAP

Challenge Handshake Authentication Protocol: Supported on lines

using PPP encapsulation, it is a security feature that identifies the remote end,
helping keep out unauthorized users. After CHAP is performed, the router or
access server determines whether a given user is permitted access. It is a
newer, more secure protocol than PAP. Compare with: PAP.

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