CCNA Cisco Certified Network Associate Study Guide - FTP Server

662 Glossary
CBR Constant Bit Rate: An ATM Forum QoS class created for use in ATM
networks. CBR is used for connections that rely on precision clocking to
guarantee trustworthy delivery. Compare with: ABR and VBR.
CD Carrier Detect: A signal indicating that an interface is active or that a
connection generated by a modem has been established.
CDP Cisco Discovery Protocol: Cisco’s proprietary protocol that is used to
tell a neighbor Cisco device about the type of hardware, software version,
and active interfaces that the Cisco device is using. It uses a SNAP frame
between devices and is not routable.
CDVT Cell Delay Variation Tolerance: A QoS parameter for traffic management
in ATM networks specified when a connection is established. The
allowable fluctuation levels for data samples taken by the PCR in CBR transmissions
are determined by the CDVT. See also: CBR and PCR.
cell In ATM networking, the basic unit of data for switching and multiplexing.
Cells have a defined length of 53 bytes, including a 5-byte header
that identifies the cell’s data stream and 48 bytes of payload. See also:
cell relay.
cell payload scrambling The method by which an ATM switch maintains
framing on some medium-speed edge and trunk interfaces (T3 or E3 circuits).
Cell payload scrambling rearranges the data portion of a cell to maintain
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 hardware
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 capability.
Therefore, all customer connections return to the CO. See also: CO.
CER Cell Error Ratio: The ratio in ATM of transmitted cells having errors
to the total number of cells sent in a transmission within a certain span
of time.