AT&T DS1/DMi/ISDN-PRI manual See network channel-terminating equipment, Glossary GL-5

GLOSSARY GL-5

channel-division multiplexer (CDM)

channel- expansion multiplexer (CEM)

channel negotiation

channel service unit (CSU)

circuit-switched transport mode

class of restriction (COR)

class of service (COS)

A device that connects directly to a System 75 or a System 85 digital signal level

1(DS1) port to provide point-to-point or multipoint nonswitched private-line data connections over the same digital facility that carries intercommunications system traffic. The CDM allows any number of preselected channels from a DS1 facility to bypass the communications system and/or terminate while passing the other channels to the system normally. The CDM is compatible with both robbed-bit (voice-grade) and alternate voice/data (AVD) signaling techniques, and provides a number of interface options, such as RS-232C, RS-449, and V.35.

A device that doubles the channel capacity of a 1.544M bps digital signal level 1 (DS1) private-line facility by compressing up to 48 voice-band channels onto a single DS1 facility. Only 64K-bps voice, and voice-band data signals of up to 4.8K-bps, can be compressed; however, the CEM can be configured to pass selected 64K-bps channels uncompressed so that compressed and uncompressed channels can share the same DS1 facility.

An ISDN capability that determines which B-channel is used for completing a call to a terminating communications system. For example, if the B-channel selected by the originating end is not acceptable to the terminating end (such as an inconsistency between the two ends or preplanned use of the selected channel by the terminating end), the terminating end can request a change in the channel to be used. Also called exclusive-channel request and preferred-call reference.

See network channel-terminating equipment.

The condition in which a communications channel appears as a wire connecting two endpoints. For each call that requests circuit-switched transport mode, the communications system provides a 56K-bps or 64K-bps channel that can be used to transmit either voice, non-packetized data, or packetized data. The Q.931 protocol is used to establish, maintain, and clear the connection. Each data application may have additional protocol requirements for providing end-to-end data transfer. For example, both Digital Communications Protocol (DCP) and basic rate interface (BRI) data modules use digital multiplexed interface (DMI) data modes to control the end-to-end data transfer.

On a System 75 or DEFTNITY® Communications System Generic 1, a feature that allows definition of up to 64 classes of call-origination and call-termination restrictions for telephones, telephone groups, data modules, and trunk groups. See also class of service.

1 . On a System 75, a number (0 through 15) that specifies a group of feature-access permissions of a group of telephones. COS specifies whether telephone users can activate certain features such as Automatic Callback and Call Forwarding — All Calls, Data Privacy, and Priority Calling. See also class of restriction.

2 . On a System 85, a numeric code that specifies a group of feature-access permissions and calling-privilege restrictions that together determine the privileges of a group of extension numbers. As many as 63 COSs are provided by System 85. See also class of restriction.