AT&T 7400 series, 7500 series, 7100 series, 2500 series manual Table D-2.Some Ccitt Analog Standards

D-8COMMUNICATIONS PROTOCOLS

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TABLE D-2.Some CCITT Analog Standards (Continued)

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⎜	⎜		⎜		⎜
⎜ Name	⎜	Title	⎜	Equivalent	⎜
⎜	⎜		⎜	Standard(s)	⎜
⎜	⎜		⎜		⎜
⎜	⎜		⎜		⎜
⎜ V.29	⎜ 9600 bps modem standardized for use on point-to-point leased		⎜ FED-STD 1007		⎜
⎜	⎜	telephone-type circuits	⎜		⎜
⎜	⎜		⎜		⎜
⎜	⎜		⎜		⎜
⎜ V.35	⎜ Data transmission at 48 kilobits per second using 60-108 kHz group		⎜ None.		⎜
⎜	⎜ band circuits		⎜		⎜
⎜	⎜		⎜		⎜
⎜	⎜	Loop test devices for modems	⎜	RS-449	⎜
⎜ V.54	⎜		⎜		⎜
⎜	⎜		⎜		⎜

Table D-3.Some CCITT ISDN Standards

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⎜	⎜		⎜		⎜
⎜ Name	⎜	Subject	⎜	Equivalent	⎜
⎜	⎜		⎜	Standard(s)	⎜
⎜	⎜		⎜		⎜
⎜	⎜	Defines the basic user-network interface, layer 1 specification	⎜	None.	⎜
⎜ I.430	⎜		⎜		⎜
________________________________________________________________________________________________________					⎜
⎜	⎜		⎜
⎜	⎜	Defines the primary rate user-network interface, layer 1 specification	⎜	None.	⎜
⎜ I.431	⎜		⎜		⎜
________________________________________________________________________________________________________					⎜
⎜	⎜		⎜
⎜ I.441	⎜	Defines the ISDN user-network interface for the data link layer	⎜	None.	⎜
⎜	⎜		⎜		⎜
⎜	⎜	Defines the ISDN user-network interface for layer 3	⎜	None.	⎜
⎜ I.451	⎜		⎜		⎜
________________________________________________________________________________________________________					⎜
⎜	⎜		⎜
⎜	⎜	Defines the data link layer (layer 2) protocol for ISDN	⎜	LAPD; CCITT I.441	⎜
⎜ Q.921	⎜		⎜		⎜
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⎜	⎜		⎜
⎜ Q.931	⎜	Defines the network layer (layer 3) protocol for ISDN	⎜	X.25; CCITT I.451	⎜
⎜	⎜		⎜		⎜

Two other CCITT protocols play important roles in the ISDN specification:

∙LAPB (link access protocol — balanced) — A link-layer protocol adopted by the CCITT as part of the X.25 packet-switched network standard. It is a subset of HDLC.

∙LAPD (link access protocol D-channel) — A link-layer protocol adopted by the CCITT for D-channel communications. At the network layer, X.25 is employed for packet switching, and I.451 is employed for control signaling.

The ISDN protocol scheme is given in Figure D-2.The figure shows that D-channel and B-channel communications are packaged in different protocol suites. In addition, when signaling, data packets, or telemetry are transmitted over the D-channel, each uses a different subset of protocols. Likewise, on the B-channel, CCITT plans for circuit-switched, leased-line, and packet-switched communication allow for differing protocol suites.