Summary

This Recommendation specifies the Link Access Procedures on the D-channel (LAPD) of an ISDN customer access. Implementations of this Recommendation are in use in existing networks.

This Recommendation has been revised for the sake of clarity, to cover new functionality, and to reflect the requirements of Q.921 in Protocol Implementation Conformance Statement (PICS) proformas.

Clarifications are:

Definition of terms used in Q.921 (new subclause 1.3);

Amendment to 5.2.1 for clarification on signalling arrangement and circumstances under which TEI management and UI frame need not be supported;

Amendment to 5.3.4 for clarification on TEI procedures;

Amendment to Annex A of Q.921 for clarification on signalling arrangement and circumstances under which TEI management need not be supported.

New functions were specified as follows:

New SAPI value 12 for teleaction communication (revised Table 2/Q.921);

New Annex E "Provision of Multi-Selective Reject option".

Protocol Implementation Conformance Statement (PICS) proformas were amended, or generated, as appropriate, as follows:

Amendment to Annex F (former Annex E) of Q.921 "PICS Basic Rate User-side" in order to reflect modifications to Q.921, as indicated above;

New Annex G to Q.921 "PICS Basic Rate Network-side";

New Annex H to Q.921 "PICS Rate User-side";

New Annex I to Q.921 "PICS Primary Rate Network-side".