INTERNATIONAL  TELECOMMUNICATION  UNION

		     ITU-T RECOMMENDATION SUMMARY


Rec. No. : Q.922

Title :	ISDN data link layer specification for frame mode bearer 
	services

Study Group : XI - Switching and Signalling

Version : New

Date of adoption : 1992

Notes :	


Recommendation Q.922 specifies the frame structure, elements of 
procedure, format of fields and procedures of the data link layer to 
support frame mode bearer services in the user plane as defined in 
Recommendation I.233.

This specification of a data link layer protocol and procedures for 
frame mode bearer services is based upon and is an extension of the 
LAPD (Link access procedure on the D-channel) protocol and procedures 
defined in Recommendation Q.921. The procedures are applicable to, but 
not restricted to, access a Frame Mode Bearer Service and are also 
designated link access procedures to frame mode bearer services, or 
LAPF. A subset of LAPF, corresponding to the data link core sublayer 
(as defined in Recommendation I.233), is used to support the Frame 
Relaying Bearer service. This subset is named "data link core 
protocol" (DL-CORE). The remainder of the LAPF is called the data 
link control (DL-CONTROL) protocol.

The purpose of the LAPF is to convey data link service data units 
between DL-service users in the U-plane for frame mode bearer services 
across the ISDN user-network interface on B-, D- or H-channels. Frame 
mode bearer connections are established using either procedures 
specified in Recommendation Q.933 or (for permanent virtual circuits) 
by subscription.

LAPF uses a physical layer service, as supported by the I.430 [4] 
Series Recommendations. LAPF allows for statistical multiplexing of 
one or more frame mode bearer connections over a single ISDN B-, D- 
or H-channel by use of LAPF and compatible HDLC procedures.

Network layer protocols which provide and support the N-Data-Transfer 
phase of the OSI connection oriented network service (CONS - See 
Recommendation X.213) may be conveyed by the service provided by 
Recommendation Q.922.

	- the Data Transfer phase of Recommendation X.25, and

	- the protocol specified in Recommendation Q.922.

DLCI assignment is performed using group signalling or by subscription 
or prior agreement.

The concepts, terminology, overview description of data link functions 
and procedures and the relationship with the Recommendations are 
described in general terms in Recommendation Q.920.



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