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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.
To order the complete text of this Recommendation, please use the
Order Form for ITU-T Recommendations. An electronic version of this
form is available on ITUDOC (Winword 2.0: UPI=ITU-5265; ASCII: UPI=ITU-2488).