ETSI TS 148 056 V17.0.0 (2022-05)

Digital cellular telecommunications system (Phase 2+) (GSM); Base Station Controller - Base Transceiver Station (BSC - BTS) interface; Layer 2 specification (3GPP TS 48.056 version 17.0.0 Release 17)

RTS/TSGR-0048056vh00

General Information

• Status: Not Published
• Technical Committee: 3GPP RAN - Technical Specification Group Radio Access Network
• Current Stage: 12 - Completion
• Completion Date: 05-May-2022

Standards Content (Sample)

ETSI TS 148 056 V17.0.0 (2022-05)






TECHNICAL SPECIFICATION
Digital cellular telecommunications system (Phase 2+) (GSM);
Base Station Controller - Base Transceiver Station (BSC - BTS)
interface;
Layer 2 specification
(3GPP TS 48.056 version 17.0.0 Release 17)

R
GLOBAL SYSTEM FOR
MOBILE COMMUNICATIONS

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3GPP TS 48.056 version 17.0.0 Release 17 1 ETSI TS 148 056 V17.0.0 (2022-05)

Reference
RTS/TSGR-0048056vh00
Keywords
GSM
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ETSI

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3GPP TS 48.056 version 17.0.0 Release 17 2 ETSI TS 148 056 V17.0.0 (2022-05)
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Legal Notice
This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
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ETSI

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3GPP TS 48.056 version 17.0.0 Release 17 3 ETSI TS 148 056 V17.0.0 (2022-05)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 4
1 Scope . 5
2 References . 5
3 Definitions and abbreviations . 6
4 General description. 6
5 Functional contents . 7
6 LAPD functions . 7
6.1 Exceptions and modifications. 7
6.1.1 Void . 7
6.1.2 Command/Response field bit (C/R) . 7
6.1.3 Service Access Point Identifier (SAPI) . 7
6.1.4 TEI for point-to-point data link connection . 8
6.1.5 Commands and responses . 8
6.1.6 Exchange identification (XID) command/response . 8
6.1.7 MDL-XID . 8
6.1.8 PH-DATA, PH DEACTIVATE and PH-ACTIVATE . 8
6.1.9 MPH-ACTIVATE, MPH-DEACTIVATE an MPH-INFORMATION . 8
6.1.10 Priority indicator . 9
6.1.11 Terminal Endpoint Identifier (TEI) management procedures . 9
6.1.11.1 General . 9
6.1.11.2 TEI assignment procedure . 9
6.1.11.3 TEI identity verify procedure . 11
6.1.11.4 Formats and codes. . 11
6.1.12 Automatic negotiation of data link layer parameters . 11
6.1.13 Establishment procedures . 11
6.1.14 N(S) sequence error . 11
6.1.15 List of system parameters . 11
6.1.15.1 Timer T200 . 12
6.1.15.2 Maximum number of retransmissions (N200) . 12
6.1.15.3 Maximum number of octets in an information field (N201) . 12
6.1.15.4 Maximum number of transmission of the TEI identity request message (N202) . 12
6.1.15.5 Maximum number of outstanding frames (K) . 12
6.1.15.6 Timer T201 . 12
6.1.15.7 Timer T202 . 12
6.1.15.8 Timer T203 . 12
6.1.16 Data link layer monitor function . 13
6.1.17 Miscellaneous . 13
Annex A (informative): Change History . 14
History . 15

ETSI

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3GPP TS 48.056 version 17.0.0 Release 17 4 ETSI TS 148 056 V17.0.0 (2022-05)
Foreword
This Technical Specification has been produced by the 3rd Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
ETSI

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3GPP TS 48.056 version 17.0.0 Release 17 5 ETSI TS 148 056 V17.0.0 (2022-05)
1 Scope
The present document specifies the link layer used for signalling on the A-bis interface between BSC and BTS. The use
and general aspects of the A-bis interface are described in 3GPP TS 48.051 and the interface aspects in 3GPP TS
48.052.
The Link Access Procedure on the D-channel (LAPD) specification used on the A-bis interface in the GSM PLMN is a
subset of the EN 300 125 which in turn has less options than the CCITT Recommendation Q.921.
This description contains first the protocol definitions and second the services provided by the layer 2 to the layer 3.
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TS 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 48.051: "Base Station Controller - Base Transceiver Station (BSC - BTS) interface;
General aspects".
[3] 3GPP TS 48.052: "Base Station Controller - Base Transceiver Station (BSC - BTS) interface;
Interface principles".
[4] Void.
[5] Void.
[6] Void.
[7] Void.
[8] Void.
[9] Void.
[10] Void.
[11] Void.
[12] Void.
[13] Void.
[14] Void.
[15] Void.
[16] Void.
[17] Void.
[18] Void.
ETSI

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3GPP TS 48.056 version 17.0.0 Release 17 6 ETSI TS 148 056 V17.0.0 (2022-05)
[19] CCITT Recommendation Q.921: "Integrated services digital network (ISDN) user-network
interface - Data link layer specification".
[20] EN 300 125: "Integrated Services Digital Network (ISDN); User-network interface data link layer
specification Application of CCITT Recommendations Q.920/I.440 and Q.921/I.441".
3 Definitions and abbreviations
Abbreviations used in the present document are listed in 3GPP TS 21.905.
4 General description
The following information categories are supported by the procedures of this layer 2 Recommendation:
- signalling (including Short Message Service (SMS) information);
- operation and maintenance;
- layer 2 management.
For each of these categories the BSC may have one or more layer 2 links to every TRX and BCF.
The signalling links over the A-bis interface are addressed to the different units by Terminal Endpoint Identifiers (TEI).
The same unit will normally have more than one functional entity. The logical links between different functional
entities are identified by functional addresses, the Service Access Points Identifier (SAPI).
Figure 1 shows the architectural model with different layer 2 links.
A number of logical links may be multiplexed on each physical link. The same layer 2 logical link may not be
distributed over more than one physical link.
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