ETSI TS 148 056 V8.0.0 (2009-01) Technical Specification Digital cellular telecommunications system (Phase 2+); Base Station Controller - Base Transceiver Station (BSC - BTS) interface; Layer 2 specification (3GPP TS 48.056 version 8.0.0 Release 8) R GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS 3GPP TS 48.056 version 8.0.0 Release 8 1 ETSI TS 148 056 V8.0.0 (2009-01) Reference RTS/TSGG-0248056v800 Keywords GSM ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE Tel.: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16 Siret N° 348 623 562 00017 - NAF 742 C Association à but non lucratif enregistrée à la Sous-Préfecture de Grasse (06) N° 7803/88 Important notice Individual copies of the present document can be downloaded from: http://www.etsi.org The present document may be made available in more than one electronic version or in print. In any case of existing or perceived difference in contents between such versions, the reference version is the Portable Document Format (PDF). 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Latest updates are available on the ETSI Web server (http://webapp.etsi.org/IPR/home.asp). Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become, essential to the present document. Foreword This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP). The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables. The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under http://webapp.etsi.org/key/queryform.asp. ETSI 3GPP TS 48.056 version 8.0.0 Release 8 3 ETSI TS 148 056 V8.0.0 (2009-01) Contents Intellectual Property Rights................................................................................................................................2 Foreword.............................................................................................................................................................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 3GPP TS 48.056 version 8.0.0 Release 8 4 ETSI TS 148 056 V8.0.0 (2009-01) 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 3GPP TS 48.056 version 8.0.0 Release 8 5 ETSI TS 148 056 V8.0.0 (2009-01) 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 3GPP TS 48.056 version 8.0.0 Release 8 6 ETSI TS 148 056 V8.0.0 (2009-01) [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. ____________________ | ________ | | | | | | | | __ | __ ______ | | || |_______RSL________SAPI_=_0___| |__| | | | || |_______OML________SAPI_=_62__| |__| | | | || |_______L2ML_______SAPI_=_63__| |__| TRX |TEI 1 | | || | | |__| | | | ||__| |__| |______| | |LAYER 2| | __ ______ | | | __ | | |__| | | | || |_____|_RSL________SAPI_=_0___| |__| | | | || |_______OML________SAPI_=_62__| |__| TRX |TEI 2 | | || |_______L2ML_______SAPI_=_63__| |__| | | | T E I || | | | |______| | | || |_______RSL________SAPI_=_0___| | ______ | | || |_______OML________SAPI_=_62__| |__| | | | || |_______L2ML_______SAPI_=_63__| |__| | | | ||__| | |__| TRX |TEI 3 | | | | | |__| | | |MANAGE-| | |__| |______| | |MENT | __ | __ ______ | | || |_______OML________SAPI_=_62__| |__| | | | || |_______L2ML_______SAPI_=_63__| |__| BCF |TEI 4 | | ||__| |__| | | | | | __ _ | __ | | | | || | _ _ | OML _ _ _ _SAPI = 62_ | |__| |TEI 65 | | || | _ _ | L2ML_ _ _ _SAPI = 63_ | |__| | | |_______||__| | |__| |______| | | |___________________| Figure 4.1: An example of Logical Layer 2 links supported by three permanent and one semipermanent links ETSI 3GPP TS 48.056 version 8.0.0 Release 8 7 ETSI TS 148 056 V8.0.0 (2009-01) 5 Functional contents The basic functional content of the layer 2 protocol is: - transparent layer 2 links and time fill; - point-to-point dedicated layer 2 links addressing both physical entities and functional entities; - point-to-multipoint addressed links used for layer 2 management; - basic functions for TEI assignment and management; - basic priority functions; - basic supervision of links when not carrying traffic; - sequence control; - transmission error control; - control of errors not recoverable by retransmission. 6 LAPD functions The LAPD functions as specified in EN 300 125 are applicable. However, the exceptions and modifications specified in the remainder of the present document shall be used. 6.1 Exceptions and modifications In the following headlines from EN 300 125 are kept and references are made to the corresponding clause of EN 300 125. 6.1.1 Void 6.1.2 Command/Response field bit (C/R) (Refer to EN 300 125, part 2, clause 3.3.2) In GSM PLMN's BSC represents the network side and TRX/BCF the user side of the interface. 6.1.3 Service Access Point Identifier (SAPI) (Refer to EN 300 125, part 2, clause 3.3.3) The SAPI values for the A-bis interface are as listed in table 6.1.3. ETSI 3GPP TS 48.056 version 8.0.0 Release 8 8 ETSI TS 148 056 V8.0.0 (2009-01) Table 6.1.3: Allocation of SAPI values and priority classes SAPI value Related layer 3 or layer management entity Priority 0 Radio signalling procedures 2 1 Reserved for packet mode communications using Q.931 call control procedures - (Not used in GSM PLMN) 16 Reserved for packet communication conforming to X.25 level 3 procedures (Not - used in GSM PLMN 62 Operation and maintenance procedure 1 63 Layer 2 management procedures 1 All others Reserved for future standardization - 6.1.4 TEI for point-to-point data link connection (Refer to EN 300 125, part 2, clause 3.3.4.2). The remaining Terminal Endpoint Identifier (TEI) values are used for the point-to-point data link connections associated with the addressed Service Access Point (SAP). The range of TEI values shall be allocated as shown in table 6.1.4. Table 6.1.4: Allocation of TEI values TEI value User type 0-63 TEI assignment for fixed TRX and BCF addresses 64-126 TEI assignment for additional, TRX or BCF addresses NOTE: A BCF is given a separate layer 2 link only if it is not integrated with a TRX. 6.1.5 Commands and responses (Refer to EN 300 125, part 2, clause 3.6.1) The XID command and response are not used. 6.1.6 Exchange identification (XID) command/response (Refer to EN 300 125, part 2, clause 3.6.12) This functionality is not used. 6.1.7 MDL-XID (Refer to EN 300 125, part 2, clause 4.1.1.9) This functionality is not used. 6.1.8 PH-DATA, PH DEACTIVATE and PH-ACTIVATE (Refer to EN 300 125, part 2, clauses 4.1.1.10 - 4.1.1.12) This functionality is not relevant. 6.1.9 MPH-ACTIVATE, MPH-DEACTIVATE an MPH-INFORMATION (Refer to EN 300 125, part 2, clauses 4.1.1.13 - 4.1.1.15) ETSI 3GPP TS 48.056 version 8.0.0 Release 8 9 ETSI TS 148 056 V8.0.0 (2009-01) This functionality is not relevant. 6.1.10 Priority indicator (Refer to EN 300 125, part 2, clause 4.1.3.1) The different SAPIs are given the priority classes as listed in table 1 when contending (with priority one as the highest). 6.1.11 Terminal Endpoint Identifier (TEI) management procedures (Refer to EN 300 125, part 2, clause 5.3) Due to the special assignment functions needed on the A-bis interface there are modifications and additions to the assignment procedures. The rest of clause 5.3 in EN 300 125, part 2, is kept if not stated otherwise. 6.1.11.1 General (Refer to EN 300 125, part 2, clause 5.3.1) TEI management for A-bis interface is based on the following procedural means: - a Subset of the TEI assignment procedures; - the TEI check procedures; - the TEI remove procedures; - an additional TEI assignment procedure. The TEI management needs procedures to check the used TEI values and procedures for reaction in situation where more than one TRX equipment uses the same TEI value. In addition to the fixed values it shall be possible to use additional TEI value to the same TRX equipment and thus increase the signalling capacity. 6.1.11.2 TEI assignment procedure (Refer to EN 300 125, part 2, clause 5.3.2) The TEI assignment procedure used on the A-bis interface has some additions to the automatic TEI assignment procedure specified in EN 300 125, part 2. To facilitate the configuration control in the BSC each TRX will have a fixed TEI and possibly get access to one or more additional TEIs assigning physical channels/layer 2 links. The layer 2 links may all be turned on and off according to the normal automatic TEI assignment scheme but the TRX may only request identified TEI values which is (semi-) permanently programmed or programmed by operation and maintenance messages. In GSM the reference number Ri is not used. It is only misoperation situations resulting from double failures that could be prevented/solved faster by this parameter. The marginal advantage is not supposed to motivate the application of a random generator and the checking procedure. The subset of the automatic assignment procedure applicable for the first layer 2 link to a TRX shall have the following modifications to EN 300 125, part 2: - the identity request shall have an Ai value in the range 0-63 identifying the TEI value which is requested for activation; - on reception of the identity request message the BSC will check that the requested TEI may be used from the configurations aspects and then perform a normal TEI check procedure to prevent a double assignment; - if the TEI request is accepted an identity assigned message with the requested TEI number is received by TRX before the expiry of timer T202; - a successful assignment procedure is shown in figure 6.1.11.2.a. ETSI