ETSI TS 148 052 V8.0.0 (2009-01) Technical Specification Digital cellular telecommunications system (Phase 2+); Base Station Controller - Base Transceiver Station (BSC-BTS) interface; Interface principles (3GPP TS 48.052 version 8.0.0 Release 8) R GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS 3GPP TS 48.052 version 8.0.0 Release 8 1 ETSI TS 148 052 V8.0.0 (2009-01) Reference RTS/TSGG-0248052v800 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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ETSI 3GPP TS 48.052 version 8.0.0 Release 8 3 ETSI TS 148 052 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 3.1 Definitions..........................................................................................................................................................6 3.2 Abbreviations.....................................................................................................................................................6 4 General.....................................................................................................................................................6 5 Functional division between BSC and BTS.............................................................................................7 5.1 General...............................................................................................................................................................7 5.2 Terrestrial channel management.........................................................................................................................7 5.3 Radio channel management................................................................................................................................7 5.3.1 Channel configuration management.............................................................................................................7 5.3.2 SDCCH (Stand alone DCCH) and TCH management..................................................................................8 5.3.2.1 Frequency hopping management............................................................................................................8 5.3.2.2 Channel selection, link supervision and channel release.........................................................................8 5.3.2.3 Power control..........................................................................................................................................8 5.3.2.4 Idle channel observation.........................................................................................................................8 5.3.3 BCCH/CCCH management..........................................................................................................................8 5.3.4 Random access..............................................................................................................................................8 5.3.5 Channel coding/decoding.............................................................................................................................8 5.3.6 Transcoding/rate adaption.............................................................................................................................9 5.3.7 Timing advance............................................................................................................................................9 5.3.8 Radio resource indication.............................................................................................................................9 5.3.9 Measurements...............................................................................................................................................9 5.3.10 LAPDm functions (Layer 2).........................................................................................................................9 5.3.11 Paging...........................................................................................................................................................9 5.3.12 Handover......................................................................................................................................................9 5.3.13 Encryption...................................................................................................................................................10 5.3.14 Mobility management and call control.......................................................................................................10 6 Transcoding/rate adaption and multiplexing..........................................................................................11 6.1 Transcoding/rate adaption in BTS....................................................................................................................11 6.2 Transcoding/rate adaption outside BTS...........................................................................................................11 7 Interface structures.................................................................................................................................12 7.1 Communication channels.................................................................................................................................12 7.2 Signalling links.................................................................................................................................................12 7.3 Signalling model..............................................................................................................................................13 Annex A (informative): Change History..............................................................................................17 History..............................................................................................................................................................18 ETSI 3GPP TS 48.052 version 8.0.0 Release 8 4 ETSI TS 148 052 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 48.052 version 8.0.0 Release 8 5 ETSI TS 148 052 V8.0.0 (2009-01) 1 Scope The use and general aspects of the A-bis interface are given in 3GPP TS 48.051. The present document gives the principle basis for the rest of the specifications specifying the interface between the Base Station Controller, BSC, and the Base Transceiver Station, BTS, with its transceivers, TRX. These components together form the Base Station System, BSS. (The interface between MSC and the BSS is specified in 3GPP TS 48.001 and 3GPP TS 48.020). The intention with this interface is to get a unified way of connecting remotely located BTSs/TRXs to a BSC allowing for the interconnection of BSCs and BTSs/TRXs from different manufacturers. In order to keep the BTS as simple as possible, BTS contains only those functions which have to recide close to the radio interface. 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 TR 21.905: "Vocabulary for 3GPP Specifications". [2] 3GPP TS 48.001: "Base Station System - Mobile services Switching Centre (BSS - MSC) interface; General aspects". [3] 3GPP TS 48.002: "Base Station System - Mobile-services Switching Centre (BSS - MSC) interface Interface principles". [4] Void. [5] 3GPP TS 48.006: "Signalling transport mechanism specification for the Base Station System - Mobile-services Switching Centre (BSS-MSC) interface". [6] Void. [7] 3GPP TS 48.020: "Rate adaption on the Base Station System - Mobile-services Switching Centre (BSS-MSC) interface". [8] 3GPP TS 48.051: "Base Station Controller - Base Transceiver Station (BSC-BTS) interface; General aspects". [9] 3GPP TS 48.058: "Base Station Controller - Base Transceiver Station (BSC-BTS) interface; Layer 3 specification". [10] 3GPP TS 48.060: "Inband control of remote transcoders and rate adaptors for full rate traffic channels". [11] 3GPP TS 48.061: "Inband control of remote transcoders and rate adaptors for half rate traffic channels". [12] Void. [13] 3GPP TS 23.002: "Network Architecture". ETSI 3GPP TS 48.052 version 8.0.0 Release 8 6 ETSI TS 148 052 V8.0.0 (2009-01) 3 Definitions and abbreviations 3.1 Definitions For the purposes of the present document, the following terms and definitions apply: Base Station System (BSS): system of base station equipment (transceivers, controllers, etc..) which is viewed by the MSC through a single interface as defined by the 3GPP TS 48.0xx series of recommendations, as being the entity responsible for communicating with Mobile Stations in a certain area. The radio equipment of a BSS may cover one or more cells. A BSS may consist of one or more base stations. If an internal interface according to the 3GPP TS 48.05x series at recommendations is implemented, then the BSS shall consist of one Base Station Controller (BSC) and several Base Transceiver Stations (BTSs). NOTE: The functionality is described in 3GPP TS 48.001. Base Station Controller (BSC): network component in the PLMN with the functions for control of one or more Base Transceiver Stations (BTSs). Base Transceiver Station (BTS): network component which serves one cell, and is controlled by a Base Station Controller. The BTS can consist of one or more TRXs with or without common control equipment. Cell: See 3GPP TS 23.002. Transceiver (TRX): in the GSM PLMN is the functional entity which supports the 8 basic radio channels of the same TDMA-frame. Base Control Function (BCF): functional entity which handles common control functions within a BTS, e.g. frequency hopping sequences etc. At a multi BTS site, one of the BCFs can also be choosen to perform functions common to the site (e.g. external alarms, power supply, time base). 3.2 Abbreviations For the purposes of the present document, the abbreviations given in 3GPP TR 21.905 apply. 4 General 3GPP TS 48.001 and 3GPP TS 48.020 specify the functional split and interface between MSC and the Base Station System, BSS, the A- interface. The BSS can be further subdivided into one BSC controlling one or more BTSs, each consisting of one or more TRXs. The interface treated by the present document is the interface between a BSC and a BTS. It is denoted the A-bis- interface. The A-bis-interface is capable of supporting three different internal BTS configurations: - one single TRX; - a collection of TRXs where all are served by a common physical connection; - a collection of TRXs, each served by its own physical connection. ETSI 3GPP TS 48.052 version 8.0.0 Release 8 7 ETSI TS 148 052 V8.0.0 (2009-01) Figure 4.1 shows some possible configurations. BSS <-----------------------------------------> | +-----+ A-b┼is +-----+ | +-------- -------| TRX | BTS1 | | | + - - | | | | BCF | | | | +-----+ | | +-----+ | | | | TRX | | | A-b┼is + - - | | | +-------- -------| TRX | BTS2 | | + - - | | | | | TRX | | | + - - | | | | | BCF | | | +-----+ +-----+ A┼ | | | +- - -+ | MSC +-------- -----------| BSC | A-b┼is |+---+| +-----+ | | +-------- --------|TRX| | | |+---+| | | | ┼ |+---+| | +-------- --------|TRX| | | | |+---+| BTS3 | | ┼ |+---+| | | +-------- --------|TRX| | | |+---+| | | | ┼ |+---+| | +-------- --------|BCF| | | | |+---+| +-----+ +-- - + Figure 4.1: BSS Subdivision and Interfaces The present document is based on the use of digital transmission system interfaces, either at 2 048 kbit/s or at 64 kbit/s. Furthermore, the use of a subrate of 16 kbit/s and/or 8 kbit/s is supported for coded speech or rate adapted data. This interface will support the transcoder positioned either inside or outside BTS. In the latter case, remote control (synchronisation) of the transcoder is used. 5 Functional division between BSC and BTS 5.1 General In Technical Specification 3GPP TS 48.001 the functional division between MSC and BSS is described. This clause describes the further subdivision of functions between BSC and BTS/TRX required for the A-bis interface. A summary can be found in table 5.1. Some general requirements on the functionality of the A-bis interface are also specified. 5.2 Terrestrial channel management There is a unique mapping from traffic channels on the radio path to the terrestrial traffic channels. BSC makes the choice of radio channel and thereby also of the terrestrial channel for a call. 5.3 Radio channel management 5.3.1 Channel configuration management The channel configuration is controlled between the BSC and OMC. Current configuration is downloaded from OMC to BSC which then controls the use of the radio channels (TDMA time slots for BCCH/CCCH, TCHs, SDCCHs etc). ETSI 3GPP TS 48.052 version 8.0.0 Release 8 8 ETSI TS 148 052 V8.0.0 (2009-01) 5.3.2 SDCCH (Stand alone DCCH) and TCH management 5.3.2.1 Frequency hopping management The hopping sequences for each BTS (cell) is downloaded from OMC to BSC. It is then the responsibility of BSC to download this information to each BTS and also to send the corresponding BCCH information to be transmitted in the BCCH time slots. 5.3.2.2 Channel selection, link supervision and channel release These functions are controlled by BSC. For channel selection BSC has to have information on blocked radio channels and also on interference level on idle channels. In the assignment messages to MS (Immediate Assign, Assign Command and Handover Command), a Starting Time parameter is included. This starting time is based on the frame number on the (new) BTS. Before sending the assign message to MS, BSC has to be informed on the current frame number in BTS. When assigning a channel, BSC shall inform BTS on relevant parameters, e.g. channel type, channel coding, rate adaption, starting time. 5.3.2.3 Power control The ordered MS power level is sent in the 16 bit L1-header of SACCH- blocks on the downlink and the actual power level used by MS is reported in the corresponding L1-header on the uplink. This header is inserted (downlink) and extracted (uplink) by BTS/TRX. The determination of required power level in MS is based on uplink radio measurements made by BTS/TRX and reported to BSC. The basic control of this power is performed by BSC and the dynamic regulation is performed by BSC or optionally by BTS. If BTS supports dynamic MS power regulation, BSC can indicate whether BTS is to regulate the MS power and if so, also the parameters required by BTS. The required TRX transmission power level on a channel is based on reported measurements performed by MS. The dynamic control of this power is optional. If supported, the basic control is performed by BSC and the dynamic regulation is performed by BSC or optionally by BTS. If BTS supports dynamic TRX transmission power regulation, BSC can indicate whether BTS is to regulate the transmission power and if so, also the parameters required by BTS. 5.3.2.4 Idle channel observation Idle channels are monitored by BTS. 5.3.3 BCCH/CCCH management TRX knows the timing of BCCH/CCCH slots (not known by BSC). The actual timing of BCCH/CCCH blocks therefore has to be made by BTS/TRX, including the scheduling of Paging Request messages on paging sub-channels. BCCH information is downloaded to BTS. 5.3.4 Random access Detection of a random access attempt has to be made by TRX which then sends a message to BSC containing the required timing advance, the frame number of the access attempt and the 8 bit Channel Request message sent by MS in the access burst. This information is then included by BSC in the following Immediate Assign message sent to MS. 5.3.5 Channel coding/decoding The error protection coding and decoding is made by BTS/TRX. Different coding and interleaving schemes are used for speech and data calls. This information has to be signalled from BSC to BTS on a per call basis. ETSI 3GPP TS 48.052 version 8.0.0 Release 8 9 ETSI TS 148 052 V8.0.0 (2009-01) 5.3.6 Transcoding/rate adaption The A-bis interface has to allow for the transcoder/rate adaptor being positioned either inside or outside BTS. 5.3.7 Timing advance Timing advance has to be determined by TRX. When MS is on a dedicated channel (SDCCH, TCH), the required timing advance (TA) is sent to MS and the actual timing advance is reported by MS in the 16 bit L1-header of the SACCH blocks. At handover access, TA is determined by TRX and reported to MS in the PHYsical INFOrmation message sent by BTS/TRX. At random access, TA is determined by TRX but in those cases, TA has to be reported to BSC for inclusion in the IMMediate ASSIGN message sent to MS by BSC. 5.3.8 Radio resource indication BTS reports on status (interference level, blocking etc.) of idle channels to BSC on a regular basis. 5.3.9 Measurements MS measures the downlink received level and quality from the serving cell and the received level from surrounding cells. The results from these measurements are reported by MS in Measurement Report messages on SACCH. Uplink received level and quality are measured by BTS/TRX. The parameters for the uplink measurements are equivalent to the parameters used by MS for the corresponding downlink measurements (averaging period and dynamic range). The support of forwarding this basic raw measurement data over the A-bis interface is mandatory. Additionally, BTS and BSC may optionally support some pre-processing in BTS of this data. 5.3.10 LAPDm functions (Layer 2) Layer 2 on the radio interface (LAPDm) is terminated at BTS/TRX. Between BTS and BSC, LAPD is used. 5.3.11 Paging Paging is initiated by MSC via BSC. BSC determines the paging group to be used based on IMSI of the MS to be paged. The paging group value is sent to BTS together with the TMSI or IMSI. Based on the paging group information, BTS/TRX will build the relevant PAGING REQUEST message and execute the transmission of the message in the correct paging sub-channel. 5.3.12 Handover No handover recognition or decision is made by BTS. However, BTS/TRX has to detect the handover access made by a handed over MS. BTS/TRX also checks the Handover Reference value sent by MS in the handover access burst against the Handover Reference value received from BSC in the channel activation command. In case of an asynchronous handover, BTS/TRX then builds the PHYsical INFOrmation message (including the Timing Advance value) and sends it to MS. The handover access is also reported to BSC. ETSI