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3 General approach
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4 The RA0 Function
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5 The RA1 Function
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................................................................................................................................... 7 6 The RA1’’ Function ................................................................................................................................ 8 7 Split/Combine and Padding Functions.................................................................................................... 8 7.1 Data Frame distribution into the channels by the Split/Combine function...............................................................8
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.....................................................................................................................................................................8 8 The RA1/RA1' Function.......................................................................................................................... 8 8.1 Radio Interface rate of 12 kbit/s...............................................................................................................................9 8.2 Radio Interface rate of 6 kbit/s.................................................................................................................................9 8.3 Radio Interface rate of 3.6 kbit/s..............................................................................................................................9
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................................................................................................................................................................9 9 THE RA1'/RAA' FUNCTION................................................................................................................. 9 9.1 Radio Interface rate of 14,5 kbit/s..........................................................................................................................10
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10 THE RAA' FUNCTION
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10.1 Coding of A-TRAU frame
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10.2 Framing Pattern Substitution in A-TRAU frame
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10.2.1 FPS encoding
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10.3 A-TRAU Synchronisation Pattern
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11 THE RAA'' FUNCTION
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12 The RA2 Function
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13 The Multiplexing Function
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14 Support of non-transparent bearer services
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........................................................................................... 14 14.1 TCH/F9.6 and TCH/F4.8 kbit/s channel codings .............................................................................................14
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15 Support of transparent bearer services
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.......................................................................................18 ETSI ETSI TS 100 591 V7.1.0 (2001-03) 4 3GPP TS 08.20 version 7.1.0 Release 1998
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15.1.4 Handling of status bits X, SA, SB
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15.2.4 Handling of status bits X and SB
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16 Frame Formats
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....................................................................................................................................... 20 Annex A (informative): Frame Pattern Substitution ......................................................................... 22 A.1 Special cases.......................................................................................................................................... 22 A.2 False Z sequence detection.................................................................................................................... 23 Annex B (informative): Change history .............................................................................................. 24 ETSI ETSI TS 100 591 V7.1.0 (2001-03) 5 3GPP TS 08.20 version 7.1.0 Release 1998 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 ETSI TS 100 591 V7.1.0 (2001-03) 6 3GPP TS 08.20 version 7.1.0 Release 1998 1 Scope The present document defines rate adaptation functions to be used in GSM PLMN Base Station Systems (BSS) transcoders and IWF for adapting radio interface data rates to the 64 kbit/s used at the A-interface in accordance with GSM 03.10. The number of Base Station System - Mobile-services Switching Centre (BSS - MSC) traffic channels supporting data rate adaptation may be limited. In this case some channels may not support data rate adaptation. Those that do, must conform to the present document. NOTE: The present document should be considered together with GSM 04.21 to give a complete description of PLMN rate adaptation. 2 References, abbreviations and definitions 2.1 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] GSM 01.04: "Digital cellular telecommunications system (Phase 2+); Abbreviations and acronyms". [2] GSM 02.34: “Digital cellular telecommunications system (Phase2+): High Speed Circuit Switched Data (HSCSD) - Stage1” [3] GSM 03.10: "Digital cellular telecommunications system (Phase 2+); GSM Public Land Mobile Network (PLMN) connection types". [4] GSM 03.34: “Digital cellular telecommunications system (Phase 2+): High Speed Circuit Switched Data (HSCSD) - Stage2”. [5] GSM 04.21: "Digital cellular telecommunications system (Phase 2+); Rate adaption on the Mobile Station - Base Station System (MS - BSS) interface". [6] GSM 04.22: "Digital cellular telecommunications system (Phase 2+); Radio Link Protocol (RLP) for data and telematic services on the Mobile Station - Base Station System (MS - BSS) interface and the Base Station System - Mobile-services Switching Centre (BSS - MSC) interface". [7] GSM 05.03: "Digital cellular telecommunications system (Phase 2+); Channel coding". [8] GSM 07.01: "Digital cellular telecommunications system (Phase 2+); General on Terminal Adaptation Functions (TAF) for Mobile Stations (MS)". [9] GSM 08.08: "Digital cellular telecommunications system (Phase 2+); Mobile Switching Centre - Base Station System (MSC - BSS) interface; Layer 3 specification". [10] GSM 09.07: "Digital cellular telecommunications system (Phase 2+); General requirements on interworking between the Public Land Mobile Network (PLMN) and the Integrated Services Digital Network (ISDN) or Public Switched Telephone Network (PSTN)". ETSI ETSI TS 100 591 V7.1.0 (2001-03) 7 3GPP TS 08.20 version 7.1.0 Release 1998 [11] ITU-T Recommendation V.110: "Support of data terminal equipment’s (DTEs) with V-Series interfaces by an integrated services digital network". [12] ITU-T Recommendation I.460:-Multiplexing, rate adaption and support of existing interfaces. 2.2 Abbreviations For the purposes of the present document, the following abbreviations apply: FPS Frame Pattern Substitution FSI Frame Start Identifier ZSP Zero Sequence Position 2.3 Definitions For the purposes of the present document, the following terms and definitions apply. Substream: Stream of data with explicit or implicit numbering between splitter and combine functions. Channel: A physical full rate channel on the radio interface (TCH/F) independent of the contents. A interface circuit: The 8 bits that constitute one 64 kbps circuit on the A interface. A interface subcircuit: One specific bit position or one specific pair of bit positions within the A interface circuit. 3 General approach GSM 03.10 (clause 6) defines the PLMN connection types necessary to support the GSM PLMN data and telematic services. Within the BSS , transcoder and IWF, there are several data rate adaptation functions which are combined as shown in GSM 03.10 as part of a connection type. These functions are RA0, RA1,RA1/RA1' , RA1’’ , RAA", RA1'/RAA', RAA' and RA2. The RA2 function is equivalent to that described in ITU-T Recommendation V.110. In addition, splitting/combining, padding and inband numbering functions as defined in GSM 04.21 and multiplexing as defined herein are used in cases where more than one channel is allowed. The RA1/RA1' and RA1'/RAA' are relay functions used as indicated in GSM 03.10. The BSS uses the information contained in the ASSIGNMENT REQUEST message on the A-interface (see GSM 08.08) to set the "E bits" and to map the "D bits" as shown below, as well as to choose the correct channel coding. 4 The RA0 Function The RA0 function is specified in GSM 04.21 5 The RA1 Function For connections where only one channel is allowed used on the radio interface, the specification in GSM 04.21 for adaptation of synchronous data rates up to and including 9,6 kbit/s to intermediate rates 8 or 16 kbit/s applies. For connection where more than one channel are used on the radio interface, rate adaptation is applied on the corresponding substreams as specified in GSM 04.21 for AIUR of 4,8 kbit/s or 9,6 kbit/s. ETSI ETSI TS 100 591 V7.1.0 (2001-03) 8 3GPP TS 08.20 version 7.1.0 Release 1998 6 The RA1’’ Function The RA1’’ function is specified in GSM 04.21. The RA1’’ function is only applicable in BSS for AIUR higher than 38,4 kbit/s. 7 Split/Combine and Padding Functions The Split/Combine-function in the IWF is used in cases when up to and including 4substreams are used. The Split/Combine-function in the BSS is used only when more than four substreams are used. 7.1 Data Frame distribution into the channels by the Split/Combine function Described in GSM 04.21 7.2 Substream numbering Described in GSM 04.21 7.3 Initial Substream Synchronisation for Transparent Services Described in GSM 04.21 7.4 Frame Synchronisation and Action on loss of Synchronisation When in the IWF, the Split/Combine function is responsible for controlling the initial frame synchronisation procedure and re-synchronisation procedure as described in GSM 09.07. 7.5 Network Independent Clocking NIC is specified in GSM 04.21 7.6 Padding Padding is specified in GSM 04.21 8 The RA1/RA1’ Function For AIURs less or equal to 38,4 kbit/s, the RA1/RA1’ function in the BSS is applied on each of the n substreams and there are no significant differences between the single slot case and the multislot case. For AIURs less or equal to 38,4 kbit/s RA1/RA1’ is as specified in GSM 04.21 for the single slot case. The table below gives a relation between the AIUR, channel coding and number of substreams. As an example from table 1: The wanted AIUR is 28,8 kbit/s, the number of substreams needed to support this rate is 3. Each individual substream is rate adapted as in the single slot case. For AIURs of 48 kbit/s, 56 kbit/s and 64 kbit/s, RA1/RA1’’ is as specified in GSM 04.21 for these rates. ETSI ETSI TS 100 591 V7.1.0 (2001-03) 9 3GPP TS 08.20 version 7.1.0 Release 1998 Table 1: Relationship between AIUR, channel coding and number of channels Multislot intermediaterate 8 kbps Multislot intermediate rate of 16 kbps AIUR Transparent Non-transparent Transparent Non-transparent ≤2,4 kbit/s 1 N/A N/A N/A 4,8 kbit/s 1 1 N/A N/A 9,6 kbit/s 2 2 1 1 14,4 kbit/s 3 3 2 N/A 19,2 kbit/s 4 4 2 2 28,8 kbit/s N/A N/A 3 3 38,4 kbit/s N/A N/A 4 4 48 kbit/s N/A N/A 5 N/A 56 kbit/s N/A N/A 5 N/A 64 kbit/s N/A N/A 6 N/A 8.1 Radio Interface rate of 12 kbit/s Described in GSM 04.21. 8.2 Radio Interface rate of 6 kbit/s Described in GSM 04.21. 8.3 Radio Interface rate of 3.6 kbit/s Described in GSM 04.21. 8.4 Synchronisation Refer to GSM 04.21. 8.5 Idle frames Refer to GSM 04.21 9 THE RA1’/RAA’ FUNCTION The RA1’/RAA’ is only applicable when TCH/F14.4 channel coding is used. The RA1/RAA’ converts radio interface blocks into E-TRAU frame and vice versa. The format of E-TRAU frame is specified in GSM 08.60. The RA1’/RAA’ function in the BSS is applied on each of the n substreams and there are no significant differences between the single slot case and the multislot case. The table below gives a relation between the AIUR, channel coding and number of substreams. As an example from table 2: The wanted AIUR is 28,8 kbit/s, the number of substreams needed to support this rate is 2. Each individual substream is rate adapted as in the single slot case. ETSI ETSI TS 100 591 V7.1.0 (2001-03) 10 3GPP TS 08.20 version 7.1.0 Release 1998 Table 2: Relationship between AIUR, channel coding and number of channels AIUR Transparent Non-transparent 14,4 kbit/s 1 1 28,8 kbit/s 2 2 38,4 kbit/s 3 N/A 43,2 kbit/s N/A 3 48 kbit/s 4 N/A 56 kbit/s 4 N/A 57,6 kbit/s N/A 4 64 kbit/s 5 N/A 9.1 Radio Interface rate of 14,5 kbit/s See GSM 08.60. 9.2 Synchronisation See GSM 08.60. 9.3 Idle frames See GSM 08.60. 10 THE RAA’ FUNCTION The RAA’ function is only applicable when TCH/F14.4 channel coding is used. The RAA’ converts E-TRAU frame into A-TRAU frame and vice versa. The format of the E-TRAU frame is specified in GSM 08.60. 10.1 Coding of A-TRAU frame The format of the A-TRAU frame is given in Figure 5. An A-TRAU frame carries eight 36 bit-data frames. C Bits Table 3 C1 C2 C3 C4 Date Rate 0 1 1 1 14,4 kbit/s Table 4 C5 BSS to IWF Frame Type note 1 IWF to BSS UFE (Uplink Frame Error) 1 idle framing error 0 data no framing error NOTE 1: Bit C5 corresponds to bit C6 of the E-TRAU frame as defined in GSM 08.60. ETSI ETSI TS 100 591 V7.1.0 (2001-03) 11 3GPP TS 08.20 version 7.1.0 Release 1998 M Bits Transparent data M1 and M2 are as defined in GSM 04.21. Non transparent data See subclause 14.2 of this GSM TS. Z bits Bits Zi are used for Framing Pattern Substitution. See subclause 10.2. 10.2 Framing Pattern Substitution in A-TRAU frame The Framing Pattern Substitution is used in each of the eight 36 bit data fields of the A-TRAU frame (see Figure 5) to avoid transmitting a sequence of eight zeroes (called Z sequence in the following). The purposes of FPS is to avoid erroneous synchronisation to the A-TRAU due to sixteen zeroes occurring accidentally in the data bits and to avoid erroneous synchronisation to V.110. The synchronisation pattern of two consecutive V.110 frames cannot be found within a stream of A TRAU frames. 10.2.1 FPS encoding A Zero Sequence Position (ZSP) field is used to account for the occurrence of eight zeroes in the 36 bit data field. NOTE: A sequence of eight zeroes is considered as a block (e.g. a stream of eleven consecutive zeroes produces only one ZSP and not four ZSPs). The ZSP field is defined as follows: Table 5 1 2 3 4 5 6 7 8 1 C A0 A1 A2 A3 A4 1 The meaning of the different bits of the ZSP field is : C : Continuation bit. ’0’ means that there is another ZSP in the data field. ’1’ means that there is no other ZSP. A0-A4 :address of the next Z sequence (eight zeroes) to be inserted. The address ‘00001’ corresponds to the bit D1, the value ‘11101’ to the bit D29, (A0 is the msb, A4 is the lsb). NOTE: a Z sequence substitution cannot occur at bit D30..D36 (as it is 8 bit long) 1 : locking bit prevent the false occurrence of a Z sequence. The Framing Pattern Substitution is applied in each of the eight 36 bit data field (see Figure 5). Bit Zi indicates whether FPS is used in the ith 36 bit data field (i=1 to 8). The coding of the Zi bit is the following: Table 6 Zi (i=1..8) meaning 1 no substitution 0 at least one substitution If Zi bit indicates no substitution, the output data bits of FPS are equal to the input data bits. If Zi indicates at least one substitution, the bits D1-D8 contain the first ZSP. ETSI ETSI TS 100 591 V7.1.0 (2001-03) 12 3GPP TS 08.20 version 7.1.0 Release 1998 The following description indicates the general operating procedures for FPS. It is not meant to indicate a required implementation of the encoding procedure. 1 a1 a2 bit position a3 list of addresses of the Z sequences list of the data blocks without Z sequence a1 a2 a3 1 D1 1 D2 1 D3 D4 1 a1 1 0 a2 1 0 a3 1 1 ZSP(a1) ZSP(a2) ZSP(a3) === 2 3 D2 D3 D4 D1 ZSP(a1) ZSP(a2) ZSP(a3) Zi 4 D2 D3 D4 D1 Zseq1 Zseq2 Zseq3 Continuation Bit next Z seq address a d Locking bit Figure 1 Step 1 : The input 36 bit sub frame is considered as a bit stream in which the bits are numbered from 1 to 36. This bit stream contains 0, 1 or several Z sequences, (Zseq1 to Zseq3 on the figure) The Z sequence is a sequence of 8 consecutive zeroes : ’0000 0000’ Step 2 : Starting from this bit stream, two lists are built up : 2-a : the ’a’ list which contains the address of the first bit of each Z sequences. 2-d : the ’d’ list which contains all the data blocks which do not have the Z sequence. Step 3 : The ’a’ list is transformed so as to build the ZSP list. Each ZSP element is used to indicate: at which address is the next Z sequence of the message if yet another ZSP element will be found at this address (link element) ETSI ETSI TS 100 591 V7.1.0 (2001-03) 13 3GPP TS 08.20 version 7.1.0 Release 1998 Step 4 : The output 37 bit sub frame is built from: the Zi field which indicates whether the original message has been transformed or not with this technique. In the example given in Figure 1, Zi should be set to ’0’ to indicate that at least one FPS has occurred. the ZSP and D elements interleaved. As the ZSP elements have exactly the same length as the Z sequence, the sub frame length is only increased by one (the Zi bit), whatever the number of frame pattern substitutions may be. For special cases, refer to annex A. 10.3 A-TRAU Synchronisation Pattern The frame synchronisation is obtained by means of the first two octets in each frame, with all bits coded binary "0" and the first bit in octet no 2 coded binary "1". The following 17 bit alignment pattern is used to achieve frame synchronisation : 00000000 00000000 1XXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX 11 THE RAA’’ FUNCTION On the IWF side of the A interface, the RAA" function converts between the A-TRAU format and a synchronous stream. FPS is performed by this function as well, see subclause 10.2. In transparent operation, the RAA" function handles the M1 and M2 bits as specified for the RA1’ function in clause 9 of GSM 04.21. In non-transparent operation, the RAA" function maps between the A-TRAU format and 290 bit blocks consisting of M1, M2 and 288 bits making up half of an RLP frame, see subclause 14.2 of this GSM TS. 12 The RA2 Function Described in GSM 04.21. The RA2 function is applicable only for single slot operations. 13 The Multiplexing Function The multiplexing function is only applicable for AIUR up to and including 38,4 kbit/s for multislot operations. The multiplexing function is based on the ITU-T I.460. The multiplexing function is used to combine n (n=2 to 4) substreams of multislot intermediate rate of 8 kbit/s or n substreams of multislot intermediate rate of 16 kbit/s on one 64 kbit/s stream by using subcircuits in each octet to each substream such that: i) An 8 kbit/s substream is allowed to occupy subcircuits with positions 1,3,5 or 7 of each octet of the 64 kbit/s stream; a 16 kbit/s stream occupies bit positions (1,2) or (3,4) or (5,6) or (7,8). ii) The order of the bits at each substream is identical before and after multiplexing. iii) All unused bit positions shall be set to binary “1”. iv) For transparent multislot configurations the lowest allowed subcircuits are always used. ETSI ETSI TS 100 591 V7.1.0 (2001-03) 14 3GPP TS 08.20 version 7.1.0 Release 1998 v) For non-transparent multislot configurations, the lowest allowed subcircuits shall be used at call set up and after change of channel configuration except at downgrading. At downgrading any of the used subcircuits may be released in uplink direction. Always, the released subcircuit(s) in downlink direction shall be the same as the released subcircuit(s) in uplink direction. At a possible subsequent upgrading, the lowest available bit positions shall be used for the added substreams. NOTE: The rules given here are almost identical to those of I.460, Section ‘Fixed format multiplexing’, except for the rule i) is stricter in that 8 kbit/s substreams cannot occupy any positions, iv) and v) are added. 14 Support of non-transparent bearer services 14.1 TCH/F9.6 and TCH/F4.8 kbit/s channel codings In the case of non-transparent services the RA1/RA1' function performs the same mapping as that described for transparent services, using 12 and 6 kbit/s radio interface data rates, with the following modification. The E2 and E3 bits in the modified ITU-T V.110 80 bit frames shown in Figure 3 (derived from the standard ITU-T V.110 frame shown in Figure 2) are used to indicate each consecutive sequence of ITU-T V.110 80 bit frames corresponding to the four modified ITU-T V.110 60 bit frames (Figure 4) received/transmitted in one radio interface frame. This allows 240 bit Radio Link Protocol frames to/from the MSC to be aligned with the 4x60 bit frames encoded by the radio subsystem channel coder as a single unit (see GSM 05.03). The 8 bits consisting of the E2 and E3 bits in one of the above sequences is referred to as the Frame Start Identifier. The FSI value is 00 01 10 11. This value is assigned to the E2 and E3 bits as shown in Table7. Table 7 E2 E3 First Modified ITU-T V.110 80 bit frame 0 0 Second 0 1 Third 1 0 Fourth 1 1 As each RLP frame is transported between the BSS and MSC in four modified ITU-T V.110 80 bit frames, it is necessary following a transmission break and at start up, to determine which modified ITU-T V.110 80 bit frame of the stream is the first for a particular RLP frame. This is needed so that correct alignment with the radio subsystem can be achieved. Modified V.110 80 bit frames can slip in time during re-routing, and whilst sync exists within the modified ITU-T V.110 80 bit frame to determine the modified ITU-T V.110 80 bit frame boundaries, the FSI is required to determine which quarter of an RLP frame each modified ITU-T V.110 80 bit frame contains. ETSI ETSI TS 100 591 V7.1.0 (2001-03) 15 3GPP TS 08.20 version 7.1.0 Release 1998 Table 8: Relationship between FNUR, AIUR, substream rate, number of substreams and intermediate rate FNUR AIUR Number of Channels x Substream Rate Channel Coding Multislot Intermediate Rate ≤2,4 kbit/s 2,4 kbit/s 2-8 times duplication of each bit to reach 2,4 kbit/s TCH/F4.8 8 kbit/s 4,8 kbit/s 4,8 kbit/s 4,8 kbit/s TCH/F4.8 8 kbit/s 4,8 kbit/s 9,6 kbit/s 9,6 kbit/s TCH/F9.6 16 kbit/s 9,6 kbit/s 9,6 kbit/s 2x4,8 kbit/s 2XTCH/F4.8 8 kbit/s 9,6 kbit/s 9,6 kbit/s 9,6 kbit/s TCH/F9.6 16 kbit/s 14,4 kbit/s 14,4 kbit/s 3X4,8 kbit/s 3XTCH/F4.8 8 kbit/s 14,4 kbit/s 19,2 kbit/s 2X9,6 kbit/s 2XTCH/F9.6 16 kbit/s 19,2 kbit/s 19,2 kbit/s 4X4,8 kbit/s 4XTCH/F4.8 8 kbit/s 19,2 kbit/s 19,2 kbit/s 2X9,6 kbit/s 2XTCH/F9.6 16 kbit/s 28,8 kbit/s 28,8 kbit/s 3X9,6 kbit/s 3XTCH/F9.6 16 kbit/s 38,4 38,4 kbit/s 4X9,6 kbit/s 4XTCH/F9.6 16 kbit/s NOTE: The table gives the relation between the FNUR, AIUR, Substream Rate, Channel Coding and Intermediate Rate. As an example: the wanted FNUR is 14,4 kbit/s and the selected channel coding is TCH/F9.6. The data stream is split into two substreams of 9,6 kbit/s yielding an AIUR of 19,2 kbit/s. 14.1.1 Alignment An alignment window spanning four modified ITU-T V.110 80 bit frames is used to search for the pattern of 8 bits described above in order to identify alignment with an RLP frame. In the event of failure to detect the 8 bit pattern, the alignment window is shifted one complete modified V.110 80 bit frame, discarding the contents of the most historical frame and then checking the new 8 bit pattern. 14.1.2 Support of Discontinuous Transmission (DTX) The E1 bit in the modified ITU-T V.110 80 bit frame shown in Figure 3 is used in the direction MSC-BSS to indicate that DTX may be invoked (see GSM 04.22). The E1 bit in all of the four consecutive frames relating to the RLP frame to which DTX may be applied shall be set to 1. If DTX is not to be applied, the E1 bit shall be set to 0. In the direction BSS-MSC the E1 bit shall always be set to 0. 14.1.3 Order of Transmission The first bit of each quarter of an RLP frame to be transmitted will correspond to bit D1 of a modified V.110 frame (figures 3 and 4). The remaining 59 bits of each quarter of an RLP frame will correspond to the D and D’ bits , D2 - D’12, in order left to right and top to bottom as shown in figures 3 and 4. The first quarter of an RLP frame to be transmitted will contain the E2 and E3 bit code 00 as shown in Table 1. The second quarter will contain the code 01, etc. 14.2 TCH/F14.4 channel coding In case of non-transparent service, a 576 bit RLP frame is mapped over two consecutive A-TRAU frames. Because of that mapping, it is required, following a transmission break and at start up, to determine which A-TRAU frame of the stream is the first for a particular RLP frame. This is needed so that correct alignment with the radio subsystem can be achieved. The two consecutive M1 bits are referred to as the Frame Start Identifier. The FSI value is 01. This value is assigned to the M1 bits as shown in Table 9. ETSI ETSI TS 100 591 V7.1.0 (2001-03) 16 3GPP TS 08.20 version 7.1.0 Release 1998 Table 9 M1 bit First A-TRAU frame 0 Second A-TRAU frame 1 A-TRAU frames can slip in time during re-routing, and whilst A-TRAU frame synchronisation exists, the FSI is required to determine which half of an RLP frame each A-TRAU frame contains. Table 10: Relationship between FNUR, AIUR, substream rate, number of substreams and intermediate rate FNUR AIUR Number of substreams x AIUR per substream Channel Coding Multislot intermediate Rate 14,4 kbit/s 14,4 kbit/s 14,4 kbit/s TCH/F14.4 16 kbit/s 28,8 kbit/s 28,8 kbit/s 2X14,4 kbit/s 2XTCH/F14.4 16 kbit/s 38,4 kbit/s 43,2 kbit/s 3X14,4 kbit/s 3XTCH/F14.4 16 kbit/s 48 kbit/s 57,6 kbit/s 4X14,4 kbit/s 4XTCH/F14.4 16 kbit/s 56 kbit/s 57,6 kbit/s 4X14,4 kbit/s 4XTCH/F14.4 16 kbit/s NOTE: The table gives the relation between FNUR, AIUR, Substream Rate, Channel Coding and Intermediate Rate. As an example: the wanted FNUR is 28,8 kbit/s and the selected channel coding is 14,5 kbit/s. The data stream is split into two substreams of 14,5 kbit/s yielding an AIUR of 28,8 kbit/s 14.2.1 Alignment An alignment window spanning two 290 bit blocks in case of TCH/F14.4 channel is used to search for the pattern of 2 bits ’01’ described in subclause 14.2, in order to identify alignment with an RLP frame. In the event of failure to detect the 2 bits pattern the alignment window is shifted one 290 bit block, discarding the contents of the most historical frame and then checking the new 2 bits pattern. 14.2.2 Support of Discontinuous Transmission (DTX) The M2 bit in the A-TRAU frame shown in Figure 5 is used in the direction MSC to BSS to indicate that DTX may be invoked (see GSM 04.22). The M2 bit in all of the two consecutive A-TRAU frames relating to the RLP frame to which DTX may be applied shall be set to 1. If DTX is not to be applied, the M2 bit shall be set to 0. In the direction BSS to MSC the M2 bit shall always be set to 0. 15 Support of transparent bearer services 15.1 TCH/F9.6 and TCH/F4.8 channel codings 15.1.1 User rate adaptation on the A interface, AIUR less or equal to 38,4 kbit/s The ITU-T V.110 80 bit frame is used for transparent data on the A interface. These frames are transmitted on up to four substreams multiplexed into one stream sent over the A interface. The split/combine function is applied on the substreams as specified in clause 5 of this GSM TS. The relation between the AIUR and the number of channels is specified in table11. The 64 kbit/s consists of octets, bits 1 through 8, with bit 1 transmitted first. For a 9 600 bit/s radio interface user rate the V.110 frame is carried with a 16 kbits/s stream which occupies bit positions (1,2). ETSI ETSI TS 100 591 V7.1.0 (2001-03) 17 3GPP TS 08.20 version 7.1.0 Release 1998 For radio interface user rates of either 4 800 bit/s, 2 400 bit/s, 1 200 bit/s, 300 bit/s or 1 200/75 bit/s the V.110 frame is carried with a 8 kbits/s stream which occupies bit position (1). For user rates < 1 200bit/s asynchronous characters are padded with additional stop elements by the RA0 function (in the MSC/IWF) to fit into 600 bit/s synchronous RA1 rate prior to rate adaptation to 64 kbits/s. No use of 4 kbit/s stream is foreseen. In a given V.110 frame on the A interface: - for 9 600 bit/s there is no repetition of bits D within the 16 kbit/s stream ; - for 4 800 bit/s there is no repetition of bits D within the 8 kbit/s stream ; - for 2 400 bit/s each bit D is repeated twice within the 8 kbit/s stream (D1 D1 D2 D2 etc) ; - for 1 200 bit/s each bit D is repeated four times within the 8 kbit/s stream (D1 D1 D1 D1 D2 D2 D2 D2 etc) ; - for 600 bit/s each bit D is repeated eight times within the 8kbit/s stream (D1 D1 D1 D1 D1 D1 D1 D1 D2 D2 D2 D2 D2 D2 D2 D2 etc); - for 1 200/75 bit/s each bit D is repeated four times within the 8 kbit/s stream for 1 200 bit/s. 75 bit/s will be padded by additional stop elements to fit 600 bit/s by the RA0 function. For the resulting 600 bit/s each bit D is repeated eight times within the 8kbit/s stream. 15.1.2 User rate Adaptation on the A-interface, AIUR greater than 38,4 kbit/s For AIUR of 48 kbit/s, 56 kbit/s and 64 kbit/s one stream consisting of ITU-T V.110 32 bit frames or 64 bit frames, as specified in GSM 04.21 is transmitted over the A-interface. Splitting/Combining which occurs in the BSS, is as specified in GSM 04.21. Table 11 gives the relation between the User Rate, Substream Rate Channel Coding and the Intermediate Rate. ETSI ETSI TS 100 591 V7.1.0 (2001-03) 18 3GPP TS 08.20 version 7.1.0 Release 1998 15.1.3 Relation between AIUR and the number of channels Table11: Relationship between the AIUR, substream rate, channel coding, intermediate rate and number of channels AIUR Number of channels x Substream Rate Channel Coding (Multislot) intermediate Rate (Note1) ≤2,4 kbit/s 2-8 times duplication of each bit to reach 4,8 kbit/s TCH/F4.8 8 kbit/s 4,8 kbit/s 4,8 kbit/s TCH/F4.8 8 kbit/s 9,6 kbit/s 2X4,8 kbit/s 2XTCH/F4.8 8 kbit/s 9,6 kbit/s 9,6 kbit/s TCH/F9.6 16 kbit/s 14,4 kbit/s 3X4,8 kbit/s 3XTCH/F4.8 8 kbit/s 14,4 kbit/s 2X9,6 kbit/s w/ padding 2XTCH/F9.6 16 kbit/s 19,2 kbit/s 4X4,8 kbit/s 4XTCH/F4.8 8 kbit/s 19,2 kbit/s 2X9,6 kbit/s 2XTCH/F9.6 16 kbit/s 28,8 kbit/s 3x9,6 kbit/s 3XTCH/F9.6 16 kbit/s 38,4 kbit/s 4X9,6 kbit/s 4XTCH/F9.6 16 kbit/s 48 kbit/s 5X9,6 kbit/s 5XTCH/F9.6 64 kbit/s 56 kbit/s 5X11,2 kbit/s 5XTCH/F9.6 64 kbit/s 64 kbit/s 66x11,2 kbit/s w/padd. 6XTCH/F9.6 64 kbit/s NOTE: For AIURs ≤ 38,4 kbit/s this column indicates the multislot intermediate rate: for higher AIURs it indicates the intermediate rate. 15.1.4 Handling of status bits X, SA, SB In the single slot case, status bit SA is coded repeatedly as S1, S3, S6, S8, and SB is coded repeatedly as S4 and S9 in Figure 2. In the multislot case, status bit SA is coded repeatedly as S6,S8 and SB is coded as S9 in figures 2, 5 and 6. The handling of the status bits will comply with the synchronisation procedures for transparent services which are as described in GSM 09.07 (MSC), GSM 04.21 (BSS), GSM 07.01 (MS). 15.1.5 Handling of bits E1 to E7 Bits E1 to E3 are used according to 04.21. Bits E4 to E7 may be used for network independent clocking as indicated in GSM 04.21. ETSI ETSI TS 100 591 V7.1.0 (2001-03) 19 3GPP TS 08.20 version 7.1.0 Release 1998 15.2 TCH/F14.4 channel coding 15.2.1 User rate adaptation on the A interface, AIUR less or equal to 56 kbit/s The A-TRAU frame is used for transparent data on the A interface. These frames are transmitted on up to four substreams multiplexed into one stream sent over the A interface. The split/combine function is applied on the substreams as specified in clause 7 of this TS. The relation between the AIUR and the number of channels is specified in table 12. In a given A-TRAU frame on the A interface: - for 14 400 bit/s there is no repetition of bits D within the 16 kbit/s stream in a given A-TRAU frame on the A interface. 15.2.2 User Rate Adaptation on the A-interface, AIUR greater than 56 kbit/s For AIUR of 64 kbit/s one stream consisting of ITU-T V.110 32 bit frames or 64 bit frames, as specified in GSM 04.21 is transmitted over the A-interface. Splitting/Combining which occurs in the BSS, is as specified in GSM 04.21. Table 12 gives the relation between the User Rate, Substream Rate Channel Coding and the Intermediate Rate. 15.2.3 Relation between AIUR and the number of channels Table 12: Relationship between the AIUR, AIUR per substream, channel coding, intermediate rate and number of substreams AIUR Number of substreams x AIUR per substream Channel Coding Multislot intermediate Rate (note 1) 14,4 kbit/s 14,4 kbit/s TCH/F14.4 16 kbit/s 28,8 kbit/s 2X14,4 kbit/s TCH/F14.4 16 kbit/s 38,4 kbit/s 3X14,4 kbit/s w/padding TCH/F14.4 16 kbit/s 48 kbit/s 4X14,4 kbit/s w/padding TCH/F14.4 16 kbit/s 56 kbit/s 4X14,4 kbit/s w/padding TCH/F14.4 16 kbit/s 64kbit/s 5X14,4 kbit/s w/padding TCH/F14.4 64 kbit/s NOTE: For AIURs ≤ 56 kbit/s this column indicates the multislot intermediate rate: for higher AIURs it indicates the intermediate rate. 15.2.4 Handling of status bits X and SB The X and SB bits are carried over the A interface in a multiframe structure as described in subclause 8.1.1.1 of GSM 04.21. SA bit is not carried over the A interface. The handling of the status bits will comply with the synchronisation procedures for transparent services which are as described in GSM 09.07 (MSC), GSM 04.21 (BSS), GSM 07.01 (MS). ETSI ETSI TS 100 591 V7.1.0 (2001-03) 20 3GPP TS 08.20 version 7.1.0 Release 1998 Octet Bit number No. 0 1 2 3 4 5 6 7 0 0 0 0 0 0 0 0 0 1 1 D1 D2 D3 D4 D5 D6 S1 2 1 D7 D8 D9 D10 D11 D12 X 3 1 D13 D14 D15 D16 D17 D18 S3 4 1 D19 D20 D21 D22 D23 D24 S4 5 1 E1 E2 E3 E4 E5 E6 E7 6 1 D25 D26 D27 D28 D29 D30 S6 7 1 D31 D32 D33 D34 D35 D36 X 8 1 D37 D38 D39 D40 D41 D42 S8 9 1 D43 D44 D45 D46 D47 D48 S9 Figure 2: The ITU-T V.110 80 bit frame for Transparent Data octet bit number no. 0 1 2 3 4 5 6 7 0 0 0 0 0 0 0 0 0 1 1 D1 D2 D3 D4 D5 D6 D’1 2 1 D7 D8 D9 D10 D11 D12 D’2 3 1 D13 D14 D15 D16 D17 D18 D’3 4 1 D19 D20 D21 D22 D23 D24 D’4 5 1 E1 E2 E3 D’5 D’6 D’7 D’8 6 1 D25 D26 D27 D28 D29 D30 D’9 7 1 D31 D32 D33 D34 D35 D36 D’10 8 1 D37 D38 D39 D40 D41 D42 D’11 9 1 D43 D44 D45 D46 D47 D48 D’12 Figure 3: The modified ITU-T V.110 80 bit frame for Non-Transparent Data D1 D2 D3 D4 D5 D6 D’1 D7 D8 D9 D10 D11 D12 D’2 D13 D14 D15 D16 D17 D18 D’3 D19 D20 D21 D22 D23 D24 D’4 D’5 D’6 D’7 D’8 D25 D26 D27 D28 D29 D30 D’9 D31 D32 D33 D34 D35 D36 D’10 D37 D38 D39 D40 D41 D42 D’11 D43 D44 D45 D46 D47 D48 D’12 Figure 4: Modified ITU-T V.110 60 bit frame for Non-Transparent Data ETSI ETSI TS 100 591 V7.1.0 (2001-03) 21 3GPP TS 08.20 version 7.1.0 Release 1998 bit number octet number 0 1 2 3 4 5 6 7 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 2 1 C1 C2 C3 C4 C5 M1 M2 3 Z1 D1 D2 D3 D4 D5 D6 D7 4 D8 D9 D10 D11 D12 D13 D14 D15 36 bit data field 1 5 D16 D17 D18 D19 D20 D21 D22 D23 6 D24 D25 D26 D27 D28 D29 D30 D31 7 D32 D33 D34 D35 D36 Z2 D1 D2 8 D3 D4 D5 D6 D7 D8 D9 D10 9 D11 D12 D13 D14 D15 D16 D17 D18 36 bit data field 2 10 D19 D20 D21 D22 D23 D24 D25 D26 11 D27 D28 D29 D30 D31 D32 D33 D34 12 D35 D36 Z3 D1 D2 D3 D4 D5 13 D6 D7 D8 D9 D10 D11 D12 D13 14 D14 D15 D16 D17 D18 D19 D20 D21 36 bit data field 3 15 D22 D23 D24 D25 D26 D27 D28 D29 16 D30 D31 D32 D33 D34 D35 D36 Z4 17 D1 D2 D3 D4 D5 D6 D7 D8 18 D9 D10 D11 D12 D13 D14 D15 D16 36 bit data field 4 19 D17 D18 D19 D20 D21 D22 D23 D24 20 D25 D26 D27 D28 D29 D30 D31 D32 21 D33 D34 D35 D36 Z5 D1 D2 D3 22 D4 D5 D6 D7 D8 D9 D10 D11 23 D12 D13 D14 D15 D16 D17 D18 D19 36 bit data field 5 24 D20 D21 D22 D23 D24 D25 D26 D27 25 D28 D29 D30 D31 D32 D33 D34 D35 26 D36 Z6 D1 D2 D3 D4 D5 D6 27 D7 D8 D9 D10 D11 D12 D13 D14 28 D15 D16 D17 D18 D19 D20 D21 D22 36 bit data field 6 29 D23 D24 D25 D26 D27 D28 D29 D30 30 D31 D32 D33 D34 D35 D36 Z7 D1 31 D2 D3 D4 D5 D6 D7 D8 D9 32 D10 D11 D12 D13 D14 D15 D16 D17 33 D18 D19 D20 D21 D22 D23 D24 D25 36 bit data field 7 34 D26 D27 D28 D29 D30 D31 D32 D33 35 D34 D35 D36 Z8 D1 D2 D3 D4 36 D5 D6 D7 D8 D9 D10 D11 D12 37 D13 D14 D15 D16 D17 D18 D19 D20 36 bit data field 8 38 D21 D22 D23 D24 D25 D26 D27 D28 39 D29 D30 D31 D32 D33 D34 D35 D36 Figure 5: A-TRAU 320 bit frame octet bit number no. 0 1 2 3 4 5 6 7 0 0 0 0 0 0 0 0 0 1 1 D1 D2 D3 D4 D5 D6 S1 2 1 D7 D8 D9 D10 D11 D12 X 3 1 D13 D14 D15 D16 D17 D18 S3 4 1 D19 D20 D21 D22 D23 D24 S4 5 1 E1 E2 E3 E4 E5 E6 E7 6 1 1 1 1 1 1 1 S6 7 1 1 1 1 1 1 1 X 8 1 1 1 1 1 1 1 S8 9 1 1 1 1 1 1 1 S9 Figure 6: The modified ITU-T V.110 80 bit frame padded for 4,8 kbit/s transparent data at intermediate rate 16 kbit/s ETSI ETSI TS 100 591 V7.1.0 (2001-03) 22 3GPP TS 08.20 version 7.1.0 Release 1998 Annex A (informative): Frame Pattern Substitution A.1 Special cases If the sub frame starts with a Zseq, D1 is empty. With the above example, the resulting input and output sub frames are the following: 1 a1 a2 bit position list of addresses of the Z sequences list of the data blocks without Z sequence 1 a1 a2 1 D2 1 D3 D4 D2 D3 D4 ZSP(1) ZSP(a1) ZSP(a2) 0 D2 D3 D4 Zseq1 Zseq2 Zseq3 a d In the same case as above but with only one ZSP, the resulting input and output sub frames are the following: list of addresses of the Z sequences list of the data blocks without Z sequence 1 D2 D2 ZSP(1) 0 D2 Zseq1 a d ETSI ETSI TS 100 591 V7.1.0 (2001-03) 23 3GPP TS 08.20 version 7.1.0 Release 1998 A.2 False Z sequence detection The Framing Pattern Substitution algorithm presented in subclause 10.2 ensures sure that all the Z sequences found in the original sub frame are removed, but it must be checked that the transformations performed do not introduce new unwanted Z sequences. The goal of this subclause is to show that the transformed sub frame will not contain new Z sequences introduced by the algorithm itself. The coding of the ZSP is the key point to avoid such an emulation. The different cases are considered below. 1: Sequence ZSP The worst case is when the address is equal to 1 : 1 C A0 A1 A2 A3 A4 1 1 0 0 0 0 0 1 1 There is a maximum of 5 zeroes. 2: Sequence Di / ZSP. By definition, a data block always ends up with a one (except the last one of the message) and the ZSP always starts with a 1. 3: Sequence ZSP / Di ZSP always ends up with a 1 and Di has a maximum of 7 zeroes : it is not possible to find 16 zeroes in a row. 4: Sequence Di / Dj Di is not the last data block of the message. As already mentioned, Di ends up with a one (except the last one) : this is the same case as 3. 5: Sequence Zi / D or D / Zi This case only occurs when there is no substitution. In this case, the Zi bit close to the D field is always a one: this does not change the number of zeroes in sequence. 6: Sequence last Di / new framing pattern The last D sequence can end up with up to 7 zeroes, followed by the 16 zeroes of the next frame. There is anyhow no ambiguity, when considering that the framing pattern is made up of 16 zeroes followed by a one. 7: Sequence last Di / Z bit of the next sub frame The last D sequence can end up with up to 7 zeroes, followed in the worst case by Z=0 and then a ZSP. As a ZSP starts with a one, this makes a maximum of 8 zeroes in a row. 8: Sequence ZSP / ZSP (not shown on the figure) This case arrives when the original message has at least 16 zeroes in a row. As the ZSP element always starts and ends up with a one, this always induces two consecutive ones. ETSI ETSI TS 100 591 V7.1.0 (2001-03) 24 3GPP TS 08.20 version 7.1.0 Release 1998 Annex B (informative): Change history Change history Date TSG # TSG Doc. CR Rev Subject/Comment Old New 04-1999 SMG#27 A005 Sychronization 5.3.0 7.0.0 03-2001 TSG#11 NP-010040 A012 Correction of downgrading procedure for HSCSD 7.0.1 7.1.0 25 ETSI ETSI TS 100 591 V7.1.0 (2001-03) 3GPP TS 08.20 version 7.1.0 Release 1998 History Document history V7.0.1 July 1999 Publication V7.1.0 March 2001 Publication
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1 Scope
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The present document specifies the layer 3 procedures used on the Base Station System (BSS) to Mobile-services Switching Centre (MSC) interface for control of GSM services. For the purposes of call control and mobility management, messages are not interpreted at the Base Station System (BSS) which acts as a relay function. These messages and procedures are documented in GSM 04.08, the only relevant issues covering these messages in the present document are those concerned with error conditions at the interface, and the headers that are required for the correct addressing of the messages. This is specified in more detail in GSM 08.06. The functional split between MSC and BSS is defined in GSM 08.02 and states that the BSS is responsible for local radio resource allocation and in order to support this the required procedures between BSS and MSC are defined in detail in the present document. GSM 08.02 also states that the BSS is responsible for the scheduling of all CCCH/BCCH messages and therefore some procedures for providing the BSS with the necessary information to be passed on these channels for individual calls (i.e. paging) are defined in the present document, but the scheduling is not discussed. This interface and consequently these layer 3 procedures are designed to support BSSs providing one or more cells.
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1.1 References
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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. • A non-specific reference to an ETS shall also be taken to refer to later versions published as an EN with the same number. • For this Release 1997 document, references to GSM documents are for Release 1997 versions (version 6.x.y). [1] GSM 01.04: "Digital cellular telecommunications system (Phase 2+); Abbreviations and acronyms". [2] GSM 03.03: "Digital cellular telecommunications system (Phase 2+); Numbering, addressing and identification". [3] GSM 03.09: "Digital cellular telecommunications system (Phase 2+); Handover procedures". [4] GSM 03.34: "Digital cellular telecommunications system (Phase 2+); High Speed Circuit Switched Data (HSCSD)". [5] GSM 04.08: "Digital cellular telecommunications system (Phase 2+); Mobile radio interface layer 3 specification". [6] GSM 04.21: "Digital cellular telecommunications system (Phase 2+); Rate adaption on the Mobile Station - Base Station System (MS - BSS) interface". [7] GSM 05.01: "Digital cellular telecommunications system (Phase 2+); Physical layer on the radio path; General description". [8] GSM 05.02: "Digital cellular telecommunications system (Phase 2+); Multiplexing and multiple access on the radio path". [9] GSM 05.03: "Digital cellular telecommunications system (Phase 2+); Channel coding". [10] GSM 05.04: "Digital cellular telecommunications system (Phase 2+); Modulation". ETSI ETSI TS 100 590 V6.5.0 (2000-06) 10 (GSM 08.08 version 6.5.0 Release 1997) [11] GSM 05.05: "Digital cellular telecommunications system (Phase 2+); Radio transmission and reception". [12] GSM 05.08: "Digital cellular telecommunications system (Phase 2+); Radio subsystem link control". [13] GSM 05.90: "Digital cellular telecommunications system; GSM Electro Magnetic Compatibility (EMC) considerations". [14] GSM 05.10: "Digital cellular telecommunications system (Phase 2+); Radio subsystem synchronization". [15] GSM 08.02: "Digital cellular telecommunications system (Phase 2+); Base Station System - Mobile-services Switching Centre (BSS - MSC) interface; Interface principles". [16] GSM 08.06: "Digital cellular telecommunications system (Phase 2+); Signalling transport mechanism specification for the Base Station System - Mobile-services Switching Centre (BSS - MSC) interface". [17] GSM 08.20: "Digital cellular telecommunications system (Phase 2+); Rate adaption on the Base Station System - Mobile-services Switching Centre (BSS - MSC) interface". [18] GSM 12.00: "Digital cellular telecommunications system (Phase 2); Objectives and structure of Network Management (NM)". [19] GSM 12.01: "Digital cellular telecommunications system (Phase 2); Common aspects of GSM Network Management (NM)". [20] GSM 12.02: "Digital cellular telecommunications system (Phase 2); Subscriber, Mobile Equipment (ME) and services data administration". [21] GSM 12.03: "Digital cellular telecommunications system (Phase 2); Security management". [22] GSM 12.04: "Digital cellular telecommunications system (Phase 2); Performance data measurements". [23] GSM 12.05: "Digital cellular telecommunications system (Phase 2+); Subscriber related event and call data". [24] GSM 12.06: "Digital cellular telecommunications system (Phase 2); GSM Network change control". [25] GSM 12.11: "Digital cellular telecommunications system (Phase 2); Maintenance of the Base Station System (BSS)". [26] GSM 12.20: "Digital cellular telecommunications system (Phase 2); Network Management (NM) procedures and messages". [27] GSM 12.21: "Digital cellular telecommunications system (Phase 2); Network Management (NM) procedures and message on the A-bis interface". [28] GSM 12.22: "Digital cellular telecommunications system (Phase 2); Interworking of GSM Network Management (NM) procedures and messages at the Base Station Controller (BSC)".
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1.2 Abbreviations
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Abbreviations used in the present document are listed in GSM 01.04, see clause 5 for Vocabulary. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 11 (GSM 08.08 version 6.5.0 Release 1997)
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2 Application to interface structures
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The underlying transport mechanism defined to carry signalling information between the BSS and the MSC is the Message Transfer Part (MTP), and the Signalling Connection Control Part (SCCP) of Signalling System No.7. The MTP and SCCP are used to support communication between the MSC and two conceptual entities within the BSS, these are: - the BSS Operation and Maintenance Application Part (BSSOMAP); - the BSS Application Part (BSSAP). The BSS Application Part is split into two sub application parts, these are: - the BSS Management Application Part (BSSMAP); - the Direct Transfer Application Part (DTAP). Distribution of messages between the two sub application parts is described in GSM 08.06. Figure 1 is a diagrammatical representation of these conceptual entities. It should be noted that this is not intended to imply a particular implementation and is only for the purposes of specifying the interface. Differentiation between BSSAP and BSSOMAP is by addressing mechanisms within the SCCP, using the subsystem number (see GSM 08.06).
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2.1 The BSS Operation and Maintenance Application Part
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If operation and maintenance messages are transferred by means of this interface then they shall use SCCP messages. The application protocol for the Operation and Maintenance Application Part is defined in the GSM 12 series Technical Specifications. The routing and addressing is provided by the SCCP and allows the MSC and the O&M centre to be addressed directly by the BSS using, for example, two E164 numbers. The operator may also use an X.25 connection for the transfer of O&M messages between the BSS and the OMC. This option is not further discussed in the present document.
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2.2 The Direct Transfer Application Part
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The Direct Transfer Application Part (DTAP) is used to transfer call control and mobility management messages between the MSC and the MS. The DTAP information in these messages is not interpreted by the BSS. GSM 08.06 contains more detail relating to the handling of DTAP messages at the BSS, the multiplexing of the messages onto the relevant signalling channels of the radio interface, and the use of the SCCP services. Messages received from the MS are identified as DTAP by the Protocol Discriminator Information Element as described in GSM 04.08, except for Initial Layer 3 messages (see subclause 3.1.16). The majority of radio interface messages are transferred across the BSS MSC interface by the DTAP, the exceptions being messages belonging to the Radio Resource (RR) management protocol.
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2.3 The BSS Management Application Part
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2.
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3 The BSS Management Application Part
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The BSSMAP supports all of the procedures between the MSC and the BSS that require interpretation and processing of information related to single calls, and resource management. Some of the BSSMAP procedures result in, or are triggered by, Radio Resource (RR) management messages defined in GSM 04.08. The BSSMAP procedures are described in clause 3. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 12 (GSM 08.08 version 6.5.0 Release 1997)
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2.4 Handling of abnormal events related to the BSSAP Header
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The BSSAP header is specified in GSM 08.06. Several abnormal events may be detected by the receiver: - use of a reserved value in the DLCI or discriminator; - length octet with value zero; - length octet with a value inconsistent with that indicated by the SCCP. In these cases the receiver may send a BSSMAP CONFUSION message as specified in subclause 3.2.1. If so, depending on the error in the BSSAP header, the error pointer shall be set to one of the values reserved for the BSSAP header in subclause 3.2.2.32. Spare bits in the BSSAP header shall not be checked by the receiving entity. 3 The BSS Management Application Part
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3.1 BSSMAP Procedures
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This subclause describes the procedures used in the BSS Management Application Part. There are the following main procedures: * Assignment figure 2 # Blocking figure 10 and 25 # Resource indication figure 12 # Reset figure 11 * Handover required indication figure 4 * Handover resource allocation figure 5 * Handover execution figure 3 # Handover candidate enquiry figure 13 * Release figures 6 and 7 # Paging figure 15 # Flow control figure 14 * Classmark update figure 9 * Cipher mode control figure 17 * Trace invocation * Initial MS message * Queuing indication * Data link control SAPI not equal to 0 figure 18 # Reset circuit * PDSS1 flow control * Circuit re-selection figure 26 These procedures are documented separately and are intended to be used by the operators/manufacturers to build up complete call sequences, in a flexible manner. Any sequences given where more than one procedure is shown concatenated are only for illustrative purposes. Each of the above procedures is qualified by either an asterisk (*) or a hash symbol (#). The hash symbol (#) denotes a global procedure which concerns a complete cell or BSS, or specific terrestrial circuits. The asterisk symbol (*) denotes a dedicated procedure which concerns a single dedicated radio resource on the radio interface, or in the case of a multislot configuration, all radio resources allocated to one mobile station. Messages used to support global procedures are sent using the connectionless services of the SCCP. Messages used to support dedicated procedures are sent using the connection oriented services of the SCCP, on the connection which has been set up to support that call or transaction. The establishment of SCCP connections is detailed in GSM 08.06. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 13 (GSM 08.08 version 6.5.0 Release 1997) In the following description of each procedure it is explicitly stated whether the procedure is global or not, and hence the type of SCCP service used to support the procedure is defined. The handling of unknown terrestrial circuits is defined in subclause 3.1.19.6 and the procedures of subclause 3.1.19.6 take precedence over those of the rest of subclause 3.1. The procedures of the rest of subclause 3.1 assume that the terrestrial circuit is known by the entity concerned.
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3.1.1 Assignment
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The purpose of the assignment procedure is to ensure that the correct dedicated radio resource(s) can be allocated or reallocated to a MS that requires it. However, the initial random access by the MS and "Immediate Assignment" to a DCCH is handled autonomously by the BSS without reference to the MSC.
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3.1.1.1 Successful Operation
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The initial conditions are assumed to be that the MS is in contact with the fixed infrastructure of a PLMN by means of one or more dedicated radio resources (and possibly a terrestrial resource), and that the MSC has analysed any relevant call control information and wishes to allocate or reallocate to the MS one or more radio resources (and possibly a terrestrial resource). The MSC is the entity that carries out the necessary analysis on the call control information received from the MS or fixed network customer. On the basis of this analysis a resource request is made to the appropriate BSS by sending it an ASSIGNMENT REQUEST message. This message contains details of the resource(s) required (for instance channel rate, channel type, data adaption, priority level etc.). If the requested resource(s) is/are for speech or data it also may indicate the terrestrial circuit that shall be used between the MSC and BSS. The description of the resource(s) can either be a complete specification, or give the BSS some freedom in the selection (for instance channel rate selection, speech version selection etc.). The ASSIGNMENT REQUEST message may also contain CLASSMARK information in case such information is available in the MSC, but assumed not to be available in the BSS. A full description of the message is given in subclause 3.2.1.1. In the present document a "pool" is a group of circuits supporting the same channel types. The ASSIGNMENT REQUEST message is sent via the BSSMAP and is analysed within the BSS. Based on this analysis, which is not defined further in the present document, the BSS chooses the appropriate radio resource(s) and allocates the appropriate resources for transcoding, rate adaptation etc. On the terrestrial route connecting the BSS and MSC, certain circuits can be used for different combinations of bearer capabilities. This can be modelled by grouping the circuits into "pools" supporting the same channel types. The MSC holds this information as route data. If the MSC allocates an A interface circuit, it should only ever ask for resources from the BSS that it knows are not totally incompatible with the nominated circuit. The BSS will construct and send the appropriate radio assignment messages, if required (i.e., if the radio resource(s) has/have to be changed), as described in GSM 04.08 and start timer T10. The ASSIGNMENT REQUEST message includes sufficient information to allow the BSS to construct the necessary layer 3 radio messages. If the BSS allocates the A interface circuits, and such a circuit is needed, the BSS shall allocate a circuit. In the case where several circuit pools (groups of circuits supporting the same channel types) are available on the BSS MSC interface, the terrestrial circuit allocated by the MSC, if any, is chosen taking into account the circuit pool the circuit belongs to and the required channel type. The management of priority levels is implementation dependent, under operator control. If queuing is managed, new requests which cannot be served immediately are put in the queuing file according to the indicated priority levels. The priority levels and the preemption indicators may (singularly or in combination) be used to determine whether the assignment has to be performed unconditionally and immediately. This would lead to triggering of the preemption procedure which may then cause the forced release or forced handover of a lower priority connection if no free resource is immediately available. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 14 (GSM 08.08 version 6.5.0 Release 1997) Whilst the process and the extent of the preemption procedure is operator dependent, the preemption indicators (refer to subclause 3.2.2.18.), if given in the ASSIGNMENT REQUEST, shall be treated on a per connection basis as follows: - the last received "Preemption Vulnerability indicator" and priority levels shall prevail. - if the "Preemption Capability indicator" bit is set to 1, then this allocation request can trigger the running of the preemption procedure. - if the "Preemption Capability indicator" bit is set to 0, then this allocation request cannot trigger the preemption procedure. - if the "Preemption Vulnerability" bit is set to 1, then this connection is vulnerable and shall be included in the preemption process or procedure and as such may be subject to forced release or forced handover. - if the "Preemption Vulnerability" bit is set to 0, then this connection is not vulnerable to preemption and shall not be included in the preemption process and as such may not be subject to forced release or forced handover. - if no priority Information Element has been received, both "Preemption Capability" and "Preemption Vulnerability" bits shall be regarded as set to 0. The BSS shall ignore the classmark information included in the ASSIGNMENT REQUEST message if such information has already been received from the MS. The radio assignment procedure on the radio path is described in GSM 04.08. When the BSS is satisfied that the radio assignment procedure has been successfully accomplished (e.g. by receipt of a radio interface ASSIGNMENT COMPLETE message) it will stop timer T10 and return an ASSIGNMENT COMPLETE message over the BSS MSC interface. This will implicitly release the old dedicated radio resource(s) at the BSS. If an intra-BSS cell change has occurred during the assignment, the new cell identity is included in the ASSIGNMENT COMPLETE message and a HANDOVER PERFORMED message is not required. If the MSC gave the BSS some freedom in resource type selection, the choices made by the BSS are indicated in the ASSIGNMENT COMPLETE message. If the BSS has to allocate a circuit, the ASSIGNMENT COMPLETE message includes the identity of the circuit allocated by the BSS. When several circuit pools are present on the BSS MSC interface, and when the circuit is allocated by the MSC, the "circuit pool" information element shall be included in the ASSIGNMENT COMPLETE. The "circuit pool" field will indicate to the MSC the circuit pool of the CIC given in the ASSIGNMENT REQUEST message. If the assignment did not require a change of radio resource(s), and consequently no 04.08 radio assignment procedure had been invoked, then the ASSIGNMENT COMPLETE message shall be returned to the MSC as soon as the requested resources have been allocated within the BSS. If the assignment requires a change of terrestrial circuit or in the case of assignment for signalling the release of a previously used terrestrial circuit, the change or release shall be performed before the ASSIGNMENT COMPLETE message is sent and the BSS shall consider that the old terrestrial circuit is idle. After the completion of the assignment procedure, until the connection is released or the MSC performs a new assignment, any dedicated resource assigned to the mobile station, e.g. at internal handover, must be in accordance with the description in the ASSIGNMENT REQUEST message. In the case of voice group calls the MSC may inform the BSS to which voice group call an MS belongs to and whether the MS is a talker or listener in the voice group call, the BSS may decide to allocate and assign a voice group call channel relating to the group call reference. If the BSS allocates a voice group call channel it will send the ASSIGNMENT COMPLETE message and then immediately afterwards send a CLEAR REQUEST cause "Joined group call channel". ETSI ETSI TS 100 590 V6.5.0 (2000-06) 15 (GSM 08.08 version 6.5.0 Release 1997)
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3.1.1.2 Assignment Failure
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The following failure conditions may occur: The BSS may not be able to use the terrestrial resource that the MSC has indicated in which case an ASSIGNMENT FAILURE message will be returned to the MSC with the cause set to "requested terrestrial resource unavailable". If the requested channel type or resource (e.g. channel rate, speech version, etc.) indicated in the ASSIGNMENT REQUEST message is not available in the BSS, then an ASSIGNMENT FAILURE message shall be returned to the MSC. The appropriate failure cause will be included in the message (Cause value: "requested transcoding/rate adaptation unavailable" or "requested speech version unavailable"). If, on reception by the BSS of an ASSIGNMENT REQUEST message allocating a circuit, the circuit pool implied by the CIC information element is incompatible with the channel type indicated (that is, the pool does not support any of the radio resources indicated by the channel type) an ASSIGNMENT FAILURE shall be returned to the MSC with the failure cause set to "circuit pool mismatch". If, on reception by the BSS of an ASSIGNMENT REQUEST message allocating a circuit, the circuit pool implied by the CIC is compatible with the channel type indicated (that is, the pool supports at least one of the radio resource types indicated by the channel type), but the BSS still wishes to change the circuit pool, it sends an ASSIGNMENT FAILURE with the cause "switch circuit pool" and the "circuit pool list" information element. The "circuit pool" information element, when present in the ASSIGNMENT FAILURE, indicates to the MSC which circuit pool the CIC indicated in the ASSIGNMENT REQUEST belongs to. This can be used by the MSC to correct its tables (CIC/circuit pool). The "circuit pool list" information element, when present in the ASSIGNMENT FAILURE, is used when the BSS wishes to indicate to the MSC its preferred circuit pools. The circuit pools in the "circuit pool list" information element shall be given in order of preference. In the case of an ASSIGNMENT FAILURE with the cause "circuit pool mismatch", the MSC may decide to block the circuit and to send an O & M notification. The BSS may not receive a radio interface ASSIGNMENT COMPLETE message from the MS in which case the timer T10 will expire. In this case an ASSIGNMENT FAILURE message is returned to the MSC and the assignment procedure is terminated (cause value: radio interface message failure). If the cell for which the assignment is intended is congested, the BSS may indicate an impending directed retry attempt by sending ASSIGNMENT FAILURE (Cause value: directed retry). If the radio channel assignment fails for any other reason then an ASSIGNMENT FAILURE message will be returned to the MSC, the procedure will terminate, and the associated references concerning the old dedicated resource(s) should be maintained until explicitly released by the MSC. It should be noted that if the MS fails to assign after receiving a radio interface ASSIGNMENT COMMAND and returns to the old channels as detailed in GSM 04.08, then the radio interface ASSIGNMENT FAILURE message received from the MS will cause an ASSIGNMENT FAILURE message to be returned to the MSC (cause value: "Radio interface failure, reversion to old channel"). Other possible Cause values which may be returned with the ASSIGNMENT FAILURE message are: "equipment failure", "no radio resource available", "O&M intervention". If an unrecognised cause value is received, the Class of the cause value should be used to determine the MSC's action. In the case where the MSC has attempted to assign a terrestrial circuit and an ASSIGNMENT FAILURE message has been returned then both the MSC and the BSS shall consider that the terrestrial circuit is idle (except as described below in subclause 3.1.1.3) and therefore no explicit clearing sequence is needed. The MSC may not be able to use the terrestrial resource that the BSS has indicated. In this case, the procedure is nevertheless considered terminated successfully, and it is up to the MSC to correct the situation, e.g., by a circuit re- selection procedure. All messages concerned with an assignment are sent using the connection oriented mode of the SCCP.
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3.1.1.3 Abnormal Conditions
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If the BSS receives an ASSIGNMENT REQUEST message calling up a terrestrial circuit that is already assigned to another call then an ASSIGNMENT FAILURE message will be returned with a Cause value of: "terrestrial circuit already allocated" and no action will be taken on the radio interface. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 16 (GSM 08.08 version 6.5.0 Release 1997) If the BSS receives an ASSIGNMENT REQUEST message allocating a terrestrial circuit which has been blocked by a global block message, then an ASSIGNMENT FAILURE message shall be sent (Cause value: "requested terrestrial resource unavailable"). A single global BLOCK message (not repeated and not guarded by timer T1) shall be sent for that concerned terrestrial circuit. If an external handover becomes necessary during an assignment, for reasons of radio conditions or congestion (directed retry), the BSS may initiate the handover whilst the assignment is in progress. In this situation, if a HANDOVER COMMAND is received by the BSS, it must not be ignored.
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3.1.2 Blocking and Unblocking
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As described in subclause 3.1.1 the assignment procedure depends upon one side, the MSC or the BSS, choosing the terrestrial resource to be used. If the entity on one side puts out of service any terrestrial circuit, it needs to inform the peer entity on the other side of the interface. This is performed by using a simple blocking/unblocking procedure. The block messages used to support this procedure are sent as global messages (i.e. using the SCCP connectionless mode). Each message refers to one or more terrestrial circuits accessed through the BSS MSC interface. The circuit is identified by its Circuit Identity Code. The support of blocking/unblocking procedures is dependent on which side allocates the circuits. A circuit is said to be « locally blocked » on a given side if it has been put out of service for a local reason, and to be « remotely blocked » if a BLOCK message about this circuit has been received from the peer entity.
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3.1.2.1 Successful Operation
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The procedure operates as follows: Initial conditions are assumed to be that all circuits are remotely unblocked. An entity may locally block a terrestrial circuit because: - Operation and Maintenance intervention makes the circuit unavailable for use (Cause value: "O and M intervention"). - An equipment failure makes the circuit unavailable (Cause value: "equipment failure"). - Radio resource is not accessible from the terrestrial circuit (Cause value: "no radio resource available"). When and if the party that does not allocate the circuits (the Circuit Slave) decides to locally block a terrestrial circuit, it shall immediately mark that terrestrial circuit as "blocked" (to stop any future allocation of that terrestrial circuit) and shall then send a block message to the peer entity allocating the circuits (the Circuit Master) and start timer T1 (T20, T21, T22). The BLOCK message contains the Circuit Identity Code indicating the terrestrial circuit that is to be remotely blocked and a Cause Information Element indicating the reason for blocking. Typical Cause values are: "no radio resources available", "O and M intervention", "equipment failure". A BLOCK message in the MSC to BSS direction may also contain an indication that the connection using the circuit, if any, must be released ; in such a case the circuit master shall check if the circuit is in use and shall release the connection that uses it. NOTE: This allows the MSC to simultaneously block the circuit and to release the connection using the circuit, if any, and then to prevent use of the circuit by the BSS between connection release and blocking. If the CIRCUIT GROUP BLOCK message is applied by the circuit slave the circuits to be remotely blocked are indicated in the status field of the Circuit Identity Code List (3.2.2.31). Receipt of a block message (BLOCK or CIRCUIT GROUP BLOCK) at the circuit master from the circuit slave will indicate to the circuit master that the identified circuits are unavailable for reselection. If a call is in progress on any of the identified terrestrial circuits then it will be unaffected by this procedure unless explicitly requested, the circuits will however be "camp on blocked". Such circuits shall be remotely blocked as soon as that call is no longer in progress, or active. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 17 (GSM 08.08 version 6.5.0 Release 1997) On receipt of a BLOCK message asking for the release of the connection using the circuit if any, and if the BSS detects that there exists a connection using the indicated circuit, the BSS shall attempt to release that connection, e.g., by sending a CLEAR REQUEST message on the corresponding SCCP connection. As specified in subclause 3.1.17, if the SCCP connection has been lost, the BSS will detect it when attempting to release the connection and the whole connection is released as a consequence. An appropriate blocking acknowledge message (BLOCKING ACKNOWLEDGE or CIRCUIT GROUP BLOCKING ACKNOWLEDGE) will be returned to the circuit slave by the circuit master to acknowledge receipt of the block message and to indicate that any necessary action has been taken. The CIRCUIT GROUP BLOCKING ACKNOWLEDGEMENT message is accepted as the appropriate acknowledgement only if the indicated Circuit Identity Code and the returned Range field of the Circuit Identity Code List match the corresponding parameter values of the respective initiating message. Otherwise the message is considered as not expected. On receipt of the blocking acknowledge the circuit slave shall stop timer T1 (T20, T21, T22). The resource involved will be assumed to be remotely blocked by the circuit master until either an unblock (UNBLOCK or CIRCUIT GROUP UNBLOCK) or RESET message is received relevant to that resource. If the circuit slave wishes to unblock a blocked circuit and return it to service then it shall immediately mark the circuit as "locally unblocked" and then send an unblock message, and start timer T1 (T20, T21, T22). If an unblock message (UNBLOCK or CIRCUIT GROUP UNBLOCK) is received at the circuit master for a blocked resource then the resource will be marked as not remotely blocked and an unblocking acknowledge message (UNBLOCKING ACKNOWLEDGE or CIRCUIT GROUP UNBLOCKING ACKNOWLEDGE) will be returned to the circuit slave. The circuit slave shall stop timer T1 (T20, T21, T22) on receipt of this unblocking acknowledge. The CIRCUIT GROUP UNBLOCKING ACKNOWLEDGEMENT message is accepted as the appropriate acknowledgement only if the indicated Circuit Identity Code and the returned Range field of the Circuit Identity Code List match the corresponding parameter values of the respective initiating message. Otherwise the message is considered as not expected. Figure 10 shows an overview of the blocking procedure in the case the circuit slave is the BSS. NOTE: Timer T1 is used to supervise a single circuit block/unblock procedure on the BSS side, whilst T20 is used to supervise the circuit group block/unblock procedure on the BSS side, timer T21 is used to supervise a single circuit block/unblock procedure on the MSC side, and T22 is used to supervise the circuit group block/unblock procedure on the MSC side.
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3.1.2.2 Abnormal Conditions
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If a blocking acknowledge message is not received for a block message within T1 (T20, T21, T22) seconds then the block message will be repeated. If this occurs a second time the circuits will be kept marked as locally blocked, and the situation must then be resolved internally within the circuit slave or by O&M procedures. If an unblocking acknowledge message is not received for an unblock message before expiry of timer T1(T20, T21, T22) then the unblock message will be repeated. If this occurs a second time, this situation may be reflected to the O&M, which shall resolve the possible conflict. The unblock message is repeated at most one time. Whatever the outcome of possible repetitions, the concerned circuits remain locally "unblocked". If the MSC allocates the circuits, and an ASSIGNMENT REQUEST or HANDOVER REQUEST message is received by the BSS allocating a circuit which is marked at the BSS as blocked then an ASSIGNMENT FAILURE message or a HANDOVER FAILURE message (respectively) followed by a BLOCK message shall be sent to the MSC. If the BSS allocates the circuits, and an ASSIGNMENT COMPLETE, HANDOVER REQUEST ACKNOWLEDGE or CHANGE CIRCUIT ACKNOWLEDGE message is received by the MSC allocating a circuit which is marked at the MSC as blocked, it is up to the MSC how to correct the situation, e.g., by performing a circuit re-selection procedure and sending a BLOCK message. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 18 (GSM 08.08 version 6.5.0 Release 1997)
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3.1.2.2.1 Applying to the Single Circuit Block Procedure
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i) If a BLOCK message is received for a circuit already remotely blocked, a BLOCKING ACKNOWLEDGE message will be sent. ii) If an UNBLOCK message is received for a remotely unblocked circuit, an UNBLOCKING ACKNOWLEDGE message will be sent. iii) If a BLOCKING ACKNOWLEDGE message, which is not expected as an acknowledgement for a BLOCK message, is received: a) relating to a circuit which is locally blocked, the BLOCKING ACKNOWLEDGE message is discarded. b) relating to a circuit, which is not locally blocked, then an UNBLOCK message will be sent. iv) If an UNBLOCKING ACKNOWLEDGE message, which is not expected as an acknowledgement for an UNBLOCK message, is received: a) relating to a circuit which is not locally blocked, the received UNBLOCKING ACKNOWLEDGE message is discarded. b) relating to a circuit, which is locally blocked, then a BLOCK message will be sent.
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3.1.2.2.2 Applying to the Circuit Group Block Procedure
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v) If a CIRCUIT GROUP BLOCK message is received relating to remotely blocked circuits then blocking acknowledgement indications for those circuits are given in the status field of the corresponding CIRCUIT GROUP BLOCKING ACKNOWLEDGE message which will be sent in response. vi) If a CIRCUIT GROUP UNBLOCK message is received relating to circuits which are not remotely blocked then unblocking acknowledgement indications for those circuits are given in the status field of the corresponding CIRCUIT GROUP UNBLOCKING ACKNOWLEDGE message which will be sent in response. vii)When the circuit master upon receipt of a CIRCUIT GROUP BLOCK (UNBLOCK) message is not able to give an appropriate blocking (unblocking) acknowledgement indication for each Circuit Identification Code (e.g. because that/those Circuit Identification Code(s) is (are) not allocated to any circuit at the receiving entity) for which a block (unblock) indication is given in the status field of the received CIRCUIT GROUP BLOCK (UNBLOCK) message, then no blocking (unblocking) acknowledgement relating to that/those Circuit Identification Code(s) will be given in the status field of the corresponding CIRCUIT GROUP BLOCKING (UNBLOCKING) ACKNOWLEDGE message which will be sent in response. viii) If a CIRCUIT GROUP BLOCKING ACKNOWLEDGE message in response to a CIRCUIT GROUP BLOCK message is received by the circuit slave containing in the status field no blocking acknowledgement for circuits which are to be blocked due to the previously sent CIRCUIT GROUP BLOCK message, then the CIRCUIT GROUP BLOCK message will be repeated for the circuit(s) concerned. If this occurs a second time the concerned circuit(s) will be kept marked as locally blocked, and the situation must then be resolved internally within the circuit slave or by O&M procedures. ix) The same rule applies to the Circuit Group Unblocking procedure with the only difference that the involved terrestrial circuits are kept marked as locally "not blocked". x) If a CIRCUIT GROUP BLOCKING ACKNOWLEDGE message in response to a CIRCUIT GROUP BLOCK message is received by the circuit slave containing in the status field blocking acknowledgement indications for circuits which are not to be blocked, then an appropriate unblock message will be sent for the circuit(s) concerned. xi) If a CIRCUIT GROUP UNBLOCKING ACKNOWLEDGE message in response to a CIRCUIT GROUP UNBLOCK message is received by the circuit slave containing in the status field unblocking acknowledgement indications for circuits which have to remain marked as locally blocked then an appropriate block message will be sent for the circuit(s) concerned. xii)If a CIRCUIT GROUP BLOCKING ACKNOWLEDGE message which is not expected and not accepted as an acknowledgement for a CIRCUIT GROUP BLOCK message is received: ETSI ETSI TS 100 590 V6.5.0 (2000-06) 19 (GSM 08.08 version 6.5.0 Release 1997) a) relating to circuits which all are in the status locally blocked, then the received CIRCUIT GROUP BLOCKING ACKNOWLEDGE message will be discarded; b) related to circuits part or all of which are not in the status locally blocked then an appropriate unblock message will be sent for the relevant circuit(s). xiii) If a CIRCUIT GROUP UNBLOCKING ACKNOWLEDGE message which is not expected and not accepted as an acknowledgement for a CIRCUIT GROUP UNBLOCK message is received: a) relating to circuits none of which is in the status locally blocked, then the received CIRCUIT GROUP UNBLOCKING ACKNOWLEDGE message will be discarded; b) related to circuits part or all of which are locally blocked then an appropriate block message will be sent for the relevant circuit(s).
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3.1.3 Resource Indication
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The purpose of the resource indication procedure is: - To inform the MSC of the amount; - of radio resource that is spare at the BSS and available for traffic carrying purposes; and - of the total amount of the accessible radio resource (i.e. available for service or currently assigned). This cannot easily be derived from the traffic that the MSC is carrying. The MSC may take these pieces of information into account for the external handover decision.
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3.1.3.1 Successful Operation
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The procedure relates to a single cell. The MSC determines the resource information (i.e. the resource available information and optionally the total resource accessible information) and the manner in which the BSS transfers this resource information to the MSC by sending a RESOURCE REQUEST message to the BSS. This message shall contain a Resource Indication Method Information Element which can be set to one of the following values: i) (Spontaneous resource information expected): The BSS shall send the first RESOURCE INDICATION message without any resource information to the MSC immediately as an acknowledgement to the RESOURCE REQUEST message and then any further RESOURCE INDICATION messages spontaneously every time conditions, defined by O&M, are met in the BSS for the considered cell (e.g. traffic thresholds, or time interval between two messages). If the O&M conditions for sending RESOURCE INDICATION messages are met, the BSS may use the Periodicity IE received in the RESOURCE REQUEST message to determine the time interval between indications, except that, if the MSC sets the Periodicity IE to zero then the BSS shall ignore the Periodicity IE. The BSS stays in this mode until the receipt of a new RESOURCE REQUEST message for the same cell, or a reset occurs; ii) (One single resource information expected): The BSS shall return a single RESOURCE INDICATION message with some resource information immediately. If the RESOURCE REQUEST message does not contain an Extended Resource indicator IE the BSS shall then cease any resource information transfer related to the cell until the receipt of either a new RESOURCE REQUEST message or a reset. If the RESOURCE REQUEST message contains an Extended Resource Indicator IE the BSS shall obey the 'Subsequent Mode' field; iii) (Periodic resource information expected): The BSS shall return a RESOURCE INDICATION message with some resource information immediately, and then periodically, with a period set by MSC*, until the receipt of either a new RESOURCE REQUEST message for the same cell or a reset. * (The period shall equal the value of the periodicity parameter times 100 ms. If the value of the periodicity parameter is zero, then the message should be treated as one containing an incorrect value according to subclause 3.1.19.4, case 2). ETSI ETSI TS 100 590 V6.5.0 (2000-06) 20 (GSM 08.08 version 6.5.0 Release 1997) iv) (No resource information expected): The BSS shall immediately return a single RESOURCE INDICATION message without any resource information as an acknowledgement to the RESOURCE REQUEST message and then the BSS to MSC transfer of resource information related to the cell is disabled until the receipt of either a new RESOURCE REQUEST message for the same cell or a reset. The default mode is iv); after a reset, this mode is set for all the cells of a BSS. The transfer of resource information related to a given cell from the BSS to the MSC occurs when the Resource Indication Method Information Element is set to one of the values i) to iii) in the BSS. The BSS sends RESOURCE INDICATION messages to the MSC, under the conditions explained above. The RESOURCE INDICATION message shall contain the Resource Indication Method Information Element with the same value as it was requested by the MSC, i.e. the BSS is not allowed to select a method different from the one requested by the MSC. Furthermore, the RESOURCE INDICATION message may contain the Resource Available IE and the Total Resource Accessible IE dependent on the selected method and, in case of the Total Resource Accessible IE, also dependent on the request from the MSC. If the RESOURCE INDICATION message is just taken as a simple acknowledgement as stated in method i) and iv), the Total Resource Accessible IE shall not be returned independent of whether it was requested by the MSC or not. For each idle channel the level of interference will be averaged over a period of Intave. (Intave is a parameter set by O&M command on a per cell basis). This averaging will be performed immediately before the transmission of the RESOURCE INDICATION message. The result of this averaging will be used to classify the average interference level on the idle channels into five interference bands. The Resource Available Information Element contains two pieces of information for each of the five interference bands: - The number of half rate TChs available in that band. - The number of full rate TChs available in that band. The levels of the five bands are defined by O&M.
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100 590
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3.1.4 Reset
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100 590
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3.1.4.1 Global Reset Procedure
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The purpose of the reset procedure is to initialise the BSS and MSC in the event of a failure. The procedure is a global procedure applying to a whole BSS, and therefore all messages relating to the reset procedure are sent as global messages using the connectionless mode of the SCCP. If only a limited part of the MSC or BSS has suffered a failure then clearing procedures can be used to clear only those affected calls.
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100 590
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3.1.4.1.1 Reset at the BSS
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In the event of a failure at the BSS which has resulted in the loss of transaction reference information, a RESET message is sent to the MSC. This message is used by the MSC to release affected calls and erase all affected references, and to put all circuits into the idle state. After a guard period of T2 seconds a RESET ACKNOWLEDGE message is returned to the BSS indicating that all references have been cleared. After the sending of the RESET to the MSC a BSS that does not allocate the circuits shall initiate blocking procedures (Block or Circuit group block procedures) for all circuits that are locally blocked on the BSS side, the MSC shall respond as specified in subclause 3.1.2. The sending of block messages shall be done without waiting for the acknowledgement to the RESET message. Upon receipt of a RESET message from the BSS an MSC that does not allocate the circuits shall send block messages (BLOCK or CIRCUIT GROUP BLOCK) for all circuits that are locally blocked on the MSC side, the BSS shall respond to these with blocking acknowledge messages as described in subclause 3.1.2. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 21 (GSM 08.08 version 6.5.0 Release 1997)
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100 590
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3.1.4.1.2 Reset at the MSC
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In the event of a failure at the MSC which has resulted in the loss of transaction reference information, a RESET message is sent to the BSS. This message is used by the BSS to release affected calls and erase all affected references. After the sending of the RESET to the BSS, an MSC that does not allocate the circuits shall initiate blocking procedures (Block or Circuit group block procedures) for all circuits that are locally blocked on the MSC side, the BSS shall respond as specified in subclause 3.1.2. The sending of block messages shall be done without waiting for the acknowledgement to the RESET message. Upon receipt of a RESET message from the MSC a BSS that does not allocate the circuits shall send block messages (BLOCK or CIRCUIT GROUP BLOCK) for all circuits that were previously locally blocked on the BSS side, the MSC shall respond to these with blocking acknowledge messages as described in subclause 3.1.2. After a guard period of T13 seconds a RESET ACKNOWLEDGE message is returned to the MSC, indicating that all MSs which were involved in a call are no longer transmitting and that all references at the BSS have been cleared.
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100 590
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3.1.4.1.3 Abnormal Conditions
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3.1.4.1.3.1 Abnormal Condition at the BSS If the BSS sends a RESET message to the MSC and receives no RESET ACKNOWLEDGE message within a period T4 then it shall repeat the entire reset procedure. The sending of the RESET message is repeated a maximum of "n" times where n is an operator matter. After the n-th unsuccessful repetition the procedure is stopped and the maintenance system is informed. 3.1.4.1.3.2 Abnormal Condition at the MSC If the MSC sends a RESET message to the BSS and receives no RESET ACKNOWLEDGE message within a period T16 then it shall repeat the entire reset procedure. The sending of the RESET message is repeated a maximum of "n" times where n is an operator matter. After the nth unsuccessful repetition the procedure is stopped and the maintenance system is informed.
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100 590
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3.1.4.2 Reset Circuit
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The purpose of the reset circuit procedure is to restore the information in MSC/BSS in the case of a failure which has affected only a small part of the equipment (e.g. abnormal SCCP connection release).
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100 590
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3.1.4.2.1 Reset Circuit at the BSS
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If a circuit has to be put to idle at the BSS due to an abnormal SCCP-connection release, a RESET CIRCUIT message will be sent to the MSC. When the MSC receives this message, it clears the possible call and puts the circuit, if known, to the idle state. If the circuit is known, a RESET CIRCUIT ACKNOWLEDGE message is returned to the BSS. If circuit allocation is done by the BSS and if the circuit is locally blocked at the MSC a BLOCK message shall be returned to the BSS. The BSS shall then respond with a BLOCKING ACKNOWLEDGE message, as described in subclause 3.1.2. If the circuit is unknown in the MSC, an UNEQUIPPED CIRCUIT message is returned to the BSS. Timer T19 is used at the BSS to supervise the reset circuit procedure. If the timer elapses before a response (RESET, RESET CIRCUIT ACKNOWLEDGE or UNEQUIPPED CIRCUIT) is returned to the BSS, the procedure is repeated.
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100 590
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3.1.4.2.2 Reset Circuit at the MSC
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If a circuit has to be put to idle at the MSC due to an abnormal SCCP-connection release, a RESET CIRCUIT message will be sent to the BSS. When the BSS receives a RESET CIRCUIT message, it shall respond with a RESET CIRCUIT ACKNOWLEDGE message in case the circuit can be put to idle. If circuit allocation is done by the MSC and if the circuit is locally blocked at the BSS a BLOCK message shall be returned to the MSC. The MSC shall then respond with a BLOCKING ACKNOWLEDGE message, as described in subclause 3.1.2. If the circuit is unknown at the BSS, the BSS shall return an UNEQUIPPED CIRCUIT message to the MSC. Timer T12 is used at the MSC to supervise the reset circuit procedure. If the Timer elapses before a response (RESET, RESET CIRCUIT ACKNOWLEDGE, UNEQUIPPED CIRCUIT or BLOCK) the reset circuit procedure is repeated. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 22 (GSM 08.08 version 6.5.0 Release 1997)
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100 590
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3.1.4.2.3 Abnormal conditions
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If a RESET message is received after sending of a RESET CIRCUIT message and before receipt of the corresponding response the respective reset circuit procedure is stopped, i.e. reception of the corresponding RESET CIRCUIT ACKNOWLEDGE message is not required and no repetition is necessary. If a RESET CIRCUIT message is received immediately after a RESET CIRCUIT message has been sent for the same circuit, the corresponding acknowledgement messages are returned. The sending of the RESET CIRCUIT message is repeated a maximum of "n" times where n is an operator matter. After the n-th unsuccessful repetition the procedure is stopped and the maintenance system is informed.
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100 590
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3.1.5 External Handover
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The details of the radio information as far as handover is concerned are given in GSM 04.08. The relevant network information is given in GSM 03.09. Using this protocol the BSS should support handover transitions to and from any combinations of the following: Channel SDCCH Full Rate TCH Half Rate TCH Multiple Full Rate TCHs In the present document three procedures are defined which can be used for handover. They are: - Handover Required Indication; - Handover Resource Allocation; - Handover Execution. (Figure 16 shows an example of a complete handover procedure). For any HANDOVER REQUIRED message at most one HANDOVER COMMAND message may be sent. In the case of inter-MSC handover the term "the MSC" in this subclause is taken to mean the relevant MSC in the handover operation. The handover procedures are specified in the following subclauses. All messages concerned with handover, with the exception of HANDOVER CANDIDATE ENQUIRE and HANDOVER CANDIDATE RESPONSE messages, are sent using the connection oriented mode of the SCCP.
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100 590
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3.1.5.1 Handover Required Indication
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The handover required indication procedure allows a BSS to request that a handover is to be carried out for a particular MS, currently allocated one or more dedicated resources. This is done by generating a HANDOVER REQUIRED message and sending it from the BSS to the MSC. If so required by the BSS the MSC informs the BSS if the handover cannot be carried out. This is done by a HANDOVER REQUIRED REJECT message. The HANDOVER REQUIRED message is sent using the BSSAP SCCP connection already set up for that transaction. As part of the BSS's functions, the BSS continually monitors all radio information, and compares it with parameters such that if the transmission quality of a given parameter (or set of parameters) passes a predetermined threshold (set by O&M) then a HANDOVER REQUIRED message is generated and sent to the MSC. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 23 (GSM 08.08 version 6.5.0 Release 1997)
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100 590
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3.1.5.1.1 Generation of the HANDOVER REQUIRED message
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Generation of the HANDOVER REQUIRED message can be for the following reasons: - The BSS has detected that a radio reason exists for a handover to occur. - The MSC has initiated a handover candidate enquiry procedure, and this MS is currently a candidate. - A cell change is required at call setup due to congestion, e.g. directed retry. The HANDOVER REQUIRED message contains the following information elements: - Message Type; - Cause; - Cell Identifier List (preferred). It should also contain the information elements: "Current channel type 1", "old BSS to new BSS information" and, in case the current channel mode is speech, "Speech version (used)". The "Old BSS to New BSS information" is used to pass Field Elements from the old BSS to the new BSS. The information in the "Old BSS to New BSS information" is transparent for the MSC. When the "Old BSS to New BSS information" is present in the HANDOVER REQUIRED message the MSC shall pass it unchanged to any BSS associated to "Cell Identifier List (preferred)" when initiating the Handover resource allocation procedure. The old BSS must ensure that the information contained in the "Old BSS to New BSS information" information element is valid for all cells in the "Cell Identifier List (preferred)". Sec. 3.2.1.9. gives coding details of the above message. The "Cause" field indicates the reason for the HANDOVER REQUIRED message e.g. "uplink quality poor" or "response to MSC invocation" in the case of traffic reasons indicated by the MSC. The Cause value sent should be an indication which can be taken into account at the target BSS in future handover decision processes, e.g. to reduce oscillations between BSSs due to the fact that some information (on which the old BSS decided to initiate the handover) is not available at the target BSS (e.g. distance, traffic...). If present the "Response Request" Information Element indicates, that the BSS requires an indication if the HANDOVER REQUIRED message does not result in a HANDOVER COMMAND message. If the BSS wants to change the CIC due to a channel change, the BSS sends a HANDOVER REQUIRED message with the cause "switch circuit pool" and the "circuit pool list" information element. The "circuit pool list" information element will allow the BSS to indicate to the MSC from which circuit pool or pools the new CIC should be chosen. The "Cell Identifier List (preferred)" shall identify "n" preferred cells. The identified cells are given in order of preference. The algorithm by which the BSS produces this list is Operator dependent and is not addressed in the present document. The "n" number of preferred cells is a parameter set by O&M and shall range from 1 to 16. If "n" number of cells cannot be identified, then only as many as are available shall be encoded and sent (as specified in section 3.2.2.27). It is mandatory for the BSS to be able to produce this "Cell Identifier List (preferred)". The sending of this list is controlled by the O&M parameter "n". It is mandatory for the MSC to be able to receive and interpret this Information Element. The BSS may recommend to the MSC to allow queuing or not in the handover resource allocation procedure by indication in the “Queuing indicator” information element within the HANDOVER REQUIRED message. The old BSS may inform the new BSS of the presently configured channel in the Current Channel Type 1 information element and in the Current Channel type 2 Field Element. The information contained may be used by the new BSS (e.g. when building the radio interface HANDOVER COMMAND message). Where discrepancies occur between the Current Channel Type 1 and the Current Channel Type 2 then the information in the Current Channel Type 2 shall take precedence if understood by the new BSS. If, for this mobile station, the old BSS has received a Gb interface SUSPEND ACK PDU, then the old BSS shall include the GPRS Suspend information field in the Old BSS to New BSS IE in the HANDOVER REQUIRED message. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 24 (GSM 08.08 version 6.5.0 Release 1997) If the old BSS received a GPRS Suspend information field in the Old BSS to New BSS IE in any preceding HANDOVER REQUEST message received by the old BSS, then, the old BSS shall include the GPRS Suspend information field in the Old BSS to New BSS IE in the HANDOVER REQUIRED message. The old BSS may recommend to the new BSS to allow pre-emption or not allow pre-emption by sending the “prec” bit. The new BSS may take this information into account when performing the Handover resource allocation procedure. The old BSS may inform the new BSS of radio information pertaining to the target cell in the “Target cell radio information” field element. The old BSS shall only send the “Target cell radio information” field element when it sends a single cell in the “Cell Identifier List (preferred)”. This field element may be used by the new BSS (e.g. for radio channel selection). NOTE: It is not recommended that this information element is included if more than one cell is sent in the “Cell Identifier List (preferred)”. The old BSS may inform the new BSS of the presently configured channel in the Current Channel Type 1 information element and in the Current Channel type 2 Field Element. The information contained may be used by the new BSS (e.g. when building the radio interface HANDOVER COMMAND message). Where discrepancies occur between the Current Channel Type 1 and the Current Channel Type 2 then the information in the Current Channel Type 2 shall take precedence if understood by the new BSS. The HANDOVER REQUIRED message shall be updated and repeated by the BSS with a periodicity of T7 until: - A HANDOVER COMMAND message is received from the MSC, or; - A RESET message is received, or; - The reason for the original HANDOVER REQUIRED message disappears e.g. the MS transmission improves, or; - All communication is lost with the MS as defined in GSM 04.08, and the transaction is abandoned, or; - The transaction ends, e.g., call clearing.
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100 590
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3.1.5.2 Handover Resource allocation
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This procedure has been defined to allow the MSC to request resources from a BSS in a manner similar to that used for the assignment case. However it does not result in the transmission of any messages over the radio interface, only in the reservation of the resource(s) identified at the BSS, which awaits access of a MS on the reserved channel(s). These reserved resources are then indicated back to the MSC. In order to support this procedure the MSC sets up a BSSAP SCCP connection to the BSS. This connection is then used to support all BSSAP messages related to the dedicated resource(s).
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100 590
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3.1.5.2.1 Operation of the procedure
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The correct operation of the handover resource allocation procedure is as follows: The MSC sends a HANDOVER REQUEST message to the new BSS (note) from which it requires radio resources. This message contains details of the resource(s) required. If the MSC allocates the A interface circuits, and if the requested resource(s) is/are for speech or data the message also indicates the terrestrial resource that shall be used between the MSC and the BSS. The MSC should only ever ask for resources from the BSS that it knows are not totally incompatible with the nominated circuit. The type of channel(s) required can be different from the type of channel(s) in use, e.g. in the case of directed retry. The description of the resource(s) can either be a complete specification, or give the BSS some freedom in the selection (for instance channel rate selection, speech version selection etc.). The message may also specify the channel(s) in use, and, in case current channel mode is speech, the speech version used. On receipt of this message the new BSS shall choose suitable idle radio resources and, if the BSS allocates the A interface circuits and if needed, a terrestrial resource. The management of priority levels - relating to the Information Element "Priority" within the HANDOVER REQUEST message - is implementation dependent, under operator control. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 25 (GSM 08.08 version 6.5.0 Release 1997) If queuing is managed, new requests which cannot be served immediately are put in the queuing file according to the indicated priority levels. (Refer to subclause 3.1.17 for Queuing Procedure). As a further operator option, the pre-emption indicators may (alone or along with the priority levels) be used to manage the pre-emption process, which may lead to the forced release or forced handover of lower priority connections. However, the pre-emption indicators (refer to subclause 3.2.2.18), if given in the HANDOVER REQUEST, shall be treated on a per connection basis as follows: - the last received "Pre-emption Vulnerability" indicator and priority levels shall prevail. - if the "Pre-emption Capability" bit is set to 1, then this allocation request can trigger the running of the pre-emption procedure. - if the “Pre-emption Recommendation” bit indicates that pre-emption is recommended by the old BSS, then the new BSS may obey the recommendation and act appropriately based on “Pre-emption Capability Indication” bit. - if the “Pre-emption Recommendation” bit indicates that pre-emption is not recommended by the old BSS, then the new BSS may obey this recommendation and ignore the “Pre-emption Capability” bit if it is set to 1. - if the “Pre-emption Recommendation” bit is not present then the pre-emption procedure can be run. - if the "Pre-emption Capability" bit is set to 0, then this allocation request cannot trigger the pre-emption procedure. - if the "Pre-emption Vulnerability" bit is set to 1, then this connection is vulnerable and shall be included in the pre-emption process or procedure and as such may be subject to forced release or forced handover. - if the "Pre-emption Vulnerability" bit is set to 0, then this connection is not vulnerable to pre-emption and shall not be included in the pre-emption process and as such may not be subject to forced release or forced handover. - if no Priority Information Element has been received, both "Pre-emption Capability" and "Pre-emption Vulnerability" bits shall be regarded as set to 0. If a radio resource is available then this will be reflected back to the MSC in a HANDOVER REQUEST ACKNOWLEDGE message. If the MSC gave the BSS some freedom in resource type selection, the choices made by the BSS are indicated in the HANDOVER REQUEST ACKNOWLEDGE message. If the BSS allocates the A interface circuits and such a circuit is needed, the circuit allocated by the BSS is indicated in the HANDOVER ACKNOWLEDGE message. The HANDOVER REQUEST ACKNOWLEDGE message sent by the new BSS shall contain the radio interface message HANDOVER COMMAND within its "Layer 3 Information" Information Element. This "Layer 3 Information" (which is in fact the RR-Layer 3 HANDOVER COMMAND) is transferred by the controlling MSC to the old BSS using the BSSMAP message HANDOVER COMMAND also within the Information Element "Layer 3 Information" of that BSSMAP message. The old BSS then sends to the MS over the radio interface the RR-Layer 3 HANDOVER COMMAND message. Information about the appropriate new channels and a handover reference number chosen by the new BSS are contained in the HANDOVER COMMAND. Knowledge of the channel in use at the old BSS allows the new BSS to minimize the size of the HANDOVER COMMAND message (i.e. to decide whether the mode of the first channel IE need not be included in the HANDOVER COMMAND). NOTE: The new BSS and the old BSS may be the same. When several circuit pools are present on the BSS MSC interface, and a circuit has been allocated by the HANDOVER REQUEST message, the "circuit pool" information field shall be included in the HANDOVER REQUEST ACKNOWLEDGE. The "circuit pool" field will indicate to the MSC the circuit pool of the CIC given in the HANDOVER REQUEST message. The sending of the HANDOVER REQUEST ACKNOWLEDGE by the new BSS to the MSC ends the Handover Resource Allocation procedure. The Handover Execution procedure can now proceed and this is given in subclause 3.1.5.3. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 26 (GSM 08.08 version 6.5.0 Release 1997) The new BSS shall then take all necessary action to allow the MS to access the radio resource(s) that the new BSS has chosen, this is detailed in the GSM 05 series of Technical Specifications. If the radio resource(s) is a traffic channel or a group of traffic channels, then the new BSS shall at this point switch it through to the terrestrial resource indicated in the HANDOVER REQUEST message, and the necessary transcoding/rate adaption/encryption equipment enabled as detailed in GSM 04.08. The optimum procedure for switching through to the target cell at the MSC is not defined in these Technical Specifications.
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100 590
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3.1.5.2.2 Handover Resource Allocation Failure
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The following failure conditions of this procedure may occur: The BSS may not be able to use the terrestrial resource that the MSC has indicated in which case a HANDOVER FAILURE message will be returned with the Cause value set to: "requested terrestrial resource unavailable". The BSS may not be able to support the requested ciphering algorithm and in this case a HANDOVER FAILURE message shall be returned to the MSC with the Cause value "Ciphering algorithm not supported". If the requested channel type or resource (e.g. channel rate, speech version, etc.) indicated in the HANDOVER REQUEST message is not available in the BSS, then a HANDOVER FAILURE message shall be returned to the MSC. The appropriate failure cause will be included in the message (Cause value: "requested transcoding/rate adaptation unavailable" or "requested speech version unavailable"). The generation of the HANDOVER FAILURE message terminates the procedure and allows all references in the new BSS to be released. If, on reception of the HANDOVER REQUEST by the BSS, the circuit pool implied by the CIC information element is incompatible with the channel type indicated (that is, the pool does not support any of the radio resources indicated by the channel type) a HANDOVER FAILURE shall be returned to the MSC with the failure cause set to "circuit pool mismatch". If, on reception of the HANDOVER REQUEST by the BSS, the circuit pool implied by the CIC is compatible with the channel type indicated (that is, the pool supports at least one of the radio resource types indicated by the channel type), but the BSS still wishes to change the circuit pool, it sends a HANDOVER FAILURE with the cause "switch circuit pool" and the "circuit pool list" information element. The "circuit pool" information element, when present in the HANDOVER FAILURE, indicates to the MSC which circuit pool the CIC indicated in the HANDOVER REQUEST belongs to. This can be used by the MSC to correct its tables (CIC/circuit pool). The "circuit pool list" information element, when present in the HANDOVER FAILURE, is used when the BSS wishes to indicate to the MSC its preferred circuit pools. The circuit pools in the "circuit pool list" information element shall be given in order of preference. In the case of a HANDOVER FAILURE with the cause "circuit pool mismatch", the MSC may decide to block the circuit and to send an O & M notification. Other possible cause values which may be returned with the HANDOVER FAILURE message are: "equipment failure", "no radio resource available", "O&M intervention". The MSC may not be able to use the terrestrial resource that the BSS has indicated. In this case, the procedure is nevertheless considered terminated successfully, and it is up to the MSC to correct the situation, e.g., by a circuit re- selection procedure. Further actions in the MSC concerning handover depend upon the handover algorithm which is operator dependent. If an unrecognised Handover Failure cause value is received, the Class of the cause value should be used to determine the MSC's action. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 27 (GSM 08.08 version 6.5.0 Release 1997)
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100 590
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3.1.5.2.3 Abnormal conditions
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If after receipt of a HANDOVER REQUEST message, the new BSS receives another HANDOVER REQUEST message on the same SCCP connection, then the later message will be discarded. If the BSS receives a HANDOVER REQUEST allocating a terrestrial circuit which the BSS has marked as blocked by a previous blocking procedure, then a HANDOVER FAILURE shall be returned to the MSC with the Cause set to "requested terrestrial resource unavailable". A single global BLOCK message (not repeated and not guarded by timer T1) shall be sent for that concerned terrestrial circuit. If the BSS receives a HANDOVER REQUEST message indicating a target cell which is not controlled by the BSS, then a HANDOVER FAILURE message shall be returned to the MSC with the cause set to "invalid cell".
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100 590
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3.1.5.3 Handover execution
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Handover execution in the context of the BSS/MSC interface is the process whereby an MSC instructs an MS to tune to a new dedicated radio resource or to a group of radio resources, which may be on a different cell.
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100 590
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3.1.5.3.1 Operation of the procedure
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The correct operation of the procedure is as follows: The BSSMAP HANDOVER COMMAND message is generated by the MSC and transmitted over the BSSAP connection to the old BSS which is currently supporting the concerned MS. At the old BSS timer T8 is started on the receipt of the BSSMAP HANDOVER COMMAND message. A radio interface HANDOVER COMMAND message is then sent by the old BSS, to the concerned MS. The message contains a handover reference number, previously allocated by the new BSS. The BSSMAP HANDOVER COMMAND message generated by the MSC may optionally contain a Cell Identifier IE which indicates to the old BSS the target cell identity to which the handover is to be performed. In case of failure, this information allows the old BSS to know on which cell the handover failed. When the MS accesses the radio resource(s) of the new BSS with a HANDOVER ACCESS burst which contains the received handover reference number then: The new BSS checks the handover reference number to ensure that it is the same as expected, and hence that there is a high probability that the correct MS has been captured (if the handover reference is not as expected then the new BSS shall wait for an access by the correct MS); If the handover reference number is as expected, the new BSS shall send a HANDOVER DETECT message to the MSC; When the MS is successfully in communication with the network, i.e. the RR message HANDOVER COMPLETE has been received from the MS, then the new BSS will immediately send a BSSMAP message HANDOVER COMPLETE to the MSC and terminate the procedure. In the case where the new BSS hands the MS to a Group call channel, the BSS shall send a CLEAR REQUEST with cause "Joined group call channel" directly after having sent the HANDOVER COMPLETE message. In the case of point to point calls the MSC shall terminate the procedure with the old BSS by sending a CLEAR COMMAND with cause "Handover successful". In the case of a handover from a Group call channel the MSC shall terminate the procedure by sending a HANDOVER SUCCEEDED message. The old dedicated radio resource(s) and connected terrestrial resource shall remain assigned until either the MSC instructs the old BSS to release the resource(s) by a CLEAR COMMAND or a reset occurs. After the completion of the handover procedure, until the connection is released or the MSC performs an assignment, any dedicated resource assigned to the mobile station, e.g. at internal handover, must be in accordance with the description in the HANDOVER REQUEST message. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 28 (GSM 08.08 version 6.5.0 Release 1997) If either: a CLEAR COMMAND is received from the MSC; or a reset is received from the MSC; before a MS with the correct handover reference accesses the new BSS then the radio resources shall be released and the terrestrial resources marked as idle. The relevant radio interface layer 3 procedures are described in GSM 04.08. The MSC always terminates this procedure by use of a clear sequence as follows: The MSC sends a CLEAR COMMAND to the old BSS. On receipt of a CLEAR COMMAND from the MSC the old BSS shall stop timer T8 and release all involved resources that were allocated to the MS that had been handed over and returns a CLEAR COMPLETE message to the MSC. On receipt of the CLEAR COMPLETE, the MSC shall initiate the release of the SCCP connection to the old BSS and thereby terminate association with the old BSS for this process.
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
|
3.1.5.3.2 Handover Failure
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If a HANDOVER FAILURE radio interface message is received from the MS on the old (main) channel by the old BSS, the old BSS shall then send to the MSC the BSSMAP message HANDOVER FAILURE. If the radio interface HANDOVER FAILURE message is the result of the MS returning to the old BSS after failing to establish on the new BSS, then the cause value "radio interface failure, reversion to old channel" shall be included in the BSSMAP message HANDOVER FAILURE. Furthermore, it is recommended that the air interface RR cause be included as well in this message. If the MSC receives the BSSMAP HANDOVER FAILURE message from the old BSS (with any cause value), the handover procedure at the target new BSS is then terminated by the MSC using a clear sequence as follows: The MSC sends a CLEAR COMMAND cause “Radio interface failure, reversion to old channel” to the new BSS. On receipt of a CLEAR COMMAND from the MSC the new BSS shall release all involved resources that were allocated during the handover resource allocation procedure and returns a CLEAR COMPLETE message to the MSC. On receipt of the CLEAR COMPLETE, the MSC shall initiate the release of the SCCP connection to the new BSS and thereby terminate association with the new BSS for this process. The call between the MS and the old BSS and between the old BSS and the MSC shall continue as if there had been no handover attempt. Further actions in the MSC concerning handover depends on the handover algorithm which is operator dependent. In the case of a talker on a group call channel the MS may release the uplink whilst the handover is being performed, in this case the old BSS shall cancel the handover internally, the MSC should cancel the handover and initiate the release of the A interface resources allocated in the new BSS.
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
|
3.1.5.3.3 Abnormal Conditions
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Whilst the handover execution procedure is in operation, any other messages received at the old BSS relating to this connection and concerning assignment, handover, or cipher mode control should be discarded. Whilst the handover execution procedure is in operation the old BSS should not attempt to invoke any other procedure related to this call e.g. handover required indication. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 29 (GSM 08.08 version 6.5.0 Release 1997) If at the old BSS a CLEAR COMMAND message from the MSC or a HANDOVER FAILURE message from the MS is not received before the expiry of timer T8 then the old BSS shall release the dedicated radio resources. A BSSMAP message CLEAR REQUEST is also sent to the MSC with a cause "Radio Interface Message Failure". The terrestrial resource in the old BSS shall remain assigned until a CLEAR COMMAND is received from the MSC, at which point the old BSS shall mark the terrestrial resources as IDLE and return a CLEAR COMPLETE message to the MSC. The MSC shall subsequently release the SCCP connection to the old BSS and thereby terminate association with the old BSS for this process. The MSC shall also initiate release of the resources allocated by the new BSS during the handover resource allocation procedure by sending a CLEAR COMMAND to the new BSS. The new BSS shall release all the resources that were assigned for that aborted handover and return a CLEAR COMPLETE to the MSC. The MSC shall subsequently release the SCCP connection to the new BSS and thereby terminate association with the new BSS for this process.
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bf8e452635c0e3fa50938ae3618b9b7d
|
100 590
|
3.1.6 Internal Intra-Cell Handover Procedure
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The definition of internal intra cell handover is given in clause 5. It is optional that a BSS support internal intra-cell handover. However if it is supported, it should be as follows: It should be possible to inhibit internal intra-cell handover at an BSS that supports it by operation and maintenance command. Internal intra-cell handover occurs between channels on the same cell. It is decided and executed autonomously by the BSS, so that no message is generated at the BSS-MSC interface, until the completion of the handover execution, when the BSS sends a HANDOVER PERFORMED message over the SCCP and terrestrial resources that are presently assigned to that call. Changes in type of resources (for instance channel rate change, speech version change, ciphering algorithm change) are indicated in the HANDOVER PERFORMED message. The decision process in the BSS is based on the internally available radio and resource parameters taking into account the previously received information from the MSC in the ASSIGNMENT REQUEST or HANDOVER REQUEST. The relevant radio interface layer 3 procedures (dedicated channel assignment) are described in GSM 04.08. In the case of group calls the BSS may perform an intra-cell handover for a talker from a dedicated channel to a group call channel, in this case the HANDOVER PERFORMED message is sent by the BSS over the SCCP connection that was previously assigned to the talker, followed by a CLEAR REQUEST with the cause "Joined group call channel", the MSC shall release the dedicated A interface resources. In the case of group calls the BSS may perform an Intra-cell handover for a talker from a Group call channel to a dedicated channel, in this case the BSS performs external handover.
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
|
3.1.7 Internal Inter-Cell Handover Procedure
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The definition of internal inter-cell handover is given in clause 5. It should be possible to inhibit internal inter-cell handover at a BSS that supports it by operation and maintenance command. Multi cell BSSs would normally be expected to support internal inter-cell handover, however it is optional that they do so. However if it is supported, it should be as follows: Internal inter-cell handover occurs between channels pertaining to different cells of the same BSS. It is decided and executed autonomously by the BSS, so that no message is generated at the BSS-MSC interface, until the completion of the handover execution, when the BSS sends a HANDOVER PERFORMED message over the SCCP and terrestrial resources that are presently assigned to that call. Changes in type of resources (for instance channel rate change, speech version change, ciphering algorithm change) are indicated in the HANDOVER PERFORMED message. A special case of internal handover occurs when the handover is triggered by the assignment procedure, e.g. directed retry. In this case the HANDOVER PERFORMED message need not be sent as the equivalent response is provided by the ASSIGNMENT COMPLETE message. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 30 (GSM 08.08 version 6.5.0 Release 1997) The decision process in the BSS is based on the internally available radio and resource parameters taking into account the previously received information from the MSC in the ASSIGNMENT REQUEST or HANDOVER REQUEST. The relevant radio interface layer 3 procedures (for handover) are described in GSM 04.08. Internal inter-cell handover for group calls may be performed from either dedicated to dedicated channels, or dedicated to group call channels, or group call to group call channels. In the case of group calls, the BSS may perform an internal inter-cell handover for a talker from a dedicated channel to a Group call channel, in this case the HANDOVER PERFORMED message is sent by the BSS over the SCCP connection that was previously assigned to the talker. The BSS will send a CLEAR REQUEST with the cause "Joined group call channel".
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
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3.1.8 Handover Candidate Enquiry
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The purpose of this procedure is to allow the MSC to ascertain if it is possible to handover any MSs that are currently being served by a particular cell to another nominated cell. The procedure uses both global and dedicated resource messages, and is relevant to an individual cell. The algorithm in which a MSC decides on starting a handover enquiry procedure is operator dependent.
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
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3.1.8.1 Successful Operation
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The procedure operates as follows: The MSC sends a HANDOVER CANDIDATE ENQUIRE message to a BSS. The message indicates that the MSC wishes the BSS to identify handover candidates in a particular cell, that can be handed over to other nominated cells. The maximum number of candidates is also indicated to the BSS. For each selected MS candidate the BSS will send to MSC a single, once only, HANDOVER REQUIRED message (not guarded by timer T7), over each of the appropriate SCCP connections. If the BSS was already generating HANDOVER REQUIRED messages for a selected MS then the BSS will continue to do so. However the Cause IE of the next HANDOVER REQUIRED message (at the expiry of timer T7) will be set to "Response to MSC invocation" to indicate that the message is generated in response to a HANDOVER CANDIDATE ENQUIRE message. But as this HANDOVER REQUIRED was already being generated before the handover enquiry procedure was started, that HANDOVER REQUIRED would be guarded by timer T7. So in the instance of next expiry of timer T7, the BSS shall continue sending HANDOVER REQUIRED message but the Cause IE value shall revert back to the original Cause IE value. When the last HANDOVER REQUIRED message has been sent for all the selected MS candidates, the BSS returns to the MSC a HANDOVER CANDIDATE RESPONSE message giving the number of candidates identified, and terminating the handover enquiry procedure. Only one handover enquiry procedure may be invoked on any given cell at any one time.
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
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3.1.8.2 Abnormal conditions
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If at the BSS a HANDOVER CANDIDATE ENQUIRE message is received when a handover enquiry procedure has already been invoked then the new HANDOVER CANDIDATE ENQUIRE message shall be discarded.
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
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3.1.9 Release of Radio Resource And Terrestrial Resource
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
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3.1.9.1 Release Due To Transaction Completion
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The release of assigned radio resources at the end of a transaction will take place as follows: Release negotiation will take place directly between the MS and MSC using transparent messages via the DTAP in the BSS (see GSM 04.08). The MSC will then send a BSSMAP CLEAR COMMAND, indicating that the radio resource(s) should be released. After the BSSMAP CLEAR COMMAND has been sent, the MSC shall not send further BSSAP connection oriented messages on this particular connection, except CLEAR COMMAND. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 31 (GSM 08.08 version 6.5.0 Release 1997) If the BSS allocates the A interface circuits, the MSC shall release the circuit allocated to the connection, if any, before sending the CLEAR COMMAND. When the BSS receives the CLEAR COMMAND: the guard timer defined in GSM 04.08 is started and clearing on the radio interface initiated. the BSS marks any assigned terrestrial resources as idle and returns a CLEAR COMPLETE message to the MSC. (The BSS need not wait for the radio channel release to be completed or for the guard timer to expire before returning the CLEAR COMPLETE message). If the MSC allocates A interface circuits, on receipt of CLEAR COMPLETE, the MSC releases any assigned terrestrial resources.
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
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3.1.9.2 Release due to BSS generated reason
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If a radio channel release is required because of a BSS generated reason (e.g. "O and M intervention", "equipment failure") then, the BSS shall generate a CLEAR REQUEST message towards the MSC. This message shall include a Cause Information Element, indicating the reason for the failure. If transmission from the MS is lost then a CLEAR REQUEST message shall be sent to the MSC. On receipt of a CLEAR REQUEST the MSC shall initiate the release, as defined above, by sending a CLEAR COMMAND message. On receipt of this message the BSS shall, if the resources are not already internally released, release the resources in the normal way. The procedure is always terminated with a CLEAR COMPLETE to the MSC. In the case of a group call talker the BSS may handover the mobile on to a group call channel, in this case the BSS shall initiate a release of A interface resources by sending a CLEAR REQUEST with the cause "Joined group call channel". The MSC in its turn shall release the dedicated resources associated with the talker.
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
|
3.1.9.3 Release due to successful handover
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If a radio channel release is required because of a handover being successfully completed on another BSS, then the resources at the old BSS are released by the MSC using the clearing sequence with a Cause value; "handover successful". In the case of handover of a group call talker from a group call channel the MSC shall send a HANDOVER SUCCEEDED message to the old BSS.
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bf8e452635c0e3fa50938ae3618b9b7d
|
100 590
|
3.1.10 Paging
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PAGING messages for all MSs shall be sent via the BSSMAP as a connectionless message. These will include the IMSI of the MS to allow derivation of the paging population number; they may also include an indication of which combination of channels will be needed for the subsequent transaction related to the paging. This type of PAGING message will then be stored and a corresponding radio interface paging message transmitted over the radio interface at the appropriate time. It should be noted that each PAGING message on the MSC-BSS interface relates to only one MS and therefore the BSS has to pack the pages into the relevant GSM 04.08 radio interface paging message. If a radio interface PAGING RESPONSE message is received then the relevant connection is set up towards the MSC as described in GSM 08.06 and the radio interface PAGING RESPONSE message is passed to the MSC in a COMPLETE LAYER 3 INFORMATION message. A single PAGING message across the MSC to BSS interface contains information on the cells in which the page shall be broadcast.
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
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3.1.11 Trace Invocation
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The purpose of the trace invocation procedure is to inform the receiving entity that it should begin producing a trace record on this particular transaction. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 32 (GSM 08.08 version 6.5.0 Release 1997) The trace is invoked either by the MSC sending a MSC INVOKE TRACE message to the BSS or by the BSS sending a BSS INVOKE TRACE message. The events and parameters to be recorded are indicated in the "Trace type" information element. A "Forwarding indicator" element may be used in the BSS INVOKE TRACE to indicate if the trace is to be continued after handover to another BSS. If thus indicated, The MSC should forward the BSS INVOKE TRACE to the BSS-B and also store it to send to any subsequent BSS during the lifetime of the call. The remaining elements, when received, are to be passed transparently to the OMC receiving the trace record. The element "OMCId", if present, indicates the OMC to which the record is destined. In sending the BSS INVOKE TRACE message, the BSS may allocate and include a "BSS transaction reference". Similarly in the MSC INVOKE TRACE message, the MSC may allocate and include an "MSC transaction reference" (typically a call reference). The transaction reference is contained in the information element "TransactionId". The message includes a trace reference which is allocated by the entity which triggered the trace. The element "TriggerId", if present, indicates the entity which triggered the trace. The trace reference, triggerId and transactionId Information Elements are used to tag the trace record to allow simpler construction of the total record by the entity which combines trace records. The messages are not acknowledged and are sent as a connection oriented message on the connection on which a trace is required.
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
|
3.1.12 Flow Control
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These procedures are defined to give some degree of flow control. At the BSS processor overload and CCCH scheduler overload are catered for, and at the MSC processor overload is catered for.
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bf8e452635c0e3fa50938ae3618b9b7d
|
100 590
|
3.1.12.1 Philosophy
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The philosophy used is to stem the traffic at source with known effect on the service. The algorithm used is: - On receipt of the first OVERLOAD message or signalling point congested information, the traffic is reduced by one step. At the same time, timers T5(T17) and T6(T18) are started. During T5(T17) all received overload messages or signalling point congested information are ignored in order not to reduce the traffic too rapidly. Reception of an OVERLOAD message or signalling point congested information after expiry of T5(T17) but still during T6(T18) , will decrease the traffic load by one more step, and restart T5(T17) and T6(T18). - This step by step reduction of traffic is continued until maximum reduction is obtained by arriving at the last step. If T6(T18) expires (i.e. no OVERLOAD message or signalling point congested information is received during T6(T18)) the traffic will be increased by one step and T6(T18) will be started, unless full load has been resumed. NOTE: Timers T5 and T6 are running in the MSC whilst Timers T17 and T18 are running in the BSS. - The number of steps and the method of reducing the load is considered to be an implementation specific function. There may be other traffic control mechanisms from O and M activities occurring simultaneously.
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
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3.1.12.2 Processor Overload at the MSC
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The MSC can indicate to the BSS that it is in a congested state by sending an OVERLOAD message. This is sent as a connectionless global message. At the BSS receipt of this message causes the reduction of random access traffic using the method described in subclause 3.1.12.1. For example, the amount of random access traffic could be reduced by using the access control class in the system information message of GSM 04.08. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 33 (GSM 08.08 version 6.5.0 Release 1997)
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bf8e452635c0e3fa50938ae3618b9b7d
|
100 590
|
3.1.12.3 Processor/CCCH overload at the BSS
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If the CCCH scheduler at the BSS is overloaded (queue passed a predefined threshold) then the BSS sends an OVERLOAD message to the MSC with the appropriate cause (Cause value: "CCCH overload") and indicating the cell in question. If the BSS processing is overloaded then the BSS sends an OVERLOAD message with the Cause value: "processor overload". The MSC originated traffic is reduced in accordance with the method described in subclause 3.1.12.1.
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bf8e452635c0e3fa50938ae3618b9b7d
|
100 590
|
3.1.12.4 Message throughput congestion
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If the lower layers of the protocol become congested then it is assumed that the MTP congestion indication will take place (see GSM 08.06) and the source of the traffic will receive primitives from the transport protocols resulting in it reducing the generated load. A suitable method to achieve this reduction could be based on that given in subclause 3.1.12.1.
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
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3.1.13 Classmark Handling Procedures
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bf8e452635c0e3fa50938ae3618b9b7d
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100 590
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3.1.13.1 Classmark request procedure
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The purpose of this procedure is to allow the MSC to trigger a classmark updating procedure. This is done by sending a CLASSMARK REQUEST message to the BSS on the appropriate SCCP connection. When receiving this message the BSS shall initiate the appropriate actions on the radio path.
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bf8e452635c0e3fa50938ae3618b9b7d
|
100 590
|
3.1.13.2 Classmark updating procedure
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The purpose of the classmark updating procedure is to inform the receiving entity about classmark information received from the MS. At any point when an SCCP connection has been established for BSSAP messages, the BSS must be able to send to the MSC a CLASSMARK UPDATE message if a classmark update is received from the MS. This message contains information on several transmission parameters relevant to the MS in communication with the network. If the MSC has already initiated a handover for the concerned MS by sending a HANDOVER REQUEST message when the CLASSMARK UPDATE message is received, the MSC shall send a CLASSMARK UPDATE message to the target BSS when the MS is successfully in communication with the network on the new (main) channel. If this CLASSMARK UPDATE message is received in the target BSS after a new classmark has been received from the Mobile Station the CLASSMARK UPDATE message from the MSC shall be ignored. This message is sent as a BSSAP message over the appropriate SCCP connection This procedure will be used where the power class of the MS changes or if the network requests the MS to send the classmark information whilst the MS has one or more dedicated resources. The procedure will also be used to send classmark information to the MSC if the MS immediately after initial L3 message sends additional classmark information. In this case the BSS may as an option suppress or delay the sending of the CLASSMARK UPDATE message to the MSC.
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bf8e452635c0e3fa50938ae3618b9b7d
|
100 590
|
3.1.14 Cipher Mode Control
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bf8e452635c0e3fa50938ae3618b9b7d
|
100 590
|
3.1.14.1 Successful Operation
|
The cipher mode control procedure allows the MSC to pass cipher mode information to the BSS to select and load the user data and signalling encryption device with the appropriate key. ETSI ETSI TS 100 590 V6.5.0 (2000-06) 34 (GSM 08.08 version 6.5.0 Release 1997) This is achieved by sending the BSS a CIPHER MODE COMMAND message. Receipt of the message at the BSS will cause the generation of a radio interface CIPHERING MODE COMMAND message and, if applicable, invoke the encryption device and start stream ciphering as described in GSM 04.08 and GSM 03.20. If within the CIPHER MODE COMMAND, the signalling element "Cipher response mode" is present and indicates "IMEI must be included by the Mobile Station", then the BSS shall request in the radio interface message CIPHERING MODE COMMAND the Mobile Station to include its IMEI in the radio interface CIPHERING MODE COMPLETE message (see GSM 04.08, subclause ‘Ciphering mode setting initiation’). In the CIPHER MODE COMMAND the MSC specifies which of the ciphering algorithms may be used by the BSS. The BSS then selects an appropriate algorithm, taking into account the MS ciphering capabilities. The CIPHER MODE COMPLETE message returned to the MSC indicates the chosen ciphering algorithm. The set of permitted ciphering algorithms specified in the CIPHER MODE COMMAND shall remain applicable for subsequent Assignments and Intra- BSS Handovers. The CIPHER MODE COMMAND and CIPHER MODE COMPLETE messages are sent as connection oriented messages via the appropriate SCCP connection. Receipt of the radio interface CIPHERING MODE COMPLETE message (or other correctly deciphered layer 2 frame) from the radio interface is used internally within the BSS to achieve radio interface ciphering synchronisation (see GSM 04.08). When the BSS receives the radio interface CIPHERING MODE COMPLETE from the MS a CIPHER MODE COMPLETE message is returned to the MSC. If the CIPHERING MODE COMPLETE message received on the radio interface contained more than two octets, then the BSS shall include in the BSSMAP CIPHER MODE COMPLETE message a "Layer 3 message contents" signalling element containing octets 3 up to n (where n is the length of that CIPHERING MODE COMPLETE radio interface message) of that radio interface CIPHERING MODE COMPLETE message.
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bf8e452635c0e3fa50938ae3618b9b7d
|
100 590
|
3.1.14.2 Abnormal Conditions
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If the BSS is unable to support the ciphering algorithm specified in the CIPHER MODE COMMAND message then it shall return a CIPHER MODE REJECT message with Cause value "Ciphering algorithm not supported". A CIPHER MODE REJECT message shall also be returned if the MSC requests a change of ciphering algorithm when ciphering is already active.
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