Bssmap Assignment Failure To Launch

Thread: Assignment procedure in GSM call flow

  1. 04-15-2012, 02:26 PM#1


    Assignment procedure in GSM call flow

    Telecom Source

    The assignment procedure is used to assign the MS to the correct TCH. The selection of the TCH is based on the information received from the MSC.
    The assignment procedure is presented in the following figure:



    ASSIGNMENT REQUEST message

    The MSC sends an ASSIGNMENT REQUEST (a) message to the BSC for the assignment of channels on the A interface and the radio interface. The MSC also runs a supervisory timer for the assignment procedure.
    The BSS responds by sending the MSC the ASSIGNMENT COMPLETE, ASSIGNMENT FAILURE or the QUEUEING INDICATION message. If the MSC fails to receive any of the messages within the time limit defined by the timer, it clears the call with a CLEAR COMMAND message. The BSS releases the MS connection with the channel release procedure.

    The BSC expects to receive the following fields in the ASSIGNMENT REQUEST message:

    • channel type: radio channel required for the call type
    • L3 header info
    • priority (optional)
    • circuit identification code (CIC) indicating the channel to be used on the A interface
    • downlink DTX flag (optional)
    • radio channel identity (optional)
    • interference band to be used (optional).

    The MSC uses the priority element to define whether the request is allowed to be queued and, if so, to define the queueing priority level. If the priority element is not present, it is assumed that the request can be queued if it cannot be served immediately. Furthermore, if the priority is not indicated, the message is queued according to the priority associated with the request type, which is defined internally within the BSS. If the request is queued, a QUEUEING INDICATION message is returned to the MSC.
    The downlink DTX flag element is also optional: it is present only when the MSC controls the downlink DTX in a speech call.

    If the BSC identifies any of the following situations on analysing the ASSIGNMENT REQUEST message, it rejects the request by sending the ASSIGNMENT FAILURE message to the MSC, without taking any action towards the BTS:


    1. If the BSC is not able to use the A channel indicated in the CIC, due to it being used for another call, the BSC rejects the request with the cause requested terrestrial circuit already allocated.
    2. If the BSC is not able to use the A channel indicated in the CIC, due to it being marked as undefined, the BSC rejects the request with the cause requested terrestrial resource unavailable.
    3. If the CIC is blocked, the BSC rejects the request with the cause requested terrestrial resource unavailable and sends a BLOCK message to the MSC. For reasons when a circuit is blocked by the BSC, see 3GPP 48.008.
    4. If there is no circuit pool on the A interface that is able to support the requested TCH type, the BSC rejects the request with the cause requested transcoding/rate adaption not available.
    5. If there is a circuit pool on the A interface that is able to support the requested TCH type, but the pool implied by the CIC is totally contradictory with the required TCH type, the BSC rejects the request with the cause circuit pool mismatch.
    6. If the circuit pool implied by the CIC is at least partially compliant with the requested TCH type, change of the circuit pool may be required. Reasons for the change include the actual TCH resource situation of the cell and the attempt to allocate the resources in the most optimal way. In this case the BSC rejects the request with the cause switch circuit pool.
    7. If the requested speech coder versions are not supported, the BSC rejects the request with the cause requested speech version unavailable.
    8. If the radio interface data rate requirement is totally contradictory with the requested TCH rate, the BSC rejects the request with the cause invalid message contents.

    On receiving the ASSIGNMENT FAILURE message, the MSC can either issue a CLEAR COMMAND or retry.
    If the MSC receives the ASSIGNMENT FAILURE message with a cause indicating a CIC problem, the MSC may send another ASSIGNMENT REQUEST for the same call using a different circuit.

    TCH assignment procedure in the BSS

    After the ASSIGNMENT REQUEST, the BSC proceeds to perform the TCH assignment procedure.
    The BSC sends the PHYSICAL CONTEXT REQUEST message (b) to the BTS. In this message it requests for the timing advance of mobile transmission. The SDCCH sends the timing advance via the TCH and the BTS to the MS, which requires it when moving onto a new radio channel.

    If the BSC fails to receive the PHYSICAL CONTEXT CONFIRM message (c) within the time limit defined by the GSM timer T9108, the BSC returns an ASSIGNMENT FAILURE message to the MSC with the cause radio interface message failure. This applies also when the PHYSICAL CONTEXT CONFIRM message does not contain all the expected information. The MSC either aborts with a CLEAR COMMAND or retries.

    On receiving the PHYSICAL CONTEXT CONFIRM message, the BSC searches for the relevant TCH using the channel reservation procedure described in Channel reservation procedure.

    If the request cannot be acted upon, the BSC returns an ASSIGNMENT FAILURE message with the cause no radio resource available. The reason for this is that all radio channels are reserved, the queue is full, the request has been in the queue for too long, or exceptional conditions such as restart or reset.

    TCH activation

    After a successful channel reservation, the BSC sends a CHANNEL ACTIVATION message to the BTS. In this message it tells the BTS to activate the required radio channel. The BSC also starts the GSM timer T9103.
    The CHANNEL ACTIVATION message contains the following data:

    • message type
    • channel number: Lm/Bm + AGCH
    • activation type: normal assignment
    • channel mode: DTX indication and channel type. The channel type is either a speech or data channel. If it is a speech channel, the speech encoding algorithm is included; if it is a data channel, the transparent or the non-transparent mode is included. The data rate is also given.
    • channel identification (optional)
    • encryption information if received from the MSC (optional)
    • BS power as received in the PHYSICAL CONTEXT CONFIRM (optional)
    • MS power as received in the PHYSICAL CONTEXT CONFIRM (optional)
    • timing advance as received in the PHYSICAL CONTEXT CONFIRM (optional)
    • SACCH information (optional)
    • multirate configuration (optional).


    The channel identification information is included only when activating a TCH under DFCA TRX. For more information, see Dynamic Frequency and Channel Allocation.The SACCH information is used in a dual band cell or when IMSI Based Handover is enabled in the BSC.
    The multirate configuration element is present in calls using multirate speech codec.



    The BTS returns the CHANNEL ACTIVATION NACK message in the following situations. The BSC indicates the failure to the MSC by sending the ASSIGNMENT FAILURE message with the relevant assignment failure cause value, which can be one of the following:

    • radio interface message failure, due to a message format error
    • requested transcoding/rate adaption not available, due to the requested service not being supported
    • radio resource not available, due to radio channel problems
    • radio channel already activated; the radio channel is already in use
    • equipment failure
    • service or option not available
    • not implemented unspecified
    • mandatory IE error
    • general IE error.


    If no response is received from the BTS within the time limit defined by the GSM timer T9103, the BSC sends the MSC an ASSIGNMENT FAILURE message with the cause equipment failure. The MSC either aborts or retries.

    When the BTS has successfully activated the radio traffic channel, it returns the CHANNEL ACTIVATION ACKNOWLEDGE message (containing the current frame number) to the BSC.

    TCH radio channel assignment in the BSS

    The BSC sends the ASSIGNMENT COMMAND message (f, g) to the MS and starts the GSM timer T3107. This command is transparent to the BTS and is transferred as the DATA REQUEST message over the Abis interface.
    The ASSIGNMENT COMMAND gives the MS all the information necessary for it to change over to the TCH. The message consists of:

    • header
    • channel description
    • power command: max. MS power
    • frequency list (optional)
    • cell channel description (optional)
    • channel mode: speech full rate, half rate or data (optional)
    • mobile allocation (optional)
    • cipher mode setting (optional)
    • multirate configuration (optional).


    The cipher mode setting element is present if ciphering is to be applied and ciphering algorithm is changed during TCH assignment.

    On receiving the ASSIGNMENT COMMAND over the radio interface, the MS changes over from the SDCCH to the TCH it has been assigned to. The MS sends a layer 2 SABM (h) on the TCH. The BTS acknowledges the SABM with a UA frame (j) and sends the ESTABLISH INDICATION (i) message to the BSC. Synchronisation with the transcoder starts at this point and the BSC connects the Abis channel to the A channel and the speech path is switched through.

    On receiving the UA frame (j), the MS indicates to the BSC with an ASSIGNMENT COMPLETE message (k) that it has successfully changed over to the TCH. This message is transparent to the BTS and is transferred over the Abis interface as a DATA INDICATION message (l). The BSC sends the information to the MSC in the DT1 (ASSIGNMENT COMPLETE) message (m) with the RR cause normal release.
    After a successful assignment procedure, the BSC releases the SDCCH channel.

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  3. 04-18-2012, 02:47 AM#2

    Level 1 Users
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    gooooooooooooooooooooooooood


  4. 05-17-2012, 12:30 PM#3


  5. 12-11-2012, 09:49 PM#4

    Junior Member
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    its very useful easy to understand and details information .................like it.....


  6. Post Thanks / Like - 0 Thanks, 1 Likes, 0 Dislikes

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GSM A interface - BSS Application Part

The A interface is located between the MSC (mobile service switching centre) and the BSS (base station system or radio sub-system).

Standard reference: GSM 08-08 § 2, MSC to BSS - Layer 3

The A interface supports several Applications Parts:

BSSMAP messages

Standard reference: GSM 08-08 § 3, MSC to BSS - Layer 3

BSSMAP messages (Base Station System Management Application Part), for a GSM A interface located between the MSC (mobile service switching centre) and the BSS (base station system or radio sub-system) are listed and ordered according to their hexadecimal code or their type (abreviation).

Message list: hex codes 
CodeAbreviationBSSMAP: message designation
01ASS-REQAssignment request.
02ASS-COMAssignment complete.
03ASS-FAILAssignment failure.
20CLEAR-COMClear command.
21CLEAR-COMPClear complete.
22CLEAR-REQClear request.
23SAPI-CL-COMSAPI "n" clear request.
24SAPI-CL-COMPSAPI "n" clear complete.
25SAPI-REJSAPI "n" rejected.
30RESETReset.
31RESET-ACKReset acknowledge.
32OVERLOADOverload.
33TRACE-INVTrace investigation.
34RESET-CIRReset circuit.
35RST-CI-ACKReset circuit acknowledge.
40BLOCKResource blocked.
41BLOCK-ACKAcknowledgement resource blocked.
42UNBLOCKResource un-blocked.
43UNBLOCK-ACKAcknowledgement resource un-blocked.
50RESOURC-REQResource request.
51RESOURC-INDResource indication.
52PAGINGPaging.
53CYPHER-COMCypher mode command.
54CLASS-UPD"Classmark" update.
55CYPHER-COMPCypher mode complete.
56QUEUEING-INQueuing-in.
57LAYER-3-INFLayer 3 information.
80HAND-REQHandover request.
81HAND-RQDHandover requested.
82HND-RQ-ACKHandover request acknowledge.
83HAND-COMHandover command.
84HAND-COMPHandover complete.
86HAND-FAILHandover failure.
87HAND-PERFORMHandover performed.
88HND-CAND-ENQHandover candidate enquiry.
89HND-CAND-REQHandover candidate request.
8AHAND-REQ-REJHandover request rejection.
8BHAND-DETECTHandover detection.
Message list: types
AbreviationCodeBSSMAP: message designation
ASS-COM02Assignment complete.
ASS-FAIL03Assignment failure.
ASS-REQ01Assignment request.
BLOCK40Resource blocked.
BLOCK-ACK41Acknowledgement resource blocked.
CLASS-UPD54"Classmark" update.
CLEAR-COM20Clear command.
CLEAR-COMP21Clear complete.
CLEAR-REQ22Clear request.
CYPHER-COM53Cypher mode command.
CYPHER-COMP55Cypher mode complete.
HAND-COM83Handover command.
HAND-COMP84Handover complete.
HAND-DETECT8BHandover detection.
HAND-FAIL86Handover failure.
HAND-PERFORM87Handover performed.
HAND-REQ80Handover request.
HAND-REQ-REJ8AHandover request rejection.
HAND-RQD81Handover requested.
HND-CAND-ENQ88Handover candidate enquiry.
HND-CAND-REQ89Handover candidate request.
HND-RQ-ACK82Handover request acknowledge.
LAYER-3-INF57Layer 3 information.
OVERLOAD32Overload.
PAGING52Paging.
QUEUEING-IN56Queuing-in.
RESET30Reset.
RESET-ACK31Reset acknowledge.
RESET-CIR34Reset circuit.
RESOURC-IND51Resource indication.
RESOURC-REQ50Resource request.
RST-CI-ACK35Reset circuit acknowledge.
SAPI-CL-COM23SAPI "n" clear request.
SAPI-CL-COMP24SAPI "n" clear complete.
SAPI-REJ25SAPI "n" rejected.
TRACE-INV33Trace investigation.
UNBLOCK42Resource un-blocked.
UNBLOCK-ACK43Acknowledgement resource un-blocked.

DTAP Call Control messages

Standard reference: GSM 04-08 § 5, §9.3, §10.4, MSC to BSS - Layer 3

DTAP (Direct Transfer Application Part) Call Control messages , for a GSM A interface located between the MSC (mobile service switching centre) and the BSS (base station system or radio sub-system) are listed and ordered according to their hexadecimal code or their type (abreviation).

Message list: hex codes
CodeAbreviationDTAP Call Control message
01 ALERTING Alerting.
02 CALL-PROCEED Call proceeding.
03 PROGRESS Progress.
05 SETUP Setup.
07 CONNECT Connect.
08 CALL-CONFIRM Call confirmed.
0D EMERG-SETUP Emergency setup.
0F CONNECT-ACK Connect acknowledged.
10 USER-INFO User information.
13 MODIFY-REJ” Modify reject.
17 MODIFY Modify
1F MODIFY-COMP Modify complete.
25 DISCONNECT Disconnect.
2A RELEASE-COMP Release complete.
2D RELEASE Release.
31 STOP-DTMF Stop DTMF.
32 STOP-DTMF-ACK Stop DTMF acknowledge.
34 STATUS-ENQ Status enquiry.
35 START-DTMF Start DTMF.
36 START-DTMF-AC Start DTMF acknowledge.
37 START-DTMF-RE Start DTMF reject.
39 CONGEST-CTRL Congestion control.
3D STATUS Status.
3E NOTIFY Notify.
Message list: types
AbreviationCodeDTAP Call Control message
ALERTING 01 Alerting.
CALL-CONFIRM 08 Call confirmed.
CALL-PROCEED 02 Call proceeding.
CONGEST-CTRL 39 Congestion control.
CONNECT 07 Connect.
CONNECT-ACK 0F Connect acknowledged.
DISCONNECT 25 Disconnect.
EMERG-SETUP 0D Emergency setup.
MODIFY 17 Modify
MODIFY-COMP 1F Modify complete.
MODIFY-REJ” 13 Modify reject.
NOTIFY 3E Notify.
PROGRESS 03 Progress.
RELEASE 2D Release.
RELEASE-COMP 2A Release complete.
SETUP 05 Setup.
START-DTMF 35 Start DTMF.
START-DTMF-AC 36 Start DTMF acknowledge.
START-DTMF-RE 37 Start DTMF reject.
STATUS 3D Status.
STATUS-ENQ 34 Status enquiry.
STOP-DTMF 31 Stop DTMF.
STOP-DTMF-ACK 32 Stop DTMF acknowledge.
USER-INFO 10 User information.

DTAP Radio Resources Management messages

Standard reference: GSM 04-08 § 3, §9.1, §10.4, MSC to BSS- Layer 3

DTAP (Direct Transfer Application Part) Radio Resources Management messages , for a GSM A interface located between the MSC (mobile service switching centre) and the BSS (base station system or radio sub-system) are listed and ordered according to their hexadecimal code or their type (abreviation).

Message list: hex codes
CodeAbreviationDTAP Radio Resources Management
0APARTIAL-RELPartial release.
0DCHANNEL-RELChannel release.
0FPART-REL-COMPartial release complete.
10CHAN-MODIFYChannel mode modify.
12RR-STATUSRR status.
14FREQ-REDEFFrequency redefinition.
15MEASUR-REPMeasurement report.
16CLASSM-CHGClassmark change.
17CHAN-MOD-ACKChannel mode modify acknowledge.
19SYS-INFO-T1System information type 1.
1ASYS-INFO-T2System information type 2.
1BSYS-INFO-T3System information type 3.
1CSYS-INFO-T4System information type 4.
1DSYS-INFO-T5System information type 5.
1ESYS-INFO-T6System information type 6.
21PAG-REQ-T1Paging request type 1.
22PAG-REQ-T2Paging request type 2.
24PAG-REQ-T3Paging request type 3.
26ASS-COMMANDAssignment command.
27PAGING-REPPaging response.
28HAND-FAILUREHandover failure.
29ASS-COMPLETEAssignment complete.
2BHAND-COMMHandover command.
2CHAND-COMPHandover complete.
2DPHYS-INFOPhysical layer information.
2FASS-FAILUREAssignment failure.
32CIPH-M-COMPCiphering mode complete.
35CIPH-M-COMMCiphering mode command.
39IMM-ASS-EXTImmediate assignment extended.
3AIMM-ASS-REJImmediate assignment reject.
3BADD-ASSAdditional assignment.
3FIMM-ASSImmediate assignment.
Message list: types
AbreviationCodeDTAP Radio Resources Management
ADD-ASS3BAdditional assignment.
ASS-COMMAND26Assignment command.
ASS-COMPLETE29Assignment complete.
ASS-FAILURE2FAssignment failure.
CHAN-MOD-ACK17Channel mode modify acknowledge.
CHAN-MODIFY10Channel mode modify.
CHANNEL-REL0DChannel release.
CIPH-M-COMM35Ciphering mode command.
CIPH-M-COMP32Ciphering mode complete.
CLASSM-CHG16Classmark change.
FREQ-REDEF14Frequency redefinition.
HAND-COMM2BHandover command.
HAND-COMP2CHandover complete.
HAND-FAILURE28Handover failure.
IMM-ASS3FImmediate assignment.
IMM-ASS-EXT39Immediate assignment extended.
IMM-ASS-REJ3AImmediate assignment reject.
MEASUR-REP15Measurement report.
PAG-REQ-T121Paging request type 1.
PAG-REQ-T222Paging request type 2.
PAG-REQ-T324Paging request type 3.
PAGING-REP27Paging response.
PART-REL-COM0FPartial release complete.
PARTIAL-REL0APartial release.
PHYS-INFO2DPhysical layer information.
RR-STATUS12RR status.
SYS-INFO-T119System information type 1.
SYS-INFO-T21ASystem information type 2.
SYS-INFO-T31BSystem information type 3.
SYS-INFO-T41CSystem information type 4.
SYS-INFO-T51DSystem information type 5.
SYS-INFO-T61ESystem information type 6.

DTAP Mobility Management messages

Standard reference: GSM 04-08 § 4, §9.2, §10.4, MSC to BSS - Layer 3

DTAP (Direct Transfer Application Part) Mobility Management messages , for a GSM A interface located between the MSC (mobile service switching centre) and the BSS (base station system or radio sub-system) are listed and ordered according to their hexadecimal code or their type (abreviation).

Message list: hex codes 
CodeAbreviationDTAP Mobility Management message
01IMSI-DET-INDIMSI detach indication.
02LOC-UPD-ACCLocation updating accept.
04LOC-UPD-REJLocation updating reject.
08LOC-UPD-REQLocation updating request.
11AUTHENT-REJAuthentication reject.
12AUTHENT-REQAuthentication request.
14AUTHENT-RESPAuthentication response.
18IDENTITY-REQIdentity request.
19IDENTITY-RESPIdentity response.
1ATMSI-REA-COMMTemporary mobile identity reallocation command.
1BTMSI-REA-COMPTemporary mobile identity reallocation complete.
21CM-SERV-ACCConnection management service accept.
22CM-SERV-REJConnection management service reject.
26CM-SERV-REQConnection management service request.
28CM-REESTABLConnection management re-establishment request.
31MM-STATUSStatus.
Message list: types
AbreviationCodeDTAP Mobility Management message
AUTHENT-REJ11Authentication reject.
AUTHENT-REQ12Authentication request.
AUTHENT-RESP14Authentication response.
CM-REESTABL28Connection management re-establishment request.
CM-SERV-ACC21Connection management service accept.
CM-SERV-REJ22Connection management service reject.
CM-SERV-REQ26Connection management service request.
IDENTITY-REQ18Identity request.
IDENTITY-RESP19Identity response.
IMSI-DET-IND01IMSI detach indication.
LOC-UPD-ACC02Location updating accept.
LOC-UPD-REJ04Location updating reject.
LOC-UPD-REQ08Location updating request.
MM-STATUS31Status.
TMSI-REA-COMM1ATemporary mobile identity reallocation command.
TMSI-REA-COMP1BTemporary mobile identity reallocation complete.

 

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