01-11 Mobile Originating Call Establishment

11 Mobile Originating Call Establishment

About This Chapter

Mobile originating call refers to an MS calling another MS or a fixed phone.

11.1 Mobile Originating Call Establishment ProcedureIn terms of the assignment type, the mobile originating call establishment procedure iscategorized into the early assignment procedure, late assignment procedure, and very earlyassignment procedure. The MSC determines the early assignment procedure and the lateassignment procedure. The BSS determines the very early assignment procedure based on theradio resources.

11.2 Internal BSC Signaling Procedure of Mobile Originating Call EstablishmentThis describes the internal BSC signaling procedure of mobile originating call establishment.

11.3 Abnormal Mobile Originating Call Establishment CasesThis topic describes the abnormal mobile originating call establishment cases.

HUAWEI BSC6000 Base Station SubsystemBSS Signaling Analysis Guide 11 Mobile Originating Call Establishment

Issue 01 (2007-11-26) Huawei Technologies Proprietary 11-1

11.1 Mobile Originating Call Establishment ProcedureIn terms of the assignment type, the mobile originating call establishment procedure iscategorized into the early assignment procedure, late assignment procedure, and very earlyassignment procedure. The MSC determines the early assignment procedure and the lateassignment procedure. The BSS determines the very early assignment procedure based on theradio resources.

11.1.1 Early Assignment ProcedureThis topic describes the early assignment procedure, namely the mobile originating callestablishment without OACSU procedure.

11.1.2 Late Assignment ProcedureThis topic describes the late assignment procedure, namely the mobile originating callestablishment with OACSU procedure.

11.1.3 Very Early Assignment ProcedureThis topic describes the very early assignment procedure, namely the Mobile Originating CallEstablishment with OACSU procedure.

11.1.1 Early Assignment ProcedureThis topic describes the early assignment procedure, namely the mobile originating callestablishment without OACSU procedure.

Figure 11-1 shows the early assignment procedure.

11 Mobile Originating Call EstablishmentHUAWEI BSC6000 Base Station Subsystem

BSS Signaling Analysis Guide

11-2 Huawei Technologies Proprietary Issue 01 (2007-11-26)

Figure 11-1 Early assignment procedure

MS BTS MSC

Setup(5)

BSC

FACCH

SDCCH

Immediate Assignment Procedure

Establish Indication(CM Service Request)(1)

CC(3)

CR(L3:CMService Request)(2)

CM Service Accepted(4)

Call Proceeding(6)SDCCH

TCH Assignment Procedure

FACCH

Alerting(7)

FACCH

Connect(8)

Connect Acknowledge(9)SDCCH

Talking(10)

Release Procedure

The early assignment procedure is as follows:

1. The BTS sends the BSC an Establishment Indication message. The EstablishmentIndication message accurately indicates the reason for the access of an MS, for example,the cause values for mobile originating call establishment and for IMSI detach are different.The message also carries the content of the CM Service Request message.

2. The BSC establishes an SCCP link connection on the A interface and sends the MSC a CMService Request message.

3. The MSC sends the BSC a Connect Confirm message.4. The MSC sends the MS a CM Service Accepted message on the SDCCH on the Um

interface.



5. The calling MS sends a Setup message on the SDCCH. The Setup message carries all theinformation required on the network side for processing the call, including the number ofthe called MS.

6. The MSC sends the calling MS a Call Proceeding message on the SDCCH on the Uminterface. The Call Proceeding message indicates that a call is being processed and themobile originating call processing procedure is initiated.

7. The MSC sends the MS an Alerting message on the FACCH on the Um interface. Thenthe calling MS hears a ringing tone.

8. The MSC sends the calling MS a Connect message on the FACCH on the Um interface.The Connect message is used to notify the MS that the connection is established.

9. The calling MS responds to the MSC with a Connect Acknowledge message on theFACCH.

10. The calling and the called MSs enter the session state.

11.1.2 Late Assignment ProcedureThis topic describes the late assignment procedure, namely the mobile originating callestablishment with OACSU procedure.

Figure 11-2 shows the late assignment procedure.




Figure 11-2 Late assignment procedure

MS BTS MSC

Setup(5)

BSC

SDCCH

SDCCH

Immediate Assignment Procedure


CC(3)



Call Proceeding(6)SDCCH

TCH Assignment Procedure

SDCCHAlerting(7)

FACCH

Connect(8)

Connect Acknowledge(9)SDCCH

Talking(10)

Release Procedure

For details about the late assignment procedure, refer to 11.1.1 Early Assignment Procedure.

1. The difference between the late assignment procedure and the early assignment procedureis that the assignment procedure of the former takes place after the Alerting message issent.

2. The late assignment saves the seizure time of speech channels.3. The disadvantage of the procedure shown in Figure 11-2 is that if the subsequent

assignment is unsuccessful, the called MS can only hear the ring tone but cannot makecalls.Therefore, in actual application, the early assignment procedure is used instead of the lateassignment procedure.



11.1.3 Very Early Assignment ProcedureThis topic describes the very early assignment procedure, namely the Mobile Originating CallEstablishment with OACSU procedure.

Figure 11-3 shows the very early assignment procedure.

Figure 11-3 Very early assignment procedure

MS BTS MSC

Setup(5)

BSC

FACCH

FACCH

Immediate Assignment TCH Procedure


CC(3)



Call Proceeding(6)FACCH

TCH Mode Modify

FACCHAlerting(7)

FACCH

Connect(8)

Connect Acknowledge(9)FACCH

Talking(10)

Release Procedure

For details about the very early assignment procedure, refer to 11.1.1 Early AssignmentProcedure.

1. The difference between the very early assignment procedure and the 11.1.1 EarlyAssignment Procedure is that in the former, the TCH is assigned as a signaling channelduring the immediate assignment procedure. Therefore, no TCH needs to be assignedduring the assignment procedure, and the assigned TCH is adjusted to a speech channelthrough the Mode Modify message.




2. During the immediate assignment procedure, if no idle SDCCHs but TCHs are availableand TCH immediate assignment is allowed in the BSC data configuration, the very earlyassignment procedure will take place.

11.2 Internal BSC Signaling Procedure of MobileOriginating Call Establishment

This describes the internal BSC signaling procedure of mobile originating call establishment.

The internal BSC signaling procedure of mobile originating call establishment is as follows:

1. On receiving the Channel Required message from the BTS, the BSC assigns a signalingchannel according to the channel type and channel assignment algorithm in the ChannelRequired message. The TCH Immediate Assignment Allowed in the Cell Attributeswindow may be involved in the channel assignment.

2. During random access, on receiving the Establish Indication message from the BTS, theBSC sends the MSC a CM Service Request message that carries the target CGI based onthe MCC, MNC, LAC, and CI.

3. On receiving the Assignment Request message from the MSC, the BSC checks the channeltype. Choose Other Attributes > Advanced > Other Parameters. Check whether DataService Allowed is supported.

4. If the data service is not supported, an Assignment Failure message is returned. Based onthe CIC in the Assignment Request message, the BSC checks the E1 timeslots on the Ainterface and confirms the existence of CIC. It also checks whether the circuit pool of theconfigured CIC, the channel type in the Assignment Request message, and the capacity ofthe GDPUC are collided. If they are collided, the BSC responds with an Assignment Failuremessage.

5. On receiving the Assignment Complete message from the MS, the BSC fills the messagewith the A Interface Tag and sends the message to the MSC. You can choose BSCProperty > Basic Data to display the A Interface Tag.

11.3 Abnormal Mobile Originating Call EstablishmentCases

This topic describes the abnormal mobile originating call establishment cases.

11.3.1 Calling MS Cannot Be HeardThis topic describes the fault, probable causes, and handling suggestions.

11.3.2 MSC Releasing the Call after Sending a CM Service Reject MessageThis topic describes the fault, probable causes, and handling suggestions.

11.3.3 Abnormal Procedure Caused by MS in Busy StateThis topic describes the fault, probable causes, and handling suggestions.

11.3.4 MSC Sending a Disconnect Message Instead of an Assignment Request MessageThis topic describes the fault, probable causes, and handling suggestions.

11.3.5 Abnormal Procedures Caused by MS HangupThis topic describes the fault, probable causes, and handling suggestions.



11.3.6 Abnormal Procedures Caused by MSC Sending a Clear Command Message or aDisconnect MessageThis topic describes the fault, probable causes, and handling suggestions.

11.3.7 LAPD Reporting an Error Indication Message During Call EstablishmentThis topic describes the fault, probable causes, and handling suggestions.

11.3.1 Calling MS Cannot Be HeardThis topic describes the fault, probable causes, and handling suggestions.

FaultWhen late assignment is enabled, the called MS cannot hear the calling MS.

Probable CausesTCH assignment fails.

Handling SuggestionsDisable the late assignment.

11.3.2 MSC Releasing the Call after Sending a CM Service RejectMessage

This topic describes the fault, probable causes, and handling suggestions.

FaultAfter sending a CM Service Reject message, the MSC sends a Clear Command message torelease the call.

Probable CausesThe probable causes are as follows:

l The MSC cannot find the subscriber information and considers that the subscriber is illegal.

l Authentication or encryption fails.

l The MSC does not support the applied service in the CM Service Request message.

l The MSC has no sufficient resources for the access, for example, no idle CICs.

Handling SuggestionsThe handling suggestions are as follows:

l The MS makes a subscription under the MSC.

l Check the subscriber information.

l Hand over the MS to a cell under another MSC.

l Wait for the MSC to release the resources, or expand the MSC transmission capability onthe A interface.




11.3.3 Abnormal Procedure Caused by MS in Busy StateThis topic describes the fault, probable causes, and handling suggestions.

FaultAfter the assignment success of the calling MS, the network sends a Disconnect message withthe cause value User Busy. The onhook by the calling MS or a Clear Command message sentby the MSC triggers the release of the BSC resources.

Probable CausesThe MS is busy.

Handling SuggestionsWait for the onhook of the called MS and make a second call.

11.3.4 MSC Sending a Disconnect Message Instead of anAssignment Request Message


FaultThe MSC does not send an Assignment Request message. It sends a Disconnect message to clearthe call.

Probable CausesThe A interface may be faulty.

Handling SuggestionsCheck the following:

l The state of the A interface circuit on the MSC side

l The consistency of the A interface data on the MSC and the BSC, especially the circuitpool data

11.3.5 Abnormal Procedures Caused by MS HangupThis topic describes the fault, probable causes, and handling suggestions.

FaultThe call establishment procedure is terminated.

Probable Causesl The MS hangs up.

l The calling or the called MS hangs up during a procedure, which causes abnormality in thesubsequent procedures. For example, after the BSC receives an Assignment Request



message from the MSC, the MS suddenly hangs up. In that case, the call establishmentprocedure may be terminated before the BSC responds to the MSC with an AssignmentComplete message or an Assignment Failure message. As a result, the procedure is neithera successful assignment procedure (The BSC sends an Assignment Complete message.)nor an unsuccessful assignment procedure (The BSC sends an Assignment Failuremessage.).

Handling Suggestions

No handling is required.

11.3.6 Abnormal Procedures Caused by MSC Sending a ClearCommand Message or a Disconnect Message


Fault

The MSC sends a Clear Command message or a Disconnect message.

Probable Causes

Check the following:

l The cause value in the Clear Command messageIf a call terminates normally, the cause value in the Clear Command message is CallControl. Otherwise, the cause value may be Protocol Error or Equipment Failure.

l The time difference between the previous message and the Clear Command message or theDisconnect messageCheck whether the abnormal procedure is triggered by timeout.

Handling Suggestionsl If the cause value in the Clear Command message is Call Control, no abnormality exists.

If the cause value in the Clear Command message is Protocol Error, refer to the relatedprotocols. If the cause value in the Clear Command message is Equipment Failure, checkthe related BSC hardware:– Connection on the Ater interface

– GEIUA in the GTCS

l Check the timeout values of the related timers.

11.3.7 LAPD Reporting an Error Indication Message During CallEstablishment


Fault

The LAPD reports an Error Indication message during call establishment.




Probable CausesThe probable causes are as follows:

l Inconformity with protocols

l LAPD link failure

l Timer T200 expiry

l MS failure in receiving a UA frame

Handling SuggestionsThe handling suggestions are as follows:

l Check the contents of the frames at the data link layer.

l Check the status of the data link layer.

l Check the timeout value of timer T200.

l Check contents of the SABM frame.



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01-11 Mobile Originating Call Establishment