01-09 inter-rat handover procedure

9 Inter-RAT Handover Procedure

About This Chapter

The inter-RAT handover procedure is performed to hand over a UE from a WCDMA cell to aGSM cell or the other way round. This chapter describes inter-RAT handover in terms of types,protocols, triggering conditions, signaling procedure of a successful inter-RAT handover,signaling tracing on the RNC LMT, and elementary procedures. This chapter also describes theelementary procedures in terms of functions, triggering conditions, procedure, and signaling inabnormal conditions.

9.1 Types of Inter-RAT HandoverBased on the direction of handover, inter-RAT handover is categorized into two types: inter-RAT handover from WCDMA to GSM and inter-RAT handover from GSM to WCDMA.

9.2 Inter-RAT CS Handover from WCDMA to GSMThe procedure of inter-RAT CS handover from WCDMA to GSM is performed to hand overthe CS services of a UE from the WCDMA system to the GSM system.

9.3 Inter-RAT CS Handover from GSM to WCDMAThe procedure of inter-RAT CS handover from GSM to WCDMA is performed to hand overthe CS services of a UE from the GSM system to the WCDMA system.

9.4 Inter-RAT PS Handover from WCDMA to GSMThe procedure of inter-RAT PS handover from WCDMA to GSM is performed to hand over thePS services of a UE from the WCDMA system to the GSM system.

9.5 Inter-RAT PS Handover from GSM to WCDMAThe procedure of inter-RAT PS handover from GSM to WCDMA is performed through cellreselection to WCDMA initiated by the UE.

RANSignaling Analysis Guide 9 Inter-RAT Handover Procedure

Issue 01 (2007-04-20) Huawei Technologies Proprietary 9-1

9.1 Types of Inter-RAT HandoverBased on the direction of handover, inter-RAT handover is categorized into two types: inter-RAT handover from WCDMA to GSM and inter-RAT handover from GSM to WCDMA.

Based on services, the inter-RAT handover from WCDMA to GSM and that from GSM toWCDMA are further categorized into the following types:l Inter-RAT CS handover from WCDMA to GSM

l Inter-RAT PS handover from WCDMA to GSM

l Inter-RAT CS handover from GSM to WCDMA

l Inter-RAT PS handover from GSM to WCDMA

9.2 Inter-RAT CS Handover from WCDMA to GSMThe procedure of inter-RAT CS handover from WCDMA to GSM is performed to hand overthe CS services of a UE from the WCDMA system to the GSM system.

9.2.1 Protocols Related to Inter-RAT CS Handover from WCDMA to GSMThe procedure of inter-RAT CS handover from WCDMA to GSM complies with some 3GPPTS25 protocols.

9.2.2 Triggering Conditions of Inter-RAT CS Handover from WCDMA to GSMThe signal quality of the WCDMA cell where the UE camps on is dissatisfactory or the load ofthe serving cell is heavy.

9.2.3 Signaling Procedure of Successful Inter-RAT CS Handover from WCDMA to GSMThis part describes the signaling procedure of a successful inter-RAT CS handover fromWCDMA to GSM. For the messages related to handover failures, refer to the elementaryprocedures.

9.2.4 Using the RNC LMT to Trace the Procedure of Inter-RAT CS Handover from WCDMAto GSMThe signaling tracing function of the RNC LMT can be used to trace the signaling of an inter-RAT CS handover from WCDMA to GSM.

9.2.5 Elementary Procedures of Inter-RAT CS Handover from WCDMA to GSMThis part describes the elementary procedures of inter-RAT CS handover from WCDMA toGSM in terms of triggering conditions and signaling procedures in normal and abnormalconditions.

9.2.1 Protocols Related to Inter-RAT CS Handover from WCDMAto GSM

The procedure of inter-RAT CS handover from WCDMA to GSM complies with some 3GPPTS25 protocols.

The compliance protocols are as follows:l 3GPP TS25.331 "Radio Resource Control (RRC)"

l 3GPP TS25.413 "UTRAN Iu interface RANAP signalling"

9 Inter-RAT Handover ProcedureRAN

Signaling Analysis Guide

9-2 Huawei Technologies Proprietary Issue 01 (2007-04-20)

l 3GPP TS25.433 "UTRAN Iub interface Node B Application Part (NBAP) signalling"

9.2.2 Triggering Conditions of Inter-RAT CS Handover fromWCDMA to GSM

The signal quality of the WCDMA cell where the UE camps on is dissatisfactory or the load ofthe serving cell is heavy.

In such a condition, if the signal quality of a neighboring GSM cell is satisfactory and its loadis relatively light, the UE will be handed over from the WCDMA cell to the GSM cell.

9.2.3 Signaling Procedure of Successful Inter-RAT CS Handoverfrom WCDMA to GSM

This part describes the signaling procedure of a successful inter-RAT CS handover fromWCDMA to GSM. For the messages related to handover failures, refer to the elementaryprocedures.

Figure 9-1 shows the signaling procedure of a successful inter-RAT CS handover fromWCDMA to GSM.

Figure 9-1 Signaling procedure of a successful inter-RAT CS handover from WCDMA to GSM

Note the following information about the procedure shown in Figure 9-1:l This figure presents only a brief of the signaling between the MSC server and the MSC

(GSM) and that between the MSC (GSM) and the BSC (GSM).l The SRNC sends a HANDOVER FROM UTRAN COMMAND message to the UE. The

message contains the RAB ID, the activation time, the GSM frequency, and the GSMinformation in bit strings.



9.2.4 Using the RNC LMT to Trace the Procedure of Inter-RAT CSHandover from WCDMA to GSM

The signaling tracing function of the RNC LMT can be used to trace the signaling of an inter-RAT CS handover from WCDMA to GSM.

Prerequisitel The RNC LMT works properly.

l You have logged in to the RNC with an account authorized to perform tracing management.

ContextTable 9-1 lists the messages to be traced.

Table 9-1 Messages to be traced

InterfacesandProtocols toBe Traced

Message Name on the LMT Message Name in Protocols

Uu

RRC_HO_FROM_UTRAN_CMD_GSM

HANDOVER FROM UTRANCOMMAND

RRC_HO_FROM_UTRAN_FAIL

HANDOVER FROM UTRANFAILURE

IubNBAP_RL_DEL_REQ RADIO LINK DELETION REQUEST

NBAP_RL_DEL_RSP RADIO LINK DELETION RESPONSE

Iu

RANAP_RELOCATION_REQUIRED RELOCATION REQUIRED

RANAP_RELOCATION_COMMAND RELOCATION COMMAND

RANAP_RELOCATION_PREPARATION_FAILURE

RELOCATION PREPARATIONFAILURE

RANAP_IU_RELEASE_COMMAND IU RELEASE COMMAND

RANAP_IU_RELEASE_COMPLETE IU RELEASE COMPLETE

Procedure

Step 1 Create a Uu tracing task by referring to Creating an RNC Tracing Task.Figure 9-2 shows an example of Uu signaling tracing result.




Figure 9-2 Example of Uu signaling tracing result

Step 2 Create an Iub tracing task by referring to Creating an RNC Tracing Task.Figure 9-3 shows an example of Iub signaling tracing result.

Figure 9-3 Example of Iub signaling tracing result

Step 3 Create an Iu tracing task by referring to Creating an RNC Tracing Task.Figure 9-4 shows an example of Iu signaling tracing result.

Figure 9-4 Example of Iu signaling tracing result

----End

9.2.5 Elementary Procedures of Inter-RAT CS Handover fromWCDMA to GSM

This part describes the elementary procedures of inter-RAT CS handover from WCDMA toGSM in terms of triggering conditions and signaling procedures in normal and abnormalconditions.

9.2.5.1 Relocation Preparation ProcedureThe relocation preparation procedure is performed to prepare resources for relocation of theSRNS.

9.2.5.2 Iu Release ProcedureThe Iu release procedure is performed for the CN to release an Iu connection and all the UMTSTerrestrial Radio Access Network (UTRAN) resources related only to that Iu connection.

9.2.5.3 Radio Link Deletion ProcedureThe radio link deletion procedure is performed to release resources in a NodeB for one or moreestablished radio links towards a UE.

Relocation Preparation ProcedureThe relocation preparation procedure is performed to prepare resources for relocation of theSRNS.

Triggering ConditionsThe relocation preparation procedure can be triggered in either of the following conditions:l During an SRNS relocation, the SRNC sends a RELOCATION REQUIRED message.



l During an inter-RAT CS handover from WCDMA to GSM, the SRNC sends aRELOCATION REQUIRED message.

ProcedureFigure 9-5 shows the relocation preparation procedure.

Figure 9-5 Relocation preparation procedure

The procedure shown in Figure 9-5 is described as follows:

1. The SRNC sends a RELOCATION REQUIRED message to the CN. The message containscertain information such as relocation type, relocation cause, source PLMN, source LAC,source SAC, target PLMN, and target LAC.

2. The CN interacts with the target RNC or the target network system, such as the GSMsystem, to prepare relevant resources.

3. The CN sends a response message to the SRNC.l If the target RNC or the target network system prepares the relevant resources

successfully, the CN sends a RELOCATION COMMAND message when thepreparation is complete. The message contains the L3 information IE, which carries theinformation about the relevant resources allocated by the target RNC or the targetnetwork system.

l If the resources partially or totally fail to be allocated, the CN sends a RELOCATIONPREPARATION FAILURE message.

Iu Release ProcedureThe Iu release procedure is performed for the CN to release an Iu connection and all the UMTSTerrestrial Radio Access Network (UTRAN) resources related only to that Iu connection.

Triggering ConditionsThe Iu release procedure can be triggered in one of the following conditions:




l The transaction between the UE and the CN is complete.

l The UTRAN requests the CN to release the resources on the Iu interface by, for example,sending an IU RELEASE REQUEST message.

l The Serving Radio Network Subsystem (SRNS) is relocated.

l The SRNS relocation is canceled after a relocation resource allocation procedure iscomplete.

ProcedureFigure 9-6 shows the Iu release procedure.

Figure 9-6 Iu release procedure


1. The CN sends an IU RELEASE COMMAND message to the SRNC to initiate the Iu releaseprocedure. The message indicates the cause for the release of the signaling connection.

NOTE

After sending the IU RELEASE COMMAND message, the CN shall not send further RANAPconnection-oriented messages on this particular connection.

2. The SRNC releases the related UTRAN resources and then sends an IU RELEASECOMPLETE message to the CN.

Radio Link Deletion ProcedureThe radio link deletion procedure is performed to release resources in a NodeB for one or moreestablished radio links towards a UE.

Triggering ConditionsThe CRNC sends a RADIO LINK DELETION REQUEST message.

ProcedureFigure 9-7 shows the radio link deletion procedure.



Figure 9-7 Radio link deletion procedure


1. The CRNC sends a RADIO LINK DELETION REQUEST message to the NodeB. Uponreception of the message, the NodeB shall delete the radio links specified by the message.

2. The NodeB sends a response message to the CRNC.l If all the radio links are deleted, the NodeB sends a RADIO LINK DELETION

RESPONSE message.l If any radio link fails to be deleted, the NodeB sends a RADIO LINK DELETION

RESPONSE message. The Criticality Diagnostics field in the message indicates thefailure cause.

9.3 Inter-RAT CS Handover from GSM to WCDMAThe procedure of inter-RAT CS handover from GSM to WCDMA is performed to hand overthe CS services of a UE from the GSM system to the WCDMA system.

9.3.1 Protocols Related to Inter-RAT CS Handover from GSM to WCDMAThe procedure of inter-RAT CS handover from GSM to WCDMA complies with some 3GPPTS25 protocols.

9.3.2 Triggering Conditions of Inter-RAT CS Handover from GSM to WCDMAThe signal quality of the GSM cell where the UE camps on is dissatisfactory or the load of theserving cell is heavy.

9.3.3 Signaling Procedure of Successful Inter-RAT CS Handover from GSM to WCDMAThis part describes the signaling procedure of a successful inter-RAT CS handover from GSMto WCDMA. For the messages related to handover failures, refer to the elementary procedures.

9.3.4 Using the RNC LMT to Trace the Procedure of Inter-RAT CS Handover from GSM toWCDMAThe signaling tracing function of the RNC LMT can be used to trace the signaling of an inter-RAT CS handover from GSM to WCDMA.

9.3.5 Elementary Procedures of Inter-RAT CS Handover from GSM to WCDMAThis part describes the elementary procedures of inter-RAT CS handover from GSM toWCDMA in terms of triggering conditions and signaling procedures in normal and abnormalconditions.




9.3.1 Protocols Related to Inter-RAT CS Handover from GSM toWCDMA

The procedure of inter-RAT CS handover from GSM to WCDMA complies with some 3GPPTS25 protocols.

The compliance protocols are as follows:l 3GPP TS25.331 "Radio Resource Control (RRC)"



9.3.2 Triggering Conditions of Inter-RAT CS Handover from GSMto WCDMA

The signal quality of the GSM cell where the UE camps on is dissatisfactory or the load of theserving cell is heavy.

In such a condition, if the signal quality of a neighboring WCDMA cell is satisfactory and itsload is relatively light, the UE will be handed over from the GSM cell to the WCDMA cell.

9.3.3 Signaling Procedure of Successful Inter-RAT CS Handoverfrom GSM to WCDMA

This part describes the signaling procedure of a successful inter-RAT CS handover from GSMto WCDMA. For the messages related to handover failures, refer to the elementary procedures.

Figure 9-8 shows the signaling procedure of a successful inter-RAT CS handover from GSMto WCDMA.



Figure 9-8 Signaling procedure of a successful inter-RAT CS handover from GSM to WCDMA

Note the following information about the procedure shown in Figure 9-8:

l This figure presents only a brief of the signaling between the MSC server and the MSC(GSM) and that between the MSC (GSM) and the BSC (GSM).

l After receiving a RADIO LINK RESTORE INDICATION message, the RNC sends aRELOCATION DETECT message to the MSC server and informs the MSC server that theUE has been handed over from GSM to WCDMA.

l After the UE is handed over, it sends a HANDOVER TO UTRAN COMPLETE messageto the RNC. If the handover fails, the UE reports the failure to the GSM system.

l After receiving a HANDOVER TO UTRAN COMPLETE message, the RNC sends aRELOCATION COMPLETE message to the MSC server. In addition, the RNC controlsthe UE to perform the UTRAN mobility information, UE capability enquiry, and securitymode control procedures.

l The signaling messages traced may differ from the signaling messages shown in the figurein terms of the sequence.




9.3.4 Using the RNC LMT to Trace the Procedure of Inter-RAT CSHandover from GSM to WCDMA

The signaling tracing function of the RNC LMT can be used to trace the signaling of an inter-RAT CS handover from GSM to WCDMA.



ContextTable 9-2 lists the messages to be traced.




Uu

RRC_HO_UTRAN_CMP HANDOVER TO UTRAN COMPLETE

RRC_UTRAN_MOBIL_INFO UTRAN MOBILITY INFORMATION

RRC_UTRAN_MOBIL_INFO_CONFIRM

UTRAN MOBILITY INFORMATIONCONFIRM

RRC_UTRAN_MOBIL_INFO_FAILURE

UTRAN MOBILITY INFORMATIONFAILURE

RRC_UE_CAP_ENQUIRY UE CAPABILITY ENQUIRY

RRC_UE_CAP_INFO UE CAPABILITY INFORMATION

RRC_UE_CAP_INFO_CONFIRM

UE CAPABILITY INFORMATIONCONFIRM

RRC_SECURITY_MODE_CMD SECURITY MODE COMMAND

RRC_SECURITY_MODE_CMP SECURITY MODE COMPLETE

RRC_SECURITY_MODE_FAIL SECURITY MODE FAILURE

Iub

NBAP_RL_SETUP_REQ RADIO LINK SETUP REQUEST

NBAP_RL_SETUP_RSP RADIO LINK SETUP RESPONSE

RNSAP_RL_SETUP_FAIL RADIO LINK SETUP FAILURE

NBAP_RL_RESTORE_IND RADIO LINK RESTORE INDICATION





Iu

RANAP_RELOCATION_REQ RELOCATION REQUEST

RANAP_RELOCATION_REQ_ACK

RELOCATION REQUESTACKNOWLEDGE

RANAP_RELOCATION_FAILURE RELOCATION FAILURE

RANAP_RELOCATION_DETECT RELOCATION DECTECT

RANAP_RELOCATION_COMPLETE RELOCATION COMPLETE

Procedure










----End

9.3.5 Elementary Procedures of Inter-RAT CS Handover from GSMto WCDMA

This part describes the elementary procedures of inter-RAT CS handover from GSM toWCDMA in terms of triggering conditions and signaling procedures in normal and abnormalconditions.

9.3.5.1 Relocation Resource Allocation ProcedureThe relocation resource allocation procedure is performed to allocate resources from the targetRNS for an SRNS relocation.

9.3.5.2 Radio Link Setup Procedure (Intra-RNC Handover or GSM to WCDMA CS Handover)The radio link setup procedure (intra-RNC handover or GSM to WCDMA CS handover) isperformed to set up a radio link in a NodeB controlled by the SRNC for a UE.

9.3.5.3 Radio Link Restoration Procedure (Intra-RNC Handover or GSM to WCDMA CSHandover)The radio link restoration procedure (intra-RNC handover or GSM to WCDMA CS handover)is performed for a NodeB to notify the CRNC the establishment and re-establishment of uplinksynchronization of one or more radio links.

9.3.5.4 UE Capability Enquiry ProcedureThe UE capability enquiry procedure is performed to request a UE to transmit its capabilityinformation related to any radio access network so that the network can perform dataconfiguration based on the UE capability.

9.3.5.5 Security Mode Control ProcedureThe security mode control procedure is performed to configure or reconfigure one or both of theciphering and integrity protection algorithms for a UE.

9.3.5.6 UTRAN Mobility Information ProcedureThe UTRAN mobility information procedure is performed for the network to allocate a new U-RNTI or Cell Radio Network Temporary Identifier (C-RNTI) to a UE or to inform the UE ofmobility related information such as timer values and CN domain related information.

Relocation Resource Allocation ProcedureThe relocation resource allocation procedure is performed to allocate resources from the targetRNS for an SRNS relocation.

Triggering ConditionsThe relocation resource allocation procedure can be triggered in either of the followingconditions:l During an SRNS relocation, the CN applies for resources from the target RNC.



l During an inter-RAT CS handover from GSM to WCDMA, the CN applies for resourcesfrom the target RNC.

Procedure

Figure 9-12 shows the relocation resource allocation procedure.

Figure 9-12 Relocation resource allocation procedure


1. The CN sends a RELOCATION REQUEST message to the target RNC. The messagecontains certain information, such as the IMSI of the UE, CN domain indicator, target cellidentifier, encryption, integrity protection, Iu signaling connection ID, handover cause, andRAB parameters.

2. The target RNC allocates radio resources for the relocation.

3. The target RNC sends a response message to the CN.

l If the resources are allocated, the target RNC sends a RELOCATION REQUESTACKNOWLEDGE message. The message contains the radio resources and otherparameters allocated to the UE. The parameters include the UTRAN Radio NetworkTemporary Identifier (U-RNTI), RAB, transport layer and physical layer information,chosen encryption algorithm, and chosen integrity protection algorithm.

l If the resources partially or totally fail to be allocated or the target RNC rejects the SRNSrelocation for some reason, the target RNC sends a RELOCATION FAILURE message,indicating the failure cause.

Radio Link Setup Procedure (Intra-RNC Handover or GSM to WCDMA CSHandover)

The radio link setup procedure (intra-RNC handover or GSM to WCDMA CS handover) isperformed to set up a radio link in a NodeB controlled by the SRNC for a UE.




Triggering Conditions

The CRNC sends a RADIO LINK SETUP REQUEST message.

Procedure

Figure 9-13 shows the radio link setup procedure (intra-RNC handover or GSM to WCDMACS handover).

Figure 9-13 Radio link setup procedure (intra-RNC handover or GSM to WCDMA CShandover)


1. The CRNC sends a RADIO LINK SETUP REQUEST message to the NodeB. Uponreception of the message, the NodeB shall reserve the necessary resources and configurethe new radio link according to the parameters given in the message.

2. The NodeB sends a response message to the CRNC.

l If the radio link is set up, the NodeB saves the value of the Configuration GenerationID IE contained in the RADIO LINK SETUP REQUEST message and sends a RADIOLINK SETUP RESPONSE message.

l If the radio link fails to be set up, the NodeB sends a RADIO LINK SETUP FAILUREmessage. The message contains the failure cause in the Cause IE.

Radio Link Restoration Procedure (Intra-RNC Handover or GSM to WCDMA CSHandover)

The radio link restoration procedure (intra-RNC handover or GSM to WCDMA CS handover)is performed for a NodeB to notify the CRNC the establishment and re-establishment of uplinksynchronization of one or more radio links.


The NodeB receives the UL signal from the UE, that is, the NodeB finishes UL synchronizationwith the UE.



ProcedureFigure 9-14 shows the radio link restoration procedure (intra-RNC handover or GSM toWCDMA CS handover).

Figure 9-14 Radio link restoration procedure (intra-RNC handover or GSM to WCDMA CShandover)

After performing UL synchronization with the UE, the NodeB sends a RADIO LINK RESTOREINDICATION message to the CRNC.

UE Capability Enquiry ProcedureThe UE capability enquiry procedure is performed to request a UE to transmit its capabilityinformation related to any radio access network so that the network can perform dataconfiguration based on the UE capability.

Triggering ConditionsThe UTRAN sends a UE CAPABILITY ENQUIRY message to acquire the UE capabilityinformation related to any radio access network.

ProcedureFigure 9-15 shows the UE capability enquiry procedure.

Figure 9-15 UE capability enquiry procedure





1. The SRNC sends a UE CAPABILITY ENQUIRY message to the UE through the downlinkDCCH using AM RLC.

2. The UE sends a UE CAPABILITY INFORMATION message to the SRNC through theuplink DCCH using AM or UM RLC. The message contains the information about UEcapabilities.

3. The SRNC reads the UE capability information and then sends a UE CAPABILITYINFORMA CONFIRM message to the UE through the downlink DCCH using AM or UMRLC.

Security Mode Control Procedure

The security mode control procedure is performed to configure or reconfigure one or both of theciphering and integrity protection algorithms for a UE.


The ciphering or integrity protection algorithm has changed.

Procedure

Figure 9-16 shows the security mode control procedure.

Figure 9-16 Security mode control procedure


1. Through a SECURITY MODE COMMAND message to the UE, the SRNC starts orreconfigures one or both of the ciphering and integrity protection configurations for theRBs or one CN domain and for all Signaling Radio Bearers (SRBs).

2. The UE sends a response message to the SRNC.l If the UE completes configuring or reconfiguring the relevant parameters for one or

both of the ciphering and integrity protection algorithms, the UE sends a SECURITYMODE COMPLETE message to inform the SRNC of the completion.

l If the SECURITY MODE COMMAND message contains neither Ciphering mode infoIE nor Integrity protection mode info IE or if each of the two IEs has inconsistent



information, the UE sends a SECURITY MODE FAILURE message, indicating thefailure of the security mode control procedure as well as the failure cause.

UTRAN Mobility Information Procedure

The UTRAN mobility information procedure is performed for the network to allocate a new U-RNTI or Cell Radio Network Temporary Identifier (C-RNTI) to a UE or to inform the UE ofmobility related information such as timer values and CN domain related information.


The SRNC sends a UTRAN MOBILITY INFORMATION message to the UE.

Procedure

Figure 9-17 shows the UTRAN mobility information procedure.

Figure 9-17 UTRAN mobility information procedure


1. The SRNC sends a UTRAN MOBILITY INFORMATION message to the UE.

2. The UE starts to update the related fields according to the values of the IEs carried in themessage.

3. The UE sends a response message to the SRNC.

l If the UE succeeds in conducting the operations specified by the UTRAN MOBILITYINFORMATION message, the UE sends a UTRAN MOBILITY INFORMATIONCONFIRM message.

l If the UE fails to conduct the operations specified by the UTRAN MOBILITYINFORMATION message, the UE sends a UTRAN MOBILITY INFORMATIONFAILURE message, indicating the failure cause.




9.4 Inter-RAT PS Handover from WCDMA to GSMThe procedure of inter-RAT PS handover from WCDMA to GSM is performed to hand over thePS services of a UE from the WCDMA system to the GSM system.

9.4.1 Protocols Related to Inter-RAT PS Handover from WCDMA to GSMThe procedure of inter-RAT PS handover from WCDMA to GSM complies with some 3GPPTS25 protocols.

9.4.2 Triggering Conditions of Inter-RAT PS Handover from WCDMA to GSMThe signal quality of the WCDMA cell where the UE camps on is dissatisfactory or the load ofthe serving cell is heavy.

9.4.3 Signaling Procedure of Successful Inter-RAT PS Handover from WCDMA to GSMThis part describes the signaling procedure of a successful inter-RAT PS handover fromWCDMA to GSM. For the messages related to handover failures, refer to the elementaryprocedures.

9.4.4 Using the RNC LMT to Trace the Procedure of Inter-RAT PS Handover from WCDMAto GSMThe signaling tracing function of the RNC LMT can be used to trace the signaling of an inter-RAT PS handover from WCDMA to GSM.

9.4.5 Elementary Procedures of Inter-RAT PS Handover from WCDMA to GSMThis part describes the elementary procedures of inter-RAT PS handover from WCDMA toGSM in terms of triggering conditions and signaling procedures in normal and abnormalconditions.

9.4.1 Protocols Related to Inter-RAT PS Handover from WCDMAto GSM

The procedure of inter-RAT PS handover from WCDMA to GSM complies with some 3GPPTS25 protocols.

The compliance protocols are as follows:

l 3GPP TS25.331 "Radio Resource Control (RRC)"



9.4.2 Triggering Conditions of Inter-RAT PS Handover fromWCDMA to GSM

The signal quality of the WCDMA cell where the UE camps on is dissatisfactory or the load ofthe serving cell is heavy.

l When the UE is in CELL_PCH, URA_PCH, or CELL_FACH state, it initiates cellreselection to perform a handover to GSM.

l When the UE is in CELL_DCH state, the UTRAN sends a CELL CHANGE ORDERmessage to the UE to perform a handover to GSM.



9.4.3 Signaling Procedure of Successful Inter-RAT PS Handoverfrom WCDMA to GSM

This part describes the signaling procedure of a successful inter-RAT PS handover fromWCDMA to GSM. For the messages related to handover failures, refer to the elementaryprocedures.

Figure 9-18 shows the signaling procedure of a successful inter-RAT PS handover fromWCDMA to GSM.

Figure 9-18 Signaling procedure of a successful inter-RAT PS handover from WCDMA to GSM

Note the following information about the procedure shown in Figure 9-18:l When there is a low PS data volume, the UE may be in CELL_PCH, URA_PCH, or

URA_FACH states. Based on the parameters in the system information, the UE can initiatecell reselection to perform a handover to GSM. The network does not initiate any cellreselection.

l The NodeB sends a RADIO LINK FAILURE INDICATION message, because the UEshuts down transmission towards the WCDMA cell after cell reselection to a GSM cell.The procedure of inter-RAT PS handover from WCDMA to GSM does not require such amessage.

l After the UE accesses a GSM cell, the SGSN directly sends an IU RELEASE COMMANDmessage to the SRNC, if the Packet Data Protocol (PDP) context does not need to betransferred.




9.4.4 Using the RNC LMT to Trace the Procedure of Inter-RAT PSHandover from WCDMA to GSM

The signaling tracing function of the RNC LMT can be used to trace the signaling of an inter-RAT PS handover from WCDMA to GSM.



Context

Table 9-3 lists the messages to be traced.




Uu

RRC_CELL_CHANGE_ORDER_FROM_UTRAN

CELL CHANGE ORDER FROMUTRAN

RRC_CELL_CHANGE_ORDER_FROM_UTRAN_FAIL

CELL CHANGE ORDER FROMUTRAN FAILURE

Iub

NBAP_RL_FAIL_IND RADIO LINK FAILURE INDICATION

NBAP_RL_DEL_REQ RADIO LINK DELETION REQUEST

NBAP_RL_DEL_RSP RADIO LINK DELETION RESPONSE

Iu

RANAP_SRNS_CONTEXT_REQ SRNS CONTEXT REQUEST

RANAP_SRNS_CONTEXT_RESP SRNS CONTEXT RESPONSE

RANAP_SRNS_DATA_FORWARD_COMMAND SRNS DATA FORWARD COMMAND

RANAP_IU_RELEASE_COMMAND IU RELEASE COMMAND

RANAP_IU_RELEASE_COMPLETE IU RELEASE COMPLETE

Procedure









----End

9.4.5 Elementary Procedures of Inter-RAT PS Handover fromWCDMA to GSM

This part describes the elementary procedures of inter-RAT PS handover from WCDMA toGSM in terms of triggering conditions and signaling procedures in normal and abnormalconditions.

9.4.5.1 Cell Change Order from UTRAN ProcedureThe cell change order from UTRAN procedure is performed to hand over, under the control ofthe network, a UE in CELL_DCH state to a GSM cell when the RABs established in theWCDMA system are only from the PS domain.

9.4.5.2 SRNS Context Transfer ProcedureThe SRNS context transfer procedure is performed to transfer SRNS contexts from the sourceRNC to the SGSN.

9.4.5.3 Iu Release ProcedureThe Iu release procedure is performed for the CN to release an Iu connection and all the UMTSTerrestrial Radio Access Network (UTRAN) resources related only to that Iu connection.

9.4.5.4 Radio Link Deletion ProcedureThe radio link deletion procedure is performed to release resources in a NodeB for one or moreestablished radio links towards a UE.

Cell Change Order from UTRAN ProcedureThe cell change order from UTRAN procedure is performed to hand over, under the control ofthe network, a UE in CELL_DCH state to a GSM cell when the RABs established in theWCDMA system are only from the PS domain.





The network decides to hand over the UE to the GSM system.

Procedure

Figure 9-22 shows the cell change order from UTRAN procedure.

Figure 9-22 Cell change order from UTRAN procedure


1. Through a CELL CHANGE ORDER FROM UTRAN message, the SRNC orders the UEto perform a cell change to the GSM system. The message contains certain IEs about thetarget cell. The IEs include BSIC, Band indicator, BCCH ARFCN, and NC mode.

2. Upon reception of the CELL CHANGE ORDER FROM UTRAN message, the UE startstimer T309 and initiates access to the GSM cell.l If the UE accesses the GSM cell before the timer expires, the procedure ends.

l If the UE fails to access the GSM cell before the timer expires, the UE sends a CELLCHANGE ORDER FROM UTRAN FAILURE message to the SRNC.

SRNS Context Transfer Procedure

The SRNS context transfer procedure is performed to transfer SRNS contexts from the sourceRNC to the SGSN.


During the inter-RAT PS handover from WCDMA to GSM, the 2G equipment needs to get thePDP contexts of the UE from the 3G equipment.

Procedure

Figure 9-23 shows the SRNS context transfer procedure.



Figure 9-23 SRNS context transfer procedure


1. The SGSN sends an SRNS CONTEXT REQUEST message to the SRNC. The messageincludes the list of RABs whose contexts should be transferred.

2. The SRNC sends an SRNS CONTEXT RESPONSE message to the SGSN.l If the transfer is successful, the message contains RAB IDs that include the sequence

numbers for the downlink and uplink GTP PDUs and PDCP SDUs.l If the SRNC fails to identify the ID of the RAB whose context should be transferred to

the SGSN, the SRNS CONTEXT RESPONSE message contains a Cause IE whosevalue is Invalid RAB ID.

Iu Release Procedure

The Iu release procedure is performed for the CN to release an Iu connection and all the UMTSTerrestrial Radio Access Network (UTRAN) resources related only to that Iu connection.


The Iu release procedure can be triggered in one of the following conditions:l The transaction between the UE and the CN is complete.

l The UTRAN requests the CN to release the resources on the Iu interface by, for example,sending an IU RELEASE REQUEST message.

l The Serving Radio Network Subsystem (SRNS) is relocated.

l The SRNS relocation is canceled after a relocation resource allocation procedure iscomplete.

Procedure

Figure 9-24 shows the Iu release procedure.




Figure 9-24 Iu release procedure


1. The CN sends an IU RELEASE COMMAND message to the SRNC to initiate the Iu releaseprocedure. The message indicates the cause for the release of the signaling connection.

NOTE

After sending the IU RELEASE COMMAND message, the CN shall not send further RANAPconnection-oriented messages on this particular connection.

2. The SRNC releases the related UTRAN resources and then sends an IU RELEASECOMPLETE message to the CN.

Radio Link Deletion ProcedureThe radio link deletion procedure is performed to release resources in a NodeB for one or moreestablished radio links towards a UE.

Triggering ConditionsThe CRNC sends a RADIO LINK DELETION REQUEST message.

ProcedureFigure 9-25 shows the radio link deletion procedure.



Figure 9-25 Radio link deletion procedure


1. The CRNC sends a RADIO LINK DELETION REQUEST message to the NodeB. Uponreception of the message, the NodeB shall delete the radio links specified by the message.

2. The NodeB sends a response message to the CRNC.l If all the radio links are deleted, the NodeB sends a RADIO LINK DELETION

RESPONSE message.l If any radio link fails to be deleted, the NodeB sends a RADIO LINK DELETION

RESPONSE message. The Criticality Diagnostics field in the message indicates thefailure cause.

9.5 Inter-RAT PS Handover from GSM to WCDMAThe procedure of inter-RAT PS handover from GSM to WCDMA is performed through cellreselection to WCDMA initiated by the UE.

For details, refer to 4 Location Update Procedure。




01-09 inter-rat handover procedure

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