LTE, Fallback, CS, GSM

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3GPP TS 23.272 V8.1.0 (2008-09)Technical Specification

3rd Generation Partnership Project;Technical Specification Group Services and System Aspects;

Circuit Switched Fallback in Evolved Packet System;Stage 2

(Release 8)

GLOBAL SYSTEM FOR

MOBILE COMMUNICATIONS

R

The present document has been developed within the 3rdGeneration Partnership Project (3GPP TM) and may be further elaborated for the purposes of 3GPP.

The present document has not been subject to any approval process by the 3GPPOrganizational Partners and shall not be implemented.

This Specification is provided for future development work within 3GPPonly. The Organizational Partners accept no liability for any use of this Specification.

Specifications and reports for implementation of the 3GPPTMsystem should be obtained via the 3GPP Organizational Partners' Publications Offices.


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Keywords

LTE, Fallback, CS, GSM

3GPP

Postal address

3GPP support office address

650 Route des Lucioles - Sophia Antipolis

Valbonne - FRANCETel.: +33 4 92 94 42 00 Fax: +33 4 93 65 47 16

Internet

http://www.3gpp.org

Copyright Notification

No part may be reproduced except as authorized by written permission.The copyright and the foregoing restriction extend to reproduction in all media.

2008, 3GPP Organizational Partners (ARIB, ATIS, CCSA, ETSI, TTA, TTC).All rights reserved.


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Contents

Foreword ............................................................................................................................................................5

1 Scope........................................................................................................................................................62 References ................................................................................................................................................6

3 Definitions and abbreviations...................................................................................................................73.1 Definitions ............................................................... ....................................................................... ................... 73.2 Abbreviations..................................................................................................................................................... 7

4 Overall Description ..................................................................................................................................74.1 General Considerations...................................................................................................................................... 74.2 Reference Architecture .................................................................. .................................................................... 74.2.1 Reference points........................................................................................................................................... 84.3 Functional entities.............................................................................................................................................. 84.3.1 UE ........................................................ ................................................................ ........................................ 8

4.3.2 MME............................................................ .................................................................. .............................. 84.3.3 MSC ........................................................... ................................................................ .................................. 84.3.4 E-UTRAN................................................................... ............................................................. .................... 94.4 Control plane ............................................................. ..................................................................... ................... 94.4.1 MME - MSC Server.............................................................. .............................................................. ......... 94.5 Co-existence with IMS services......................................................................................................................... 9

5 Mobility Management ..............................................................................................................................95.1 General............................................................................................................................................................... 95.2 Attach procedure.............................................................................................................................................. 105.3 Detach procedure ................................................................... ................................................................... ....... 115.3.1 UE-initiated Detach procedure................................................................................................................... 115.3.2 MME-initiated Detach procedure............................................................................................................... 11

5.3.3 HSS-initiated Detach procedure................................................................................................................. 125.4 TA/LA Update procedure ............................................................ .................................................................... 135.4.1 Combined TA/LA Update Procedure......................................................................................................... 135.4.2 Periodic TA and LA Update Procedure...................................................................................................... 13

6 Mobile Originating Call .........................................................................................................................146.1 General............................................................................................................................................................. 146.2 Mobile Originating call in Active Mode - PS HO supported........................................................................... 146.3 Mobile Originating call in Active Mode No PS HO support in GERAN ..................................................... 166.4 Mobile Originating call in Idle Mode .................................................................. ............................................ 176.5 Returning back to E-UTRAN ................................................................ .......................................................... 17

7 Mobile Terminating Call ........................................................................................................................187.1 General............................................................................................................................................................. 18

7.2 Mobile Terminating call in idle mode.............................................................................................................. 187.3 Mobile Terminating call in Active Mode - PS HO supported .................................................................... ..... 217.4 Mobile Terminating call in Active Mode - No PS HO support in GERAN..................................................... 237.5 Roaming Retry for CS fallback........................................................................................................................ 247.6 Returning back to E-UTRAN ................................................................ .......................................................... 257.7 Interaction with ISR......................................................................................................................................... 267.7.1 General....................................................................................................................................................... 267.7.2 Mobile Terminating Call when ISR is active and SGs is active between MSC/VLR and MME............... 267.7.3 Mobile Terminating Call when ISR is active and Gs is active between MSC/VLR and SGSN................ 27

8 Other CS Services ..................................................................................................................................288.1 General............................................................................................................................................................. 288.2 Short Message Service (SMS) .......................................................................... ............................................... 28

8.2.1 General....................................................................................................................................................... 288.2.2 Mobile originating SMS in Idle Mode .......................................................................... ............................. 288.2.3 Mobile originating SMS in Active Mode................................................................................................... 298.2.4 Mobile terminating SMS in idle mode.................................................................... ................................... 29


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8.2.5 Mobile terminating SMS in Active Mode.................................................................................................. 308.2.6 Co-Existence with SMS over generic 3GPP IP access............................................................................... 308.3 Location Services (LCS).................................................................................................................................. 318.3.1 MO-LR procedure...................................................................................................................................... 318.3.2 MT-LR procedure ..................................................................... ................................................................. 318.3.3 NI-LR procedure ................................................................. ................................................................ ....... 32

8.3.4 Returning back to E-UTRAN..................................................................................................................... 328.3.5 Co-Existence with Other Location Services.................................................................. ............................. 328.3.5.1 Co-Existence with SUPL...................................................................................................................... 328.4 Call Independent Supplementary Services ........................................................... ........................................... 328.4.1 Mobile-Initiated Call Independent SS procedure ................................................................... .................... 328.4.2 NW-Initiated Call Independent SS procedure........................................................... ................................. 338.4.3 Returning back to E-UTRAN..................................................................................................................... 33

Annex A (informative): Solutions addressing misaligned LAs/TAs at Pool Area Boundaries........34

A.1 Solution 1: Overlapping Pool Areas with 2G/3G coverage > E-UTRAN coverage at Pool AreaBoundaries..............................................................................................................................................34

A.2 Solution 2: Overlapping Pool Areas with SGs-flex support ..................................................................35

Annex B (normative): CS Fallback to 1xRTT...................................................................................36

B.1 Overall Description ................................................................................................................................36B.1.1 General Considerations.................................................................................................................................... 36B.1.2 Reference Architecture .................................................................. .................................................................. 36B.1.2.1 Reference points......................................................................................................................................... 36B.1.3 Functional entities............................................................................................................................................ 37B.1.3.1 UE ........................................................ ................................................................ ...................................... 37B.1.3.2 MME............................................................ .................................................................. ............................ 37B.1.3.3 E-UTRAN................................................................... ............................................................. .................. 37B.1.4 Co-existence with IMS services....................................................................................................................... 37

B.2 Procedures ..............................................................................................................................................37B.2.1 Mobility Management...................................................................................................................................... 37B.2.1.1 1x RTT CS Pre-Registration over EPS Procedure ................................................................ ..................... 37B.2.1.2 S102 Tunnel Redirection............................................................................................................................ 39B.2.2 Mobile Originating Call................................................................................................................................... 39B.2.3 Mobile Terminating Call ................................................................. ................................................................ 40B.2.4 Short Message Service (SMS) .......................................................................... ............................................... 42B.2.4.1 General....................................................................................................................................................... 42B.2.4.2 Mobile originating SMS............................................................................................................................. 42B.2.4.3 Mobile terminating SMS............................................................................................................................ 44

Annex C (informative): Change history ...............................................................................................46


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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 formalTSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with anidentifying 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.


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1 Scope

This document defines the Stage 2 architecture and specification for the CS Fallback for EPS. The scope of thisdocument includes the architecture enhancements for functionality to enable fallback from E-UTRAN access to

UTRAN/GERAN CS domain access and to CDMA 1x RTT CS domain access, and functionality to reuse of voice andother CS-domain services (e.g. CS UDI video / SMS/ LCS / USSD) by reuse of CS infrastructure.

The architecture enhancements to support CS fallback for CDMA 1x RTT CS domain access are specified in Annex B.

2 References

The following documents contain provisions which, through reference in this text, constitute provisions of the present

document.

References are either specific (identified by date of publication, edition number, version number, etc.) ornon-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 (includinga GSM document), a non-specific reference implicitly refers to the latest version of that document in the sameRelease as the present document.

[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".

[2] 3GPP TS 23.401: "GPRS Enhancements for E-UTRAN Access".

[3] 3GPP TS 23.060: "General Packet Radio Service (GPRS); Service description; Stage 2".

[4] 3GPP TS 44.018: "Mobile radio interface layer 3 specification Radio Resource Control (RRC)

protocol".

[5] 3GPP TS 23.018: "Basic call handling; Technical realization".

[6] 3GPP TS 48.008: "MSC-BSS interface layer 3 specification; Protocol specification".

[7] 3GPP TS 25.331: "Radio Resource Control (RRC); Protocol specification".

[8] 3GPP TS 23.271: "Functional stage 2 description of Location Services (LCS)".

[9] Open Mobile Alliance, OMA AD SUPL: "Secure User Plane Location Architecture",http://www.openmobilealliance.org.

[10] 3GPP TS 23.090: "Unstructured Supplementary Service Data (USSD); Stage 2".

[11] Void.

[12] 3GPP TS 44.060: "MS-BSS interface; RLC/MAC protocol ".

[13] 3GPP TS 24.010: "Supplementary services specification; General aspects".

[14] 3GPP TS 23.040: "Technical realization of the Short Message Service (SMS)".

[15] 3GPP TS 23.204: "Short Message Service (SMS) over generic 3GPP Internet Protocol (IP) access".

[16] 3GPP2 A.S0008-C: "Interoperability Specification (IOS) for High Rate Packet Data (HRPD)Radio Access Network Interfaces with Session Control in the Access Network".

[17] 3GPP2 A.S0009-C: "Interoperability Specification (IOS) for High Rate Packet Data (HRPD)Radio Access Network Interfaces with Session Control in the Packet Control Function".
http://www.openmobilealliance.org/http://www.openmobilealliance.org/http://www.openmobilealliance.org/


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[18] 3GPP2 A.S0013-C: "Interoperability Specification (IOS) for cdma2000 Access Network Interfaces part 3 Features".

[19] 3GPP TR 36.938: "Improved Network Controlled Mobility between E-UTRAN and3GPP2/Mobile WiMAX Radio Technologies".

[20] 3GPP TS 23.216: "Single Radio Voice Call Continuity (SRVCC); Stage 2".

[21] 3GPP TS 24.008: "Mobile radio interface Layer 3 specification; Core network protocols; Stage 3".

[22] 3GPP2 X.S0042-0: "Voice Call Continuity between IMS and Circuit Switched System".

3 Definitions and abbreviations

3.1 Definitions

For the purposes of the present document, the terms and definitions given in TR 21.905 [1] apply. A term defined in the

present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].

1xCS:The 3GPP2 legacy circuit Switched signalling system as defined in 3GPP2 X.S0042-0 [22].

3.2 Abbreviations

For the purposes of the present document, the abbreviations given in TR 21.905 [1] apply. An abbreviation defined in

the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905 [1].

1xCS IWS Circuit Switched Fallback Interworking solution Function for 3GPP2 1xCS.

4 Overall Description

4.1 General Considerations

The CS fallback in EPS enables the provisioning of voice and other CS-domain services (e.g. CS UDI video/ SMS/LCS/ USSD) by reuse of CS infrastructure when the UE is served by E-UTRAN. A CS fallback enabled terminal,connected to E-UTRAN may use GERAN or UTRAN to establish one or more CS-domain services. This function isonly available in case E-UTRAN coverage is overlapped by either GERAN coverage or UTRAN coverage.

CS Fallback and IMS-based services shall be able to co-exist in the same operators network.

4.2 Reference ArchitectureThe CS fallback in EPS function is realized by using the SGs interface mechanism between the MSC Server and theMME.

The SGs interface functionality is based on the mechanisms specified for the Gs interface, TS 23.060 [3].


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UE

LTE-Uu

E-UTRAN MME

S1-MME

UTRAN

GERAN

Um

Uu

MSCServer

Iu-CS

A

SGs

Figure 4.2-1: CS fallback in EPS architecture

NOTE: The MGW is not shown in the figure 4.2-1 since the CS fallback in EPS does not have any impacts to theU-plane handling.

4.2.1 Reference points

SGs: It is the reference point between the MME and MSC server. The SGs reference point is used for the

mobility management and paging procedures between EPS and CS domain, and is based on the Gsinterface procedures. The SGs reference point is also used for the delivery of both mobile originating andmobile terminating SMS.

4.3 Functional entities

4.3.1 UE

The CS fallback capable UE supports access to E-UTRAN/EPC as well as access to the CS domain over GERANand/or UTRAN. It supports the following additional functions:

- Combined procedures specified in this document for EPS/IMSI attach, update and detach.

- CS fallback and SMS procedures specified in this document for using CS domain services.

4.3.2 MME

The CS fallback enabled MME supports the following additional functions:

- Deriving a VLR number and LAI out of the TAI.

- Maintaining of SGs association towards MSC/VLR for EPS/IMSI attached UE.

- Initiating IMSI detach at EPS detach.

- Initiating paging procedure specified in this document towards eNodeB when MSC pages the UE for CSservices.

- Supporting SMS procedures defined in this document.

- Rejecting CS Fallback call request (e.g. due to O&M reasons)

4.3.3 MSC

The CS fallback enabled MSC supports the following additional functions:

- Maintaining SGs association towards MME for EPS/IMSI attached UE.

- Paging on SGs and Iu/A in parallel.

- Supporting SMS procedures defined in this document.


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4.3.4 E-UTRAN

The CS fallback enabled E-UTRAN supports the following additional functions:

- Forwarding paging request and SMS to the UE.

- Directing the UE to the target CS capable cell.

4.4 Control plane

4.4.1 MME - MSC Server

SCTP

L2

L1

IP

L2

L1

IP

SCTP

SGsMME MSC Server

SGsAP SGsAP

Legend:SGsAP:This protocol is used to connect an MME to an MSC Server based on the BSSAP+.Stream Control Transmission Protocol (SCTP): This protocol transfers signalling messages.

Figure 4.4.1-1: SGs Interface

4.5 Co-existence with IMS servicesIf a UE is configured to use IMS voice services it shall, if registered to IMS, initiate voice calls over IMS, even if it isEPS/IMSI attached.

NOTE: The home operator has to be able to activate/deactivate the UE configuration to use IMS voice services bymeans of device management in order to allow alignment with HPLMN support of IMS voice services.

If a UE is configured to use SMS over IP services it shall, if registered to IMS, send SMS over IMS, even if it is

EPS/IMSI attached.

NOTE: The operator has to be able to activate/deactivate the UE configuration to use SMS over IP by means ofdevice management in order to allow alignment with HPLMN support of SMS over IP.

In special cases when the IMS registered and EPS/IMSI attached UE can not initiate an IMS voice session or SMS(because e.g. IMS voice services are not supported by the serving IP-CAN or UE) CS fallback should be applied for

voice calls and/or SMS.

5 Mobility Management

5.1 General

The CS fallback in EPS is realized by using the SGs interface mechanism between the MSC Server and the MME.


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5.2 Attach procedure

The attach procedure for the CS fallback in EPS is realized based on the combined GPRS/IMSI Attach procedurespecified in TS 23.060 [3].

1. Attach Request

3. Derive VLR number

4. Location Update Request

5. Create SGs association

7. Location Update Accept

8. Attach Accept

UE MME HSSMSC/VLR

2. Attach as specified in TS 23.401

6. Location update in CS domain

Figure 5.2-1: Attach Procedure

1)The UE initiates the attach procedure by the transmission of an Attach Request (parameters as specified inTS 23.401 [2] including the Attach Type) message to the MME. The Attach Type indicates that the UE requests

a combined EPS/IMSI attach and informs the network that the UE is capable and configured to use CS fallback.

2) The EPS Attach procedure is performed as specified in TS 23.401 [2].

3) The VLR shall be updated according to the combined GPRS/IMSI Attach procedure in TS 23.060 [3] if the

Attach Request message includes an Attach Type indicating that the UE requests a combined EPS/IMSI attach.The VLR number is derived from the TAI. The MME starts the location update procedure towards the newMSC/VLR upon receipt of the first Insert Subscriber Data message from the HSS in step 2). This operationmarks the MS as EPS-attached in the VLR.

4)The MME sends a Location Update Request (new LAI, IMSI, MME address, Location Update Type) message tothe VLR. New LAI is determined in MME based on mapping from the TA. A mapped LAI could be either

GERAN or UTRAN based on an operator configuration. MME address is an IP address.

5)The VLR creates an association with the MME by storing MME address.

6)The VLR performs Location Updating procedure in CS domain.

7)The VLR responds with Location Update Accept (VLR TMSI) to the MME.

8) The MMEsends an Attach Accept (parameters as specified in TS 23.401 [2], LAI, VLR TMSI) message to theUE. The existence of LAI and VLR TMSI indicates successful attach to CS domain.

NOTE: The case of unsuccessful attach to CS domain is documented in stage 3 specifications, taking into accountreachability for CS services of UEs that have the user preference to prioritize voice over data services and

are not configured/supporting to use IMS voice services.


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5.3 Detach procedure

5.3.1 UE-initiated Detach procedure

The UE-initiated Detach procedure for the CS fallback in EPS is realized based on the MS-Initiated Detach Procedure

specified in TS 23.060 [3].

1. Detach Request

3. IMSI Detach Indication

4. Remove SGsassociation

5. Detach Accept

UEMME HSSMSC/VLR

2. UE-initiated detach as specified in TS 23.401

Figure 5.3.1-1: UE-initiated Detach Procedure

1)The UE initiates the detach procedure by the transmission of a Detach Request (parameters as specified inTS 23.401 [2], Detach Type) message to the MME. Detach Type indicates which type of detach is to be

performed, i.e., IMSI Detach only or combined EPS and IMSI Detach.

2) If EPS detach is indicated in step 1, the EPS Detach procedure is performed as specified in TS 23.401 [2].

3) The MME sends an IMSI Detach Indication (IMSI) message to the VLR.

4)The VLR removes the association with the MME.

5)The MME sends a Detach Accept message as specified in TS 23.401 [2].

5.3.2 MME-initiated Detach procedure

The MME-initiated detach procedure for the CS fallback in EPS is realized based on the SGSN-Initiated Detach

Procedure specified in TS 23.060 [3].


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3. Remove SGs association

UEMME HSSMSC/VLR

1.MME-initiated detach as specified in TS 23.401


Figure 5.3.2-1: MME-init iated Detach Procedure

1) The MME-initiated Detach procedure is performed as specified in TS 23.401 [2].

2)The MME sends an IMSI Detach Indication (IMSI) message to the VLR.

3)The VLR removes the association with the MME.

5.3.3 HSS-initiated Detach procedure

The HSS-initiated detach procedure for the CS fallback in EPS is realized based on the HLR-Initiated Detach Procedure

specified in TS 23.060 [3].

3. Remove SGsassociation

UE MMEHSSMSC/VLR

1. HSS-initiated detach as specified in TS 23.401


Figure 5.3.3-1: HSS-ini tiated Detach Procedure

1) The HSS-initiated Detach procedure is performed as specified in TS 23.401 [2].

2)The MME sends an IMSI Detach Indication (IMSI) message to the VLR.

3)

The VLR removes the association with the MME.


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5.4 TA/LA Update procedure

5.4.1 Combined TA/LA Update Procedure

NOTE: The combined TA/LA Update procedure for the CS fallback in EPS is realized based on the combined

RA/LA Update procedure specified in TS 23.060 [3].

2. TAU Request

4. Location Update Request

6. Location Update Accept

7. TAU Accept

UE new MME HSSMSC/VLR

5. Location update in CS domain

1. UE determines toperform TAU

old MME

3. TAU as specified in TS 23.401

Figure 5.4.1-1: Combined TA / LA Update Procedure

1) The UE detects a change to a new TA by discovering that its current TAI is not in the list of TAIs that the UEregistered with the network. The combined TA/LA Update Procedure is also performed in order to re-establish

the SGs association. Therefore, when the UE performed a LAU (which releases the SGs association) and entersECM_IDLE state in an area that requires combined TA/LA Updates, then the UE performs a combined TA/LA

Update.

2) The UE initiates the TAU procedure by sending a TAU Request (parameters as specified in TS 23.401 [2], CSfallback indicator) message to the MME. The CS fallback indicator indicates that this is a combined TrackingArea/Location Area Update Request message.

3) The EPS TAU procedure is performed as specified in TS 23.401 [2].

4) If there is an associated VLR in the MM context, the VLR also needs to be updated. If the association has to beestablished or if the LA changed, the new MME sends a Location Update Request (new LAI, IMSI, MMEaddress, Location Update Type) message to the VLR. New LAI is determined in the MME based on mappingfrom the TA. Location Update Type shall indicate normal location update. The VLR number is derived from the

TAI. MME address is an IP address.

5) The VLR performs Location Update procedure in CS domain.

6) The VLR responds with Location Update Accept (VLR TMSI) to the MME.

7) The MME sends a TAU Accept (parameters as specified in TS 23.401 [2], LAI, VLR TMSI) message to the UE.The VLR TMSI is optional if the VLR has not changed. When the MME allocates the TA list to the UE, the TAlist shall be configured ensuring that all TAs in the TA list belong to the same LA.

5.4.2 Periodic TA and LA Update Procedure

When the UE is camped in the E-UTRAN, periodic LA updates shall not be performed. In this case the MSC/VLR shall

disable implicit detach for EPS-attached UEs and instead rely on the MME to receive periodic TA updates. If periodicTA updates are not received in the MME and the MME detaches the UE, the MME shall notify the MSC/VLR bysending an IMSI Detach Indication message.


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If the UE is both EPS/IMSI and GPRS/IMSI attached, the UE shall initiate combined periodic TA/LA or RA/LA updateprocedure.

6 Mobile Originating Call

6.1 General

This clause describes the mobile originating call procedures for the CS Fallback in EPS.

6.2 Mobile Originating call in Active Mode - PS HO supported

UE/MS MMEBSS/RNS MSCeNodeB SGSNServing

GW

2. Optional Measurement Report Solicitation

4. A/Iu-cs message (with CM Service Request)

4. CM Service Request

Location Area Update or Combined RA/LA Update

5. CM Service Reject 5. CM Service RejectIf the MSC

is changed

3. PS HO as specified in 23.401 [2] (preparation phase and start of execution phase)

6. CS call establishment procedure

1a. Service Request

1b. S1-AP Messa e with CS Fallback indicator

7. PS HO as specified in 23.401 [2] (continuation of execution phase)

Figure 6.2-1: CS Call Request in E-UTRAN, Call in GERAN/UTRAN

NOTE 1: DTM is not mandatory for CS Fallback to work and is not linked to PS HO.

NOTE 2: Steps 1a and 1b need to be further investigated in CT1 considering aspects such as speed and complexity.

1a. The UE sends Service Request (CS Fallback Indicator) to MME. Service Request message is encapsulated in

RRC and S1-AP messages. CS Fallback Indicator indicates MME to perform CS Fallback. The UE onlytransmits this request if it is attached to CS domain (with a combined EPS/IMSI Attach) and can not initiate anIMS voice session (because e.g. the UE is not IMS registered or IMS voice services are not supported by theserving IP-CAN, home PLMN or UE).

1b. The MME sends an S1-AP Request message to eNB that includes a CS Fallback indicator. This messageindicates to the eNB that the UE should be moved to UTRAN/GERAN.

2. The eNodeB may optionally solicit a measurement report from the UE to determine the target GERAN/UTRANcell to which PS handover will be performed.


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3. The eNodeB triggers PS handover to a GERAN/UTRAN neighbour cell by sending a Handover Requiredmessage to the MME. In the following an inter-RAT handover from E-UTRAN to UTRAN or GERAN asspecified in TS 23.401 [2] begins. As part of this handover, the UE receives a HO from E-UTRAN Commandand moves to a cell in the target RAT.

4. Target RAT is UTRAN or GERAN Iu mode: The UE establishes an RRC connection and sends an RRC Initial

Direct Transfer message as specified in TS 25.331 [7] that contains a CM Service Request. The CN DomainIndicator is set to "CS" in the Initial Direct Transfer message.

Target RAT is GERAN A/Gb mode: The UE establishes an RR connection by using the procedures specified inTS 44.018 [4] (i.e. UE requests and is assigned a dedicated channel where it sends a SABM containing a layer 3

Service Request message to the BSS and the BSS responds by sending a UA). Upon receiving the SABM(containing CM Service Request message) the BSS sends a COMPLETE LAYER 3 INFORMATION message(containing the CM Service Request message) to the MSC which indicates CS resources have been allocated inthe GERAN cell. After the establishment of the main signalling link as described in TS 44.018 [4] the UE enterseither Dual Transfer Mode or Dedicated Mode and the CS call establishment procedure completes.

5. In case the MSC serving the 2G/3G target cell is different from the MSC that served the UE while camped on

E-UTRAN, the MSC shall reject the service request, if implicit location update is not performed. The CMService Reject shall trigger the UE to perform a Location Area Update as follows:

- If the target system operates in Network Mode of Operation (NMO) I the UE shall perform a combinedRA/LA update, as defined in TS 23.060 [3].

- If the target system operates in NMO II or III the UE performs a Location Area Update towards the MSC.

6. The UE initiates the CS call establishment procedure.

7. After the UE moves to a cell in the target RAT, the inter-RAT handover from E-UTRAN to UTRAN or GERANas specified in TS 23.401 [2] is completed. At the end of this handover the UE may trigger the Routing Area

Update procedure when the sending of uplink packet data is possible. The detailed steps performed are as perTS 23.401 [2].


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6.3 Mobile Originating call in Active Mode No PS HO supportin GERAN

UE/MS MMEBSS MSCeNodeB


9. CS MO call

10b. Location Area U date

10a. Service RejectIn case MSC ischanged

10c. CS MO call

6. Location Area Update or Combined RA/LA Update

3. NACC

5. S1 UE Context Release

1a. Service Request

S-GW

4. S1-AP: S1 UE Context Release Request

1b. S1-AP message with CS Fallback indicator

7a. Suspend (see 23.060)

8. Update bearer(s)

SGSN

7b. Suspend Request / Response

Figure 6.3-1: CS Call Request in E-UTRAN, Call in GERAN

NOTE: Steps 1a and 1b need to be further investigated in CT1 considering aspects such as speed and complexity.

1a. The UE sends a Serivce Request (CS Fallback Indicator) to the MME. Service Request message is encapsulatedin RRC and S1-AP messages. CS Fallback Indicator indicates MME to perform CS Fallback. The UE onlytransmits this request if it is attached to CS domain (with a combined EPS/IMSI Attach) and can not initiate anIMS voice session (because e.g. the UE is not IMS registered or IMS voice services are not supported by theserving IP-CAN, home PLMN or UE).

1b. The MME sends an S1-AP Request message to eNB that includes a CS Fallback Indicator. This messageindicates to the eNB that the UE should be moved to UTRAN/GERAN.

2. The eNodeB may optionally solicit a measurement report from the UE to determine the target GERAN cell towhich PS handover will be performed.

3. The eNodeB triggers an inter-RAT cell change order (optionally with NACC) to a GERAN neighbour cell by

sending an RRC message to the UE.

4. The eNodeB sends an S1 UE Context Release Request (Cause) message to the MME. Cause indicates that theUE is not available for the PS service.

5. S1 UE Context in the eNodeB is released as specified in TS 23.401 [2].

6. The UE moves to the new cell in the 2G/3G RAT and establishes an RR connection using legacy procedures. Ifthe UE obtains LA/RA information of the new cell (e.g. based on the system information) and the LA/RA of thenew cell is different from the one stored in the UE, it performs a Location Area Update or a Combined RA/LAUpdate procedure in case the target system operates Network Mode of Operation (NMO) I.

7. When the target GERAN cell does not support DTM, the UE starts the Suspend procedure specified inTS 23.060 [3], clause 16.2.1.1.2. This triggers the SGSN to send a Suspend Request message to the MME. TheMME returns a Suspend Response to the SGSN, which contains the MM and PDP contexts of the UE.


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8. The MME starts the preservation of non-GBR bearers and the deactivation of GBR bearers.

9. The UE continues with the MO call setup procedure.

10a. In case the MSC serving the 2G/3G cell is different from the MSC that served the UE while camped on

E-UTRAN and if the Location Area Update / Combined RA/LA Update was not performed in step 8, the MSCshall reject the call setup service request, if implicit location update is not performed.

10b. A UE detecting that the MSC rejected the service request shall perform the Location Area Update accordingto existing GERAN or UTRAN procedures.

10c. After completion of the Location Area Update the UE continues with a MO call setup procedure.

After the CS voice call is terminated and if the UE is still in GERAN, then (as specified in TS 23.060 [3]) the UE shallresume PS services by sending a Routeing Area Update Request message to the SGSN. The Update Type depends onthe mode of operation of the GERAN network, e.g. in mode I a Combined RA/LA Update is used and in mode II or IIIRouteing Area Update is used.

6.4 Mobile Originating call in Idle Mode

Mobile Originating call in Idle Mode procedure is specified by reusing the Mobile Originating Call in Active modeprocedure with the following modifications:

- Target RAT has no PS HO capability: The UE sends Service Request (CS Fallback Indicator)to MME. Service

Request message is encapsulated in RRC and S1-AP messages. CS Fallback Indicator indicates MME to performCS Fallback.

NOTE: The above procedure needs to be further investigated in CT1 considering aspects such as speed andcomplexity.

- The UE then awaits further instructions from the serving eNodeB, e.g. the S1 connection is established to get the

UE capabilities downloaded from the MME to the eNB and the RRC connection is released with a redirectioninfo to change to CS capable RATs (RAT, frequency, cell info), optionally based on measurements. As an option

the inter-RAT system information might be provided by the eNB using the NACC procedure for GERAN.

- Target RAT has PS HO capability: The eNodeB may choose to invoke the optional Measurement ReportSolicitation during the preparation phase so that the UE is at minimum informed that its CS Call Request has

been accepted and a PS Handover is pending (i.e. so it can implicitly perform a state transition to Active mode).

The execution phase is the same as for the Mobile Originating Call in Active mode except that there are no incoming IPpackets to be delivered to the UE.

6.5 Returning back to E-UTRAN

Once CS service ends in CS domain, existing mechanisms can be used to move the UE to E-UTRAN, no specific CS

Fallback mechanisms are needed.

When the UE moves to E-UTRAN, if the EPS service was suspended during the CS service, it is resumed according tothe procedure shown in the figure 6.5-1 below.


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MMEeNodeB

1. NAS message

4. Handling NAS message

S-GW

2. Resume Request

3. Resume Request Ack

UE/MS

Figure 6.5-1: Resume Procedure returning from CS fallback no PS HO

1. The UE sends a NAS message, e.g. Service Request or TAU, to the MME.

2. If the UE context in the MME indicates that UE is in suspended status, the MME sends a Resume Request

(IMSI) message to the S-GW that requests the resumption of EPS bearers for the UE.

3. The S-GW acknowledges the Resume Request and clears the UE's suspending status.

4. The NAS message is processed accordingly.

7 Mobile Terminating Call

7.1 General

This clause describes the mobile terminating call procedures for the CS Fallback in EPS.

7.2 Mobile Terminating call in idle mode

The procedure for Mobile Terminating Call in idle mode is illustrated in figure 7.2-1.


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1. IAM

3. IAM

4. Paging

5. Paging6. Paging

8a. PS handover8b. eNB assisted cell change

8d. Paging Response

9a. Establish CS connection

2. SRI procedure in TS 23.018

G-MSCeNodeB RNC/BSCUE MME HSSMSCVLR

Location Area Update and Roaming Retry for CS Fallback (clause 7.5)

9b. RRC Release Option 2:MSC ischanged

Option 1:MSC is notchanged

9b. Connection Re ect

8d. Paging Response

8c. Location Area Update

7a. Service Request

7b. Initial UE Context Setup

Figure 7.2-1: Mobile Terminating Call in id le mode

NOTE 1: Steps 7a and 7b need to be further investigated in CT1 considering aspects such as speed and complexity.

1. G-MSC receives IAM.

2. G-MSC retrieves routing information of the terminating UE by Send Routing Info procedures as specified in

TS 23.018 [5].

3. G-MSC sends IAM to the MSC on the terminating side as specified in TS 23.018 [5].

4. The MME receives a Paging (IMSI, VLR TMSI, Location Information) message from the MSC over a SGs

interface. The TMSI (or IMSI) received from the MSC is used by the MME to find the S-TMSI which is used asthe paging address on the radio interface If location information is reliably known by MME (i.e. MME stores the

list of TAs), the MME shall page the UE in all the TAs. If the MME does not have a stored TA list for the UE,the MME should use the location information received from the MSC to page the UE.

NOTE 2: This procedure takes place before step 3, immediately after MSC receives MAP_PRN from HSS, if pre-paging is deployed.

5. The MME sends a Paging (as specified in TS 23.401 [2]) message to each eNodeB. The Paging message

includes a suitable UE Identity (i.e. S-TMSI or IMSI) and a CS Domain Indicator that indicates which domain(CS or PS) initiated the paging message. In this case it shall be set to "CS" by the MME.

6. The radio resource part of the paging procedure takes place. The message contains a suitable UE Identity (i.e.S-TMSI or IMSI) and a CN Domain indicator.

7a. The UE establishes an RRC connection and sends Service Request (CS Fallback Indicator) to MME. The UEindicates its S-TMSI in the RRC signalling. The Service Request message is encapsulated in RRC and S1-APmessages. The CS Fallback Indicator indicates to the MME that CS Fallback for this UE is required.

7b. MME sends S1-AP: Initial UE Context Setup (UE capabilities, CS Fallback Indicator and other parametersspecified in TS 23.401 [2]) to indicate the eNodeB to move the UE to UTRAN/GERAN.


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8a. Target RAT has PS HO capability: Upon receipt of the Initial UE Context Setup message with a CS FallbackIndicator the eNodeB may optionally solicit measurement reports from the UE to determine the target cell towhich PS handover will be performed. A PS handover is then performed as specified in TS 23.401 [2].

8b. Target RAT has no PS HO capability. Upon receipt of the Initial UE Context Setup message with a CS Fallback

Indicator the eNodeB may optionally solicit measurement reports from the UE to determine the target cell to

redirect the UE to. After that, the eNB releases the RRC Connection with a redirection info to change to CScapable RATs (RAT, frequency, cell info). As an option the inter-RAT system information might be provided bythe eNodeB using the NACC procedure for GERAN.

8c. If the UE obtains LA/RA information of the new UTRAN/GERAN cell (e.g. based on the system information or

redirection info) and the LA/RA of the new cell is different from the one stored in the UE, it performs a LocationArea Update or a Combined RA/LA procedure if the target system operates in Network Mode of Operation(NMO) I, according to TS 23.060 [3].

8d. The UE responds with a page response message to the MSC as follows:

- If Target RAT is UTRAN or GERAN Iu mode, the UE establishes an RRC connection and responds to the

paging in an RRC Initial Direct Transfer message as specified in TS 25.331 [7]. The CN Domain Indicator isset to "CS" in the Initial Direct Transfer message. When received at the RNC, the Paging Response message

is sent in an RANAP Initial UE message to the MSC.

- If Target RAT is GERAN A/Gb mode: the UE establishes an RR connection by using the proceduresspecified in TS 44.018 [6] (i.e. UE requests and is assigned a dedicated channel where it sends a SABMcontaining a layer 3 Service Request message = PAGING RESPONSE to the BSS and the BSS responds bysending a UA). After the establishment of the main signalling link as described in TS 44.018 [4] the UEenters either Dual Transfer Mode or Dedicated Mode and the CS call establishment procedure completes.When received at the BSC, the Paging Response message is sent in a BSSAP COMPLETE LAYER 3INFORMATION message to the MSC as specified in TS 48.008 [6].

NOTE 3: The BSS should be prepared to receive a PAGING RESPONSE even when a corresponding PAGINGREQUEST has not been sent by this BSS. Also, the MSC should be prepared to receive a paging responseafter a relatively long time from when the CS Paging was sent (step 4).

9a. In case the MSC serving the 2G/3G cell is the same as the MSC that served the UE while camped on LTE, it

shall stop the paging response timer and establish the CS connection.

9b. If the MSC that receives the paging response is different from the MSC that sent the paging request and if theLocation Area Update / Combined RA/LA Update was not performed in step 8c, the MSC shall reject the pageresponse by releasing the A/Iu-cs connection. The BSC/RNC in turn releases the RRC/RR connection. TheRRC/RR release shall trigger the UE to perform a Location Area Update as follows:

- If the target system operates in Network Mode of Operation (NMO) I the UE shall perform a combinedRA/LA update, as defined in TS 23.060 [3].


The Location Area Update triggers the Roaming Retry for CS Fallback procedure as defined in clause 7.5.


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7.3 Mobile Terminating call in Active Mode - PS HO supported

UE/MS MMEBSS/RNS MSCeNodeB SGSNServing

GW


4. A/Iu-cs message (with CM Service Request / Paging Response)

4. CM Service Request / Paging Response


5. RRC/RR Release 5. Connection RejectIf the MSCis changed

3. PS HO as specified in 23.401 [2] (preparation phase and start of execution phase)

6. CS call establishment procedure

1b. Service Request

1d. S1-AP Messa e with CS Fallback indicator

7. PS HO as specified in 23.401 [2] (continuation of execution phase)

1a. CS Paging1a. CS Paging

1c. CS Paging Reject

Figure 7.3-1: CS Page in E-UTRAN, Call in GERAN/UTRAN Preparation Phase

NOTE 1: Steps 1b and 1c need to be further investigated in CT1 considering aspects such as speed and complexity.

1a. The MSC receives an incoming voice call and responds by sending a CS Page (IMSI or TMSI, optional CallerLine Identification and Connection Management information, CS call indicator) to the MME over a SGsinterface. In active mode the MME has an established S1 connection and the MME reuses the existingconnection to relay the CS Page to the UE. The MSC only sends a CS Page for an UE that provides locationupdate information using the SGs interface.

The eNB forwards the paging message to the UE. The message contains CN Domain indicator and Caller Line

Identification if available and needed.

NOTE 2: The pre-configured policy may be used by UE to avoid being disturbed without Caller Line Identificationdisplay and the detailed handling is to be decided by CT1 and CT6.

NOTE 3: This procedure can also take place immediately after MSC receives MAP_PRN from HSS, if pre-pagingis deployed. Caller Line Identification and CS call indicator are also provided in the case of pre-paging.

1b. UE sends Service Request to MME. Service Request message is encapsulated in RRC and S1-AP messages. CSFallback Indicator indicates to the MME to perform CS Fallback. The UE may decide to reject CSFB based on

Caller Line Identification. The UE sends Service Request (CS Fallback Indicator, Reject or Accept) messagetowards the MME.

1c. Upon receiving the Service request (CSFB, Reject), the MME sends CS Paging Reject towards MSC to stop CSPaging procedure and this CSFB procedure stops.

1d. MME sends an S1-AP Request message to eNB that includes the UE Radio Capabilities and a CS Fallback

Indicator. This message: indicates to the eNB that the UE should be moved to UTRAN/GERAN.

2. The eNodeB may optionally solicit a measurement report from the UE to determine the target GERAN/UTRANcell to which PS handover will be performed.


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3. The eNodeB triggers PS handover to a GERAN/UTRAN neighbour cell by sending a Handover Requiredmessage to MME. In the following an inter-RAT handover from E-UTRAN to UTRAN or GERAN as specifiedin TS 23.401 [2] begins. As part of this handover, the UE receives a HO from E-UTRAN Command and movesto a cell in the target RAT.

4. Target RAT is UTRAN or GERAN Iu mode: The UE establishes an RRC connection and responds to the paging

by sending an RRC Initial Direct Transfer message as specified in TS 25.331 [7] that contains a CM ServiceRequest. The CN Domain Indicator is set to "CS" in the Initial Direct Transfer message.

Target RAT is GERAN A/Gb mode: The UE establishes an RR connection and responds to paging by using theprocedures specified in TS 44.018 [6] (i.e. UE requests and is assigned a dedicated channel where it sends a

SABM containing a layer 3 Service Request message = PAGING RESPONSE to the BSS and the BSS respondsby sending a UA). Upon receiving the SABM (containing a PAGING RESPONSE message) the BSS sends aCOMPLETE LAYER 3 INFORMATION message (containing a PAGING RESPONSE message) to the MSCwhich indicates CS resources have been allocated in the GERAN cell. After the establishment of the mainsignalling link as described in TS 44.018 [6] the UE enters Dual Transfer Mode and the CS call establishmentprocedure completes.

NOTE 4: The BSS should be prepared to receive a PAGING RESPONSE even when the corresponding PAGINGREQUEST has not been sent by this BSS.

5. If the MSC serving the 2G/3G target cell is different from the MSC that served the UE while camped onE-UTRAN, the MSC shall reject the page response message by releasing the Iu connection for UTRAN or theA/Gb connection for GERAN. The BSC/RNC in turn releases the RRC connection for UTRAN or the RR

connection for GERAN. The RRC/RR release shall trigger the UE to perform a Location Area Update asfollows:

- If the target system operates in Network Mode of Operation (NMO) I the UE shall perform a combinedRA/LA update, as defined in TS 23.060 [3]


The Location Area Update triggers the Roaming Retry for CS Fallback procedure as defined in clause 7.5.

6. The UE initiates the CS call establishment procedure.

7. After the UE moves to a cell in the target RAT, the inter-RAT handover from E-UTRAN to UTRAN or GERAN

as specified in TS 23.401 [2] is completed. At the end of this handover the UE may trigger the Routing AreaUpdate procedure when the sending of uplink packet data is possible. The detailed steps performed are as per

TS 23.401 [2].


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7.4 Mobile Terminating call in Active Mode - No PS HO supportin GERAN

UE/MS MMEBSS MSC

3. NACC

eNodeB

1a. CS Paging1a. CS Paging

2. Optional Measurement Report

9. Paging Response / CM Service Request

10. Establish CS connection


11. RRC Release Option 2:MSC ischanged

Option 1:MSC is notchanged

11. Connection Reject

6. Location Area Update or Combined RA/LA Update

5. S1 UE Context Release

4. S1-AP: S1 UE Context Release Request

S-GW

1b. Service Request

1d. S1-AP message with CS Fallback indicator

1c. CS Paging Reject

SGSN

7a. Suspend (see TS 23.060)

8. Update bearer(s)

7b. Suspend Request / Response

Figure 7.4-1: CS Page in E-UTRAN, Call in GERAN without PS HO

NOTE 1: Steps 1b and 1c need to be further investigated in CT1 considering aspects such as speed and complexity.

1a. The MSC receives an incoming voice call and responds by sending a CS Page (IMSI or TMSI, optional CallerLine Identification and Connection Management information) to the MME over a SGs interface. In active modethe MME has an established S1 connection and the MME reuses the existing connection to relay the CS Page tothe UE. The MSC only sends a CS Page for an UE that provides location update information using the SGsinterface.

The eNB forwards the paging message to the UE. The message contains CN Domain indicator and Caller LineIdentification if available and needed. Note that the pre-configured policy may be used by UE to avoid being

disturbed without Caller Line Identification display and the detailed handling is to be decided by CT1 and CT6.

NOTE 2: This procedure can also take place immediately after MSC receives MAP_PRN from HSS, if pre-pagingis deployed. Caller Line Identification is also provided in the case of pre-paging.

1b. UE sends Service Request (CS Fallback Indicator) to the MME. Service Request message is encapsulated inRRC and S1-AP messages. CS Fallback Indicator indicates MME to perform CS Fallback. The UE may decideto reject CSFB based on Caller Line Identification. The UE sends Service Request (CS Fallback Indicator,Reject or Accept) message towards the MME.

1c. Upon receiving the Service Request (CSFB, Reject), the MME sends CS Paging Reject towards MSC to stop CSPaging procedure and this CSFB procedure stops.

1d. The MME sends a Service Accept message encapsulated in an S1-AP message that also includes the UE Radio

Capabilities and a CS Fallback Indicator. This message: indicates to the eNB that the UE should be moved toUTRAN/GERAN.


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GMSC HLR OldVMSC/VLR

NewVMSC/VLR

MS

PRN (call ref.,GMSC@, Roaming retry) 2

PRN ACK (MSRN)SRI ACK

IAM (MSRN) Paging

LocUpdate

Authentication ProcedureUpdate Location

Cancel Location 3

Cancel Location Ack

RCH (call reference, roaming retry)

Insert Subscriber Data (multiple)

Insert Subscriber Data (continued)

Update Location Ack

Further proceduresrelated to locationupdate. e.g.ciphering, TMSIreallocation.PRN

New VMSC/VLR may delay setup until

location update procedure finishes 8

PRN ACK (MSRN) 7

LocUpdate Accept

TMSI Cmplt

Normal MT call procedure follows.

Old MSC stops paging timerand inform GMSC

2nd SRI ACK (MSRN) 7

2nd SRI (B, basic call interrogation) 5

REL RLCs 4

ACK

HLR delays the sending ofPRN until location update

procedure finishes 6

SAE/LTE

CSFallback

Paging response

SRI (B, GMSC@,call Ref.,Roamingretry)1

IAM (MSRN)

Figure 7.5-1: Roaming Retry for CS fallback

There are only 2 differences in this procedure compared to the Mobile Terminating Roaming Retry Call proceduredefined in TS 23.018 [5]. The first difference is that the paging message triggers the CS fallback including a locationupdate in the new RAT. This functionality is already supported in the CS fallback flows for terminating calls and noadditional functionality is needed. The second difference is that the UE may send a page response message afterreceiving Location Update Accept message. The new MSC will ignore or reject the page response message.

7.6 Returning back to E-UTRAN

Once CS service ends in CS domain, existing mechanisms can be used to move the UE to E-UTRAN, no specific CSFallback mechanisms are needed.

When the UE moves to E-UTRAN, if the EPS service was suspended during the CS service, it is resumed as specifiedin clause 6.5.


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7.7 Interaction with ISR

7.7.1 General

The MSC/VLR keeps either Gs association with SGSN or SGs association with MME, depending from which entity the

last location update message is received. When the MT call comes, the MSC/VLR sends CS paging message to theentity (SGSN or MME) which has Gs or SGs association with the MSC/VLR. When ISR is active, the following

mechanism is needed to ensure that CS Fallback paging is always reaching the UE.

- SGSN or MME starts a CS paging process in its domain and forwards the CS paging message to the ISRassociated entity which is MME or SGSN when ISR is active and the UE is in idle state for the CN nodes thatreceives the CS paging from the MSC/VLR (for SGSN, the UE is in PMM-IDLE (IU mode) or STANDBY(A/Gb mode) state, for MME, the UE is in ECM-IDLE).

SGSN or MME starts a CS paging process only in its own domain when ISR is not active or the UE is connected withthe CN node that receives the CS paging from the MSC/VLR (for SGSN, the UE is in PMM-connected (IU mode) or

READY (A/Gb mode), for MME, the UE is in ECM-CONNECTED).

7.7.2 Mobile Terminating Call when ISR is active and SGs is activebetween MSC/VLR and MME

Figure 7.7.2-1: Mobile Terminating Call when ISR is active and SGs is active between MSC/VLR andMME

1) G-MSC receives IAM.

2) G-MSC retrieves routing information of the terminating UE by Send Routing Info procedures as specified in

TS 23.018 [5].

3) G-MSC sends IAM to the MSC/VLR on the terminating side as specified in TS 23.018 [5].

4) The MSC/VLR sends a Page message to the MME via SGs (details on the Page message can be found in

clauses 7.2 or 7.3).

5a) The MME receives the Page message from the MSC/VLR. As the UE is in ECM-IDLE state, the MME sends aPaging (as specified in TS 23.401 [2], and CN Domain Indicator) message to each eNodeB serving the TA listthe UE is registered to as specified in clause 7.2. If the UE is in ECM-CONNECTED, the MME relays the CSPage message to the serving eNodeB over the S1 interface as specified in clause 7.3.

5b) The eNodeBs receive CS paging messages from the MME, and the procedures take place as specified inclause 7.2.

6a As ISR is active, the MME forwards the CS paging message received from the MSC/VLR to the associatedSGSN. The MME gets the SGSN information in the ISR activation process.


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6b) The SGSN receives the CS paging message from the MME, the SGSN sends paging messages to RNS/BSSs,which is described in detail in TS 23.060 [3].

6c) When RNS/BSS nodes receive paging message from the SGSN, paging is initiated as described in detail inTS 23.060 [3].

NOTE: If ISR is not active or the UE is in ECM-CONNECTED state, the MME does not send the CS paging

message to the SGSN. That means, the steps of 6a, 6b, 6c are not needed in the MT call procedure.

7) Upon receipt of a Paging Request message for a circuit-switched service, the CS Fallback (as defined in this

specification) or Cell Reselection (as defined in TS 23.060[3]) take place, and the UE accesses CS domain fromUMTS/GSM.

8) When the CS Fallback or Cell Reselection completes, the UE responds to the CS paging request and returns theCS paging response as described in detail in this specification and TS 23.060 [3] to the RNS/BSS.

9) When received at the RNS/BSS, the CS Paging Response message is sent to the MSC/VLR as described in detail

in TS 23.060 [3]. The MSC/VLR receives CS paging response contained in corresponding message which shallthen stop the paging response timer and establish the CS connection, then the MT call process as described in

detail in TS 23.018 [5].

7.7.3 Mobile Terminating Call when ISR is active and Gs is activebetween MSC/VLR and SGSN

Figure 7.7.3-1: Mobile Terminating Call when ISR is active and Gs is active between MSC/VLR andSGSN

1) G-MSC receives IAM.

2) G-MSC retrieves routing information of the terminating UE by Send Routing Info procedures as specified inTS 23.018 [5].

3) G-MSC sends IAM to the MSC/VLR on the terminating side as specified in TS 23.018 [5].

4) The MSC/VLR sends a Page message to the SGSN as described in detail in TS 23.060 [3].

5a) The SGSN receives the CS Paging message from the MSC/VLR, sends paging message to RNS/BSS nodes,which is described in detail in TS 23.060 [3].

5b) After the RNS/BSS nodes receive paging messages from the SGSN, the UE is paged by the RNS/BSS nodes,

which is described in detail in TS 23.060 [3].

6a) As ISR is active and the UE is in PMM-IDLE (IU mode) or STANDBY (A/Gb mode), the SGSN forwards the

CS paging message received from the MSC/VLR to the MME. The SGSN gets the MME information in the ISRactivation process.


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6b) The MME receives the CS Page message from the SGSN. As the UE is in ECM-IDLE state, the MME sends aPaging (as specified in TS 23.401 [2], and CN Domain Indicator) message to each eNodeB serving the TA listthe UE is registered to as specified in clause 7.2. If the UE is in ECM-CONNECTED state, the MME relays theCS Page message to the current accessed eNodeB over the S1 interface as specified in sub clause 7.3.

6c) The eNodeBs receive CS paging message from the MME, the following procedures takes place as specified in

clause 7.2 or 7.3.NOTE: If ISR is not active or the UE is in PMM-connected(IU mode) or READY(A/Gb mode), the SGSN does

not forward the CS paging message to the MME, That means, the steps of 6a, 6b, 6c are not needed in theMT call procedure.

7) Upon receipt of a Paging Request message for a circuit-switched service, the CS Fallback or Cell Reselectiontake place , the UE access from UMTS/GSM CS domain.

8) When the CS Fallback or Cell Reselection completes, the UE responds to the CS paging request and returns theCS paging response as described in detail in TS 23.060 [3] to the RNS/BSS.

9) When received at the RNS/BSS, the CS Paging Response message is sent to the MSC/VLR as described in detail

in TS 23.060 [3]. The MSC/VLR receives the CS paging response contained in corresponding message which

shall then stop the paging response timer and establish the CS connection, then the MT call process as describedin detail in TS 23.018 [5].

8 Other CS Services

8.1 General

8.2 Short Message Service (SMS)

8.2.1 General

The procedures for SMS in this specification apply only if the UE is EPS/IMSI attached and the CS access domain ischosen by the UE and/or the home PLMN for delivering short messages.

This clause describes both the mobile originating and mobile terminating SMS procedures for CS Fallback in EPS.SMS support is based on the connectionless SGs reference point between the MME and the MSC Server and use ofNAS signalling between the UE and the MME.

The SMS protocol entities are reused from the existing MS/UE and MSC implementations. This means that the SMSprocedures for CS Fallback reuse the different protocol layers as defined in TS 23.040 [14].

8.2.2 Mobile originating SMS in Idle Mode

The following sequence flow shows the delivery of mobile originating SMS in idle mode.


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MS/UE MME MSC/VLR HLR/HSS SMS-IWMSC

SC

1. CS fallback attach procedure

3. Uplink NAS Transport4. Uplink Unitdata

5. Forward Short Message6. Message transfer

7. Delivery report8. Delivery report

9. Downlink Unitdata

10. Downlink NAS Transport

2. UE triggered Service Request

Figure 8.2.2-1: Mobile originating SMS in idle mode

1. The CS Fallback attach procedure as described in clause 5.2 has been performed earlier.

2. A mobile originating SMS is triggered and the MS/UE is in idle mode. The MS/UE initiates the UE triggeredService Request procedure, which is defined in TS 23.401 [2]. The UE indicates its S-TMSI in the RRCsignalling.

3. The MS/UE builds the SMS message to be sent as defined in TS 23.040 [14] (i.e. the SMS message consists of

CP-DATA/RP-DATA/TPDU/SMS-SUBMIT parts). The SMS message is encapsulated in an NAS message andsent to the MME.

4. The MME forwards the SMS message to the MSC/VLR in an Uplink Unitdata message.

5.-8. These steps are performed as defined in TS 23.040 [14]. The SMS message is forwarded to the SC thatreturns a delivery report message.

9. The MSC/VLR forwards the received delivery report to the MME associated with the MS/UE in a DownlinkUnitdata message.

10. The MME encapsulates the received delivery report in an NAS message and sends the message to the MS/UE.

After this point, the MME may release the resources associated for the SMS transfer.

8.2.3 Mobile originating SMS in Active Mode

Mobile Originating SMS in active Mode procedure is specified by reusing the Mobile Originating SMS in Idle Modewith the following modification:

- The established signalling connection between the MS/UE and the MME is reused for the transport of the SMS

message and the delivery report (i.e. the UE triggered Service Request procedure defined in step 2 is skipped).

8.2.4 Mobile terminating SMS in idle mode

The following sequence flow shows the delivery of mobile terminating SMS in idle mode.


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SMS-

2. Message transfer

3. SendRoutingInfoForShortMessage

4. ForwardShortMessage5. Paging

6. Paging7. Paging

9. Downlink NAS Transport

10. Uplink NAS Transport 11. Uplink Unitdata

13. Delivery report12. Delivery report

8. Service Request

MS/UE eNodeB MSC/VLR HLR/HSSSMS-

GMSC

MMESMS-

GMSC

SC

1. CS fallback attach procedure

9a. Downlink Unitdata

8a. Service Request

Figure 8.2.4-1: Mobile terminating SMS in idle mode

1. The CS Fallback attach procedure as described in clause 5.2 has been performed.

2-4. The SC initiates transfer of mobile terminating SMS. The HLR is requested for routing number for SMSservices and the SMS message is forwarded to the MSC/VLR where the MS/UE is CS attached.

5. The MSC/VLR sends a Paging (IMSI, VLR TMSI, Location Information, SMS indicator) message to the MME.

6. The MME initiates the paging procedure by sending the Paging (as specified in TS 23.401 [2]) message to eacheNodeB with cells belonging to the tracking area(s) in which the UE is registered. The UE is paged with its

S-TMSI.

7. The MS/UE is paged by the eNodeBs.

8. The UE sends a Service Request message to the MME. The UE indicates its S-TMSI in the RRC signalling.

8a. The MME sends a Service Request (SMS Indicator) message to the MSC.

9a. The MSC/VLR builds the SMS message to be sent as defined in TS 23.040 [14] (i.e. the SMS message consistsof CP-DATA/RP-DATA/TPDU/SMS-DELIVER parts). The MSC/VLR forwards the SMS message to the MMEin a Downlink Unitdata message.

9. The MME encapsulates the SMS message in a NAS message and sends the message to the MS/UE.

10. The MS/UE returns a delivery report as defined in TS 23.040 [14]. The delivery report is encapsulated in anNAS message and sent to the MME.

11. The MME forwards the delivery report to the MSC/VLR in an Uplink Unitdata message.

12-13. These steps are performed as defined in TS 23.040 [14]. The delivery report is forwarded to the SC.

8.2.5 Mobile terminating SMS in Active Mode

Mobile terminating SMS in Active Mode procedure is specified by reusing the Mobile Terminating SMS in Idle Mode

with the following modification:

- There is no need for the MME to perform Paging of the MS/UE after step 5. MME continues with step 8a (i.e.steps 6 to 8 are skipped). The MME immediately sends a Downlink Unitdata to the UE.

8.2.6 Co-Existence with SMS over generic 3GPP IP access

If the home operator has deployed SMS over generic 3GPP IP access and/or SMS-Instant Messaging Interworking as

defined in TS 23.204 [15], and has configured the network and the UE for using SMS over IP or SMS-InstantMessaging Interworking, then an SMS or IM will be delivered over EPS in any visited network whether or not thevisited network supports SMS over generic 3GPP IP access.


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If the home operator has not deployed SMS over generic 3GPP IP access and the UE fails to successfully complete thecombined EPS/IMSI attach procedure in the visited network (i.e. the visited network supports SMS over generic 3GPPIP access and does not support CS fallback for SMS capability), then the UE cannot execute MT or MO SMSprocedures in the visited network.

8.3 Location Services (LCS)

8.3.1 MO-LR procedure

MO-LR procedure in the CS fallback in EPS is performed as specified in TS 23.271 [8].

When UE is in active mode, UE and the network follows the procedure in clause 6.2 "Mobile Originating Call inActive-Mode". After UE changes its RAT from E-UTRAN to UTRAN/GERAN, it performs CS-MO-LR procedures asspecified in TS 23.271 [8].

When UE is in active mode but there's no need for PS-Handover, then UE and the network follows the procedure in

clause 6.3 "Mobile Originating Call in Active Mode - No PS HO Support in GERAN". After UE changes its RAT fromE-UTRAN to UTRAN/GERAN, it performs CS-MO-LR procedure as specified in TS 23.271 [8].

When UE is in idle mode, UE follows the procedure in clause 6.4 "Mobile Originating Call in Idle Mode". After UEchanges its RAT from E-UTRAN to UTRAN/GERAN, it performs CS-MO-LR procedure as specified in TS 23.271 [8].

8.3.2 MT-LR procedure

VMSC

MSC ServerMME UE

1. Provide Subscriber Location

2. paging3. paging

PS Handover may take place

4. paging response

5. CS-MT-LR

procedure

continues

Figure 8.3.2-1: MT-LR procedure

1. MSC receives a PROVIDE_SUBSCRIBER_LOCATION message due to CS-MT-LR (TS 23.271 [8],clause 9.1.2).

2. MSC sends Paging (LCS Client Identity, LCS indicator) message to MME.

3. MME sends Paging (parameters as specified in TS 23.401 [2], CN Domain Indicator, LCS Client Identity, LCSindicator) message to UE. LCS indicator is used to inform the UE that this paging if for MT-LR request. LCS

Client Identity and LCS indicator are only included in CS Page if UE is in active mode.


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4. UE responds with Paging_Resp message in UMTS/GERAN. Service based redirection/reselection or PSHandover may take place as specified in clause 7.

5. MSC continues with the CS-MT-LR procedure as defined in TS 23.271 [8], clause 9.1.2.

8.3.3 NI-LR procedure

NI-LR procedure takes place during emergency calls, and is thus performed in GERAN/UTRAN during the MobileOriginating call procedure.

8.3.4 Returning back to E-UTRAN

Once CS service ends in CS domain, existing mechanisms as specified in TS 23.401 [2] can be used to move the UE toE-UTRAN, no specific CS Fallback mechanisms are needed.

8.3.5 Co-Existence with Other Location Services

8.3.5.1 Co-Existence with SUPLThere is no race condition between OMA AD SUPL [9] and CS Fallback for LCS. When network initiated SUPLprocedure takes place, the paging message does not contain CN Domain Indicator by default. This prevents CS Fallback

for LCS to take place. For SET initiated SUPL procedure, changing of RAT does not take place.

8.4 Call Independent Supplementary Services

8.4.1 Mobile-Initiated Call Independent SS procedure

When UE is in active mode, UE and the network follow the procedure in clause 6.2 "Mobile Originating Call inActive-Mode". After UE changes its RAT from E-UTRAN to UTRAN/GERAN, it performs Mobile-Initiated Call

Independent Supplementary Service procedure as specified in TS 24.010 [13].

When UE is in active mode and network initiates NACC procedure, then UE and the network follow the procedure inclause 6.3 "Mobile Originating Call in Active Mode - No PS HO Support in GERAN". After UE changes its RAT from

E-UTRAN to UTRAN/GERAN, it performs Supplementary Service procedure as specified in TS 24.010 [13].

When UE is in idle mode, UE and the network follows the procedure in clause "Mobile Originating Call in Idle Mode".After UE changes its RAT from E-UTRAN to UTRAN/GERAN, it performs Supplementary Services procedure asspecified in specifications such as TS 23.090 [10].


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8.4.2 NW-Initiated Call Independent SS procedure

MSC/VLR MME UE

2. Paging

3. Paging

5. Paging Response

4. Procedures Defined in Clause "Mobile Terminatin Call"

Call Inde endent Su lementar Services rocedure continue

1. Trigger

Figure 8.4.2-1: NW-Initiated Call Independent Supplementary Service procedure

1. MSC/VLR receives a trigger for NW-Initiated Call Independent SS procedure.

2. MSC/VLR sends Paging (optional Caller Line Identification, SS service ID) message to MME.

3. MME sends Paging (parameters as specified in TS 23.401 [2], CN Domain Indicator, optional Caller LineIdentification, SS service ID) message to UE. SS service ID is used to indicate the type of the supplementary

service (e.g. USSD) to the UE. Caller Line Identification and SS service ID are only included in CS Page if UEis in active mode.

4. The mobile terminating call procedure then takes place as specified in clause 7 "Mobile Terminating CallProcedure".

5. Once the paging is successfully returned to MSC, Supplementary Service procedures continues as specified in

specifications such as TS 23.090 [10].

8.4.3 Returning back to E-UTRAN

Once CS service ends in CS domain, existing mechanisms as specified in TS 23.401 [2] can be used to move the UE toE-UTRAN, no specific CS Fallback mechanisms are needed.


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Annex A (informative):Solutions addressing misaligned LAs/TAs at Pool Area

BoundariesThis annex describes alternative solutions addressing the problem of idle-mode mobility across pool area boundaries incase of misaligned LAs/TAs.

A.1 Solution 1: Overlapping Pool Areas with 2G/3Gcoverage > E-UTRAN coverage at Pool AreaBoundaries

This section defines a simple solution for misaligned LAs/TAs at pool area boundaries and is based on the concept of

overlapping and aligned MSC/MME pool areas and adequate configuration of the TAs (with respect to the LAs) at poolarea boundaries. More precisely, the TAs at pool area boundaries must be configured such that they do not extendbeyond the coverage of the corresponding LAs.

Figure A.1-1 illustrates how this solution works based on a simple example scenario. It is assumed here that the UE isinitially served by MME1 and MSC1 (i.e. Pool Area 1). When the UE reaches the TAI=3, which belongs to a differentPool Area than the service MME (MME1), the TAU to the target MME (MME2) will trigger a relocation of the MME(MME1MME2), which in turn triggers a change of the serving MSC (MSC1MSC2).

2G/3G

EUTRAN

RNC1

MSC1

Pool Area 1Pool Area 2

RNC2

MSC2

MME1 MME2

LA1 LA3

TAI=1 TAI=2 TAI=3

1. TAU

2. MME relocationand registration

of new MSC

LA2

This TAU triggers a MMErelocation, which in turntriggers the MSC change

LA2 coveragemust exceedTA2 coverageat Pool Area 1boundary

Figure A.1-1: Solut ion 1: Overlapping Pool Areas with 2G/3G coverage > EUTRAN coverage at PoolBoundaries

In the event of a TAU (Step 1) for a TA served by a different pool area, the target MME will trigger a MME relocation

(Step 2). As a consequence of the MME change, the target MME will trigger the MSC change. The VLR/HLR will beupdated accordingly.


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A.2 Solution 2: Overlapping Pool Areas with SGs-flexsupport

This section defines a simple solution for misaligned LAs/TAs at pool area boundaries based on the concepts ofoverlapping pool area and SGs-flex support. This solution does not rely on adequate configuration of the TAs andalignment of MME and MSC pool areas, but demands the MMEs to supply a configurable TAIMSC Mapping Table.

Figure A.2-1 illustrates how this solution works based on a simple example scenario. It is assumed here that the UE isinitially served by MME1 and MSC1 (i.e. Pool Area 1). When the UE reaches the TAI=2, which is served by a differentPool Area, the TAU (to MME1) will trigger the establishment of the SGs to the target MSC (MSC2). For this, theMME1 maintains a mapping table that indicates which TA should be served by which MSC.

2G/3G

EUTRAN

RNC1

MSC1

Pool Area 1 Pool Area 2

RNC2

MSC2

MME1 MME2

LA1 LA3

TAI=1 TAI=2 TAI=3

1. TAU

2. Establish SGs totarget MSC (basedon Mapping Table)

LA2

This TAU triggers the MMEto establish a SGs with the

target MSC

TAI/MSC Mapping

TAI=1 MSC1

TAI=2 MSC2

TAI=3 MSC2

Figure A.2-1: Solution 2: Overlapping Pool Areas with SGs-flex support

In the event of a TAU (Step 1) for a TA belonging to a different pool area, the serving MME will trigger theestablishment of the SGs connection to the target MSC (Step 2). The VLR/HLR will be updated accordingly.


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Annex B (normative):CS Fallback to 1xRTT

This annex describes a CS Fallback to 1xRTT solution for dual mode 1xRTT/E-UTRAN terminals.

B.1 Overall Description

B.1.1 General Considerations

The CS fallback for 1xRTT in EPS enables the delivery of CS-domain services (e.g. CS voice, SMS) by reuse of the1xCS infrastructure when the UE is served by E-UTRAN. A CS fallback enabled terminal, while connected to E-UTRAN may register in the 1x RTT CS domain in order to be able to use 1xRTT access to establish one or more CSservices in the CS domain. This function is only available where E-UTRAN coverage overlaps with 1xRTT coverage.

CS Fallback to 1xRTT and IMS-based services shall be able to co-exist in the same operator's network.

B.1.2 Reference Architecture

The CS fallback in EPS function is realised by reusing the S102 reference point between the MME and the 1xCS IWS.The reference architecture described in figure B.1.2-1 is similar to the SRVCC architecture for E-UTRAN to 3GPP21xCS described in TS 23.216 [20], with the additional aspect that the S102 session is long-lived (similar to

pre-registration for S101).

E-UTRAN

MME

Serving/PDNGW

SGi

1xRTT CSAccess

1xRTTMSC

1xCS IWS

S102

S11S1-MME

S1-U

A1

A1

Tunnelled 1xRTT messages

1xCSCSFB

UE

1xCSCSFB

UE

Figure B.1.2-1: Reference archi tecture for CS fallback to 1xRTT CS

B.1.2.1 Reference points

S102: It is the reference point between the MME and the 1xCS IWS. The S102 reference point provides a tunnelbetween MME and 3GPP2 1xCS IWS to relay 3GPP2 1xCS signalling messages. 1x CS signallingmessages are those messages that are defined for A21 interface as described in 3GPP2 A.S0008-C [16]and 3GPP2 A.S0009 [17].


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NOTE. It is up to stage 3 to determine whether the tunnelling protocol for S102 can be defined as exactly as inA21. If so, S102 is then equivalent to A21.

B.1.3 Functional entities

B.1.3.1 UE

The UE capable of CS fallback to 1xRTT supports access to E-UTRAN/EPC as well as access to the 1xCS domain over1xRTT. It supports the following additional functions:

- 1xRTT CS registration over the EPS after the UE has completed the E-UTRAN attachment;

- 1xRTT CS re-registration due to mobility;

- CS fallback procedures specified for 1xRTT CS domain voice service;

- Procedures for mobile originated and mobile terminated SMS over E-UTRAN.

B.1.3.2 MME

The MME enabled for CS fallback to 1xRTT supports the following additional functions:

- It serves as a signalling tunnelling end point towards the 3GPP2 1xCS IWS via S102 interface forsending/receiving encapsulated 3GPP2 1xCS signalling messages to/from the UE, which are encapsulated in S1-

MME S1 Information Transfer messages, as defined in TR 36.938 [19];

- 1xCS-IWS (terminating S102 reference point) selection for CSFB procedures;

- Handling of S102 tunnel redirection in case of MME relocation;

- Buffering of messages received via S102 for UEs in idle state.

B.1.3.3 E-UTRAN

The E-UTRAN enabled for CS fallback to 1xRTT supports the following additional functions:

- Provision of control information that causes the UE to trigger 1xCS registration;

- Forwarding 1x RTT CS paging request to the UE;

- Forwarding 1x RTT CS related messages between MME and UE;

- Release of E-UTRAN resources after UE leaves E-UTRAN coverage subsequent to a page for CS fallback to

1xRTT CS.

B.1.4 Co-existence with IMS services

Clause 4.4 of this specification also applies here.

B.2 Procedures

B.2.1 Mobility Management

B.2.1.1 1x RTT CS Pre-Registration over EPS ProcedureThis clause describes how the UE in an E-UTRAN system establishes and maintains pre-registration in the 1xCSsystem.


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Figure B.2.1.1-1: 1xRTT CS registration procedure

1.

UE attaches to E-UTRAN as specified in TS 23.401 [2];

2. Based on a radio layer trigger (e.g. an indication from the E-UTRAN when the UE is in connected state or anindication over the broadcast channel), the UE decides to register with the 1xRTT CS domain;

3. UE generates a 1xRTT CS registration request.

3a. The 1xRTT CS message is transferred from the UE to E-UTRAN.

3b. E-UTRAN forwards the 1xRTT CS message to the MME including the Reference CellID.

3c. MME selects a 1xCS IWS node based on Reference CellID.The IMSI is used to

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LTE, Fallback, CS, GSM