Support for CSFBSupport for CSFB

Tony Lee aslee@via-telecom.comTony Lee aslee@via-telecom.comDavid Wang David Wang davidwang@via-telecom.comdavidwang@via-telecom.com

June/15/2009

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IntroductionIntroduction

• This contribution list out some stage two concepts that needs to be incorporate into C.P0087 v2.0 to support CSFB

CSFB backgroundCSFB background

TS 23.272 CSFB in EPS stage 2, it contains the requirements for E-UTRAN to 1xRTT CSFB, which includes:• Architecture• UE• E-UTRAN• MME

ArchitectureArchitecture

E-UTRAN

MME

Serving/PDN GW

SGi

1xRTT CS Access

1xRTT MSC

1xCS IWS

S102

S11 S1-MME

S1-U

A1

A1

Tunnelled 1xRTT messages

1xCS CSFB

UE

1xCS CSFB

UE

CSFB call flow: Pre-registrationCSFB call flow: Pre-registration

1xCS CSFB

UE

E-UTRAN MME 1xCS

IWS1xRTTMSC

. -

3. 1xRTT CS registration request

3a. UL/DL InformationTransfer

3b. UL/DL S1 cdma2000Tunnelling

3c. S102 Direct Transfer

5. 1xRTT CS registration response

5c. UL/DL InformationTransfer

5b UL/DL S1 cdma2000Tunnelling

5a. S102 Direct Transfer

1. UE attaches to E-UTRAN as specified in TS 23.401

4. Location update to 1xRTT CS domain

2. Decision to register with 1xRTT CS

Pre-registrationPre-registration

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 an indication 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 distinguish S102 signalling transactions belonging to different UEs. The MME sends a S102 Direct Transfer message (IMSI, 1xCS message) to the 1xCS IWS node.

4. 1xRTT CS registration is then performed by the 1xCS IWS node based on 3GPP2 A.S0008 [16].

5a. 1xRTT CS registration response is tunnelled back to the MME in a S102 Direct Transfer message (IMSI, 1xCS message).

5b. MME forwards the 1xRTT CS message to the E-UTRAN.

5c. E-UTRAN forwards the 1xRTT CS message to the UE.

If the triggers for 1xCS registration change over time, the UE (both in idle or active state), uses this information to update the 1xCS registration via the tunnel.

CSFB call flow: Mobile OriginationCSFB call flow: Mobile Origination

1xCS CSFB

UE

E-UTRAN MME 1xCS

IWS1xRTTMSC

1. UE is E-UTRAN attached and registered with 1xRTT CS

11. 1x MO call establishment per 3GPP2 specifications

. -

4. S1 UE Context Modification

3. Service Request

S-GW

5. Optional measurement report solicitation

7. S1 UE Context Release Request

8. Suspend Request

9. Suspend Request Ack

10. S1 UE Context Release

2. UE decision to perform MO

call in 1xCS

6. E-UTRAN triggers RRC connection release with redirection or CCO to 1xCS

Mobile OriginationMobile Origination

1. UE is E‑UTRAN attached and registered with 1xRTT CS as defined in clause B.2.1.1.

2. UE makes a decision to perform a mobile originated CS call.

3. UE sends a Service Request (CS Fallback Indicator) to the MME.

4. MME sends S1-AP: UE Context Modification (UE capabilities, CS Fallback Indicator) to indicate the E‑UTRAN to move the UE to 1xRTT.

5. E-UTRAN may optionally solicit a measurement report from the UE to determine the target 1xRTT cell to which the CS Fallback will be performed.

6. E-UTRAN triggers RRC connection release with redirection to 1xCS or inter-RAT Cell Change Order to a 1xRTT neighbour cell.

7. E-UTRAN sends an S1 UE Context Release Request (Cause) message to the MME. Cause indicates that the S1 UE Context Release was caused by CS fallback to 1xRTT.

8. MME sets the UE context to suspended status and sends to the S-GW a Suspend Request (IMSI) message that requests the suspension of EPS bearers for the UE.

9. S-GW acknowledges the Suspend Request message and marks the UE as suspended. When a downlink data arrives at the S-GW, the S-GW should not send a downlink data notification message to the MME if the UE is marked as suspended.

10. S1 UE Context in the E-UTRAN is released as specified in TS 23.401 [2].

11. UE moves to 1xRTT and performs the procedure for mobile originating call as specified in 3GPP2 A.S0013 [18].

Once CS service ends in the 1xCS domain, the UE returns to E‑UTRAN by performing reselection. The EPS service is resumed as described in clause 6.5.

Mobile Termination

1xCS CSFB

UE

E-UTRAN MME 1xCS

IWS1xRTTMSC

. - 3. 1xRTT CS Paging

5b. UL/DL InformationTransfer

5a. UL/DL S1 cdma2000Tunnelling

S102 Direct Transfer

5. 1xRTT CS Paging

1. UE is E-UTRAN attached and registered with 1xRTT CS

4. If UE is idle, MME performs Network-initiated service request

2. Paging Request

15. 1x MT call establishment per 3GPP2 specifications

. -

14. 1xRTT CS Page Response Message

7. S1 UE Context Modification

6. Service Request

S-GW

8. Optional measurement report solicitation

10. S1 UE Context Release Request

11. Suspend Request

12. Suspend Request Ack

13. S1 UE Context Release

9. E-UTRAN triggers RRC connection release with redirection or CCO to 1xCS

Mobile Termination

1. UE is E-UTRAN attached and pre-registered with 1xRTT CS as defined in clause B.2.1.1.

2. 1xMSC sends a paging request to the 1xCS IWS node.

3. 1xCS IWS node forwards the 1x RTT CS paging request via the S102 tunnel to the MME.

4. If the UE is in idle state, the MME performs the network initiated Service Request procedure in order to bring the UE to active state prior to tunnelling of the 1x RTT CS paging request toward the UE.

5. MME forwards the 1xRTT CS paging request to the UE.

6. UE sends a Service Request (CS Fallback Indicator) to the MME.

7. MME sends S1-AP: UE Context Modification (UE capabilities, CS Fallback Indicator) to indicate the E UTRAN to move the UE to 1xRTT.

8. E-UTRAN may optionally solicit a measurement report from the UE to determine the target 1xRTT cell to which the CS Fallback will be performed.

9. E-UTRAN triggers RRC connection release with redirection to 1xCS or Inter-RAT Cell Change Order to a 1xRTT neighbour cell.

10. E-UTRAN sends an S1 UE Context Release Request (Cause) message to the MME. Cause indicates that the S1 UE Context Release was caused by CS fallback to 1xRTT.

11. MME sets the UE context to suspended status and sends to the S-GW a Suspend Request (IMSI) message that requests the suspension of EPS bearers for the UE.

12. S-GW acknowledges the Suspend Request message and marks the UE as suspended. When a downlink data arrives at the S-GW, the S-GW should not send a downlink data notification message to the MME if the UE is marked as suspended.

13. S1 UE Context in the E-UTRAN is released as specified in TS 23.401 [2].

14. UE tunes to 1xRTT and acknowledges the page by transmitting a 1xRTT Paging Response message over the 1x Access Channel.

15. Subsequently UE performs the procedure for mobile terminated call establishment as specified in 3GPP2 A.S0013 [18].

CSFB backgroundCSFB background

TS 36.331 Radio Resource Control, it contains requirement for:• Messages and parameters to set up 1x registration• SIB 8

• System time• Long Code State• CSFB registration parameters

Requirements for 1xRequirements for 1x

Synchronize with base station using information provided by SIB 8

Need to send LAC encapsulated message over E-UTRAN tunnel

Perform pilot measurement during E-UTRAN gap

Track registration status

Perform origination or page response with minimum delay

Proposal Overview

MAC MAC

RLC RLC

PDCP PDCP

RRC CSTCP

CSTDP

LAC

L3 CSFB Parameters

Measurement Request

1x Signaling Message

PHY PHY

LTE cdma2000 1x

Data Plane

Control Plane

Proposal: Data plane view

1x Layer 3

1x LAC

CSTDP

LTE Air

Interface

LTE Air

Interface

S1-MME

Lower Layer

S1-MME

Lower Layer

S102

Lower Layer

CSTDP

S102

Lower Layer

1x Layer 3

1x LAC

Lower Layer

A1

Out of scope

1x CSFB UE eNB MME IWS

To 1x MSC

Proposal details

CSTDP Circuit Switch Tunneling Data Protocol Encapsulate LAC messages with parameters similar to CSNA:

ARQ parameters Logical channel Protocol revision number

CSTCP Interface between E-UTRAN and 1x Base station: generate necessary 1x overhead parameters Mobile: process 1x parameter and pass this on to L3

Proposal details

Changes to 1x mobile Bypass pilot acquisition Use SIB 8 information to synchronize with base

station No need to monitor control channel, this includes

paging and BCCH No need to start any supervision timer Obtain parameters from CSTCP

Additional changes for C.S0087

Need to add MobilityParametersCDMA2000 in C.S0087 to support TS 36.331

In TS 36.331 RRC document has two messages related to CSFB CSFBParametersRequestCDMA2000 ( UE to eNB) CSFBParametersResponseCDMA2000

MobilityParametersCDMA2000 is defined, but refers to C.S0087 for details. The parameters are necessary to generate the registration message

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