ultra-flash csfb(srvcc based csfb)

HUAWEI TECHNOLOGIES CO., LTD.

Ultra-Flash CSFB(SRVCC based CSFB)

Source Company: Huawei, HiSilicon, Bharti, China Unicom, Deutsche Telekom

SA WG2 Meeting #100 S2-13431511 - 15 November 2013, San Francisco, USA

Content

Ultra-Flash CSFB introduction

Ultra-Flash CSFB Discussion

Summary


LTE

G/U

SGs

MSC

SGSN

MME

Redirection

What is Ultra-Flash CSFB?

MSC

SGSN

MME

IMS

SRVCC Session Transfer

LTE

G/U

Sv

SRVCC Inter RAT Handover

SRVCC IRAT HOSv

SRVCC Inter RAT Handover

SRVCC IRAT HO

CSFB VoLTEw/ SRVCC

Ultra-Flash CSFB is a solution used SRVCC IRAT handover to accelerate CSFB

LTE

G/U

SGs

MSC

SGSN

MME

Redirection

Ultra-Flash CSFB

Ultra-Flash CSFB, SRVCC Session Transfer is not needed as it is a CS call setup procedure rather than VoLTE to 2/3G hand over .

Ultra-Flash CSFB requires UE to support standard SRVCC feature.


Ultra Flash CSFB with SRVCC capable UE

UE eNodeB BSS/RNS MMESRVCC

MSC

1a. Extend Service Request

1b. S1-AP Message with (CSFB indicator)

2. Optional Measurement Report Solicitation

13. call proceeding

15. Disconnect(TI=0, TI Flag=0)

12. Setup(TI=0,TI Flag=0)

9 . UTRAN mobility information

10. SECURITY MODE COMMAND

8a. Handover Complete

7a. Handover Command

14. alerting

Per UE’s SRVCC capability and without a QCI=1 bearer, eNB triggers SRVCC HO during CSFB

MME does not delete a QCI=1 bearer as the SRVCC procedure is due to CSFB and there is no QCI=1 bearer

(1) The MSC does not initiate the Session Transfer procedure and only triggers a normal CS Handover preparation

(2) the MSC sends Disconnect to clear the dummy call instance due to SRVCC procedure


EBI

EMMESM-SAP

CM

MM-sublayer

RRCPDCP

E-UTRAN Access Stratum sublayer

EMMAS-SAP

GSMSESMS

EMMSMS-SAP

TI

RB 1

Bearer Control

RB 2

RB n

PDCP1-SAP

EMMEMMCoord

MMMMCoord

PDCP2-SAP PDCPn-SAP

RB1-SAP RB2-SAP RBn-SAP

RBMAS-SAP

ESM

EMMREG-SAP

ESMREG-SAP MNSMS-SAP

GSMSCC

MNCC-SAP

GSMSSS

MNSS-SAP

PD

TI

RR-SAP

MMCC-SAP

TI

MMSS-SAP

GERAN/UTRAN Access Stratum sublayer

PD

Step a2 CSFB Indication

Step a1MM connection

Req

Step a3 Extended Service Req

Step b1 HO CMD

Step b3 Access Indication

Step b6CS Call Established due to SRVCC HOStep b4

Bearer Status

Step b5 MM connection

Established

Ultra Flash CSFB with SRVCC capable UE - MO


Huawei Analysis As shown in green lines, the UE start CS call and CC sublayer allocate (TI=0,TI Flag=0) CS voice

session.

The MM sublayer find out the UE in E-UTRAN side and indicate EMM sublayer to initiate ESR procedure

The LTE AS layer forward HO CMD to GERAN/UTRAN AS layer

GERAN/UTRAN AS layer access the GERAN/UTRAN and SRVCC handling is triggeredMM sublayer gives an indication to the CC sublayer to establish CS call(TI=0,TI Flag=1)due to

SRVCC per step b6.And derives GERAN/GERAN security contexts for the CS domain from the current EPS

security context

Upon receiving step b6, CC sublayer allocates(TI=0, TI Flag=1) for SRVCC and proceed with (TI=0,TI Flag=0) call setup procedure by sending CM Service Request and Setup with TI=0.

MSC send disconnect(TI=0,TI Flag=1) to clear the dummy call object (TI=0, TI Flag = 1) in UE side.


Ultra Flash CSFB with L->U SRVCC - MT

UE eNodeBBSS/RN

SMME

SRVCC MSC

1c. S1-AP Message with (CSFB indicator)


12. Setup(TI=1)

13. call confirmed

14. alerting

1b. Extend Service Request

1a. CSFB Page

5. CS handover preparation

9 . UTRAN mobility information

10. SECURITY MODE COMMAND


6. PS to CS Response

8b. Handover Complete


15. Disconnect(TI=0)

UE establish TI=0 voice Session

Per UE’s SRVCC capability and without a QCI=1 bearer, eNB triggers SRVCC HO during CSFB

MME does not delete a QCI=1 bearer as the SRVCC procedure is due to CSFB and there is no QCI=1 bearer

(1) The MSC does not initiate the Session Transfer procedure and only triggers a normal CS Handover preparation

(2) the MSC sends Disconnect to clear the dummy call instance due to SRVCC procedure

(3)SRVCC MSC send setup(TI=1) to the UE


Ultra Flash CSFB with SRVCC capable UE - MT

EBI

EMMESM-SAP

CM

MM-sublayer

RRCPDCP

E-UTRAN Access Stratum sublayer

EMMAS-SAP

GSMSESMS

EMMSMS-SAP

TI

RB 1

Bearer Control

RB 2

RB n

PDCP1-SAP

EMMEMMCoord

MMMMCoord

PDCP2-SAP PDCPn-SAP

RB1-SAP RB2-SAP RBn-SAP

RBMAS-SAP

ESM

EMMREG-SAP

ESMREG-SAP MNSMS-SAP

GSMSCC

MNCC-SAP

GSMSSS

MNSS-SAP

PD

TI

RR-SAP

MMCC-SAP

TI

MMSS-SAP

GERAN/UTRAN Access Stratum sublayer

PD

Step a3 CSFB Indication

Step b5Bearer Status

Step a2 Paging

Step a4 Extended Service Req

Step a1Paging

Step b1 HO CMD

Step b4 Paging Response

Step b3 Access Indication

Step b7 Setup(TI=1)

Step b6CS Call Established due to SRVCC HO


Huawei Analysis

As shown in green lines, the UE(LTE part) receive CSFB paging call and trigger the CSFB procedure accordingly.

The LTE AS layer forward HO CMD to GERAN/UTRAN AS layer

GERAN/UTRAN AS layer access the GERAN/UTRAN and SRVCC handling is triggeredMM sublayer gives an indication to the CC sublayer to establish CS call with TI =0 due

to SRVCC per step b6.And derives GERAN/GERAN security contexts for the CS domain from the current EPS

security context

CC sublayer allocate TI=0 CS session per step b6

MM sublayer sends paging response to MSC and MSC sends setup(TI=1) to the UE as TI=0 is already in CC sublayer.

MSC further sends Disconnect(TI=0) to the UE in order to release the TI=0 CS session


Ultra-Flash CSFB VS NW-Initiated CS Services while UE is in IMS VoIP session in 8.4.2.2

UE/MS MME BSS/RNS MSC eNodeB SGSN Serving

GW P - GW/ GGSN


1b. Extended Service Request

1d. S1 - AP Message with CS Fallback indicator

1 a . P aging Request 1 a . CS Paging Notification

1c. CS Paging Reject 1a. Service Request

IMS VoIP Session

1. Trigger

3. SRVCC procedure in 23.216 [20] clause 6.2.2.2

4. CS procedure continues

SGSNUE eNodeB BSS MMESRVCC

MSC

1c. S1-AP Message with (CSFB indicator)


10. Setup(TI=1, TI Flag=0)

11. call confirmed

12. alerting

1a. CSFB Page

1b. Extend Service Request

1a. CSFB Page

3. Handover Required

5. CS handover preparation


6. PS to CS Response

8b. Handover Complete


13. Disconnect(TI=0, TI Flag=0)

9. Suspend

8e. Release Resources

8d. Bearer handling

Session Transfer

1a. Service Request

8.4.2.2 NW-Initiated CS Services while UE is in IMS VoIP session0

Ultra Flash CSFB


NW-Initiated CS Services while UE is in IMS VoIP session in 8.4.2.2 Vs Ultra-Flash CSFB

NW-Initiated CS Services while UE is in IMS VoIP session Ultra-Flash CSFB

1 MME Need to delete QCI=1 bearer during SRVCC Do not delete QCI=1 bearer during SRVCC as there is no QCI=1 bearer.

2 MSCInitiates Session Transfer to move VoLTE to 2/.3G CS

(1)MSC does not Initiates Session Transfer during SRVCC procedure.

(2) Send Disconnect to clear due to SRVCC HO procedure.

(3) MSC sends Setup message to UE with TI value of the voice call to "001" and TI flag value as in mobile terminated call since UE.

3 eNBBased on UE measurement reports and UE’s SRVCC capability and QCI = bearer, decides to trigger an SRVCC handover to UTRAN/GERAN.

Based on UE measurement reports and CS Fallback Indicator and UE’s SRVCC capability , decides to trigger an SRVCC handover to UTRAN/GERAN.

4 BSC/RNC No impact No impact

5 UE Standard VoLTE/SRVCC UEStandard CSFB/SRVCC UE

Content



Summary


Call Setup Time Comparison(Fall back to GSM)

SRVCC IRAT HO

Ultra-Flash CSFB to GSM

R8 R9(Flash) Ultra-Flash call Ultra-Flash

GSM Call

Ultra-Flash CSFB

2G call 2G

SRVCC/PS HO

Authentication/encryption/UE Capacity identify

CS RAB establishment

UE access to 2G cell

Read SI

Basic call procedure

Based on Huawei Lab testingLTE call LTE,

both MO/MT fall back


Call Setup Time Comparison(Fall back to UMTS)

Ultra-Flash CSFB to UMTS

R8 PSHO Ultra-Flash call Ultra-Flash

UMTS Call

Ultra-Flash CSFB

3G call 3G

Based on Huawei Lab Test

SRVCC/PS HO

Authentication/encryption/UE Capacity identify

CS RAB establishment

UE access to 3G cell

Read SI

Basic call procedure

SRVCC IRAT HO

PS HO

LTE call LTE, both MO/MT fall back


CSFB Ultra-Flash CSFB1 Cell Selection

Use redirection mechanism to access target 2/3G cell

Use SRVCC or PS IRAT handover to access target cell

2 CS RAB EstablishmentStart CS RAB setup procedure during the CS call setup procedure in 2/3G

Skipping the CS RAB setup procedure, as the RAB is pre-allocated during the SRVCC IRAT Handover procedure

3Authentication /

encryption/UE Capacity identify

Authentication/encryption/UE Capacity identify are mandatory

Authentication/encryption/UE Capacity identify were done during SRVCC handover, reduce extra time consumption

4Signaling transport channel(Only GSM)

SD(stand-alone dedicated control channel)， Shared by 8 users

TCH(Traffic Channel)， Single-user exclusive

Why Ultra-Flash CSFB Achieve the Shortest Call Setup ?

Ultra-Flash CSFB Reduce Call Setup Time in Following 4 Steps

Both Sv and SGs interfaces supported, SRVCC IRAT HO was

used to accelerate CSFB

SRVCC MSC MME

Sv

SGs3

BSC/RNC eNB1

2

4


How Ultra-Flash CSFB Reduce Impact to Current Network

CSFB Ultra-Flash CSFB

1 MSCUpgrade MSC or Proxy（ additional 1~2s

delay）Proxy solution avoid MSC upgrading（ with only

about 400ms additional delay）

2 TA/LA mappingNeed strictly planning, otherwise call setup time

would be prolonged and call success rate decrease

Don’t need strictly planning, no impact to call setup latency and call success rate

3Roaming Retry/Roaming

Forwarding All MSC must be upgraded, otherwise it will lead

to call failure in case of TA/LA misalignmentDon’t need deploy Roaming Retry/Roaming Forwarding, no impact to call success rate

4 VoLTE/SRVCC evolutionMME/MSC must be upgraded again when

deploying VoLTE/SRVCCSv interface is ready for VoLTE/SRVCC, avoid

MME/MSC upgrading again

Proxy solution, reduce the impact to CS network

eNodeB

SRVCC MSC

BSC/RNC

VMSCMME

Sv

SGs

IMS Core

EPC Naturally support VoLTE/SRVCC，without MME/MSC upgrade again

Could update some (one at the minimum) MSC Servers rather than all the MSC Servers


How Rel-8 CSFB and Ultra-Flash CSFB co-exist

IMS Core

MMEMSC

eNBBSC/RNC

SRVCC MSC

SGs

SGsSv

Per 23272-b50, during combined Attach/TAU procedure

If UE supports SRVCC, MME selects a MSC/VLR which is both SRVCC and CSFB capable

If UE does not support SRVCC, MME selects a MSC/VLR which is CSFB capable

During the CSFB procedure, based on UE capability

If UE support SRVCC capability, eNB is to perform Ultra-Flash CSFB i.e. executing SRVCC HO

If UE does not support SRVCC capability, eNB is to perform Rel-8 CSFB

Add software patch on SRVCC feature and no impact on Rel-8 CSFB.

Content



Summary


PrincipleEasy

Deployment

SRVCC UE

MSC MME eNB

• Avoid to update RNC/BSC• Fall back GSM and UMTS

Supported

3 ~ 5 S

Ultra-Flash

L->U 6 ~ 9 SL->G 10-12 S

R8 CSFB

Call Setup Time

2

LTE

MME

G/U

MSC1

23

4

In parallel UE fallback and call in MSC

Ultra-Flash CSFB Value and Principle

Shorter than the Traditional CS Call Delay

Reuse SRVCC handover to accelerate CSFB and smooth evolution to VoLTE/SRVCC

Avoid to update 2G/3G Radio

SRVCC HO

SRVCC HO

Proposed to add deployment option in Rel-12 that enables faster and more reliable CSFB for UEs and networks supporting SRVCC.

Thank youwww.huawei.com

Copyright©2013 Huawei Technologies Co., Ltd. All Rights Reserved.

The information in this document may contain predictive statements including, without limitation, statements regarding the future financial and operating results, future product portfolio, new technology, etc. There are a number of factors that could cause actual results and developments to differ materially from those expressed or implied in the predictive statements. Therefore, such information is provided for reference purpose only and constitutes neither an offer nor an acceptance. Huawei may change the information at any time without notice.


VoLTE configured UE support Ultra-Flash CSFB Directly

MME

MSC

SGW PGW

VoLTE

Ultra-Flash CSFB

IMS PS voice priority, CS Voice secondary is configured in UE

UE decide to use VoLTE or Ultra-Flash CSFB according to MME indication

1. If IMS has been deployed，MME indicate UE IMS Voice over PS session supported

2. If IMS has not been deployed，MME indicate IMS Voice over PS session NOT supported

Value：1. If IMS has not been deployed, VoLTE/SRVCC UE

can use Ultra-Flash CSFB

2. After IMS has been deployed, UE can use VoLTE directly without reconfiguration

ultra-flash csfb(srvcc based csfb)

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