SA WG2 Meeting #100
11 - 15 November 2013, San Francisco, USA
S2-134315
Ultra-Flash CSFB(SRVCC based CSFB)
Source Company: Huawei, HiSilicon,
Bharti, China Unicom, Deutsche Telekom
HUAWEI TECHNOLOGIES CO., LTD.
Page 1
Content
Ultra-Flash CSFB introduction
Ultra-Flash CSFB Discussion
Summary
What is Ultra-Flash CSFB?
LTE
MME
LTE
MME
SRVCC Inter
RAT Handover
VoLTE
w/ SRVCC
CSFB
Redirection
SGs
SGSN
SGSN
G/U
MSC
Sv
SRVCC IRAT HO
G/U
MSC
SRVCC
Session
Transfer
IMS
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
Ultra-Flash CSFB is a solution used SRVCC IRAT handover to accelerate CSFB
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Ultra Flash CSFB with SRVCC capable UE
UE
eNodeB
BSS/RNS
SRVCC
MSC
MME
1a. Extend Service Request
Per UE’s SRVCC capability and without a
QCI=1 bearer, eNB triggers SRVCC HO
during CSFB
1b. S1-AP Message with
(CSFB indicator)
2. Optional Measurement
Report Solicitation
3. Handover Required
MME does not delete a QCI=1 bearer
as the SRVCC procedure is due to
CSFB and there is no QCI=1 bearer
4. PS to CS
HO Request
5. CS handover preparation
(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
6. PS to CS
Response
7a. Handover Command
7b. Handover
Command
8a. Handover Complete
8b. Handover Complete
9 . UTRAN mobility information
10. SECURITY MODE COMMAND
11. CM service request
12. Setup(TI=0,TI Flag=0)
13. call proceeding
14. alerting
15. Disconnect(TI=0, TI Flag=0)
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Page 4
Ultra Flash CSFB with SRVCC capable UE - MO
MNSMS-SAP
ESMREG-SAP
MNCC-SAP
MNSS-SAP
CM
RB1-SAP
RB2-SAP
RBn-SAP
GSMS
ESMS
ESM
GSMS
CC
Step b6
Step a1
CS Call Established
MM connection
due to SRVCC HO
Req
TI
RB 1
Bearer
Control
RB 2
Step b4
Bearer Status
TI
EBI
GSMS
SS
TI
RB n
EMMSMS-SAP
EMMESM-SAP
EMMREG-SAP
Step b5
MMSS-SAP
MM connection
MMCC-SAP
Established
MM-sublayer
PD
Step a2 CSFB
Indication
EMM
EMM
Coord
Step a3 Extended
Service Req
PDCP1-SAP
PDCP2-SAP
PDCPn-SAP
RBMAS-SAP
MM
Coord
PD
MM
Step b3 Access
Indication
RR-SAP
EMMAS-SAP
GERAN/UTRAN
Access Stratum sublayer
E-UTRAN Access Stratum sublayer
PDCP
RRC
Step b2
Tune to 2/3G
Step b1 HO CMD
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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 triggered
MM 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.
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Page 6
Ultra Flash CSFB with L->U SRVCC - MT
UE
BSS/RN
S
eNodeB
SRVCC
MSC
MME
1a. CSFB Page
Per UE’s SRVCC capability and without a
QCI=1 bearer, eNB triggers SRVCC HO
during CSFB
1a. CSFB Page
1b. Extend Service Request
1c. S1-AP Message with
(CSFB indicator)
MME does not delete a QCI=1 bearer
as the SRVCC procedure is due to
CSFB and there is no QCI=1 bearer
2. Optional Measurement
Report Solicitation
3. Handover Required
4. PS to CS
HO Request
5. CS handover preparation
6. PS to CS
Response
7b. Handover
Command
7a. Handover Command
(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
UE establish TI=0
voice Session
8a. Handover Complete
8b. Handover Complete
9 . UTRAN mobility information
10. SECURITY MODE COMMAND
11. Paging Response
12. Setup(TI=1)
13. call confirmed
14. alerting
15. Disconnect(TI=0)
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Page 7
Ultra Flash CSFB with SRVCC capable UE - MT
MNSMS-SAP
ESMREG-SAP
MNCC-SAP
MNSS-SAP
CM
RB1-SAP
RB2-SAP
RBn-SAP
GSMS
ESMS
ESM
GSMS
CC
Step b6
CS Call Established
due to SRVCC HO
TI
RB 1
Bearer
Control
RB 2
Step b5
Bearer Status
TI
EBI
GSMS
SS
TI
RB n
EMMSMS-SAP
EMMESM-SAP
MMSS-SAP
MMCC-SAP
EMMREG-SAP
MM-sublayer
PD
Step a3 CSFB
Indication
EMM
EMM
Coord
PDCP2-SAP
PDCPn-SAP
RBMAS-SAP
PD
MM
Step a2 Paging
Step a4 Extended
Service Req
PDCP1-SAP
MM
Coord
Step b3
Access Indication
RR-SAP
EMMAS-SAP
GERAN/UTRAN
Access Stratum sublayer
E-UTRAN Access Stratum sublayer
PDCP
RRC
Step b2
Tune to 2/3G
Step a1
Paging
Step b4
Paging Response
Step b1
HO CMD
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Page 8
Step b7
Setup(TI=1)
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 triggered
MM 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
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Page 9
Ultra-Flash CSFB
UE
VS
eNodeB
BSS
NW-Initiated CS Services while UE is in IMS VoIP session in 8.4.2.2
SRVCC
MSC
MME
SGSN
UE/MS
eNodeB
BSS/RNS
MME
1a. CSFB Page
1a. CSFB Page
Serving
GW
1. Trigger
1c. S1-AP Message with
(CSFB indicator)
2. Optional Measurement
Report Solicitation
1a. Paging Request
3. Handover Required
4. PS to CS
HO Request
5. CS handover preparation
1a. CS Paging Notification
Session
Transfer
1b. Extended Service Request
7a. Handover Command
7b. Handover
Command
8b. Handover Complete
8c. PS to CS
Complete/ACK
8d. Bearer handling
8e. Release Resources
1a. Service Request
1c. CS Paging Reject
6. PS to CS
Response
8a. Handover Complete
SGSN
IMS VoIP Session
1a. Service
Request
1b. Extend Service Request
MSC
1d. S1-AP Message with CS Fallback indicator
2. Optional Measurement Report Solicitation
3. SRVCC procedure in 23.216 [20] clause 6.2.2.2
9. Suspend
10. Setup(TI=1, TI Flag=0)
4. CS procedure continues
11. call confirmed
12. alerting
13. Disconnect(TI=0, TI Flag=0)
Ultra Flash CSFB
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8.4.2.2
NW-Initiated CS Services while UE is in IMS
VoIP session0
Page 10
P-GW/
GGSN
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
1
MME
Need to delete QCI=1 bearer during SRVCC
Ultra-Flash CSFB
Do not delete QCI=1 bearer during SRVCC as there is no QCI=1
bearer.
(1)MSC does not Initiates Session Transfer during SRVCC procedure.
2
MSC
Initiates Session Transfer to move VoLTE to
2/.3G CS
(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.
Based on UE measurement reports and CS Fallback Indicator and
Based on UE measurement reports and UE’s
UE’s SRVCC capability , decides to trigger an SRVCC handover to
SRVCC capability and QCI = bearer, decides to
UTRAN/GERAN.
trigger an SRVCC handover to UTRAN/GERAN.
3
eNB
4
BSC/RNC
No impact
5
UE
Standard VoLTE/SRVCC UE
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No impact
Standard CSFB/SRVCC UE
Page 11
Content
Ultra-Flash CSFB introduction
Ultra-Flash CSFB Discussion
Summary
Call Setup Time Comparison(Fall back to GSM)
Ultra-Flash CSFB to GSM
SRVCC/PS HO
Authentication/encryption/
UE Capacity identify
2G call 2G
CS RAB
establishment
Ultra-Flash
CSFB
Read SI
SRVCC
IRAT HO
UE access to 2G
cell
Basic call
procedure
R8
R9(Flash)
LTE call LTE,
both MO/MT fall back
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Ultra-Flash call
Ultra-Flash
GSM Call
Based on Huawei Lab testing
Page 13
Call Setup Time Comparison(Fall back to UMTS)
Ultra-Flash CSFB to UMTS
SRVCC/PS HO
PS HO
Ultra-Flash
CSFB
3G call 3G
Authentication/encryption/
UE Capacity identify
CS RAB
establishment
SRVCC
IRAT HO
Read SI
UE access to 3G
cell
Basic call
procedure
R8
PSHO
LTE call LTE,
both MO/MT fall back
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Ultra-Flash call
Ultra-Flash
UMTS Call
Based on Huawei Lab Test
Page 14
Why Ultra-Flash CSFB Achieve the Shortest Call Setup ?
Sv
3
SGs
SRVCC MSC
MME
Both Sv and SGs interfaces
supported, SRVCC IRAT HO was
used to accelerate CSFB
2
BSC/RNC
4
1
eNB
Ultra-Flash CSFB Reduce Call Setup Time in Following 4 Steps
CSFB
1
2
3
4
Ultra-Flash CSFB
Use redirection mechanism to access target
Use SRVCC or PS IRAT handover to access target cell
2/3G cell
Start CS RAB setup procedure during the Skipping the CS RAB setup procedure, as the RAB is preCS RAB Establishment
CS call setup procedure in 2/3G
allocated during the SRVCC IRAT Handover procedure
Authentication /
Authentication/encryption/UE Capacity
Authentication/encryption/UE Capacity identify were done
encryption/UE Capacity
identify are mandatory
during SRVCC handover, reduce extra time consumption
identify
Signaling transport
SD(stand-alone dedicated control channel)，
TCH(Traffic Channel)，Single-user exclusive
channel(Only GSM)
Shared by 8 users
Cell Selection
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Page 15
How Ultra-Flash CSFB Reduce Impact to Current Network
IMS Core
Proxy solution, reduce the
impact to CS network
SRVCC
MSC
Sv
SGs
EPC
VMSC
Naturally support VoLTE/SRVCC，
without MME/MSC upgrade again
MME
BSC/RNC
eNodeB
1
MSC
2
TA/LA mapping
3
Roaming Retry/Roaming
Forwarding
4
VoLTE/SRVCC evolution
CSFB
Ultra-Flash CSFB
Upgrade MSC or Proxy（additional 1~2s delay）
Proxy solution avoid MSC upgrading（with only about
400ms additional delay）
Need strictly planning, otherwise call setup time
would be prolonged and call success rate
decrease
All MSC must be upgraded, otherwise it will lead
to call failure in case of TA/LA misalignment
MME/MSC must be upgraded again when
deploying VoLTE/SRVCC
Don’t need strictly planning, no impact to call setup
latency and call success rate
Don’t need deploy Roaming Retry/Roaming
Forwarding, no impact to call success rate
Sv interface is ready for VoLTE/SRVCC, avoid
MME/MSC upgrading again
Could update some (one at the minimum) MSC Servers rather than all the MSC Servers
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Page 16
How Rel-8 CSFB and Ultra-Flash CSFB co-exist
Add software patch on SRVCC
feature and no impact on Rel-8
CSFB.
SRVCC MSC
SGs
Sv
IMS Core
SGs
MME
MSC
BSC/RNC
eNB
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
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Page 17
Content
Ultra-Flash CSFB introduction
Ultra-Flash CSFB Discussion
Summary
Ultra-Flash CSFB Value and Principle
R8 CSFB
Easy
Deployment
Principle
Call Setup
Time
Ultra-Flash
4
2
SRVCC UE
SRVCC HO
MME
MSC
1
2
LTE
SRVCC HO
3
G/U
MSC
MME
eNB
• Avoid to update RNC/BSC
• Fall back GSM and UMTS Supported
In parallel UE fallback and call in MSC
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
Proposed to add deployment option in Rel-12 that enables faster and more reliable
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CSFB for UEs and networks supporting
SRVCC.
Page 19
Thank you
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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
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
MME
VoLTE
SGW
PGW
Ultra-Flash CSFB
IMS PS voice priority, CS Voice secondary
is configured in UE
MSC
UE decide to use VoLTE or Ultra-Flash
CSFB according to MME indication
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
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