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Ultra-Flash CSFB(SRVCC based CSFB)

SA WG2 Meeting #100  S2-134315 11 - 15 November 2013, San Francisco, USA. Ultra-Flash CSFB(SRVCC based CSFB) Source Company: Huawei, HiSilicon, Bharti, China Unicom, Deutsche Telekom. Content. Ultra-Flash CSFB introduction Ultra-Flash CSFB Discussion

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Ultra-Flash CSFB(SRVCC based CSFB)

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  1. SA WG2 Meeting #100  S2-134315 11 - 15 November 2013, San Francisco, USA Ultra-Flash CSFB(SRVCC based CSFB) Source Company: Huawei, HiSilicon, Bharti, China Unicom, Deutsche Telekom

  2. Content • Ultra-Flash CSFB introduction • Ultra-Flash CSFB Discussion • Summary

  3. What is Ultra-Flash CSFB? MME LTE SRVCC Inter RAT Handover SRVCC Inter RAT Handover VoLTE w/ SRVCC MME MME CSFB LTE LTE SRVCC Session Transfer Redirection Redirection SGs SGs SGSN Sv Sv G/U SGSN SGSN MSC G/U G/U MSC MSC 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. SRVCC IRAT HO SRVCC IRAT HO Ultra-Flash CSFB Ultra-Flash CSFB is a solution used SRVCC IRAT handover to accelerate CSFB

  4. Ultra Flash CSFB with SRVCC capable UE 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

  5. Ultra Flash CSFB with SRVCC capable UE- MO

  6. 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.

  7. Ultra Flash CSFB with L->U SRVCC - MT 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)SRVCCMSC send setup(TI=1) to the UE

  8. Ultra Flash CSFB with SRVCC capable UE- MT

  9. 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

  10. Ultra-Flash CSFB VS NW-Initiated CS Services while UE is in IMS VoIP session in 8.4.2.2 8.4.2.2 NW-Initiated CS Services while UE is in IMS VoIP session0 Ultra Flash CSFB

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

  12. Content • Ultra-Flash CSFB introduction • Ultra-Flash CSFB Discussion • Summary

  13. 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) Ultra-Flash call Ultra-Flash GSM Call LTE call LTE, both MO/MT fall back Based on Huawei Lab testing

  14. Call Setup Time Comparison(Fall back to UMTS) Ultra-Flash CSFB to UMTS SRVCC/PS HO PS HO Ultra-Flash CSFB Authentication/encryption/UE Capacity identify 3G call 3G CS RAB establishment SRVCC IRAT HO Read SI UE access to 3G cell Basic call procedure R8 PSHO Ultra-Flash call Ultra-Flash UMTS Call LTE call LTE, both MO/MT fall back Based on Huawei Lab Test

  15. Why Ultra-Flash CSFB Achieve the Shortest Call Setup ? Sv 3 SGs Both Sv and SGs interfaces supported, SRVCC IRAT HO was used to accelerate CSFB 2 SRVCC MSC 4 1 MME Ultra-Flash CSFB Reduce Call Setup Time in Following 4 Steps eNB BSC/RNC

  16. How Ultra-Flash CSFB Reduce Impact to Current Network IMS Core Proxy solution, reduce the impact to CS network SRVCC MSC Sv SGs EPC Naturally support VoLTE/SRVCC，without MME/MSC upgrade again VMSC MME BSC/RNC eNodeB Could update some (one at the minimum) MSC Servers rather than all the MSC Servers

  17. 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 SGs MME MSC eNB BSC/RNC • 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 IMS Core

  18. Content • Ultra-Flash CSFB introduction • Ultra-Flash CSFB Discussion • Summary

  19. Ultra-Flash CSFB Value and Principle Easy Deployment Principle Call Setup Time 4 2 SRVCC HO SRVCC UE MSC MME MSC eNB MME 1 3 2 Ultra-Flash R8 CSFB • Avoid to update RNC/BSC • Fall back GSM and UMTS Supported SRVCC HO LTE G/U In parallel UE fallback and call in MSC L->U 6 ~ 9 s L->G 10-12 s 3 ~ 5 s 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 CSFB for UEs and networks supporting SRVCC.

  20. VoLTE configured UE support Ultra-Flash CSFB Directly • If IMS has been deployed，MMEindicateUE IMS Voice over PS session supported • If IMS has not been deployed，MMEindicate IMS Voice over PS session NOT supported MME VoLTE PGW SGW Ultra-Flash CSFB IMS PS voice priority, CS Voice secondary is configured in UE MSC Value： • If IMS has not been deployed, VoLTE/SRVCC UE can use Ultra-Flash CSFB • After IMS has been deployed, UE can use VoLTE directly without reconfiguration UE decide to use VoLTE or Ultra-Flash CSFB according to MME indication

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