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 Summary

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

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

Ultra Flash CSFB with SRVCC capable UE - MO 2017/3/22

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.

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

Ultra Flash CSFB with SRVCC capable UE - MT 2017/3/22

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

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

NW-Initiated CS Services while UE is in IMS VoIP session in 8. 4. 2 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 MSC Initiates 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 eNB Based 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 5 UE Standard VoLTE/SRVCC UE Standard CSFB/SRVCC UE

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 CS RAB establishment UE access to 2G cell Read SI Basic call procedure 2G call 2G Ultra-Flash CSFB SRVCC IRAT HO Per Huawei lab testing, L->G measurement takes about 700-800ms. If DRX based measurement is used, L->G measurement could takes about 200ms i.e. the real measurement time is (800/40)*6=120ms that can be done in DRX 256ms with short active time. R8 R9(Flash) Ultra-Flash call Ultra-Flash GSM Call LTE call LTE, both MO/MT fall back Based on Huawei Lab testing

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

Why Ultra-Flash CSFB Achieve the Shortest Call Setup ? SRVCC MSC MME Sv SGs 3 BSC/RNC eNB 1 2 4 Both Sv and SGs interfaces supported, SRVCC IRAT HO was used to accelerate CSFB Ultra-Flash CSFB Reduce Call Setup Time in Following 4 Steps CSFB Ultra-Flash CSFB 1 Cell Selection Use redirection mechanism to access target 2/3G cell Use SRVCC or PS IRAT handover to access target cell 2 CS RAB Establishment Start 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 3 Authentication / 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 4 Signaling transport channel(Only GSM) SD(stand-alone dedicated control channel)，Shared by 8 users TCH(Traffic Channel)，Single-user exclusive

How Ultra-Flash CSFB Reduce Impact to Current Network IMS Core Proxy solution, reduce the impact to CS network eNodeB SRVCC MSC BSC/RNC VMSC MME Sv SGs EPC Naturally support VoLTE/SRVCC，without MME/MSC upgrade again CSFB Ultra-Flash CSFB 1 MSC Upgrade MSC or Proxy（additional 1~2s delay） Proxy solution avoid MSC upgrading（with only about 400ms additional delay） 2 TA/LA mapping Need 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 3 Roaming Retry/Roaming Forwarding All MSC must be upgraded, otherwise it will lead to call failure in case of TA/LA misalignment Don’t need deploy Roaming Retry/Roaming Forwarding, no impact to call success rate 4 VoLTE/SRVCC evolution MME/MSC must be upgraded again when deploying VoLTE/SRVCC Sv interface is ready for VoLTE/SRVCC, avoid MME/MSC upgrading again Ultra-Flash CSFB additionally requires SRVCC IRAT Handover and has no impact on Terminals and GERAN /UTRAN. However, Ultra-Flash CSFB requires some light software updates in eNB/MME/MSC Server. Thanks to SRVCC IRAT Handover during CSFB procedure, Ultra-Flash CSFB can provide quicker &easier deployment: (1)Operator only need to update certain (one in minimum) MSC Servers rather than all the MSC Servers surrounding the LTE coverage. (2)The network is certainly know about which 2/3G cell is the best target for the handover, which means the strict TA/LA mapping is not needed and TA/LA misalignment is naturally resolved by SRVCC HO (3)Therefore there is no need of MTRR or MTRF. CSFB only requires a light SRVCC IRAT Handover rather than a full SRVCC deployment: (1)Similar to the legacy CSFB, Ultra-Flash CSFB still relies on the legacy 2/3G CS domain to provide voice and has nothing to do with IMS and therefore there is no need of SRVCC Session Transfer procedure. (2)Ultra-Flash CSFB is a call-setup procedure rather than the VoLTE to 2/3G CS call handover procedure and therefore there is no requirement in terms of voice interruption time i.e. less than 300ms. 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 Add software patch on SRVCC feature and no impact on Rel-8 CSFB. IMS Core SRVCC MSC SGs Sv 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

Content Ultra-Flash CSFB introduction Ultra-Flash CSFB Discussion Summary

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

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