SRVCC trigger enhancement feature and parameter description

SRVCC trigger enhancement feature and parameter description

1. MBB CS TS SRAN Deep Feature Analysis X L17 LTE3290 SRVCC trigger enhancements < xiaoyu zhao > <TS Hangzhou> <28//11/2016>

2. Agenda < LTE3290 SRVCC trigger enhancements > Key Functionality Configuration and Deployment Aspects Simulation and Test Results Hints for Troubleshooting Operational Hints and Guidelines References

3. Key functionality ◄ Back <LTE3290 SRVCC trigger enhancements>

4. SRVCC (Single Radio Voice Call Continuity) is a measurement based handover between LTE and WCDMA/GSM/CDMA RATs, performed for UE with being established or ongoing voice call (active or inactive/on hold) . The reason for such RAT change is reaching LTE coverage edge, meaning SRVCC is a critical , coverage-based handover * . LTE is data only network and may offer voice calls using voice over PS techniques (with build in quality of service) / VoLTE In WCDMA and GSM networks voice calls use circuit switched bearers, thus call transfer from LTE mean a session transfer and domain change from PS to CS in the Core Network/CN. CN require modification and SRVCC supporting functions in legacy and IMS network elements and interfaces ( SRVCC in MSC, MME support & S v interface towards MSC, SCC AS in IMS/Open TAS, HLR/HSS registers). From radio interface & RAN perspective SRVCC is a regular HO and it is supported by software features [(e) NodeB /BTS]. C-Plane U-Plane Key functionality SRVCC basics Relocation procedure Sv SRVCC session transfer PS → CS SRVCC RAT change SCC -AS SRVCC LTE cell WCDMA or GSM cell RNC /BSC Voice call (VoLTE) /ECM-CONNECTED/ MGW MME S/P-GW IMS/TAS BGW/MGW Terminating network SRVCC capable UE B party SRVCC PS to CS request SIP INVITE Handover required ② The need for handover detected (measurements) ① ③ ⑦ ⑤ ⑥ SIP path prior SRVCC MSC ④

5. Key functionality LTE3290 - w ith and w/out the feature B2 event * (WCDMA/GSM) Handover Required B2 events (initiate SRVCC to 3G or 2G) B2 event (WCDMA/GSM) Suitable GSM cell found * LTE cell signal is low & 3G/2G cell signal/quality is good enough With LTE3290 UE MME eNB W/out LTE3290 SRVCC trigger Delay timer During voice call establishment any SRVCC triggers are ignored by eNB, while dedicated delay timer counts down calling (VoLTE) calling (VoLTE) CN/IMS w/out aSRVCC or bSRVCC c all answered Time MME PS to CS request Handover Required (initiate SRVCC to 3G or 2G) PS to CS request ringing ringing  SRVCC accepted [call in post (pre) alerting phase] SRVCC rejected [call in (pre) alerting phase]  CN/IMS w/out aSRVCC or bSRVCC

6. Key functionality SRVCC triggered during VoLTE alerting or pre-alerting phase - with and w/out LTE3290 used LTE3290 not available/disabled * SRVCC in alerting phase (3GPP Rel10/11) LTE3290 enabled Part B CN/IMS with SRVCC (& w/out a SRVCC * support) WCDMA/GSM LTE Time UE Remote network VoLTE UE SRVCC capable UE initiates VoLTE call (inter-RAT measurements ongoing) CN/IMS call setup in progress (Part B altering started) Bad LTE cell signal/quality detected. eNB turns on WCDMA/GSM measurements Good enough WCDMA/GSM cell reported by UE (inter-RAT SRVCC HO trigger detected by eNB) eNB initiates SRVCC towards the CN/MME HO starts but SRVCC in early call setup phase is not properly handled by CN/IM ringing WCDMA/GSM LTE Time UE Remote network VoLTE UE SRVCC capable CN/IMS call setup in progress (Part B altering started) Bad LTE cell signal/quality detected. eNB turns on WCDMA/GSM measurements Good enough WCDMA/GSM cells reported by UE (meas. ignored by eNB while timer is running) ringing Part B  CN/IMS with SRVCC ( w/out a SRVCC) SRVCC attempt fails B2 measurement report B2 measurement report B2 measurement report B2 measurement report S RVCC during VoLTE call delay timer Part B answer s (VoLTE call setup finalized)  Measurement not ignored & reports good WCDMA/GSM cell eNB initiates SRVCC during ongoing VoLTE call UE initiates VoLTE call (intra-RAT measurements started) S RVCC in (pre)alerting phase eNB may re-attempt SRVCC

7. Configuration and Deployment Aspects ◄ Back <LTE3290 SRVCC trigger enhancements>

8. Abbreviated name Full name Description LNBTS :srvccDelayTimer SRVCC delay timer Configuration and Deployment Aspects New basic parameters The delay timer for SRVCC procedure. It is triggered after establishment of first QCI1 bearer for given UE. While timer is running, eNodeB does not start SRVCC to WCDMA nor GSM (SRVCC to CDMA is not effected by this parameter) . The parameter is also used as enable/disable switch for related LTE3290 feature: it is deactivated when parameter is set to 0 and activated otherwise. RRC Measurement Report (B2 event WCDMA/GSM) srvccDelayTimer >0 RRC Measurement Report (B2 event WCDMA/GSM)   UE eNB SRVCC delay timer SRVCC to WCDMA/GSM procedure RRC Measurement Report (B2 event WCDMA/GSM) RRC Measurement Report (B2 event WCDMA/GSM) SRVCC not allowed SRVCC allowed srvccDelayTimer = UE eNB SRVCC to WCDMA/GSM procedure Note: SRVCC to be enabled, i.e. actSrvccToGSM=1 (LTE873 enabled) or/and actSrvccToWcdma=1 (LTE872 enabled) QCI1 DRB setup request QCI1 DRB setup request ◄ Back

9. a) CN/IMS with aSRVCC support b) CN/IMS w/out aSRVCC support Abbreviated name Full name Description LNBTS :actAcSrvcc Activate AC triggered SRVCC Configuration and Deployment Aspects Related parameters This parameter activates the functionality to accept an E-RAB with QCI1 in overloaded LTE cell by overbooking and immediate triggering of SRVCC to WCDMA for respective UE (LTE2832 / SRVCC due to admission control rejection) This is an opposite to LTE3290 proceeding, therefore: actAcSrvcc =1 (or 0) srvccDelayTimer =0 (>0)  LTE3290 and LTE2832 can not be enabled simultaneously Note: SRVCC to be enabled, i.e. actSrvccToGSM=1 (LTE873 enabled) or/and actSrvccToWcdma=1 (LTE872 enabled) actAcSrvcc =0 (1) srvccDelayTimer =1 (or 0)  LTE3290 can not be enabled with LTE2832. In any case it should NOT be enabled in this scenario, since the feature is a workaround for networks w/out aSRVCC support LTE2832 is design for networks with aSRVCC support and may be enabled in eNB experiencing congestion and enabled for voice services (VoLTE) LTE2832 should NOT be enabled as it increase call drop rate by forcing SRVCC in (pre) alerting phase, not supported in this scenario. Moreover SRVCC are started in entire LTE cell area unlike in typical SRVCC started at cell edge. LTE3290 is design for networks w/out aSRVCC support and may be enabled in this scenario when SRVCC failures happen in alerting phase.

10. Configuration and Deployment Aspects Recap: measurement events used by coverage-based SRVCC (trigger 1) Event type Meas. type Action on event Triggering condition A1 intra- freq , serving cell Cancel ongoing WCDMA or GSM B2 m easurements Serving cel signal / quality becomes good : RSRP serv_cell > Thr A 1 + hysThreshold2a for at least a1TimeToTriggerDeactInterMeas A2 Intra- freq , serving cell Start WCDMA or GSM B2 measurements Serving cel signal / quality becomes bad: RSRP /RSRQ serv_cell < Thr A2_servCell 1 – hysThreshold2Wcdma for at least a2TimeToTriggerActWcdmaMeas B2 Inter-RAT, adjacent WCDMA cells Start SRVCC to WCDMA Serving cell signal/quality is bad: RSRP /RSRQ serv_cell < Thr B2 wcdma / Gsm _ servCell 1 – hysB2Threshold [ Rsrq ] Utra /GERAN for at least: b 2TimeToTriggerActxxxMeas AND Adj. cell signal/quality is good enough : RSCP WCDMA_cell > Thr B2_RSCP_WCDMA 1 + hysB2ThresholdUtra – offsetFreqUtra OR 2 EcNo WCDMA_cell > Thr B2_EcNo_WCDMA 1 + hysB2ThresholdUtra – offsetFreqUtra for at least b2TimeToTriggerUtraMeas Inter-RAT, adjacent GSM cells Start SRVCC to GSM RSSI GSM_cell > Thr B2_RSSI_GSM 1 + hysB2ThresholdGERAN for at least b2TimeToTriggerGeranMeas 1 See slide SRVCC measurements thresholds 2 Equation depends on selected measurement WCDMA quantity, i.e. RSCP or EcNo using parameter: measQuantityUtra

11. Configuration and Deployment Aspects Recap: Nokia A2, B1, B2 measurement thresholds for SRVCC purpose Event type Meas. type / Purpose Threshold [PS & SRVCC HOs] (w/out LTE2112 & LTE64 ) Threshold [ SRVCC HO] (with LTE2112 & LTE64 ) LTE2832 * mapping A1 Serving cell RSRP , RSRQ LNCEL: threshold2a , LNCEL: threshold2a Rsrq LNCEL: threshold2aQci1 , LNCEL: threshold2a Rsrq N/A A2 Serving cell RSRP , RSRQ / SRVCC to WCDMA LNCEL: threshold2Wcdma , LNCEL: threshold2 MobRsrq 1 LNCEL: threshold2WcdmaQci1 , LNCEL: threshold2 MobRsrq N/A A2 Serving cell RSRP / SRVCC to GSM LNCEL: threshold2Geran , LNCEL: threshold2 MobRsrq LNCEL: threshold2GeranQci1 , LNCEL: threshold2 MobRsrq N/A B2 Serving cell RSRP, RSRQ / SRVCC to WCDMA LNHOW: b2Threshold1Utra, LNHOW: b2Threshold1RsrqUtra 2 LNHOW: b2Threshold1UtraQci1, LNHOW: b2Threshold1RsrqUtra Qci1 3 N/A B2 Target cell RSCP / SRVCC to WCDMA LNHOW: b2Threshold2UtraRscp LNHOW: b2Threshold2UtraRscpQci1 Used as B1 threshold B2 Target cell E c N o / SRVCC to WCDMA LNHOW: b2Threshold2UtraEcn0 LNHOW: b2Threshold2UtraEcn0Qci1 Used as B1 threshold B2 Serving cell RSRP, RSRQ / SRVCC to GSM LNHOG: b2Threshold1GERAN, LNHOG: b2Threshold1RsrqGERAN 2 LNHOG: b2Threshold1GERANQci1, LNHOG: b2Threshold1RsrqGERAN Qci1 3 N/A B2 Target cell RSSI / SRVCC to GSM LNHOG: b2Threshold2RssiGERAN LNHOG: b2Threshold2RssiGERANQci1 N/A A2 Serving cell RSRP / HOs to CDMA 4 LNCEL: threshold2C2k LNCEL:threshold2C2kQci1 N/A 1 Threshold available with activated LTE1198 ( RSRQ triggered mobility ) 3 SRVCC specific B2 parameters foreseen in next software releases 2 Threshold added by LTE2572 RSRQ based B2 (xL17 software release) 4 LTE738 SRVCC to 1xRTT/CDMA * LTE3290 and LTE2832 (SRVCC due to AC rejection) may not be simultaously enabled in the cell (!)

12. Parameter relationship : Configuration

13. Simulation and Test Results ◄ Back < LTE3290 SRVCC trigger enhancements >

14. ◄ Back < LTE3290 SRVCC trigger enhancements >

15. Operational Hints and Guidelines ◄ Back <LTE3290 SRVCC trigger enhancements>

16. Technical details The delay timer is started for the first QCI1 bearer active in UE The timer is not stopped or restarted when call ends normally or abnormally nor in a new cell after handover/call reestablishment Time ECM-CONNECTED ECM-IDLE SRVCC delay timer voice call request (QCI1 bearer) voice call request Normal call end 1st call on hold Call ended while ringing 1st call retrieved voice call request voice call request (2 nd call /1 st inactive) Intra or IF handover ( no timer restart) LTE cel A LTE cel B 2nd call normal end SRVCC delay timer restarted (always started upon E-RAB setup or Initial Context request for fist QCI1 bearer) SRVCC delay timer not restarted for next QCI1 E-RAB

17. WCDMA/GSM LTE Deployment Aspects SRVCC delay timer settings: a statistical compromise Too short timer – no improvement Too long timer – risk of loosing coverage UE SRVCC triggers Part B not answered yet SRVCC HO CN/IMS eNB SRVCC triggers INVITE  180 RINGING WCDMA/GSM LTE UE INVITE CN/IMS 180 RINGING eNB ringing  200 OK (INVITE) triggers LTE coverage lost before delay timer expired LTE3290 mechanism is basically not needed within LTE coverage area. It is recommended to enable the feature only on LTE border cells or once with degraded statistics (SRVCC in preparation phase). Setting SRVCC delay timer is a tradeoff between t o o long values, increasing SRVCC failures, and too short, providing no improvement to SRVCC in call (pre)alerting phase. The initial delay timer (in network w/out aSRVCC) can be slightly higher then lower bound mentioned on previous slide. It may be then gradually increased until IMS statistics for e.g. PS-CS session transfer failure s stop improving . SRVCC trigger Distance traveled in between B2 reports ( reportInterval xxx ) call answered ringing SRVCC delay timer ... del. timer

18. Hints for Troubleshooting ◄ Back <LTE3290 SRVCC trigger enhancements>

19. Protocol IE SRVCC operation possble MS Network Capability in EMM:ATTACH REQUEST includes SRVCC capability.

20. UE Capability ( RRC:UeCapabilityInformation ) FGI bits #9 & #23 are evaluated within UE-EUTRAN Capabilities This flag states whether both UE & MME are capable of SRVCC. It needs to be stored in the UE Context when received within : S1AP: INITIAL CONTEXT SETUP REQUEST,

21. Event A2 Threshold configuration Event A2 : Serving becomes worse than threshold) 61 + (-140) = -79 dBm -140 is RSRP minimum value Measurement Report for A2 Threshold value in RRC Connection Reconfiguration RSRP : 47 < 61 -0 , Event A2 is received.

22. Event B2 Procedure : Event B2:Serving becomes worse than threshold1 and inter RAT neighbour becomes better than threshold2 Event B2 threshold in RRC Connection Reconfiguration 60 + (-140) = -80 dBm , 50 + (-110) = -60 dBm Serving Cell RSRP : 26 < ( 60 – 4 ); GERAN cell RSSI : 63 > (50 + 4 ), Event B2 is received. Event B2 Threshold configuration

23. SRVCC trigger : S1AP:HandoverRequired SRVCC to GSM without DTM support

24. Deployment Aspects Feature activation Activate mandatory features : 1 Verify SRVCC failure statistics to determine potential candidate cells for LTE3290 activation & enabled using: srvccDelayTimer > 0 disabling LTE3290 in the same time : actAcSrvcc= (false) Note: LTE3290 is a workaround for problems with SRVCC failures in VolTE call pre-alerting or alerting phase and modifies LTE872 or LTE873 behavior (at least one is assumed to be already activated 1 ). LTE3290 shall not be enabled on cells where such problems do not appear. Configure delay timer: 2 Determine the initial value of SRVCC delay timer. The E2E IMS statistics for voice call setup time from INVITE to 180 RINGING may be used to determine the lower bound value (if no aSRVCC support) . Do not start from too long timer value as in some cases it may worsen call drop statistics insetad of improving others . x -check SRVCC setting 3 LTE3290 ignores SRVCC trigger during the delay timer. Check A2 & B2 events thresholds to validate whether inter-RAT measurements are started and results reported early enough 2 , so that UE likely stays within LTE cell coverage during delay timer count down. With B2 periodicity a distance traveled between B2 reports may be estimated. A2 & B2 serving cell thresholds should be aligned & target cell thresholds not too demanding . 1 Activation of LTE872 and LTE873 and interdependent features: LTE7, LTE10, LTE56 is described in SRVCC to WCDMA/GSM NEI) 2 The feature LTE2112 may be useful to avoid too early inter-RAT measurements activation for non voice E - RAB sessions

25. Deployment Aspects The lower or upper bound value of SRVCC delay timer: time between INVITE and 180 RINGING CSCF_97: Average Originating Session Setup Duration (P-CSCF): 4,12 sec P-CSCF CSCF _ 97 a Average Originating Session setup duration Average Originating Session Setup Duration calculated with the division of accumulated originating sessions setup duration (from receiving the initial invite as originating P-CSCF, till receiving 180) by the total number of sessions Release: IMS 9.2 Counters: SipOrigSessSetupDur; SuccSessionOrig Formula: sum(SipOrigSessSetupDur)/sum(SuccSessionOrig) The graph presents result of call setup duration measured at CSCF/TAS in example network. The P-CSCF value (here about 4 seconds ) can be considered as lower bound for SRVCC delay timer in networks w/out aSRVCC support (alerting phase) . When aSRVCC is suported by network and UEs, but not supported in pre-alerting phase (bSRVCC) then the same time can be considered as upper bound for SRVCC delay timer.

26. Reference ◄ Back <LTE3290 SRVCC trigger enhancements> Index Document name Version Location – web-link 1 Spec DOORS: //LTE System/CFAM/LTE/LTE3200-3399

27. SRVCC (Single Radio Voice Call Continuity) is a measurement based handover between LTE and WCDMA/GSM/CDMA RATs, performed for UE with being established or ongoing voice call (active or inactive/on hold) . The reason for such RAT change is reaching LTE coverage edge, meaning SRVCC is a critical , coverage-based handover * . LTE is data only network and may offer voice calls using voice over PS techniques (with build in quality of service) / VoLTE In WCDMA and GSM networks voice calls use circuit switched bearers, thus call transfer from LTE mean a session transfer and domain change from PS to CS in the Core Network/CN. CN require modification and SRVCC supporting functions in legacy and IMS network elements and interfaces ( SRVCC in MSC, MME support & S v interface towards MSC, SCC AS in IMS/Open TAS, HLR/HSS registers). From radio interface & RAN perspective SRVCC is a regular HO and it is supported by software features [(e) NodeB /BTS]. C-Plane U-Plane Key functionality SRVCC basics Relocation procedure Sv SRVCC session transfer PS → CS SRVCC RAT change SCC -AS SRVCC LTE cell WCDMA or GSM cell RNC /BSC Voice call (VoLTE) /ECM-CONNECTED/ MGW MME S/P-GW IMS/TAS BGW/MGW Terminating network SRVCC capable UE B party SRVCC PS to CS request SIP INVITE Handover required ② The need for handover detected (measurements) ① ③ ⑦ ⑤ ⑥ SIP path prior SRVCC MSC ④

28. Relocation req . Measurement report ( s ) Handover required Introduction SRVCC handover – the simplified messages flow (IMS details not included) SRVCC MSS/ TargetMSS UE MME eNB IMS Handover decision Resource s reservation RNC/BSC S/P-GW Target SGSN ① ② PS to CS request Bearer splitting Relocation/HO required ( voice part) non-voice part if exist ( in multi-bearer connections) Forward Relocation required voice call (& PS i f also requested) Relocation/HO request acknowledge ④ SRVCC initiation / voice part Fwd : Relocation request acknowledge Relocation req. acknowledge PS to CS response Handover command HO from EUTRAN command UE change RAT Handover detection (in target 2G/3G cell) Relocation/HO complete (CS) PS to CS complete/ ack Session transfer B2 measurements activated upon A2 event (LTE signal low) Triggered upon B2 event (good enough 3G/2G signal) SRVCC indicated voice & non voice PS bearers follow different procedure s (CS to PS, PS to PS HO ) PS to PS HO (non-voice part) for voice call (&PS if also needed) details of reserved resources (to be delivered to UE) ③ MME must synchronize relocations for voice & non-voice part if the latter is also used by UE) ⑥ UE detection (in target 2G/3G cell), handover detection in RNC/BSC, handover completion by UE Fwd : Relocation/HO complete Relocation/HO complete ( P S) Resources released in eNB, S/P-GW , MME Initiation of session transfer with INVITE ⑤ Remote access leg update procedure Release of source access leg procedure ⑦

29. Thank you ! 12/7/2016