VoLTE_training_2017_NAM.pptx
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NPO Enabling: VoL oLTE TE Trai aini ning ng Detailed Analysis for Radio 13 March 2017
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© Nokia Solutions and Networks 2014
Contents • VoLTE KPI Performance • VoLTE KPI benchmarking
• VoL VoLTE TE Voice Quality
• VoLTE Radio Optimization • Periodical CQI reporting • QCI1 specific T310 and T31 T311 1 timers
• Voice quality analysis
• DRX DRX – – optimized algorithm
• PDCP discard timer & SN size
• High speed users
• VoL VoLTE TE Mobility Mobi lity
• VoLTE Call Flow Analysis
• VoL VoLTE TE layering layer ing
• Registration procedure
• SRVCC thresholds
• Mobile originated VoLTE call • Mobile terminated VoLTE call • SRVCC to 3G
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VoL oLTE TE KPI Perf Performa ormance nce
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VoLTE KPI Benchmarking Call setup success rate for QCI1 • VoLTE Call Setup Success KPI (LTE_5204c) measures both initial or an additional ERAB establishments for QCI1 voice bearer. -
In practise, QCI1 E-RAB is usually setup after the non-GBR E-RAB for application data and SIP signalling so the ‘additional’ E-RAB counters are typically incremented for VoLTE.
E-UTRAN E-RAB Setup Success Ratio, QCI1 (LTE_5204c) = 100*sum(ERAB_INI_SETUP_SUCC_QCI1 + ERAB_ADD_SETUP_SUCC_QCI1 - ERAB_REL_TEMP_QCI1 ) sum(ERAB_INI_SETUP_ATT_QCI1 + ERAB_ADD_SETUP_ATT_QCI1)
- ERAB_REL_TEMP_QCI1: number of temporary admitted QCI1 bearer release due to an overbooking timer expiry (LTE2832 SRVCC due to admission control rejection), i.e. these bearers were temporarily setup but not successfully handed over to UTRAN.
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LTE2832 SRVCC due to Admission Control Rejection QCI1 bearer release due to an overbooking timer expiry UE
• eNB establishes temporary the DRB with QCI1 and configures the UE with event B1 based measurements within RRC:ConnectionReconfiguration • AC Overbooking Supervision Timer expired before preparation phase and thus, eNB releases E-RAB with QCI1: - ERAB_REL_TEMP_QCI1 is incremented on transmission of an S1AP: E-RAB RELEASE INDICATION message (eNB -> MME; 3GPP TS 36.413) due to an overbooking timer expiry for a temporarily admitted QCI1 bearer. 5
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eNB
MME
S1AP: E-RAB SETUP REQUEST QCI=1
Admission Control rejection Temporary overbooking is possible
DRB with QCI1 establishment + configuration event B1
RRC Connection Reconfiguration
AC Overbooking Supervision Timer
RRC Connection Reconfiguration Complete S1AP: E-RAB SETUP RESPONSE
DRB with QCI1 deactivation + deconfiguration event B1
RRC Connection Reconfiguration
AC Overbooking Supervision Timer
RRC Connection Reconfiguration Complete S1AP: E-RAB RELEASE INDICATION
VoLTE KPI Benchmarking Call setup success rate for QCI1 • KPI does not reflect the end user experience in case of failures in the following procedures:
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RACH and RRC signalling establishment
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S1 signalling setup
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Security and authentication
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IMS bearer (QCI5) setup
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SIP message delivery over radio interface.
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Mobility during E-RAB setup
© Nokia Solutions and Networks 2014
VoLTE Call Setup Success GBR vs. non-GBR eRAB setup performance • QCI1 E-RAB setup success rate is slightly worse than nonGBR E-RAB setup success rate due to following factors:
GBR and non-GBR E-RAB Setup Success (%) E -R AB Se tu p A tt em pt s, QC I1
E -R AB Se tu p S uc ce ss Ra te
E -R AB Se tu p S uc ce ss Ra te ,Q CI 1
L in ea r ( E- RA B S et up At te mp ts , Q CI 1)
100.00
400 000
720 users - 15 MHz
99.90
99.80
350 000
Admission Control Threshold – 75%
600 users - 10 MHz
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Much less QCI1 bearer setups compared to data bearers and thus, the weight of setups attempted under poor radio conditions is increased
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If a handover becomes necessary during E-RAB Setup, the eNB may interrupt the ongoing E-RAB Setup procedure as specified in 36.413 (chapter 8.2)
300 000 99.70
)
) % 99.60 ( e t a R 99.50 s s e c c 99.40 u S
250 000 # (
s t p m 200 000 e t t A 1 I C 150 000 Q
99.30 100 000 99.20 50 000
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VoLTE Call Setup Failure due to Handover in Progress MME bearer request handling • 3GPP 36.413 (chapter 8.2): If a handover becomes necessary during E-RAB Setup, the eNB may interrupt the ongoing E-RAB Setup procedure and initiate the Handover Preparation procedure as follows: -
The eNB shall send the E-RAB SETUP RESPONSE message in which the eNB shall indicate, if necessary all the E-RABs fail with an appropriate cause value, e.g. , ”S1 intra system Handover triggered”, “S1 inter system Handover triggered” or “X2 Handover triggered”.
• Therefore, MME needs to resend the E-RAB Setup Request when it receives the Path Switch Request after the failed E-RAB setup (applies for E-RAB release or modify procedure as well) – feature implemented in Nokia MME (NS15 onwards). -
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In case the SGW is changed due the HO then MME should send the Create Bearer Response message to SGW indicating rejected E-RAB with cause 110 “Temporarily rejected due to handover/TAU/RAU procedure in progress“.
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VoLTE Call Setup Failure due to Handover in Progress PGW bearer request handling • 3GPP TS 23.401: Upon reception of a rejection for an EPS bearer(s) PDN GW i nitiated procedure with an indication that the request has been temporarily rejected due to mobility procedure in progress, the PDN GW start a locally configured guard timer. The PDN GW shall re-attempt, up to a pre-configured number of times, when either it detects that the Tracking Area Update procedure is completed or has fail ed using message reception or at expiry of the guard timer.
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PDN GW which initiated the bearer related request (e.g.Create / Update / Delete Bearer request) is supposed to handle the rejection by re-sending the request after handover is completed.
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Nokia PGW (NG3.2 onwards) has re-attempt mechanism, with the default value “handoverrejection-guard-timer-reattempt-count ” = 2, i.e. when PGW receives the rejection, it will re-initiate rejected EPS bearer procedure to MME.
© Nokia Solutions and Networks 2014
VoLTE Call Setup Failure due to Handover in Progress Failure message sequence S-eNB
T-eNB
MME
S-SGW
T-SGW
SIP:INVITE SIP: TRYING SIP: SESSION PROGRESS
Radio Handover in Progress Create Bearer Request
Create Bearer Request (QCI1)
E-RAB Setup Request E-RAB Setup Response (failure) Cause: X2-Handover-Triggered PatchSwitchRequest Create Bearer Response (failure) SIP: 503 Service Unavailable
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Cause: Temporarily Rejected due to Handover Procedure in Progress
PGW
VoLTE Call Setup Failure due to Handover in Progress Correct message sequence T-eNB
S-eNB
MME
S-SGW
T-SGW
PGW
SIP:INVITE SIP: TRYING SIP: SESSION PROGRESS
Radio Handover in Progress Create Bearer Request
Create Bearer Request (QCI1)
E-RAB Setup Request E-RAB Setup Response (failure) Cause: X2-Handover-Triggered PatchSwitchRequest Create Bearer Response Cause: Temporarily Rejected due to Handover Procedure in (failure) Progress Create Session Request (QCI5) Modify Bearer Request Modify Bearer Response Create Session Response Patch Switch Request Ack
Delete Access Bearer in S-eNB and Session in S-SGW SIP: PRACK
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Create Bearer Request
Create Bearer Request (QCI1)
R e t r a n s m i s s i o n
VoLTE Call Setup Failure in Poor Coverage SIP message delivery failure •
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The UL SIP message SESSION PROGRESS (183) delivery is unsuccesful and thus, VoLTE call setup fails. -
IP packet including SIP message is more than 1500B which leads to packet fragmentation in the application layer (mandatory).
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Under poor radio conditions, it takes too long time to deliver the 1st piece of SIP message and therefore, the 2nd piece of SIP message in eNB buffer is discarded due to expiry of PDCP tDiscard timer .
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The entire SIP message can NOT be concatenated in application layer, which leads VoLTE call failure
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Please note, in such case the UE doesn’t generate new PDCP SN for buffered data which means that data is kind of silently discarded and thus, eNB’s PM counter or internal logs can’t reflect this failure.
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QCI5 the parameter tDiscard is recommended to set to “infinity” to overcome this issue under very poor UL channel.
VoLTE KPI Benchmarking Drop ratio for QCI1 – radio perspective • VoLTE E-RAB QCI1 Drop Ratio (RAN View) KPI describes the ratio of abnormally released (dropped) QCI1 E-RABs from RAN point of view. -
Abnormal E-RAB drops which are initiated by eNB are only counted.
E-UTRAN E-RAB QCI1 Drop Ratio, RAN View (LTE_5572e) = 100*sum( E R AB _REL_HO_PART_QCI1 + ER AB _RE L_ENB_QCI1 - ERAB_REL_ENB_RNL_INA_QCI1 ERAB_REL_ENB_RNL_RED_QCI1 -ERAB_REL_ENB_RNL_RRNA_QCI1 - ERAB_REL_TEMP_QCI1) sum(ERAB_REL_ENB_QCI1 + ERAB_REL_HO_PART_QCI1 + EPC_EPS_BEAR_REL_REQ_N_QCI1 +EPC_EPS_BEAR_REL_REQ_D_QCI1 + EPC_EPS_BEAR_REL_REQ_R_QCI1 + EPC_EPS_BEAR_REL_REQ_O_QCI1 + ERAB_REL_EPC_PATH_SWITCH_QCI1 - ERAB_REL_TEMP_QCI1 + ERAB_REL_SUCC_HO_UTRAN_QCI1 + ERAB_REL_SUCC_HO_GERAN_QCI1)
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VoLTE KPI Benchmarking Drop ratio for QCI1 – end user perspective • VoLTE E-RAB QCI1 Drop Ratio (user perspective) KPI describes the ratio of abnormally released (dropped) QCI1 E-RABs from end user point of view. -
Abnormal E-RAB drops initiated both by eNB and EPC are counted.
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Call drops due to duplicated S1 connections and SRVCC during alerting are counted.
ERAB QCI1 drop ratio, user perspective (LTE_1263h) = 100 * SUM( E PC_EPS_BEAR_REL_REQ_R_QCI1 + EPC_EPS_BEAR_REL_REQ_O_QCI1 + ERAB_REL_EPC_PATH_SWITCH_QCI1 + ERAB_REL_HO_PART_QCI1 + ERAB_REL_ENB_QCI1 ERAB_REL_ENB_RNL_INA_QCI1 - ERAB_REL_ENB_RNL_RED_QCI1 - ERAB_REL_ENB_RNL_RRNA_QCI1 ERAB_REL_TEMP_QCI1) SUM(EPC_EPS_BEAR_REL_REQ_N_QCI1 + EPC_EPS_BEAR_REL_REQ_D_QCI1 + EPC_EPS_BEAR_REL_REQ_R_QCI1 + EPC_EPS_BEAR_REL_REQ_O_QCI1 + ERAB_REL_ENB_QCI1 + ERAB_REL_HO_PART_QCI1 + ERAB_REL_EPC_PATH_SWITCH_QCI1 - ERAB_REL_TEMP_QCI1 + ERAB_REL_SUCC_HO_UTRAN_QCI1 + ERAB_REL_SUCC_HO_GERAN_QCI1)
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VoLTE Drop Call Rate Duplicated S1 Connection • Duplicated S1 connection occurs when the UE tries to make HO from eNB-A cell to eNB-B cell but the HO fails and following RRC connection re-establishment fails (no LTE1617) and therefore, UE makes new RRC setup attempt in eNB-B cell which causes new (duplicated) S1 connection establishment towards the MME -
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The MME notices that there are two S1 connections for the UE and releases the old one (eNB-A). This release can be done with cause: NORMAL release or RADIO, where the latter causes dropped call counting (EPC initiated E-RAB release due RNL) After activation of LTE1617 there is no gain expected in dropped call rate if the MME releases the duplicated S1 connection with NORMAL release cause (only gain on t he reduced mute time). © Nokia Solutions and Networks 2014
MME eNB-B UE
eNB-A UE
VoLTE KPI Benchmarking Drop ratio for QCI1 – active drops • VoLTE E-RAB QCI1 Drop Ratio (active drops) KPI describes E-RAB QCI1 with data in the queue drop ratio. -
ERAB_REL_ENB_ACT_QCI1: number of released active E-RABs, i.e. when there was user data in the queue at the time of release with QCI1 characteristics. The release is initiated by the eNB due to radio connectivity problems.
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E-RAB releases due to "No Radio Resources Available" initiated by eNB are counted as normal releases from RAN perspective as drops are not resulted from any radio quality problems.
E-UTRAN E-RAB QCI1 with data in the queue drop ratio (LTE_5571f) = 100*sum( E RAB_REL_ENB_ACT_QCI1 ) sum(ERAB_REL_ENB_QCI1 + ERAB_REL_HO_PART_QCI1 + EPC_EPS_BEAR_REL_REQ_N_QCI1 + EPC_EPS_BEAR_REL_REQ_D_QCI1 + EPC_EPS_BEAR_REL_REQ_R_QCI1 + EPC_EPS_BEAR_REL_REQ_O_QCI1 + ERAB_REL_EPC_PATH_SWITCH_QCI1 - ERAB_REL_TEMP_QCI1 + ERAB_REL_SUCC_HO_UTRAN_QCI1 + ERAB_REL_SUCC_HO_GERAN_QCI1) 16
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VoLTE KPI Benchmarking Active call drop counters • Note that some network vendors are counting only the drops when there is data in the eNB buffer to be transmitted to the UE in case of both eNB triggered and EPC triggered abnormal releases. -
The difference is quite large between all drops (during inactivity) and drops only in case there is data in buffer as shown in the graph on the right: • 0.4%-0.8% for all drops • 0.05%- 0.15% for only drops with data in buffer
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ERAB DR, RAN View, QCI1, LTE_5572A ERAB DR, QCI1 w/ data in buffer, LTE_5571B 1.00 0.90 0.80 0.70 0.60 0.50 % 0.40 0.30 0.20 0.10 0.00
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 : 0 7 4 1 4 1 8 1 8 5 2 5 2 9 2 9 6 3 6 3 0 3 0 7 0 0 1 2 0 1 1 0 0 1 2 0 1 1 0 0 1 2 0 1 2 0 1 1 0 0 0 0 1 1 1 2 2 2 2 3 3 3 4 4 4 4 5 5 5 6 6 6 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
VoLTE Drop Call Rate GBR vs. non-GBR drop calls GBR and non-GBR E-RAB Drop Rate (%) VoLTE Drops EPCinitiated
VoLTE Drops eNB initiated
E-RAB Drop Rate, UserPerspective (eNB pre-emptions excluded)
VoLTE Drop Rate
2.00
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720 users - 15 MHz
1.80
Admission Control Threshold – 75%
1.60
600 users - 10 MHz
5 000
1.40 4 000
) # ( s p o 3 000 r D 1 I C Q
) 1.20 % ( e t a1.00 R p o r D0.80
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0.40 1 000 0.20
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• QCI1 E-RAB drop rate is much worse compared to non-GBR traffic. • VoLTE (QCI1) bearer drop rate has an increasing trend up to 1.6% with increased voice traffic. -
The QCI1 session time (activity time) is much longer compared to the non-GBRQCI and therefore, QCI1 is much more sensitive to mobility related performance challenges (too late HO, too early HO, RRC reestablishments)
VoLTE KPI Benchmarking Active Drops per Session Time • The simple dropped call rate calculation (drops/setup E-RABs per QCI) is not necessarily a good metric due to the extremely large difference in session times between QCI1 (100s – 200s) and Non-GBR : (0.5s – 1.5s) • The QCI1 performance in terms of drops per minute is much better compared to the non-GBR, i.e. QCI1 performance should be also monitored by active drops per active in session time.
active drops per active minute QCI1 active drops per active minute non-GBR non-GBR to QCI1 ratio 0.0035 0.003
© Nokia Solutions and Networks 2014
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VoLTE Drop Call Rate DCR vs. Release Causes iPhone6 VoLTE launch
• After iPhone6/6Plus launched with VoLTE enabled, the VoLTE calls increased by 6 times. • VoLTE drop rate KPI is stable with ~1.6% level with more call attempts. • Howeve, abnormal VoLTE call release distribution is as follows:
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~80% calls are caused by EPC release due to Radio cause
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~10% calls are caused by ENB release due to Radio cause
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~10% calls are caused by ENB release due to Other cause
VoLTE KPI Benchmarking SRVCC success ratio – UTRAN • VoLTE SRVCC Success Ratio KPI describes inter-RAT HO to UTRAN with SRVCC success ratio when the source eNB receives information that the U E is successfully connected to the target cell (UTRAN). -
This KPI is not triggered by load balancing cases to UTRAN.
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Reception of an S1AP:UE CONTEXT RELEASE COMMAND message (source eNB threshold2Wcdma) • SRVCC to trigger 2-3dB earlier than PS handover to maintain voice service quality perceived by end users (b2threshold1UtraQci1 > b2Threshold1Utra).
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SRVCC Performance SRVCC I-RAT measurements Modus
avg time
Blind redirection w/o SRVCC and no 3G MEAS
110 ms
3G MEAS 1 neighbour 3G cell @ 1 UTRAN carrier
556 ms
3G MEAS 6 neighbour 3G cells @ 1 UTRAN carrier
707 ms
3G MEAS 12 neighbour 3G cells @ 1 UTRAN carrier
760 ms
3G MEAS 6+6 neighbour 3G cells @ 2 UTRAN carriers
853 ms
•
If the measurements are started too late (low A2 threshold) and too large amount of 3G neighbors the UE does not have enough time to send measurement reports (B2) hence the call drops.
•
If A2 is set very close to B2 threshold this will reduce the time during which the measurement gaps are scheduled to the mobile which may lead to non -optimal choice of target RAN cell if UE does not have time to measure the best target cell (e.g. long neighboring list).
•
However, if the SRVCC is triggered too early there might be too many SRVCC attempts and aSRVCC attempts causing further challenges in case not supported by IMS.
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SRVCC Performance Setting B2 threshold • If RRC release with redirect is triggered before SRVCC the VoLTE call drops. Especially, high speed users can experience this problem.
VoLTE call drop case by redirect (from field measurement) No SRVCC RSRP suddenly degraded
• Sufficient margin between SRVCC and RRC release with redirect threshold need to be assigned. • In FL15A new parameter a2RedirectQci1 = disabled allows to disable redirection for VoLTE users 52
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VoLTE call dropped
SRVCC Performance Disabling redirection for QCI1 • After disabling the redirection for QCI1: -
Volte drop call rate (LTE_771 + LTE_5572) reduce significantly
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This indirectly cause higher SRVCC attempts, though SRVCC FR still remain at similar level
2.5
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LTE_771b Rel R, QCI1 ENB rel, RNL Redir
LTE_5562a Inter RAT HO Att, UTRAN, SRVCC
LTE_5572b E-RAB QCI1 DR, RAN view
LTE_5563a Inter RAT HO FR, UTRAN, SRVCC
Parameter Name a2RedirectQci1 53
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MOC LNCEL
Full Name
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A2 based redirect for VoLTE calls
Current value (Internal) Proposed value (Internal) enabled (1)
disabled (0)
SRVCC RSRQ based SRVCC HO • If SRVCC triggering threshold is set to very low value the user might experience bad RF quality before RSRP threshold is reached. • However, SRVCC trigger (B2) is typically based on RSRP and thus, SRVCC is not triggered once RSRQ degrades. • LTE2572 RSRQ based B2 feature is available from FL17 onwards. Do we need RSRQ based SRVCC triggering? VoLTE (QCI1)
LTE
WCDMA SRVCC threshold (current:-113dBm)
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SRVCC threshold(after)
SRVCC RSRQ based SRVCC HO • Relation between RSRQ and UL BLER shows that VoLTE voice quality deteriorates when RSRQ becomes lower than -14dB @ UL BLER = 20% RSRQ
Call drop
Clear voice quality
BLER 20%
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Relation between voice quality and RSRQ
Legend ○
Clear voice
Partially missing voice ▲ Almost Missing voice × Call drop △
VoLTE Mobility Handling Features
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ServicebasedMobilityTrigger Servicebasedmobilitythresholds DedicatedVoLTEinter-frequencytarget frequencylist QCI1EstablishmentTriggeredProtection Timer
© Nokia Solutions and Networks 2014
DedicatedMobilityThresholdsforSRVCC SRVCCTriggerEnhancements SRVCCduetoAdmissionControlRejection RSRQbasedB2 VoLTEqualitytriggeredSRVCCtoGSM
VoLTE Radio Optimization Periodical CQI Reporting
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VoLTE Drop Call Optimization CQI report failure detected on PUCCH •
*Only 1 days data
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From Traffica news, more than 50% call failures are cause by CQI report failure detection on PUCCH
VoLTE Drop Call Optimization eNB Detected Radio Link Failures (RLF) – CQI DTX Detection • Nokia eNB can use periodic CQI reports for radio link failure detection on PUCCH and PUSCH -
If MAC layer receives nCqiDtx consecutive reports from UL PHY, the MAC declares CqiRlf_ON (this can be seen in BTS log and Emil)
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If the MAC has set CqiRLF_ON for a specific UE and nCqiRec consecutive CQI reports are again detected successfully for that UE, the MAC sets CqiRlf_OFF.
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When a radio link problem is detected, an eNB-internal timer (T_RLF = T310 + T311 + 2200ms) is started and stopped in case of radio link recovery or otherwise RRC+S1 release is triggered by eNB
• In case the periodical CQI reporting periodicity is increased (or detection is disabled) the dropped call rate decreases as some of the unnecessary call releases can be avoided. • NOTE: CQI_RLF detection does not apply to aperiodic CQI report in PUSCH 59
© Nokia Solutions and Networks 2014
VoLTE Drop Call Optimization eNB Detected Radio Link Failures (RLF) – CQI DTX Detection RLF timer running
T_RLF = t310 + t311
I Q C d e c t i c d t e o i e r d I X e Q P T C D
d e t c e t e d I Q C c i d o i r e P
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time LNCEL/cqiPerNp=10ms Example Vendor Parameter Values: nCqiDtx=4 nCqiRec=2 60
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CQI_RLF ON
CQI_RLF OFF
VoLTE Drop Call Optimization •
E-RAB drop call rate has increased from mid-March and it goes up to 0.2%, i.e. 2x higher than before. •
However VoLTE drop looks no difference.
•
Samsung Galaxy Note 3 was launched at mid of March
ERAB Drop increased suddenly From mid of March
No Changes in VoLTE Drop Ratio
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VoLTE Drop Call Optimization Samsung Mobile Issue •
Due to Missing CQI report from Galaxy Note3 (NB3, NBD, NC3 version), eNB detect CqiRLF_ON and send UEcontextReleaseRequest to MME with “radio connection with ue lost” Cause
Nomal case – CQI report
Abnormal case – no CQI report
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VoLTE Drop Call Optimization nCqiDtx from 100 to 0 • Both E-RAB DR(LTE_5025D) and E-RAB DR, QCI1(LTE_5572A) is decreased
•
•
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eNB RLF detection based on periodic CQI reporting was disabled (nCqiDtx=0): E-RAB DR (LTE_5025D) is dropped from 0.068% to 0.055% in average (19% improvement) E-RAB DR, QCI1(LTE_5572A) is decreased from 0.116% to 0.094% in average (19% improvement)
LTE2206: Extended RLF handling Feature in the Nutshell • FL16 feature allows tuning RLF detection sensitivity at eNB in order to keep UEs longer in RRC connection state. • It applies to cases the eNB indicates RLF due to CQI DTX - The tuning is possible by setting LNBTS:nCqiDtx and LNBTS:nCqiRec parameters • LTE2206 does not change RLF detection functionality, sensitivity RLF indication is issued Before introduction LTE2206 feature:
With LTE2206 feature: Range and step
LNBTS:nCqiDtx==100 LNBTS:nCqiRec==2
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Hardcoded values
LNBTS:nCqiDtx LNBTS:nCqiRec
0…250 step 1 1…8 step 1
VoLTE Radio Optimization QCI1 Specific T310 and T311 Timers
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VoLTE Drop Call Optimization Physical Layer Failure & Recovery • Timer T310 supervises the recovery from physical layer problems and Timer T311 supervises the RRC connection re-establishment.
1. UE detects 1st out of synchronization
3. T310 expires -> detection of radio link failure : all RBs are suspended except SRB0, the UE tx turned off in 40ms, the UE initiates RRC re-establishment process and searches for the best cell. T311 is started
6. UE acquires UL grant via random access procedure and physical layer sends RRC connection re-establishment request message
4. UE finds suitable cell
T310 running 2. UE detects n310 amount of out of synchronization -> The UE starts timer T310
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Time
T311 running
5. UE acquired System Information of the target cell. The UE layer 3 sends RRC connection re-establishment message to the lower layers. T311 is stopped and T301 started.
7. UE receives RRC connection reestablishment message and timer T301 is stopped. SRB1 is resumed and layer 3 sends RRC connection re-establishment complete message to physical layer and procedure ends.
LTE1569: QCI1 Specific RLF and Re-establishment Control QCI1 specific T310 and N310 Only UEs Rel. 9 and higher are benefiting from LTE1569 LTE1569 allows to configure QCI1 specific settings of N310 (LNCEL:n310qci1) and T310 (LNCEL:t310qci1) which are provided to the UE during QCI1 bearer establishment by RRC Connection Reconfiguration message (overwriting SIB2 broadcasted values). When UE is ending the VoLTE call, eNB sends RRC Connection Re-configuration message to release QCI1 DRB, this message includes also RLF-TimersAndConstants-r9 IE with legacy values of T310 and N310 (LNCEL:t310 and LNCEL:n310 ).
System Information Block Type 2 Information Element
Parameter
RRC Connection Reconfiguration Information Element
Parameter
RLF-TimersAndConstants-r9
Ue-TimersAndConstans > t300
LNCEL:t300
> t300-r9
LNCEL:t300
> t301
LNCEL:t301
> t301-r9
LNCEL:t301
> t310
LNCEL:t310
> t310-r9
LNCEL:t310qci1
> n310
LNCEL:n310
> n310-r9
LNCEL:n310qci1
> t311
LNCEL:t311
> t311-r9
LNCEL:t311
> n311
LNCEL:n311
> n311-r9
LNCEL:n311
Ue-TimersAndConstans from broadcasted SIB2 are replaced in the UE by parameters from RLF-TimersAndConstants-r9 in RRC Connection Reconfiguration
The rest of the parameters needed for rlf-TimersAndConstants IE are taken from legacy parameters used for SIB2.
Note: If configured QCI1 specific T310 and N310 are equal to legacy values, eNB will not include rlf-TimersAndConstants IE. 67
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VoLTE Drop Call Optimization Field Trial Settings • Tests were performed with 3 different parameter settings: Abbreviate d Name
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Full Name
MO Modification Class
Range and step
Set 1: Feature OFF
n310Qci1
N310 for QCI1
LNCEL
On-line
1:n1;2:n2;3:n3;4:n4;6:n6;8:n8;10:n10;20:n20
-
t310Qci1
T310 for QCI1
LNCEL
On-line
0:0ms;50:50ms;100:100ms;200:200ms;500:500ms;1 000:1000ms;2000:2000ms
-
n310
Maximumnumberof out-of-sync LNCEL indications
On-line
0:n1;1:n2;2:n3;3:n4;4:n6;5:n8;6:n10;7:n20
t310
Timer T310
LNCEL
On-line
0:0ms;1:50ms;2:100ms;3:200ms;4:500ms;5:1000ms ;6:2000ms
N311
Maximumnumberof LNCEL in-syncindications
On-line
0:n1;1:n2;2:n3;3:n4;4:n5;5:n6;6:n8;7:n10
T311
Timer T311
LNCEL
On-line
t301
Timer T301
LNCEL
On-line
© Nokia Solutions and Networks 2014
0:1000ms;1:3000ms;2:5000ms;3:10000ms;4:15000 ms;5:20000ms;6:30000ms 0:100ms;1:200ms;2:300ms;3:400ms;4:600ms;5:100 0ms;6:1500ms;7:2000ms
-
n6 1000ms
1000ms
n1
n1
n1
3000ms
3000ms
3000ms
400ms
400ms
400ms
VoLTE Drop Call Optimization Field Trial Results • Set 1: initial ERAB drop rate for QCI1 with feature not activated: 0.14% • Set 2: reduction of T310qci1 to 500ms improvement of ERAB DR QCI1 to 0.10% • Set 3: reduction of N310qci1 from n6->n4 n6 ->n4 did not lead to further furt her reduction, result:0.13% result: 0.13%
VoLTE capable Rel. 9 UEs during test: >95% => Higher penetration would even improve result 69
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VoLTE Drop Call Optimization Field Trial Results • Target is to start early re-establishment re -establishment procedure by UE before call drop drop,, but not to trigger too early re-establishements and therefore, increase the risk to drop the call by a failed re-estabishment re -estabishment procedure itself
• Set 1: 1: Default parameters are T310=2000ms and N310=n10 -> Network was already adapted to T310=1000ms, N310=n6 which leads to an improved ERAB DR. tr iggering of re-establishment procedure • Set 2: QCI1 specific T310qci1 reduction leads to earlier triggering by UE and therewith to a further improvement of ERAB QCI1 DR from 0.14% -> 0.10%
• Set 3: 3: Further parameter adaptions to trigger re-establishment procedure by UE even earlier lead to an increase of DR compared to previous setting (Set 2) -> increased amount of reestablishement procedures finally lead to an increased DR as re-establishement re -establishement procedure might fail as well -
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It is recommend recommended ed to activate activate feature LTE161 TE1617 7 RLF trigger triggered ed handove handoverr to improve improve reestabliment success in overall. © Nokia Solutions and Networks 2014
VoLTE Radio Optimization DRX – DRX – Optimized Algorithm
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VoLTE Handset Power Consumption
Battery consumption:
E G N E L L A H C E H T
VoLTE users have a high battery consumption due to a long call session time compared to data users Voice application running in the handset application processor requires a lot of power
40 ms
Sleep mode
1 ms
VoLTE packets
Handset power consumption is generally minimized by integrating a VoLTE client into the modem processor (chipset)
DRX (Discontinuous Reception) functionality uses sleep mode in the handset between VoLTE packet receptions – eVTT profile further enhances battery savings
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VoLTE Handset Power Consumption VoLTE VoL TE optimized op timized DRX • Different voice services tested on same smartphone -
3G CS AM AMRR-WB WB an and d AM AMRR-NB NB
-
Native VoLTE
-
VoIP (Viber)
• Without VoLTE optimized DRX -
VoL oLTE TE cons consume umes s up to 88% 88% highe higherr power power tha than n 3G CS call
-
Viber con Viber consum sumed ed up to to two two times times mor more e powe powerr than 3G CS call
• With VoLTE optimized DRX -
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VoL oLTE TE has has simil similar ar power power con consum sumpti ption on as as 3G CS CS call © Nokia Solutions and Networks 2014
300
VoLTE 248
250 ) 200 A m ( t n150 e r r u C
235
154 129
131
125
121
100 50 0 3G CS 3G CS noDRX AMR-NB AMR-WB
DRX 20ms 6ms OnDur
DRX 40ms 6ms OnDur
DRX 40ms 4ms OnDur
Viber
VoLTE Drop Call Optimization DRX Impact on Poor RF • The current analysis of DRX problems indicate that in case of poor RF the DRX causes additional dropped calls: -
These The se dro droppe pped d call calls s coul could d be be cause caused d by by additional delays caused by DRX
-
Meas Me asur urem emen entt de dela lay ys for handovers
-
Measur Meas urem emen entt in inac accu cura raci cies es of CQI (reported CQI in DRX active state might not correctly reflect the RF quality due to the DRX sleep state)
-
Due to th thiis th the e LA might not work accurately and fast enough to be able to react on changing CQI in poor RF and UE might never hear the HO command
• The DRX feature can be improved so that it could be turned off in poor RF (based on CQI) and turned on in case of improved i mproved RF (improving absolute CQI value)
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VoLTE Drop Call Optimization DRX Optimized Algorithm for VoLTE • If UE has QCI-1 DRB and DRX is currently enabled, and C-plane receives RL Status Indication for this UE indicating “ BadChannelQuality BadChannelQuality”” then C-plane C-plane sends RRC Reconfiguration message to UE to disable DRX: rrcConnectionReconfiguration-r8 : rrcConnectionReconfiguration-r8 { radioResourceConfigDedicated { mac-MainConfig explicitValue : { drx-Config release : NULL,
… }
• If UE has QCI-1 DRB and DRX was previously disabled due to Poor RF RF,, and C-plane receives new RL Status Indication for this UE indicating “ GoodChannelQuality GoodChannelQuality”, ”, then CCplane sends RRC Reconfiguration message to UE to re-install the DRX profile (i.e. reenable DRX) provided that other DRX feature add conditions (feature flag, configuration, etc.) are satisfied 75
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VoLTE Optimized DRX Thresholds • The parameters should be set according to the network statistics i.e. - qci1DrxOnThreshold (default=9) should be set according to the average reported CQI across the whole network i.e. if average reported CQI = 9 then CDrxOnThreshold should be set to 9. - qci1DrxOffThreshold (default=7) should be set 2 steps below the above parameter value
• Above parameters will be tunable parameters in release 16 (defaults used as above) 76
© Nokia Solutions and Networks 2014
VoLTE Optimized DRX DRX Optimized Algorithm for VoLTE – Field Test • CQI threshold for deactivation and activation need to be set according to network performance DRX OFF
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CQI 7-9
DRX OFF
CQI 9-11
Average CQI is 11 or higher in the cluster and therefore, CQI thresholds needs to be set higher
High Speed Users Optimization
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High Speed Users Optimization Doppler shift • When a user is moving relative to an eNodeB, the transmit frequency of the eNodeB is different from the receive frequency of the user due to the Doppler shift.
Access Point
• In an LTE system, this Doppler shift causes interference in or between OFDM symbols.
• The faster the speed the greater the shift and thus, the interference.
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The highest Doppler shift is experienced by the UE that is in the middle of the two cells that are pointing towards each other
High Speed Users Optimization High speed UE definition •
UE should be considered as high speed UE in case Doppler shift at eNB is higher than 400Hz
•
LTE48 Support of High Speed Users feature improves the eNB UL reception performance for the high speed users but does not bring any gain for the low speed user (Doppler shift less than 400 Hz)
•
Because of the frequency offset estimation and the signal correction, the computation complexity and the processing latency are increased at eNB - Therefore the feature activation should be a subject for consideration during the network planning by the customer
•
Table below shows exemplary calculations for different frequency bands:
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Frequency Band [MHz]
High speed UE in case UE speed is higher than app.[km/h]
1900
>110
2300
>90
2600
>80
© Nokia Solutions and Networks 2014
v [km/ h]
F _ o[ H z ]
2 F _ c [G H z ] 0.926
High Speed Users Optimization LTE48 Support of High Speed Users • LTE48 Support of High Speed Users feature can be activated by setting the parameter prachHsFlag = ‘true’ (requires object locking) - The range of allowed rootSeqIndex values becomes limited (restricted set) and the number of PRACH sequences which can be generated from each root sequence is no longer fixed -> RSI re-planning is required.
- hsScenario must be configured to ‘ scenario1’ or ‘scenario 3’ dependently on the deployment scenario - Scenario 1 (open space scenario) and scenario 3 (tunnel scenario) defined by 3GPP - ulCombinationMode must be set to ‘MRC’, i.e. LTE1402 Intra eNB UL CoMP cannot be used.
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High Speed Train Optimization KPI Improvement after prachHsFlag=true RRC Performance
DRB Performance
Total Att LTE_753A
CSSR LTE_5218C
100.00
20,000
98.00
15,000
96.00
10,000
94.00 92.00
5,000
90.00
0
before
Stp ATT LTE_5116A
SR LTE_5220A
after
Data SR LTE_5117A
100.00
100,000
98.00
80,000
96.00
60,000
94.00
40,000
92.00
20,000
90.00
0 6 2 8 0 6 2 8 0 6 2 8 0 6 2 8 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 . . . . . . . . . . . . . . . . 8 8 8 8 9 9 9 9 0 0 0 0 1 1 1 1 2 2 2 2 2 2 2 2 3 3 3 3 0 0 0 0 . . . . . . . . . . . . . . . . 4 4 4 4 4 4 4 4 4 4 4 4 5 5 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stp Att LTE_5118A
eRAB Performance
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100.00
40,000
95.00
20,000
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DR LTE_5025C
8.00
Normal, NW view LTE_5024C
… … … … … … … … … … … … … … 2 . 2 . 2 . 2 . 2 . 2 . 2 . 3 . 3 . 3 . 3 . 0 . 0 . 0 . 4 4 4 4 4 4 4 4 4 4 4 5 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 7 4 1 4 1 8 1 8 5 2 5 2 9 0 0 1 2 0 1 1 0 0 1 2 0 1 1 . . . . . . . . . . . . . . 8 8 8 8 9 9 9 0 0 0 0 1 1 1 2 2 2 2 2 2 2 3 3 3 3 0 0 0 . . . . . . . . . . . . . . 4 4 4 4 4 4 4 4 4 4 4 5 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Stp SR LTE_5017A
90.00
Data stp SR LTE_5003A
0
6.00 4.00 2.00 0.00 0 7 4 1 4 1 8 1 8 5 2 5 2 9 0 0 1 2 0 1 1 0 0 1 2 0 1 1 . . . . . . . . . . . . . . 8 8 8 8 9 9 9 0 0 0 0 1 1 1 2 2 2 2 2 2 2 3 3 3 3 0 0 0 . . . . . . . . . . . . . . 4 4 4 4 4 4 4 4 4 4 4 5 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0
High Speed Train Optimization KPI Improvement after prachHsFlag=true
Intra ENB HO Att LTE_5124A
Inter ENB HO Att LTE_5125A
Intra ENB HO Prep att LTE_5123A
Inter ENB HO Prep att LTE_5126A
Intra ENB HO SR total LTE_5043A
Inter ENB HO SR total LTE_5058B
Intra ENB HO SR LTE_5035A
Inter ENB HO SR LTE_5048B
Intra ENB HO Prep SR LTE_5036A
Inter ENB HO Prep SR LTE_5049B
100.00 99.00 98.00 97.00 96.00
before
after
95.00 0 7 4 1 4 1 8 1 8 5 2 5 2 9 0 0 1 2 0 1 1 0 0 1 2 0 1 1 . . . . . . . . . . . . . . 8 8 8 8 9 9 9 0 0 0 0 1 1 1 2 2 2 2 2 2 2 3 3 3 3 0 0 0 . . . . . . . . . . . . . . 4 4 4 4 4 4 4 4 4 4 4 5 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0
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45,000 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0
100.00
45,000 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0
99.00 98.00 97.00 96.00 95.00 0 6 2 8 0 6 2 8 0 6 2 8 0 6 2 8 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 . . . . . . . . . . . . . . . . 8 8 8 8 9 9 9 9 0 0 0 0 1 1 1 1 2 2 2 2 2 2 2 2 3 3 3 3 0 0 0 0 . . . . . . . . . . . . . . . . 4 4 4 4 4 4 4 4 4 4 4 4 5 5 5 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
High Speed Train Optimization LTE2445: Combined Supercell • High speed users handovers occur very frequently causing a large amount of signaling. Moreover, the train is running between cell centers and cell edges, which significantly impacts data rates even causing service drops. • LTE2445 Combined Supercell feature reduces drastically the handover frequency in high speed scenarios.
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The UE can move seamlessly between subcells, without interruption by a RACH procedure due to cell change as with normal cells
-
6 RRH support allows for extended supercell coverage
© Nokia Solutions and Networks 2014
High Speed Train Optimization VoLTE tunnel performance • There are many RRC re-establishments of VoLTE call due to RLFs when train goes through a tunnel and thus, RRC re-establishment causes missing voice packets and end user experience is degraded. RSRP
RSRQ
RRC Re-establishment
VoLTE Packet 85
Re-esta
© Nokia Solutions and Networks 2014
Re-esta
Re-esta
Re-esta
High Speed Train Optimization VoLTE tunnel performance • LTE drop rate is around 38% but WCDMA’s drop rate is lower than LTE in tunnel sites.
Drop Rate (ADR) [%]
LTE
60
WCDMA
50
WCDMA Voice should be used when train goes through a tunnel
40 30
Lower drop rate
20 10 0
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High Speed Train Optimization Possible design concept • To make UEs enter tunnels continuously without drop, our new design forces VoLTE UEs to move to WCDMA by SRVCC in tunnel adjacent sites and tunnel si tes. Forced SRVCC to WCDMA AMR
Tunnel
VoLTE
LTE WCDMA
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AMR
© Nokia Solutions and Networks 2014
AMR
High Speed Train Optimization TAC design • In case VoLTE is launched for certain areas only the design of TAC and eNB QCI1 support needs to be as below SRVCC to WCDMA AMR
VoLTE area
Non VoLTE area
LTE WCDMA
TAC Configuration
eNB Configuration 88
VoLTE ON site
VoLTE OFF site
VoLTE OFF site
VoLTE ON TAC
VoLTE OFF TAC
VoLTE OFF TAC
VoLTE ON
VoLTE ON
VoLTE ON
© Nokia Solutions and Networks 2014
High Speed Train Optimization Considerations • If VoLTE is supported by the target eNB but the TAC of the target eNB does not support VoLTE then the HO for QCI1 should go through and path switch should be possible. However there might be differences in different vendor’s MMEs. • Also whether the UE SIP client drops the call or not (UE sending SIP : BYE message) when TAC without VoLTE support is detected depends on the UE implementation. • Therefore SRVCC to WCDMA is recommended to be triggered.
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VoLTE Call Flow Analysis
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VoLTE Call Flows: Registration Procedure
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VoLTE Call Flows: Registration Procedure (1/3)
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VoLTE Call Flows: Registration Procedure (2/3)
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VoLTE Call Flows: Registration Procedure (3/3)
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VoLTE Call Flows: Mobile Originated VoLTE Call
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VoLTE Call Flows: Mobile Originated VoLTE Call (1/2)
user’s perspective, Accessibility is typically considered from 180 RINGING or ACK (200 OK)
Call Setup time : SIP INVITE – SIP 180 Ringing = 4910 ms = 4.9 s
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VoLTE Call Flows: Mobile Originated VoLTE Call (1/2)
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VoLTE Call Flows: Mobile Originated VoLTE Call (2/2)
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VoLTE Signaling Flows: Mobile Terminated VoLTE Call
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VoLTE Signaling Flows •
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Mobile Terminated VoLTE Call (1/2)
© Nokia Solutions and Networks 2014
VoLTE Signaling Flows •
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Mobile Terminated VoLTE Call (2/2)
© Nokia Solutions and Networks 2014
Back to list of call flows
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VoLTE Call Flows SRVCC to 3G
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VoLTE Signaling Flows •
SRVCC to 3G
Measurement event B2 (UTRA) reported
SRVCC/HO command
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