WCDMA Call ReEstablishment
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Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents 1. Call Call Re-E Re-Est stab ablilish shme ment nt Over Overvi view ew
2. Call Re-Establishment Causes a) Downlink RL failure b) Uplink RL failure c) SRB Reset d) UE SRB Reset 3. Related Configuration 4. Case Analysis
Call reestablishment is a function by which radio links (RLs) are reestablished when a service interruption or an access failure occurs due to bad RF environment. that cause significant signal quality fluctuation.
Call reestablishment can be initiated by a UE or the RAN.
Call reestablishment initiated by a UE: The UE sends a call reestablishment request to the network to restore services upon detecting a downlink RL failure or a signaling radio bearer (SRB) reset.
Call reestablishment initiated by the RAN: The RAN informs the UE to start call reestablishment upon detecting a service interruption or an access failure.
Benefits
Call reestablishment improves user experience by increasing the radio access bearer (RAB) setup success rate and reducing the call drop rate.
Contents 1. Call Re-Establishment Overview 2. Call Call Re-Es Re-Esta tabl blis ishm hmen entt Caus Causes es a) Downlink RL failure b) Uplink RL failure c) SRB Reset d) UE SRB Reset 3. Related Configuration 4. Case Analysis
The possible causes of a service interruption or an access failure that may result in call re-establishment are :
Downlink RL failure
Uplink RL failure
SRB reset
UE SRB reset
Before releasing RLs due to the preceding causes in those processes, the RAN detects the service interruption or access failure and initiates call reestablishment,..
Contents 1. Call Re-Establishment Overview 2. Call Re-Establishment Causes a) Downli nlink RL fai failure b) Uplink RL failure c) SRB Reset d) UE SRB Reset 3. Related Configuration 4. Case Analysis
Downlink RL Failure Detection
UE monitors downlink RL quality.
UE receives
UE starts the
N313 number T313
of "out-sync" indications
timer and didn’t receive N315 "in-sync" indications within it
(as if so UE will not send Cell Update message)
CELL_B
N313
Downlink RL Failure Call Reestablishment Reestablishment Triggering
CELL_A
UE will enter in call reestablishment procedure
Downlink RL Failure Call Reestablishment Implementation Implementation
T313 N315
UE transmits the Cell Update message with cause value "Radio Link Failure" to
Cell Update
the RNC for call reestablishment.
Meanwhile, the UE starts
T314 timer
RL S RL Setu etu p p R eq eq
services which is maximum allowed time for UE to try to send Cell Update message
UE can resend Cell Update message if he didn’t have a reply from network every T302 time for maximum N302 number of times
If faulty RLs are restored before T314/T315 expires, the call reestablishment is successful. Interrupted services are restored or UE access succeeds.
If faulty RLs are not restored before T314/T315 expires, the call reestablishment fails. And UE access fails.
100
for CS services or the T315 timer for PS
T314+T302*N302
R L Set Setup up Rsp
RL Del Req RL Del Rsp Cell Update Confirm Physical CH Reconfig CMP
Contents 1. Call Re-Establishment Overview 2. Call Re-Establishment Causes a) Downlink RL failure b) Uplink RL RL fa failure c) SRB Reset d) UE SRB Reset 3. Related Configuration 4. Case Analysis
Uplink RL Failure Detection
NodeB monitors uplink RL quality.
NodeB receives NOUTSYNCIND number of "out-sync" indications
NodeB starts the
NodeB didn’t receive TRlFailure
TRlFailure timer NINSYNCIND "in-sync"
indications within
timer (as if so the NodeB stops and resets the timer) timer)
RNC activates a synchronization timer
NodeB does not detect uplink RL synchronization before synchronization timer expires
Uplink RL Failure Call Reestablishment Triggering
RNC sends to NodeB the Radio Link Activation Command message containing IE "deactivate“
NodeB stops downlink power transmission for the UE's RL sets
RNC starts the timer for call reestablishment ( RsvdPara2 timer for CS services and
RsvdPara3 timer
for PS services)
If RNC receives Cell Update message from UE before previous timer expires, the RNC stops the timer and initiates call reestablishment. reestablishment. (as if received after, after, call drops or UE access fails)
Uplink RL Failure Call Reestablishment Implementation
After the NodeB stops downlink power transmission for a UE's RLs, UE will receive
N313 number
UE starts the
T313
of "out-sync" indications
timer and didn’t receive N315 "in-sync"
indications within it (as if so UE will not send Cell Update message)
UE transmits the Cell Update message with cause value "Radio Link Failure" to the RNC for call reestablishment.
Meanwhile, the UE starts
T314 timer
for CS services or the T315
timer for PS services which is maximum allowed time for UE to try to send Cell Update message
UE can resend Cell Update message if he didn’t have a reply from network every
T302
time for maximum
N302 number
of times
If faulty RLs are restored before T314/T315 expires, the call reestablishment is successful. Interrupted services are restored or UE access succeeds.
If faulty RLs are not restored before T314/T315 expires, the call reestablishment fails. Services are released or UE access fails.
Contents 1. Call Re-Establishment Overview 2. Call Re-Establishment Causes a) Downlink RL failure b) Uplink RL failure c) SRB Reset d) UE SRB Reset 3. Related Configuration 4. Case Analysis
SRB Reset Detection
AMRlcDiscardMode parameter
is set to NO_DISCARD
RNC sends a signaling message in acknowledged mode (AM) to UE
RNC does not receive a response from the UE before the number of SRB RLC PDU retransmissions reaches the value of the
NoDiscardMaxDAT parameter. parameter.
RNC triggers an SRB reset and sends the Reset PDU message to the UE to reestablish RLC entities on both sides
SRB Reset Call Reestablishment Reestablishment Triggering
Same as UL RL Failure
SRB Reset Call Reestablishment Implementation
Same as UL RL Failure
Contents 1. Call Re-Establishment Overview 2. Call Re-Establishment Causes a) Downlink RL failure b) Uplink RL failure c) SRB Reset d) UE SRB Reset 3. Related Configuration 4. Case Analysis
UE SRB Detection
UE SRB occurred
UE SRB Call Reestablishment Reestablishment Triggering
RNC does not send the Radio Link Activation Command message containing the "deactivate" IE to the NodeB. Therefore, the NodeB do es not stop downlink power transmission for the UE's RL sets.
CELL_A
CELL_B
Instead, the RNC initiates call reestablishment upon receiving the Cell Update message UE SRB RESET
from the UE.
UE SRB Call Reestablishment Implementation Implementation
Cell Update( UE SRB RESET)
Iu Release Req RL Setu Setu p Req 100
Same as UL RL Failure
T314+T302*N302
RL Setu Setu p Rsp
RL Del Req RL Del Rsp Cell Update Confirm Physical CH Reconfig CMP
Contents 1. Call Re-Establishment Overview 2. Call Re-Establishment Causes a) Downlink RL failure b) Uplink RL failure c) SRB Reset d) UE SRB Reset 3. Rela Relate ted d Co Conf nfig igur urat atio ion n 4. Case Analysis
Related Configuration
Call reestablishment is controlled by service switch, process switch, and cause switch parameters. Enable the corresponding service switch before enabling a process switch or a cause switch Parameter Name
Sub-Parameter
Huawei
Recommen
Name
Default value
ded Value
RSVDBIT1_BIT24
Disabled
Enabled
Switch that controls call reestablishment for CS services (CS+PS combined services is also controlled by this switch)
Switch
RSVDBIT1_BIT25
Disabled
Enabled
Switch that controls call reestablishment for PS services
Cause
RSVDBIT1_BIT22
Disabled
Enabled
Switch that controls call reestablishment triggered by SRB resets
Switch
RSVDBIT1_BIT23
Disabled
Enabled
Switch that controls call reestablishment triggered by RL failures
Service
Remark
Related Configuration (Cont.) Parameter Name
Huawei Default value
Recommended
Remark
Value
NOutsyncInd
50
8
Times of successive out-sync indications required for starting the radio link failure timer.
NInsyncInd
5
8
Times of successive in-sync indications required for the NodeB to trigger the radio link recovery process
TRlFailure
5sec
5sec
NodeB starts the timer after it receives successive out-of-sync indications indications of the number defined by NOutsyncInd. The NodeB shall stop and reset the timer after receiving successive in-sync indications of the number defined by NInsyncInd.
RsvdPara1:RSVD BIT1_BIT28
1
0
Switch that controls Synchronization Timer for CS reestablishment reestablishment triggered, 1:RlRstrTmr,0:T313 1:RlRstrTmr,0:T313
RlRstrTmr
11000msec
11000msec
A timer to RNC wait for radio link restoration restoration indication in the radio link procedure.
RsvdPara2
0msec
15000msec
CS Timer for Enhanc ed Call Reestablish ment, start after RNC send the RL Active CMD , stop after RNC receives cell update message.
RsvdPara3
0msec
30000msec
PS Timer for Enhanced Call Reestablishment, Reestablishment, , start after RNC send the RL Active CMD , stop after RNC receives cell update message.
N313
50
20
Maximum number of successive "out of sync" indications received from L1
N315
1
1
Maximum number of successive "in sync" indications received from L1 when T313 is activated
T313
3sec
3sec
T313 is started after the UE d etects consecutive consecutive N313 "out of sync“ indications from L1. T313 is stopped after the UE detects consecutive N315 "in sync" indications from L1
T314
0sec
12sec
T314 is started when the criteria for CS radio link failure are fulfilled and only radio bearers associated with T314 exist.T314 is stopped after the Cell Update procedure has been completed. (must be greater than T302*N302)
T315
0sec
30sec
T315 is started when the criteria for PS radio link failure are fulfilled, and only radio bearer associated with T315 exists.T315 is stopped after the Cell Upd ate procedure has been completed (must be greater than T302*N302)
N302
3
3
Maximum number of retransmissions of CELL UPDATE/URA UPDATE
T302
2000msec
1400msec
CELL UPDATE/URA UPDATE will be resent upon expiry of the timer if V302 less than or equal to N302
Related Configuration (Cont.) Parameter Name
Huawei Default value
Recommended
Remark
Value
HoAsuTmr
5000msec
10000msec
A timer to RNC wait for the response to active set update in soft handover procedure.
HoCellUpdateRspTmr
5000msec
10000msec
A timer to RNC wait for the response to the cell update confirm from UE in forward handover procedure.
HoPhychRecfgTmr
5000msec
10000msec
A timer to RNC wait for the response to physical channel reconfiguration reconfiguration in hard handover procedure
RbSetupRspTmr
5000msec
10000msec
A timer to RNC wait for the RB setup response from UE in the RB procedure.
RbRecfgRspTmr
5000msec
10000msec
Timer used to wait for the RB reconfiguration response from UE in the RB procedure
RsvdPara1:RSVDBIT1_BI
Disabled
Enabled
To enable to perform call reestablishment If the RNC receives the Cell Update message containing the
T26
cause value "RLC Unrecoverable Error" from the UE
Contents 1. Call Re-Establishment Overview 2. Call Re-Establishment Causes a) Downlink RL failure b) Uplink RL failure c) SRB Reset d) UE SRB Reset 3. Related Configuration 4. Case An Analysis
Case Analysis (Overview)
This feature have been implemented and gave good results in following Countries / Operators:
M1 in Singapore
3GIS in Switzerland
X operator in Spain
X operator in Norway
Turkcell in Turkey
DU in UAE
Etisalat in Egypt
Vodafone in Egypt
…
Case Analysis (1)
From below two RNCs’ CS&PS CDR trend, after activating the Call Re -establishment we could see that CDR has step improvement.
Case Analysis (2)
From RNC analysis, found that most call drop happens due to RL Failure Row Labels DropCall_CombinedService DropCall_DueTo_BadCoverage DropCall_DueTo_CNRelated DropCall_DueTo_High_RTWP DropCall_DueTo_IU_Related DropCall_DueTo_IUR_Related DropCall_DueTo_MISSING_NEIGHBOR DropCall_DueTo_RadioResCong DropCall_DueTo_RAN Dropcall_Dueto_RL_Failure DropCall_DueTo_Slow_SHO DropCall_InterFreq/InerRat Related DropCall_Pilot_Pollution
Count of count 1 30 4 28 4 4 8 5 3 82 23 2 20
So we activated Call Re-establishment which improved CDR Rate
Case Analysis (3)
From below RNC PS CDR trend, after activating the Call Re-establishment we could see that CDR has step improvement.
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