LTE OPT
Drop Call analysis
By: Dr. Richard Scharp PhD in Wireless Communication and Convenience Store Management
Soc Classification level
1
© Nokia Siemens Networks
Presentation / Author / Date
Outline
• UE-detected RF problems: RRC Connection Re-Establishment
• eNB-detected radio link problems
•
•
•
•
– PUSCH RLF
– CQI RLF
– Ack/Nack RLF
– SRS RLF
eNB-initiated release: TA timer expiry
eNB-initiated release: maximum RLC retransmissions exceeded
eNB-initiated release: GTP-U failure
Timers and constants (3GPP)
Soc Classification level
2
© Nokia Siemens Networks
Presentation / Author / Date
RRC connection Re-Establishment by UE
• When UE is in RRC_CONNECTED and RRC security is
active, it can trigger RRC Connection Re-establishment
–
–
–
–
upon T310 expiry
upon reaching the maximum number of UL RLC retransmissions
upon handover failure (T304 expiry)
upon non-HO related random access problem
• If successful, RRC Conn Re-Establishment
– reconfigures SRB1 to resume data transfer of RRC msgs
– re-activates RRC security without changing algorithms
• NOTE: if UE is in RRC_CONNECTED while RRC security is
not active, UE goes to RRC_IDLE, performs cell reselection
and TAU
Soc Classification level
3
© Nokia Siemens Networks
Presentation / Author / Date
RLF due to T310 expiry at UE
Second Phase
First Phase
normal operation
radio
problem
detection
no recovery during T310
no recovery during T311
goes back to idle
RRC_IDLE
RRC_CONNECTED
radio link failure
n310
consecutive
out-of-sync
indications
•
RRC connection
re-establishment
attempted during
t311
For UE “normal operation” in the figure above means :
–
–
–
–
•
n311 consecutive
in-sync indications
during t310
UE not waiting for RRC Connection Setup/Reject (T300 not running)
UE not waiting for RRC Re-establishment Establishment/Reject (T301 not running)
handover not ongoing (T304 not running)
No RLF recovery ongoing (T311 not running)
NOTE: the terms in-sync and out-of-sync refer to L1 problems, not to timing alignment
Soc Classification level
4
© Nokia Siemens Networks
Presentation / Author / Date
Cell reselection
and Tracking Area
Update if RRC
Re-Establishment
fails
RLF due to T310 expiry, in-sync and out-of-sync
definition, without DRX, 3GPP TS 36.133 Sec 7.6
• When the downlink radio link quality estimated over the last [200] ms period
becomes worse than the threshold Qout, Layer 1 of the UE shall send an out-of-sync
indication to the higher layers within [200] ms Qout evaluation period.
• When the downlink radio link quality estimated over the last [100] ms period
becomes better than the threshold Qin, Layer 1 of the UE shall send an in-sync
indication to the higher layers within [100] ms Qin evaluation period.
• The threshold Qout is defined as the level at which the downlink radio link cannot be
reliably received and shall correspond to [10%] block error rate of a hypothetical
PDCCH transmission taking into account the PCFICH errors with transmission
parameters specified in Table 7.6.1-1 of 3GPP TS 36.133.
• The threshold Qin is defined as the level at which the downlink radio link quality can
be significantly more reliably received than at Qout and shall correspond to [2%] block
error rate of a hypothetical PDCCH transmission taking into account the PCFICH
errors with transmission parameters specified in Table 7.6.1-2 of 3GPP TS 36.133.
• UE timer T310 is started after n310 successive out-of-sync indications from
physical layer. Two successive in-sync/out-of-sync indications from physical layer
shall be separated by at least [10] ms.
• NOTE: 3GPP notation [.] means that the final numerical values have not been agreed in the specification.
Soc Classification level
5
© Nokia Siemens Networks
Presentation / Author / Date
In-sync and out-of-sync definition without DRX
• Window to estimate if BLER > out-sync threshold is [200ms]
• Hence: out of last 200 TTIs at least 20 PDCCH have been received in error
• Window to estimate if BLER < in-sync threshold is [100ms]
• Hence: out of last 100 TTIs at most 2 PDCCH have been received in error
in-sync
in-sync
in-sync
out-sync
out-sync
out-sync
out-sync
out-sync
out-sync
out-sync
out-sync
BLER of reference
PCFICH + PDCCH
10%
2%
>10ms
time
• NOTE: 3GPP notation [.] means that the final numerical values have not been agreed in the specification.
• Reference PDCCH and PCFICH configuration used in the BLER estimation is defined by 3GPP
Soc Classification level
6
© Nokia Siemens Networks
Presentation / Author / Date
RLF due to maximum RLC retx reached
First Phase
normal operation
Second Phase
RLC retransmissions until max value
no recovery during T311
RRC_CONNECTED
goes back to idle
RRC_IDLE
radio link failure
RLC
retransmissions until
max RLC retx
threshold is reached
RRC connection
re-establishment
attempted during
t311
from RRC Connection Reconfiguration:
drb-ToAddModList
drb-ToAddModList value 1
drb-Identity
:1
rlc-Config
am
ul-AM-RLC
t-PollRetransmit : ms40
pollPDU
pollByte
maxRetxThreshold
Soc Classification level
7
© Nokia Siemens Networks
Presentation / Author / Date
: p32
: kB25
: t8
Cell reselection
and Tracking Area
Update if RRC
Re-Establishment
fails
RLF due to HO failure
First Phase
normal operation
Second Phase
Attempting PRACH to target cell
no recovery during T311
RRC_CONNECTED
goes back to idle
RRC_IDLE
radio link failure
RRC Conn ReConf
with MobilityInfo
(”HO command”)
T304 running
while UE
attempting access
to target cell.
T304 expires
from RRC Connection Reconfiguration:
mobilityControlInfo
targetPhysCellId
: 33
t304
: ms1000
newUE-Identity
Bin
: 14 EB (= 5355)
Soc Classification level
8
© Nokia Siemens Networks
Presentation / Author / Date
RRC connection
re-establishment
attempted to
source or target
cell during t311
Cell reselection
and Tracking Area
Update if RRC
Re-Establishment
fails
RLF due to non-HO random access failure
First Phase
normal operation
Second Phase
Attempting PRACH to serving cell
no recovery during T311
RRC_CONNECTED
goes back to idle
RRC_IDLE
radio link failure
Example: Random
Access triggered due
to missing PUCCH
SR resources, or
PDCCH order
UE attempting
random access to
serving cell.
RACH failure
• Non-HO random access means
– PDCCH order -triggered RA (RL30/RL25)
– Random Access Scheduling Request
Soc Classification level
9
© Nokia Siemens Networks
Presentation / Author / Date
RRC connection
re-establishment
attempted to
serving cell during
t311
Cell reselection
and Tracking Area
Update if RRC
Re-Establishment
fails
Re-establishment causes
Source: 3GPP TS 36.331
• UE sets the reestablishmentCause as follows:
 if the re-establishment procedure was initiated due to RRC reconfiguration
failure (i.e., the UE is unable to comply with the reconfiguration), UE sets the
reestablishmentCause to the value 'reconfigurationFailure'
 if the re-establishment procedure was initiated due to intra-LTE handover
failure or inter-RAT mobility from EUTRA failure, UE sets the
reestablishmentCause to the value 'handoverFailure'
 Otherwise UE sets the reestablishmentCause to the value 'otherFailure‘.
NOTE: This includes T310 RLF failure.
• In RL30/RL25 there are counters for re-est causes received
– … but no counter for re-est due to RRC reconfiguration failure
Soc Classification level
10
© Nokia Siemens Networks
Presentation / Author / Date
RRC Re-establishment Request, example
RRC SIGNALING MESSAGE
Time: 9:38:13.165
RRCConnectionReestablishmentRequest
(3GPP TS 36.331 ver 8.7.0 Rel 8)
UL-CCCH-Message
message
c1
rrcConnectionReestablishmentRequest
criticalExtensions
rrcConnectionReestablishmentRequest-r8
ue-Identity
c-RNTI
Bin
: 4C F0 (= 19696)
physCellId
: 30
shortMAC-I
Bin
: AB 7D (= 43901)
reestablishmentCause
: otherFailure
spare
Bin
: 0 (2 bits)
Data (hex):
09 9E 01 EA B7 D8
Soc Classification level
11
© Nokia Siemens Networks
Presentation / Author / Date
This is the PCI of the
cell where UE was
last succesfully
connected to.
Example ‘UE drop call’ signalling RL20/RL15
EventId
Time
Channel
Direction
Message
RRCSM
10:36:32.194
DCCH
Uplink
RRCConnectionReconfigurationComplete
RRCSM
10:36:32.216
BCCH-SCH
Downlink
SystemInformationBlockType1
RRCSM
10:36:32.345
BCCH-SCH
Downlink
SystemInformation
RRCSM
10:36:32.662
DCCH
Uplink
MeasurementReport
RRCSM
10:36:33.617
DCCH
Uplink
MeasurementReport
RRCSM
10:36:33.779
DCCH
Downlink
RRCConnectionReconfiguration
RRCSM
10:36:33.779
DCCH
Uplink
RRCConnectionReconfigurationComplete
RRCSM
10:36:35.344
BCCH-BCH
Downlink
MasterInformationBlock
RRCSM
10:36:35.362
BCCH-SCH
Downlink
SystemInformationBlockType1
RRCSM
10:36:35.383
BCCH-SCH
Downlink
SystemInformation
RRCSM
10:36:35.383
BCCH-SCH
Downlink
SystemInformation
RRCSM
10:36:35.422
BCCH-SCH
Downlink
SystemInformation
RRCSM
10:36:35.422
CCCH
Uplink
RRCConnectionReestablishmentRequest
RRCSM
10:36:35.555
CCCH
Downlink
RRCConnectionReestablishmentReject
RRCSM
10:36:36.254
BCCH-BCH
Downlink
MasterInformationBlock
RRCSM
10:36:36.254
BCCH-SCH
Downlink
SystemInformationBlockType1
L3SM
10:36:36.254
Uplink
TRACKING_AREA_UPDATE_REQUEST
RRCSM
10:36:36.254
CCCH
Uplink
RRCConnectionRequest
RRCSM
10:36:36.328
CCCH
Downlink
RRCConnectionSetup
RRCSM
10:36:36.328
DCCH
Uplink
RRCConnectionSetupComplete
RRCSM
10:36:41.382
DCCH
Downlink
DLInformationTransfer
L3SM
10:36:41.382
Downlink
TRACKING_AREA_UPDATE_ACCEPT
L3SM
10:36:41.382
Uplink
TRACKING_AREA_UPDATE_COMPLETE
Soc Classification level
12
© Nokia Siemens Networks
Presentation / Author / Date
HO command
In new cell
Outline
• UE-detected RF problems: RRC Connection Re-Establishment
• eNB-detected radio link problems
•
•
•
•
– PUSCH RLF
– CQI RLF
– Ack/Nack RLF
– SRS RLF
– PDCCH Order RLF
eNB-initiated release: TA timer expiry
eNB-initiated release: maximum RLC retransmissions exceeded
eNB-initiated release: GTP-U failure
Timers and constants (3GPP)
Soc Classification level
13
© Nokia Siemens Networks
Presentation / Author / Date
RL problem detection at eNB, intro
•
eNB radio link problem detection mechanisms are NSN-internally
specified
Multiple methods (called “link monitors”) are defined to detect a radio
link problem in the eNB.
When one link monitor detects a problem, it is really a radio link problem
even if other link monitors have not yet indicated anything.
Each link monitor has its internal criteria to decide when radio link
problem is flagged and de-flagged (radio link recovers).
If the RLP persists longer than T_RLF, RRC+S1 release is triggered
•
•
•
•
–
•
T_RLF = t310 + t311 (eNB-internal timer)
Link monitors in RL20/RL15:
1.
2.
3.
4.
5.
Uplink PUSCH DTX detection for scheduled uplink data (RRM SFS ID 2041)
CQI DTX detection for periodic CQI reports in PUCCH and PUSCH (Radio L1 SFS)
Uplink Ack/Nack DTX detection for transmitted downlink data (RRM SFS ID 2006)
PDCCH Order RLF (RL30)
SRS DTX detection (RL15)
Soc Classification level
14
© Nokia Siemens Networks
Presentation / Author / Date
PUSCH RLF: RlsCause_PuschRlf_ON
• When UE is scheduled for PUSCH transmission, eNB expects to receive
UL transmission on the scheduled PRBs
• If signal from UE cannot be detected at all, PUSCH DTX is declared
– NOTE: The case where UL TBS is received but it fails CRC check is not DTX (it’s a
NACK)
• DTX PUSCH indication is provided by the UL physical layer.
• The result is received by LTE MAC in reliableULtransmissionFlag
parameter (which can be seen in UL TTI trace).
• Both counter-based and timer-based RLF detection is supported
• Timer-based PUSCH RLF detection:
– If “DTX“ is received on the PUSCH for a configurable period of time (rlpDetMaxTimeUl),
PUSCH RLF is set on
• Counter-based PUSCH RLF detection:
– If “DTX“ is received on the PUSCH for a consecutive number of times (rlpDetMaxNoUl),
PUSCH RLF is set on
• The recovery of the radio link is indicated when for a configurable number
of contiguous UL resource assignments data is detected on PUSCH (ACK
or NACK received).
– Defined by parameter rlpDetEndNoUl.
Soc Classification level
15
© Nokia Siemens Networks
Presentation / Author / Date
PUSCH RLF: RlsCause_PuschRlf_ON, timer-based
detection details
RLF timer-based detection in case of rlpDetMaxTUl is not zero:
• LTE MAC shall start timer rrmUlPuschDtxTimer with value for
•
•
•
•
the UE to which indication with
reliableULtransmissionFlag=FALSE is received when the
previous indication was reliableULtransmissionFlag=TRUE.
The timer rrmUlPuschDtxTimer shall be stopped when
indication with reliableULtransmissionFlag=TRUE is received
for the UE.
If the timer rrmUlPuschDtxTimer reaches rlpDetMaxTUl
value, LTE MAC shall indicate RLF of the UE to LTE UEC
(UE Control program block) by using
MAC_RadioLinkStatusInd message with rlsCause value
RlsCause_PuschRlf_ON.
RlsCause_PuschRlf_ON can be read in Emil trace or BTS
UDP log
reliableULtransmissionFlag can be read in UL TTI trace
Soc Classification level
16
© Nokia Siemens Networks
Presentation / Author / Date
PUSCH RLF: RlsCause_PuschRlf_ON, counterbased detection details
RLF counter-based detection in case of rlpDetMaxNUl is not
zero:
• LTE MAC shall count consecutive indications with
reliableULtransmissionFlag=FALSE in UE basis and store the
counter value to internal parameter
rrmUlPuschDtxDetections.
• LTE MAC shall initialize the counter to zero and reset it after
every indication with reliableULtransmissionFlag=TRUE.
• If the counter rrmUlPuschDtxDetections for the UE reaches
rlpDetMaxNUl value, LTE eNB MAC layer indicates RLF to
higher layers by using MAC_RadioLinkStatusInd message
with rlsCause value RlsCause_PuschRlf_ON.
Soc Classification level
17
© Nokia Siemens Networks
Presentation / Author / Date
PUSCH RLF: RlsCause_PuschRlf_ON, recovery
from RLF
Recovery from PUSCH RLF is counter-based
• LTE MAC shall count consecutive indications with
reliableULtransmissionFlag=TRUE for those UEs for which
the indication is sent and store the counter value to internal
parameter rrmUlPuschTxDetections.
• LTE MAC shall initialize the counter to zero and reset it after
every indication of reliableULtransmissionFlag=FALSE.
• If the counter rrmUlPuschTxDetections of a UE reaches
rlpDetEndNUl value, eNB MAC layer shall indicate RLF
cancellation of the UE to higher layers by using
MAC_RadioLinkStatusInd message with rlsCause value
RlsCause_PuschRlf_OFF.
– Message can be seen in Emil or BTS log
Soc Classification level
18
© Nokia Siemens Networks
Presentation / Author / Date
PUSCH RLF: RlsCause_PuschRlf, counter-based
RLF detection example RLF timer running
uplink
time
PUSCH_RLF
ON
downlink
UL
grant
UL UL
grant grant
UL
UL UL
UL
UL
UL
grant grant grant grant grant grant
T_RLF = T310 + T311
Soc Classification level
19
© Nokia Siemens Networks
Presentation / Author / Date
UL
UL
UL
UL
grant grant grant grant
PUSCH_R
LF OFF
vendor-file parameters in this example:
<p name="rlpDetMaxNUl">3</p>
<p name="rlpDetEndNUl">2</p>
Periodic CQI RLF: RlsCause_CqiRlf_ON
Source: Radio L1 SFS
• The eNB supports CQI DTX detection for periodic CQI reports on PUCCH
and PUSCH.
• If MAC layer receives nCqiDtx consecutive reports from UL PHY, the
MAC declares CqiRLF_ON
– can be seen in BTS log and Emil
• 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
• The parameters nCqiDtx and nCqiRec are in the vendor-specific
parameter file
• For both PUSCH and PUCCH the periodic CQI is encoded using a Reed
Muller block code and comes along without any CRC. Hence, the UL PHY
indicates a DTX detection for periodic CQI reports on PUCCH or PUSCH
whenever a report is configured but no reliable transmission from the UE
could be detected. So the output of the detector shall be either the
detected CQI report or a DTX indication.
• NOTE: CQI_RLF detection does not apply to aperiodic CQI report on
PUSCH
Soc Classification level
20
© Nokia Siemens Networks
Presentation / Author / Date
Periodic CQI RLF: RlsCause_CqiRlf, example
RLF timer running
LNCEL/cqiPerNp=10ms
vendor-file parameters in this example:
<p name="nCqiDtx">6</p>
<p name="nCqiRec">1</p>
Soc Classification level
21
© Nokia Siemens Networks
Presentation / Author / Date
time
CQI_RLF
ON
CQI_RLF
OFF
T_RLF = T310 + T311
Uplink RF problems, Emil example
Example
of UL
problems
Soc Classification level
22
© Nokia Siemens Networks
Presentation / Author / Date
Ack/Nack RLF: RlsCause_AckNackRlf_ON
Source: RRM SFS ID 2006
• After DL scheduled data, eNB expects HARQ ACK or NACK on PUCCH
or PUSCH at known UL TTI
• Timer-based ACK/NACK RLF detection:
– If ACK/NACK “DTX“ is received for a configurable period of time (rlpDetMaxTimeDl),
ACK/NACK RLF is set on
• Counter-based ACK/NACK RLF detection:
– If ACK/NACK “DTX“ is received for a consecutive number of times (rlpDetMaxNoDl),
ACK/NACK RLF is set on
• The recovery of the RLF is indicated when for a configurable number of
contiguous ACK/NACK opportunities ACK or NACK is detected on
PUSCH (no DTX).
– Defined by parameter rlpDetEndNoDl.
• Setting rlpDetMaxTimeDl=0 switches off time-based radio problem
detection.
• Setting rlpDetMaxNoDL=0 switches off counter-based radio problem
detection.
• If both counter-based and time-based options are disabled, radio problem
detection based on UL Ack/Nack is disabled completely.
Soc Classification level
23
© Nokia Siemens Networks
Presentation / Author / Date
PDCCH Order RLF
Source: L2 SFS
• If there DL data in eNB buffer and UE is out-of-sync, UE must be brought
back to in-sync (time aligned) with a RA procedure before DL data can be
sent
• Signalling of dedicated RA preamble via PDCCH (so-called PDCCH order)
is done using DCI format 1A
• In case that PDCCH order fails for a UE (i.e., no transmission of assigned
dedicated preamble detected by eNodeB, or no msg3 transmission) the
PDCCH order shall be repeated noRepPdcchOrder times (R&D configurable
parameter, range 0-3, default 1), again using the selected preamble and
considering DRX status of the UE accordingly.
• Final failure of the PDCCH order process shall be indicated as radio link
problem to higher layers with cause “PDCCH order failure” (see
UESTATE.1496).
Soc Classification level
24
© Nokia Siemens Networks
Presentation / Author / Date
SRS RLF
Source: L1 TD SFS
• The eNB supports SRS DTX detection for radio link problem detection
• If MAC layer receives nSrsDtx consecutive reports from UL PHY, the
MAC declares SRS RLF
• If the MAC has set SRS RLF for a specific UE and nSrsRec consecutive
SRS transmissions are succesfully detected the UE, the MAC sets SRS
RLF OFF
– Hence the SRS RLF has similar mechanism as CQI DTX RLF
• The parameters nSrsDtx and nSrsRec are operator-configurable
• P7 default values from RL15 SCF:
<p name="nSrsDtx">8</p>
<p name="nSrsRec">1</p>
Soc Classification level
25
© Nokia Siemens Networks
Presentation / Author / Date
RLF related parameters in vendor file, RL10
?xml version="1.0"?>
<raml version="2.1" xmlns="raml21.xsd">
<cmData scope="all" type="actual">
<header>
<log action="created" appInfo="AppName" appVersion="LN1.0"
dateTime="2010-11-17T10:28:13" user="Golden Vendor File
Inc22"></log>
<log dateTime="Mon Jan 01 01:32:14 +0000 1990" action="modified"
appInfo="RAMLH"></log>
</header>
<managedObject class="LNBTS" distName="LNBTS-*" operation="update"
version="LN1.0">
<p
<p
<p
<p
<p
<p
<p
<p
name="nCqiDtx">6</p>
name="nCqiRec">1</p>
name="rlpDetEndNoDl">3</p>
name="rlpDetEndNUl">3</p>
name="rlpDetMaxNoDl">1000</p>
name="rlpDetMaxNUl">20</p>
name="rlpDetMaxTimeDl">5000</p>
name="rlpDetMaxTUl">0</p>
Soc Classification level
26
© Nokia Siemens Networks
Presentation / Author / Date
When is RRC + S1 release (=drop) triggered by
eNB?
Source: UE State handling SFS (July 29 2010)
• 3GPP does not specify eNB radio link failures, but NSN eNB
mimics the behaviour of the UE RLF specified in 3GPP.
• When a radio link problem is detected, an eNB-internal timer
(T_RLF) is started. The timer T_RLF is stopped when in case
of radio link failure recovery.
• For a given UE, T_RLF is started when any of the PUSCH
RLF, CQI RLF or AckNack RLF is set to ON state
• For a given UE, T_RLF is stopped only if all RLFs are OFF
• When the timer T_RLF expires, the UE is released from the
eNB using eNB initiated S1 release + RRC connection
release –> call drop
• T_RLF = T310 + T311
Soc Classification level
27
© Nokia Siemens Networks
Presentation / Author / Date
RLF triggering by eNB, signalling
UE
UE in
RRC-CONNECTED
eNB
MME
S-GW
Detect radio link
problem, T_RLF
expires
S1AP: UE Context Release Request
S1AP: UE Context Release Command
RRC: RRC Connection Release
Set UE to
RRC-IDLE
Soc Classification level
28
© Nokia Siemens Networks
S1AP: UE Context Release Complete
Release all UE related
resources,
remove UE context
Presentation / Author / Date
S11 interaction to inform S-GW
about connection release
Set UE to
ECM-IDLE
Cause Value to be used
Cause Values for eNB
initiated UE S1
Context release
These can be read
from Emil or Wireshark
to help to understand
why the call dropped.
RNL Unspecified
RNL User Inactivity
RNL Radio Connection
with UE Lost
RNL Failure in the Radio
Interface Procedure
RNL TX2RELOCoverall Expiry
RNL TS1RELOCoverall Expiry
RNL E-UTRAN Generated
Reason
RNL Inter-RAT Redirection
TNL Transport Resource
Unavailable
TNL Unspecified
Soc Classification level
29
© Nokia Siemens Networks
Presentation / Author / Date
Use Case Description
(triggering eNB initiated UE context release)
Ongoing X2 handover is aborted for any reason where
the UE has left the source cell and is not allowed to
return
Ongoing S1 handover is aborted for any reason where
the UE is not allowed to continue in the source cell
Related SFS
Requirements
MM.1033
S1AP: ERROR INDICATION [syntax error] received
at Source eNB in response to S1AP: HANDOVER
CANCEL message
MM.1191
Security configuration becomes permanently
inoperable and no other defense action is defined (or
was unsuccessful)
Key refresh procedure
eNB initiated release due to user inactivity
eNB-initiated release due to radio link failure
Rejection of RRC Connection Re-establishment
Request
eNB initiated Release due to UE being out-of-sync
Handling of Event “Maximum number of RLC
retransmissions reached”
Timer THOoverall expiry
Source eNB initiates UE context release due to a
rejected RRC Connection Re-establishment
RRC Connection Re-establishment rejected at Target
eNB for a UE performing Measurement
Configuration
Failure to send RRC Connection Reconfiguration at
Target eNB
Handover Handling due to timer
TRECGuardTimerRadioBearerManagement expiry
Timer TX2RELOCoverall expiry at Source eNB
Timer TS1RELOCoverall expiry at Source eNB
Initiating UE context release with Redirect to LTE
SEC.704 &
SEC.1003
Initiating UE context release without Redirect
(redirection fails)
Initiating UE context release with Redirect to other
RAT
Handling of Event “GTP-U Error Indication” (S-GW
has rejected the reception of uplink data packets)
MM.1095
SEC.694
UESH.420
UESH.720
UESH.807
UESH.974
BM.462
MM.990
MM.1255
MM.1257
MM.1060
MM.1076
MM.852
MM.1144
MM.1522 &
UESH.1078
MM.1523 &
UESH.1192
MM.1522 &
UESH.1078
BM.389
eNB intiated release due to GTP-U path failure
detection
(Note: Not used in RLT/RL05TD.)
UESH.1267
Path Switch Request Failure at Target eNB
MM.725
Timer TX2RELOCcomp expiry at Target eNB
MM.805
Outline
• UE-detected RF problems: RRC Connection Re-Establishment
• eNB-detected radio link problems
•
•
•
•
– PUSCH RLF
– CQI RLF
– Ack/Nack RLF
– SRS RLF
eNB-initiated release: TA timer expiry
eNB-initiated release: maximum RLC retransmissions exceeded
eNB-initiated release: GTP-U failure
Timers and constants (3GPP)
Soc Classification level
30
© Nokia Siemens Networks
Presentation / Author / Date
UL in-sync and out-of-sync substates
• RRC_CONNECTED substates: UL in-sync and UL out-of-sync
E-UTRA
RRC_CONNECTED
Expiry of Short Inactivity Timer (intentional)
Timing maintenance issue (unintentional)
TA
UL in-sync
TA
UL out-of-sync
Contention-based RA success after UL data arrival
PDCCH order success after DL data arrival
PDCCH order success after Inactivity timer expiration
RRC Connection Reestablishment
RRC Connection Release
RRC Connection Setup
RRC Connection Release
Radio link failure
E-UTRA
RRC_IDLE
Soc Classification level
31
© Nokia Siemens Networks
Presentation / Author / Date
In RL20/RL15, if eNB
detects UE out-of-sync,
S1 + RRC are released
(dropped call)
TA timer expiry at UE
3GPP TS 36.321: When timeAlignmentTimer expires at UE, UE
MAC layer shall:
- flush all HARQ buffers;
- notify RRC layer to release PUCCH/SRS;
- clear any configured downlink assignments and uplink grants
3GPP TS 36.331: Upon receiving a PUCCH/ SRS release
request from MAC layer, the UE RRC shall:
• release periodic CQI reporting config, ie it stops CQI
reporting on PUCCH
• release Scheduling Request Config
– Radio L2 SFS: For RL20/RL15 the approach is to keep the UE always in-sync in UL. For
later releases an alignment with RRC may be required in order to indicate to reassign
PUCCH and SRS resources (i.e., at least on expiry of the timing alignment timer). The
details are FFS yet.
– Bearer Management SFS: L1 reconfiguration to recover from TA expiry is not supported
in RL20/RL15
Soc Classification level
32
© Nokia Siemens Networks
Presentation / Author / Date
TA timer expiry at eNB
Maintenance of UL Time Alignment by eNB (source: Radio L2 SFS)
• UL TA update is done periodically and in addition on per-need basis. MAC entity
provides PHY layer the information when a TA update is needed together with the
TA update value. MAC entity in eNB shall send it to UE via Timing Alignment MAC
control element.
• As UE detects Out-of-Sync status using a Timing Alignment Timer, the timer
shall be started or restarted whenever an initial TA or a TA update command is
received (see [3GPP-36.321], section 5.2). If the timer expires, the UE detects
out-of-sync status.
• eNB needs to prevent UE TA timer from expiring, because in RL20/RL15 there is
no way to bring UE back in-sync (without dropping call) if TA timer expires
• The interval between periodic TA update commands is based on the Timing
Alignment Timer reduced by a configurable offset taTimerMargin.
• Radio L2 SFS: TA command period = TimeAlignTimer – taTimerMargin
• A configurable parameter TimeAlignmentMaxOffset is used to determine the
maximum allowed timing alignment offset before a per-need timing alignment
update is required.
Soc Classification level
33
© Nokia Siemens Networks
Presentation / Author / Date
TA timer expiry at eNB
• If the TA offset measured by the UL PHY layer is greater than the configurable threshold
TimeAlignmentMaxOffset then a TA command is sent to the UE.
• If the reported TA offset also exceeds a threshold calculated as taSchedulingThreshold
= max(taOffsetSchedMgn, TimeAlignmentMaxOffset +0.5µs), the UL scheduler is
informed that the UE is drifting out of alignment
• When HARQ ACK feedback is received for the TA command then:
• For a per-need TA command and when taSchedulingThreshold (see above) was
exceeded: the UL scheduler is informed that the TA is OK again.
• The periodic timing alignment timer is (re)started.
• If no HARQ ACK feedback is received for a TA command within the maximum number of
DL HARQ transmissions then:
• The TA update command shall be repeated up to a configurable maximum
number of times taCommandMaxRetries or until the timing alignment timer expires;
the latest available timing advance estimation shall be used for every repetition.
• If the maximum number of retries is exceeded or the timing alignment timer has expired,
then status UE UL out-of-sync is detected  TatExpiry seen in UDP Log and Emil
• Immediate release of RRC and S1 follows (there is no waiting for T_RLF expiry)
Soc Classification level
34
© Nokia Siemens Networks
Presentation / Author / Date
TA timer expiry at eNB
UE
UE in
RRC-CONNECTED
eNB
NOTE: TA out-ofsync causes
immediate release
(no T_RLF involved)
MME
S-GW
TA timer expires
S1AP: UE Context Release Request
S1AP: UE Context Release Command
RRC: RRC Connection Release
Set UE to
RRC-IDLE
Soc Classification level
35
© Nokia Siemens Networks
S1AP: UE Context Release Complete
Release all UE related
resources,
remove UE context
Presentation / Author / Date
S11 interaction to inform S-GW
about connection release
Set UE to
ECM-IDLE
TA timer expiry at eNB, Emil example
TaTExpiry followed
by immediate S1 +
RRC release
Soc Classification level
36
© Nokia Siemens Networks
Presentation / Author / Date
TA timer expiry at eNB, user-configurable
parameters
Parame Description
ter
abbrevi
ated
Name
Access
taTimer
RW
O
BTS
restart
taMaxOf
fset
Determines the number of
subframes after which a
UE assumes being Out-ofSync in UL if no Time
Alignment Command was
received.
Determines the maximum
allowed time alignment
offset. If value is
exceeded the need for
time alignment update is
given.
RW
Para Range/
meter Step-size
Type
O
{500, 750,
1280,
1920,
2560,
5120,
10240}
0..5/0.01
Unit: μs
Default Paravalue
meter
Scope
Reference
Multiplicity
1280
cell
36.331
1
timeAlignme
ntTimer
0.52
cell
TF_LTE_SFS_ 1
RL2_697
(corres
ponds
to
16*Ts)
Always check the current values (defaults and the actual used) of the eNB
sw version in use.
Soc Classification level
37
© Nokia Siemens Networks
Presentation / Author / Date
TA timer expiry at eNB, vendor parameters
Parame Description
ter
abbrevi
ated
Name
Access
Para Range/
meter Step-size
Type
Default Paravalue
meter
Scope
Reference
taTimer
Margin
RW
O
0..2560/1
Unit:
subframes
89
Cell
TF_LTE_SFS_ 1
RL2_697
R
V
1.5…4/0.1
unit: µs
2
BTS
TF_LTE_SFS_ 1
RL2_697
R
V
0..10/1
1
BTS
TF_LTE_SFS_ 1
RL2_697
Used to control the
interval between
periodic timing
alignment commands being
sent to the UE.
Multiplicity
The actual time interval
between updates will be
TimeAlignTimer –
taTimerMargin
taOffSc
heMarg
taCmdMa
xRetry
The upper value is
constrained by the value
of TimeAlignTimer.
Used to determine when
to no longer consider a
UE that is drifting out
of time alignment in
uplink scheduling;
The number of times the
TA command will be
retried before MAC
assumes the UE has gone
out-of-sync.
Always check the current values (defaults and the actual used) of the eNB
sw version in use.
Soc Classification level
38
© Nokia Siemens Networks
Presentation / Author / Date
eNB differentiation between in-sync and out-sync
(RL30)
• RRC connected substates: UL in-sync and UL out-of-sync
E-UTRA
RRC_CONNECTED
Expiry of Short Inactivity Timer (intentional)
Timing maintenance issue (unintentional)
TA
UL in-sync
TA
UL out-of-sync
Contention-based RA success after UL data arrival
PDCCH order success after DL data arrival
PDCCH order success after Inactivity timer expiration
RRC Connection Reestablishment
RRC Connection Setup
RRC Connection Release
Radio link failure
E-UTRA
RRC_IDLE
Soc Classification level
39
© Nokia Siemens Networks
Presentation / Author / Date
PDCCH order failure after DL data arrival
PDCCH order failure after Inactivity timer expiration
Uplink RA SR or
downlink PDCCH
order to bring UE
back in-sync
(RL30)
Ue out-of-sync recovery (RL30)
• If UE goes loses timing alignment, it listens to PDCCH but is allowed to
transmit only on PRACH
– Periodic CQI reporting is stopped, SR and UL ACK/NACK cannot be sent
– NOTE: pending UL ACK/NACK transmission will not trigger RA Scheduling Request
• If there is DL data to be sent, eNB uses PDCCH order to trigger RA
• If there is UL data to be sent, UE uses RA SR
• After UE has valid TA, eNB re-establishes CQI/SR/SRS config via RRC
Conn Reconfig
• Note: following successful UE resynchronization, higher layers will reassign dedicated
resources on PUCCH and for SRS to the UE. As long as these are the same resources or at
least resources with the same periodicity and reporting instances, there is no need to
reconfigure the DRX Start Offset. Further development: As soon as this is not the case any
more, configuration of dedicated resources on PUCCH will require reconfiguration of UEs
DRX Start Offset; this in turn will require to enhance DRX reconfiguration procedure
substantially as the restrictions as defined in RRM.2504 may no longer apply.
• Note: it is not foreseen that MAC control elements for the DL also trigger a resynchronization
of a UE as there should be no need to transmit those in UL out-of-sync state.
Soc Classification level
40
© Nokia Siemens Networks
Presentation / Author / Date
Random Access Scheduling Request detection
• RA_SR link state notification in eNB is triggered when eNB receives a
RACH msg3 which contains a C-RNTI and the UE with this C-RNTI is
already active in the cell (time alignment status for the UE is ‘in-sync’).
• This is not a real radio link failure, but only result of UE PUCCH
Scheduling Request failing multiple times and UE sending SR on PRACH
Soc Classification level
41
© Nokia Siemens Networks
Presentation / Author / Date
Random Access Scheduling Request and L1
PUCCH reconfiguration, example from RL20
• First RA_SR detected indicating that SR sending on PUCCH has failed and
PUCCH SR and CQI config was released by UE  RA SR triggered
RA SR detected
from UE
L1 PUCCH
reconfiguration
Soc Classification level
42
© Nokia Siemens Networks
Presentation / Author / Date
Random Access Scheduling Request and L1
PUCCH reconfiguration, example from RL20
DL-DCCH-Message : {
message c1 : rrcConnectionReconfiguration : {
rrc-TransactionIdentifier 1,
criticalExtensions c1 : rrcConnectionReconfiguration-r8
: {
radioResourceConfigDedicated {
physicalConfigDedicated {
Periodic CQI reporting
cqi-ReportConfig {
cqi-ReportModeAperiodic rm30,
on PUCCH
nomPDSCH-RS-EPRE-Offset 0,
reconfigured
cqi-ReportPeriodic setup : {
cqi-PUCCH-ResourceIndex 10,
cqi-pmi-ConfigIndex 27,
cqi-FormatIndicatorPeriodic widebandCQI : NULL,
ri-ConfigIndex 161,
simultaneousAckNackAndCQI TRUE
}
},
soundingRS-UL-ConfigDedicated release : NULL,
schedulingRequestConfig setup : {
sr-PUCCH-ResourceIndex 35,
sr-ConfigIndex 24,
dsr-TransMax n64
Scheduling Request
}
}
resource on PUCCH
}
reconfigured
}
}
}
Soc Classification level
43
© Nokia Siemens Networks
Presentation / Author / Date
Outline
• UE-detected RF problems: RRC Connection Re-Establishment
• eNB-detected radio link problems
•
•
•
•
– PUSCH RLF
– CQI RLF
– Ack/Nack RLF
– SRS RLF
eNB-initiated release: TA timer expiry
eNB-initiated release: maximum RLC retransmissions exceeded
eNB-initiated release: GTP-U failure
Timers and constants (3GPP)
Soc Classification level
44
© Nokia Siemens Networks
Presentation / Author / Date
RLC layer STATUS polling mechanism
Source: 3GPP 36.322 v8.8.0, June 2010, Bearer Management SFS, PDDB
• RLC layer retransmissions only in RLC acknowledged mode
• RLC AM transmitter requests a STATUS PDU from RLC receiver (sets
poll bit on in RLC header)
– After the number of bytes transmitted since previous poll exceeds the value of
amRlcPBTab3ulPollByte (uplink, ue cat3) or amRlcPBTab3dlPollByte (downlink,
ue cat3), or
– After pollPdu RLC PDUs have been transmitted since previous poll
– in the last data PDU in the RLC transmit buffer
• The RLC AM receiver responds to polling request by transmitting a
STATUS PDU which acknowledges successfully received PDUs and also
selectively nacks unsuccessfully received PDUs (“selective NACK”).
– RLC receiver will not send STATUS PDU more often than interval defined by
parameter tProhib.
– RLC receiver also sends STATUS PDU if tReord timer expires (but not if timer
tProhib is running).
– NOTE: default PDDB settings tProhib=50ms and tReord=50ms.
• If RLC transmitter receives no STATUS PDU within tPollretr, a new poll
request along with unacknowledged data will be sent to RLC receiver
• RLC AM window size is fixed to 512 RLC PDUs (segments of an RLC
PDU are counted as one PDU).
Soc Classification level
45
© Nokia Siemens Networks
Presentation / Author / Date
RLC layer ARQ mechanism
Source: 3GPP 36.322 v8.8.0, June 2010, Bearer Management
SFS, PDDB
• RLC transmitter will retransmit all data that is nacked in the
STATUS PDU
• Maximum number of UL and DL RLC retransmissions is
defined by vendor parameter drbAmMxRtxTh (default=16)
Ttransfer-1
Twait<= tProhib
Ttransfer-2
Rx
C
R
Po LC
ll b PD
it U
se
t
RL
us
at
St
Tx
time
Polling trigger reached
ACKed RLC PDUs can
be removed from buffer
AM RLC Round Trip Time
Soc Classification level
46
© Nokia Siemens Networks
Presentation / Author / Date
Release due to maximum number of RLC
retransmissions (eNB-triggered)
Source: Bearer Management SFS
• RL10: When eNB detects that an RLC PDU has reached the
maximum number of retransmissions, eNB releases the UE
(S1 + RRC release).
– vendor parameter drbAmMxRtxTh (default=16)
• RL30 (when RRC Conn Re-Est is supported): after max RLC
retransmissions has been reached
 eNB starts a timer to wait for an UE triggered RRC Connection
Reestablishment. If the timer expires: eNB releases the UE.
 Otherwise: UE has triggered a RRC Connection Reestablishment procedure
and eNB performs the RRC Connection Reestablishment procedure (as for a
RLF).
Soc Classification level
47
© Nokia Siemens Networks
Presentation / Author / Date
Release due to maximum number of RLC
retransmissions (eNB-triggered, RL30)
Source: Bearer Management SFS
UE
NOTE: In RL20/RL15,
eNB releases S1 + RRC
immediately (since RRC
Conn Re-Est not
supported)
eNB
MME
eNB detects RLC
maximum
retransmission event
eNB waits for RRC
reestablishment by
UE (timer controlled)
Case Timer expiration
Timer expires
S1AP: UE CONTEXT RELEASE REQUEST
UE CONTEXT RELEASE procedure
UE starts Reestablishment
UE detects RLF or
RLC maximum
retransmission event
RRC Connection Reestablishment procedure
Soc Classification level
48
© Nokia Siemens Networks
Presentation / Author / Date
NOTE:
supported in
RL30
Release due to maximum number of RLC
retransmissions (eNB-triggered, RL10 example)
Max DL RLC retrans
 RRC release
Soc Classification level
49
© Nokia Siemens Networks
Presentation / Author / Date
Outline
• UE-detected RF problems: RRC Connection Re-Establishment
• eNB-detected radio link problems
•
•
•
•
– PUSCH RLF
– CQI RLF
– Ack/Nack RLF
– SRS RLF
eNB-initiated release: TA timer expiry
eNB-initiated release: maximum RLC retransmissions exceeded
eNB-initiated release: GTP-U failure
Timers and constants (3GPP)
Soc Classification level
50
© Nokia Siemens Networks
Presentation / Author / Date
Release due to GTP-U Error Indication from S-GW
(eNB-triggered)
Source: Bearer Management SFS
• Handling of Event "GTP-U Error Indication" (single S1 bearer,
RL10)
• eNB may receive a “GTP-U Error Indication” on an active
(single) S1 bearer (S-GW has rejected the reception of uplink
data packets) - for more details see [DATAPATH SFS].871.
In that case eNB shall send the S1AP message UE
CONTEXT RELEASE REQUEST with cause “TNL Cause
Transport Resource Unavailable” to MME - for details see
[UESTATE SFS].720).
Soc Classification level
51
© Nokia Siemens Networks
Presentation / Author / Date
Release due to GTP-U Error Indication from S-GW
(eNB-triggered)
GTP-U Error
received from S-GW
 release S1 + RRC
Soc Classification level
52
© Nokia Siemens Networks
Presentation / Author / Date
Outline
• UE-detected RF problems: RRC Connection Re-Establishment
• eNB-detected radio link problems
•
•
•
•
– PUSCH RLF
– CQI RLF
– Ack/Nack RLF
– SRS RLF
eNB-initiated release: TA timer expiry
eNB-initiated release: maximum RLC retransmissions exceeded
eNB-initiated release: GTP-U failure
Timers and constants (3GPP)
Soc Classification level
53
© Nokia Siemens Networks
Presentation / Author / Date
Timers (3GPP 36.331 v8.8.0)
Timer
Start
Stop
At expiry
T300
Transmission of RRCConnectionRequest
Reception of
RRCConnectionSetup or
RRCConnectionReject message,
cell re-selection and upon
abortion of connection
establishment by upper layers
Perform the actions as specified in
5.3.3.6
T301
Transmission of
RRCConnectionReestabilshmentRequest
Reception of
RRCConnectionReestablishment
or
RRCConnectionReestablishment
Reject message as well as when
the selected cell becomes
unsuitable
Go to RRC_IDLE
T302
Reception of RRCConnectionReject while
performing RRC connection establishment
Upon entering
RRC_CONNECTED and upon
cell re-selection
Inform upper layers about barring
alleviation as specified in 5.3.3.7
T303
Access barred while performing RRC
connection establishment for mobile
originating calls
Upon entering
RRC_CONNECTED and upon
cell re-selection
Inform upper layers about barring
alleviation as specified in 5.3.3.7
T304
Reception of
RRCConnectionReconfiguration message
including the MobilityControl Info or
reception of
MobilityFromEUTRACommand message
including CellChangeOrder
Criterion for successful
completion of handover to
EUTRA or cell change order is
met (the criterion is specified in
the target RAT in case of interRAT)
In case of cell change order from EUTRA or intra E-UTRA handover, initiate
the RRC connection re-establishment
procedure; In case of handover to EUTRA, perform the actions defined in
the specifications applicable for the
source RAT.
Soc Classification level
54
© Nokia Siemens Networks
Presentation / Author / Date
Timers (3GPP 36.331 v8.8.0)
Timer
Start
Stop
T305
Access barred while
performing RRC connection
establishment for mobile
originating signalling
Upon entering RRC_CONNECTED
and upon cell re-selection
Inform upper layers about barring
alleviation as specified in 5.3.3.7
T310
Upon detecting physical
layer problems i.e. upon
receiving N310 consecutive
out-of-sync indications from
lower layers
Upon receiving N311 consecutive
in-sync indications from lower
layers, upon triggering the handover
procedure and upon initiating the
connection re-establishment
procedure
If security is not activated: go to
RRC_IDLE else: initiate the
connection re-establishment
procedure
T311
Upon initiating the RRC
connection reestablishment procedure
Selection of a suitable E-UTRA cell
or a cell using another RAT.
Enter RRC_IDLE
T320
Upon receiving t320 or
upon cell (re)selection to EUTRA from another RAT
with validity time configured
for dedicated priorities (in
which case the remaining
validity time is applied).
Upon entering RRC_CONNECTED,
when PLMN selection is performed
on request by NAS, or upon cell
(re)selection to another RAT (in
which case the timer is carried on to
the other RAT).
Discard the cell reselection priority
information provided by dedicated
signalling.
T321
Upon receiving measConfig
including a reportConfig
with the purpose set to
reportCGI
Upon acquiring the information
needed to set all fields of
cellGlobalId for the requested cell,
upon receiving measConfig that
includes removal of the
reportConfig with the purpose set to
reportCGI
Initiate the measurement reporting
procedure, stop performing the
related measurements and remove
the corresponding measId
Soc Classification level
55
© Nokia Siemens Networks
Presentation / Author / Date
At expiry
Constants (3GPP 36.331 v8.8.0)
Constant
Usage
N310
Maximum number of consecutive "out-of-sync" indications
received from lower layers
N311
Maximum number of consecutive "in-sync" indications received
from lower layers
Here the terms “in-sync” and “out-of-sync” refer to generic PHY layer problems, not Time
Alignment timer expiry. Condition for in-sync and out-of-sync is defined in 3GPP TS 36.133
V8.9.0 (2010-03), Section 7.6.
Soc Classification level
56
© Nokia Siemens Networks
Presentation / Author / Date