microsoft powerpoint - oeo000020 lte eran6.0 access fault diagnsis issue1
TRANSCRIPT
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LTE eRAN6.0 Access Fault Diagnosis
Copyright © 2013 Huawei Technologies Co., Ltd. All rights reserved.
Objectives
� Upon completion of this course, you will be able to:
� Get deep understanding of UE initial access flow
� Describe the typical access fault scenarios
� Describe how to locate the access fault
� Typical methods for fault analysis
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Contents
1. EUTRAN Typical Signaling Procedure
2. Typical Access Fault Analysis and Process
3. Case Study
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UE Initialization Flow
Invisible flow
Visible flow
Partial visible flow
UE idle
behavior phase
UE access phase
UE power on
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UE Initial Attach Procedure UE
eNodeBMME
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Service Request Procedure UE eNodeB MME
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TAU Update ProcedureUE eNodeB MME
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Random Access Procedure Overview
� Purpose of random access
� Get uplink synchronization
� Send schedule request if no PUCCH resource
� Scenarios:
� Case1: UE initial attach
� Case2: RRC reestablishment after RLF
� Case3: Handover in a new cell
� Case4: UE sends uplink data while RLF occurs
� Case5: UE notices that downlink data arrival while RLF occurs
� Case6: When UE trigger LCS(Location service)
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Classification of Random Access
� UE randomly selects a
preamble and sends it,
conflict might occurs
� Can be used for all cases
UEeNodeB UE
eNodeB
Contention based Non-contention based
� Before random access,
eNodeB assigns a dedicated
preamble to UE, so there is
no conflict.
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Preamble Index Configuration
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Preamble Format 0 ms 1 ms 2 ms 3 ms
CP0.1
Sequence 0.8
0.1 Format 0
CP0.68
Sequence 0.8
Guard Period0.52
Format 1
CP0.2
Sequence 1.6
0.2 Format 2
CP0.68
Sequence 1.6
Guard Period0.72 Format 3
5102 xTs
Format 4
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Preamble Sending
� In contention based case, UE randomly select a preamble based
on RACH configuration and send it on the corresponding time slot
� Once the frequency and time is determined, the corresponding
RA_RNTI is already known by the UE, where RA_RNTI= 1 +
t_id+10*f_id (t_id indicates the start subframe number, f_id
indicate the frequency offset of RACH)
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Random Access Response
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UL Data Sending (Msg 3)
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Contention Resolution
Case1: Detect C-RNTI on PDCCH
Case2: Detect temporary C-RNTI on PDCCH and decode the corresponding MAC PDU on PDSCH.In the MAC PDU, it contains the UE ID that send in Msg 3
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RRC Connection Setup Procedure
A
B
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RRC Cause
� According to different NAS procedure, the RRC cause can
be MO-singling, MO-data, MT-access, and emergency
NAS Procedure RRC Cause Type of call
Attach MO – signaling Original signaling
TAU MO – signaling Original signaling
Service RequestMO - data Original call
MT – access Terminated call
Extended Service Request
MO – data (original CSFB) Original call
MT – access (terminated CSFB) Terminated call
Emergency (emergency CSFB) Emergency call
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UEeNodeB
MME
Initial ERAB Setup
B
A
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S1 Initial UE Message
NAS PDU
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S1 Initial Context Setup Request
NAS PDU
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Security Mode Setup
� Purpose:
� Activated AS security algorithms, including integrity protect and
ciphering
� Integrity protect: only for signaling, support AES, snow3G and Null
� Ciphering: both for signaling and data, support AES, snow3G and
Null Page20
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UE Capability Query
� If no UE capability in MME, eNodeB will trigger UE
capability query and store it and also inform MME
� If MME already stored UE capability, it will forward to eNode
via S1 initial contexts setup request message
UE eNodeB MME
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SRB2 Setup
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Measurement Control
Measurement Configuration
- measObjectToRemoveList- measObjectToAddModList- reportConfigToRemoveList
- reportConfigToAddModList- measIdToRemoveList
- measIdToAddModList- quantityConfig- measGapConfig
- s-Measure
RRC Connection Reconfiguration Request
RRC Connection Reconfiguration Complete
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S1 Initial Context Setup Response
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NAS Procedure
UEeNodeB MME
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Contents
1. EUTRAN Typical Signaling Procedure
2. Typical Access Fault Analysis and Process
3. Case Study
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Access Performance Evaluation
� From performance management
� Access successful ratio = RRC setup successful ratio x ERAB
setup successful ratio
� Random access and NAS failures are not considered in
eNodeB performance management, but these factors also
impact user experience
� From drive test tools (probe)
� It can identify access failure caused by random access failure
and NAS failure
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General Process
� Determine the scale of problem
� From the performance statistic, we can determine the scale of the
problem, is it global problem, or cell level problem or just some individual
UE problem. Then we can select bottom N cell as optimization target
� Customer complain is an effective way to locate the individual UE
problem
� For large scale access failure
� Check eNodeB alarm and basic configuration
� Check RF channel problem
� Once RF channel is abnormal, such as high VSWR, low RSSI Too Low or RSSI
is unbalanced, then the access performance should be significantly affected.
� For individual UE problem, signaling analysis can be used to locate
the detailed cause
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Handle eNodeB Generic Alarm
� Tools: M2000 or LMT
� Procedure
� Check the generic hardware fault alarm, such as hardware
fault, board unusable , or any other alarms which are related
with hardware failure or link failure.
� Solution: Replace the faulty component.
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Check DL Power Configuration
� To ensure the coverage, the DL power parameters should be
properly set
� RS power = Maximum RRU power/channel – 10lg(total subcarriers ) +
10lg(Pb+1)
� If the single antenna, Pb=0
� If 2 or 4 antennas, Pb=1
� PDSCH power = PA + RS power
� If single antenna, PA=0
� If 2 or 4 antennas, PA=-3
� Related command:
� LST PDSCHCFG: check Pb and RS power setting
� LST CELLDLPCPDSCHPA: check PA setting
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Check CRPI Rate
� If the bandwidth is 10MHz or above, the CPRI rate should
be equal or more than 2.5Gbps, otherwise, the cell can’t be
setup
� If the rate is not correct, change the CPRI modulePage31
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Check S1 Interface Status
� If SCTP link is faulty, check the
SCTP configuration, such as peer
IP address, SCTP port number
� If S1intrface state is faulty, check
the PLMN and operator ID.
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Check Cell Barred Status
� If cell is barred, use the following command to recover it
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Check RF Channel Problem
� Due to the bad feeder quality, incorrect feeder connection or
strong interference, it might affect RF channel performance
which has impact on UE access.
� Relevant problem:
� High VSWR: ALM-26529 RF Unit VSWR Threshold Crossed
� Low RSSI: ALM-26521 RF Unit RX Channel RSSI Too Low
� RSSI unbalance: ALM-26522 RF Unit RX Channel RSSI
Unbalanced
� RSSI of the main RX channel and the RSSI of the diversity RX
channel exceeds 10 dB.
� High RSSI: Caused by interference
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Cause of High VSWR
� VSWR: Voltage Standard Wave Ratio, indicate the if feeder
impedance is match or not. The normal VSWR range is 1~1.5. If
current VSWR is more than a specified threshold, then eNodeB will
generate relevant alarm.
� Alarm generation:
� Cell is activated
� RF power is more than 34dBm/channel
� VSWR is more than a specified threshold
� Possible cause:
� Incorrect VSWR alarm threshold
� RF unit hardware fault
� RRU/RFU wrong connection
� Bad feeder quality or nonstandard feeder installation
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Solution for High VSWR
� Step 1: Check if the VSWR alarm threshold is correct (default is 2dB).
� Note: RRU TX channel will automatic closed if VSWR is extremely high (more than post-
processing threshold)
� Step 2: If alarm threshold is correct, then check if relevant feeder installation and RRU
connections are meet the standard.
� Step3: After the feeder tuning, if TX channel is closed, then activate TX channel again
� MOD TXBRANCH
Threshold for TX shutdown
Threshold VSWR alarm
generation
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Cause of Low RSSI
� Alarm generation: If RSSI is less than a specified value
� Incorrect RX attenuation setting
� If no TMA, the attenuation should be 0
� If 12dB TMA is used, the attenuation should be 4 to 11dB
� If 24dB TMA is used, the attenuation should be 11 to 22dB
� Feeder problem
� Due to bad feeder quality, causing additional loss
� RRU fault
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Solutions for Low RSSI
� Step 1: Check if RRU RX attenuation is correct
� Step2: If attenuation is correct, then check the feeder
installation and connection
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Cause of Imbalance of RSSI
� Alarm generation: RSSI of the main RX channel and the
RSSI of the diversity RX channel exceeds 10 dB.
� Possible causes
� High interference
� RRU cross connections
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Solution of Imbalance of RSSI
� UL interference check
� From web-LMT: Perform spectrum detection to evaluate UL interference
� From M2000 client: Perform interference detect monitoring
� Find out interference source
� Check RRU connections, avoid cross connections, show as below
A
N
T
1
RRU1
A
N
T
2
RRU2
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Classification of Interference
� Passive inter-module interference:
� Due to non-linearity of radio component ,the high phase
harmonic wave might be generated and inter-modulated by RX
signal, thus the new inter-module signal will arrive the receiver
causing the interference.
� External interference:
� Interference from the other system, such as 2G, 3G, CDMA,
radio, radar eg.
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How to Located Inter-modulated Interference
� This kind of interference increases with eNodeB transmit
power, so we can simulate the DL load, and check RSSI, if
it obviously increases with the DL load incensement, then
we can determine the interference
� Load simulation:
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How to Located External Interference
� If we exclude inter-modulated interference, then it should be
external interference
� Shutdown the TX of RRU/RFU, if RSSI is still high, then we
can conclude this is external interference
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Analysis of Tracing
� Driver test tracing analysis
� We can get all UU interface messages, internal UE message as well as
RSRP value
� eNdoeB tracing analysis
� We can get UU interface message and S1 interface message
� Form the above tracing analysis, we can locate the problem with the
following causes:
� Random access failure
� RRC setup failure
� NAS procedure failure
� ERAB setup failure
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Random Access Failure
� Generic scenario: There is no “RRC connect request ”message
� Possible cause:
� UE doesn’t support the band
� Scenario: UE doesn't receive any system message
� Solution: Check if UE band is identical with eNdoeB configuration
� Poor coverage
� Scenario :Due to poor DL or UL coverage, UE or eNodeB miss receiving the
relevant random access message
� Solution: Perform RF tuning. Use TMA on uplink
� Cell is barred
� Check the cell status, should be not barred.
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RRC Connection Failure
� Scenario 1: eNodeB directly send reject message
� Possible cause: No radio resource due to no enough resource
for PUCCH and SRS
� Solution: Check the cell load status, if it is very high, consider
capacity extension
UE eNodeB
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RRC Connection Failure (Cont.)
� Scenario 2: UE doesn’t receive “RRC connection setup” message,
and repeat sending request message until timer is out
� Possible cause:
� Poor DL coverage, check RSRP and RSRQ
� Solution:
� Perform RF tuning
UE eNodeB
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RRC Connection Failure (Cont.)
� Scenario 3: eNodeB send RRC setup message, but doesn’t get
complete message
� Possible cause
� If UE doesn’t reply RRC complete, it should be UE problem
� If UE already send RRC complete, then it should be poor UL
coverage
UE eNodeB
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NAS Procedure Failure
� Note: NAS failure is not counted in performance statistic
UEeNodeB MME
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ERAB Setup FailureUE
eNodeBMME
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ERAB Setup Failure Cause
� If any failure occurs during ERAB setup, we can directly get the
failure cause form performance statistic, the relevant counters are:
� L.E-RAB.FailEst.NoReply (No response from UE)
� L.E-RAB.FailEst.MME (EPC fault)
� L.E-RAB.FailEst.TNL (Transport fault)
� L.E-RAB.FailEst.RNL (Radio network fault)
� L.E-RAB.FailEst.NoRadioRes (No radio resource)
� L.E-RAB.FailEst.SecurModeFail (Security mode setup fault)
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Faulty Signaling of No UE Response
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Fault Signaling of Other Cause
� Scenario: eNodeB receives “initial context setup request” or
“E-RAB setup request” message, after that, if failures
happen, then eNB replies response message with failure
cause
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Analysis of EPC Fault
� Cause:� S1 message validity check failure, including
� Error exist in S1 message
� Duplicated ERAB ID
� Conflict with other procedures
� Solution:
� Contact EPC engineer to locate the problem
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Analysis of Transport Fault
� Possible causes:
� Transport admission failure
� S1 link failure during S1 message exchange
� Incorrect IP path configuration
� Wrong QoS configuration in EPC
� Solutions:
� Check transport admission algorithm, consider extend S1 bandwidth
� Check S1 interface
� Check IP path configuration
� Check relevant QoS configuration, AMBR should be more than 0, and for initial
ERAB setup, the QCI must be 6~9
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Analysis of Radio Network Fault
� Possible cause
� UU message process failure due to UE capability (UE doesn’t
support relevant service)
� eNodeB failure during ERAB setup
� Solutions:
� Check UE capability
� Check eNodeB status
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Analysis of No Radio Resource
� Possible cause
� Radio admission failure for ERAB
� Solution:
� Check if admission parameters is correct
� Consider to enable load balance algorithm
� Consider capacity extension
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Analysis of Security Mode Failure
� Possible cause:
� UE security capability is not identical with eNodeB security
capability
� Solution:
� Modify the eNB security algorithm to match it.
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Contents
1. EUTRAN Typical Signaling Procedure
2. Typical Access Fault Analysis and Process
3. Case Study
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Case 1 – IP Path Configuration Leads to Low Access Ratio
� Description: In one live network, ERAB setup ratio is very
low, but it’s not zero.
� Alarm info: None
� Analysis:
� Check the performance statistic of ERAB release, we found
that most of failures are caused by transport resource not
available
� From the message tracing, we can also confirm this result
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Case 1 –IP Path Configuration Leads to Low Access Ratio (Cont.)
� Now we can locate that the problem is due to IP path
configuration. We check eNodeB configuration and find a
valid IP path, the connection is valid. And it is also weird
that this problem occurs with a probability
� Then we analyze the message again, and find that in the
“UE context setup request” message delivers variable
GTPU address, and these address is not identical with
eNodeB configuration.
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Case 1 –IP Path Configuration Leads to Low Access Ratio (Cont.)
� Conclusion :As the SGW deliveries multiple GTUP address
to eNodeB, but we only configure one IP path to SGW, so it
causes the partly ERAB setup failure
� Solutions: We confirm this with EPC engineer, SGW pool
function is used, so there are multiple IP addresses for
SGW. Then we make up the IP path for all address, the
problem is cleared.
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Case 2 – Multi-mode UE Attach Failure
� Description: During the commissioning of one live network, we found that UE
attach fails.
� Alarm info: None
� Message Tracing: From the message tracing, we can see that most of access
procedures are normal, after ERAB setup, MME release the connection with
the cause “normal release”
UU trace
S1 trace
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Case 2 – Multi-mode UE Attach Failure (Cont.)
� Analysis
� Since the most of procedures are normal, and eNodeB consider
that it’s a normal release, so we locate that the problem is due to
NAS failure.
� So we continue to analyze the previous NAS message, and in the
DL NAS message, we can see that MME response the attach with
the cause “MSC-temporatily-not-reachable”, as show above. now
we can confirm that this is root cause of attach failure
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Case 2 – Multi-mode UE Attach Failure (Cont.)
� Analysis (Cont.)
� Why should UE need attach to MSC ? We check the UE model,
it ‘s Huawei E398, with multi-modes(GSM/UMTS/LTE). So we
assume that this UE performs combined attach. From the
attach request message we verify our assumption.
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Case 2 – Multi-mode UE Attach Failure (Cont.)
� Conclusion:
� We check that there is no CS domain configuration in current EPS network, so
MME only replies PS attach accept, and also inform that MSC can’t reachable
� Temporary solution:
� Change UE attach mode with PS only
� Add CS domain configuration in EPC
� Final solution:
� Update MME to compatible with combined attach even there is no CS domain
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