LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
After UE select a suitable cell, it initials attach flow, including the following procedures:
Random access
RRC connection setup (RRC cause: MO signaling)
NAS authentication procedure
E-RAB setup (Activate default EPS bearer)
Setup dedicated bearer (Optional, only for some Smart UE that support VoIP)
Above figure shows the detailed procedure
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LTE Access Fault Diagnosis
If UE request service again while in idle status, it initials “Service Request” procedure
The whole procedure are very similar as initial attach procedure except:
The cause of RRC connection is “MO Data” No authentication and UE capability query procedure as UE context already exists in MME
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LTE Access Fault Diagnosis
TAU procedure is a UE idle behavior, ensure that UE location is known by MME. The scenarios of TAU can be:
UE initial attach
UE move to a new TA area
Periodic TA update
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
There are maximum 64 preamble index, indicate all possible time slot for preamble sending
All these preambles are divided into contention based group and dedicated group.
UE acquires all RACH configuration in SIB2 message.
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LTE Access Fault Diagnosis
There are five RA preamble formats, which are used for cells of different radii. LTE FDD supports preamble formats 0-3, and LTE TDD supports preamble formats 0-4. The preamble format can be set through the PreambleFmt parameter, and the cell radius can be set through the CellRadius parameter.
Format 4 is a special RACH preamble for LTE-TDD only.
Preamble Length TCP Format
TSEQ
FDD Cell Radius (R)
TDD Cell Radius (R)
0 1
1ms 2ms
103.1 µs 800 µs 684.4 µs 800 µs
R ≤ 14.5km 1.4 km < R ≤ 14.5 km 29.5 km < R ≤ 77.3 km 29 .5km < R ≤ 77.3 km
2
2ms
203.1 µs
14 .5km < R ≤ 29.5 km 14.5 km < R ≤ 29.5 km
3
3ms
1,600 µs 1,600 684.4 µs µs
4
167.9 µs
14.58 µs
133.33 µs
77 .3km < R ≤ 100 km
77 .3km < R ≤ 100 km
Not involved.
R ≤ 1.4 km
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
Upon receiving the UE preamble, the eNodeB transmits an RA response over DLSCH.
The UE monitors the Physical Dedicated Control Channel (PDCCH) in the Transmission Time Interval (TTI) until it obtains the required RA response.
The response contains RA-Preamble Identifier, Timing Alignment Information, Initial UL Grant, and Temporary C-RNTI.
If multiple-UE send the preamble with the same RA-RNTI, then eNodeB detects that the conflict occurs. This conflict will be handled in contention resolution procedure.
A message on the DL-SCH can carry multiple RA responses to be transmitted to multiple use.
For the UE ;
If the received RA-Preamble Identifier is consistent with the identifier that the UE previously sent, the UE infers that the response is successful. Then, the UE transmits uplink scheduled data. Otherwise, the response fails. In this case, if the number of random access attempts is smaller than the maximum, the UE attempts random access again. Otherwise, random access fails.
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LTE Access Fault Diagnosis
With the grant ,the UE transmits uplink scheduled data over the UL-SCH. This message is scrambled by temporary C-RNTI. In this message, UE will carry its unique ID for contention resolution if random access conflict.
Based on different random access scenarios, the message could be
RRC connection request
RRC reestablishment request
RRC reconfiguration complete (Handover confirmation)
Other user data
In case of “RRC connection request” message, UE sends its UE ID to identify the different UE. This UE ID could be:
If UE already get S-TMIS from MME, then use S-TMIS as UE ID If UE initial attach, UE generate a random number according to its IMSI as UE ID
In the other case, UE at least send its C-RNTI to identify the different UE
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LTE Access Fault Diagnosis
After the UE sends message 3,the contention resolution timer starts. The UE monitors the PDCCH before the timer expires. In the following situations, the UE infers that the contention resolution is successful and it notifies the upper layer and stops the :
The UE obtains the C-RNTI when monitoring the PDCCH. Temporary C-RNTI is obtained when the UE monitors the PDCCH. In addition, the MAC Packet Data Unit (MAC PDU) is successfully decoded.
If the contention resolution timer expires, the UE infers that the contention resolution fails. Then, the UE performs RA again if the number of RA attempts is smaller than the maximum number of attempts.
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LTE Access Fault Diagnosis
Purpose of RRC connection
Setup SRB1
Send NAS message to EPC
Relevant counters:
A: RRC connection attempts (L.RRC.ConnReq.Att)
B: RRC connection setup successful (L.RRC.ConnReq.Succ)
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
After UE succeed attach to MME, MME initial the ERAB setup procedure, to setup dedicated S1 control plane for UE. At the same time, the default PDN connectivity and EPS bearer will also be setup. After ERAB setup, there is already IP connectivity between UE and gateway which is called “Always on line” function.
Relevant counters:
A: ERAB setup attempts (L.E-RAB.InitAttEst)
B: ERAB setup successful (L.E-RAB.InitSuccEst)
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
Trace of UE capability
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LTE Access Fault Diagnosis
After SRB2 setup, all the NAS message on UU interface in carried by SRB2 with the message RRC_DL_INFO_TRANSF or RRC_UL_INFO_TRANSF
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
NAS procedure is coming after RRC complete, including
Attach request (default)
Default EPS bearer activity (default)
Dedicate EPS bearer setup (optional)
Authentication (optional)
Identification (optional)
NAS procedure is associated with ERAB setup procedure, for NAS delivery, on UU interface NAS can be combined in common RRC message as NAS PDU or directly transferred as “RRC_DL/UL_INFO_TRANSF” message; on S1 interface, NAS can be combined in common S1AP message as NAS PDU or directly transferred as “S1AP_DL/UL_NAS_TRANS” message
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
The barred cell only impacts on initial UE access, handover in is not affected.
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
This failure is caused by eNodeB admission failure. If PUCCH or SRS resource is limited, eNodeB should stop admit all services including RRC.
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
Relevant RRC failure counter: Counter name
Description
L.RRC.SetupFail.ResFail
Number of RRC connection setup failures due to resource allocation failures
L.RRC.SetupFail.NoReply
Number of RRC connection setup failures due to no responses from the UE
L.RRC.SetupFail.Rej
Number of RRC Connection Reject messages sent to the UE in a cell
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LTE Access Fault Diagnosis
This NAS procedure refers to the procedure between UE initial message and Initial UE context setup response message, including attach, authentication, identification, default bearer activity.
If NAS procedure is failure, then MME will send a UE context release command, and the release cause is NAS, so eNodeB will consider this release is normal release and doesn’t count it in performance static.
Possible scenarios:
Authentication failure: Incorrect subscriptions user data in HSS
Solution: Check subscription data in HSS
Attach failure: Parameters between UE and EPC is not identical
Solution: Check the if the following parameters are identical with EPC 1. PLMN 2. TAC
PDN activity failure: Wrong configuration of APN in UE or EPC
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LTE Access Fault Diagnosis
This failure refers the fault between “Initial context setup request” message and “Initial context setup response” message. If any step occur fault, then ERAB setup procedure fails.
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
Scneario: the L.E-RAB.FailEst.NoReply counter is incremented each time the eNodeB receives no responses from the UE before the corresponding timer expires after sending an RRC signaling message to the UE during the initial UE context setup procedure or the E-RAB setup procedure
Possible cause:
Poor DL/UL coverage which cause message missing.
UE internal process error
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
Tracing message
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LTE Access Fault Diagnosis
Message tracing
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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LTE Access Fault Diagnosis
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