The document describes LTE access procedures including random access, RRC connection setup, E-RAB setup, and TAU procedures. It provides details on random access preamble formats, RA response transmission, contention resolution, and relevant performance counters for monitoring each step of the LTE access process. Troubleshooting tips are also given for common issues like NAS procedure failures, ERAB setup failures, and RRC connection rejections.

1. LTE Access Fault Diagnosis
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2. LTE Access Fault Diagnosis
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3. LTE Access Fault Diagnosis
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4. LTE Access Fault Diagnosis
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5. After UE select a suitable cell, it initials attach flow, including the following procedures:
LTE Access Fault Diagnosis
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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6. If UE request service again while in idle status, it initials “Service Request” procedure
LTE Access Fault Diagnosis
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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7. TAU procedure is a UE idle behavior, ensure that UE location is known by MME. The
LTE Access Fault Diagnosis
scenarios of TAU can be:
UE initial attach
UE move to a new TA area
Periodic TA update
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8. LTE Access Fault Diagnosis
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9. LTE Access Fault Diagnosis
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10. There are five RA preamble formats, which are used for cells of different radii. LTE FDD
LTE Access Fault Diagnosis
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.
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Preamble
Format
Length TCP TSEQ FDD Cell Radius (R) TDD Cell Radius (R)
0 1ms 103.1 µs 800 µs R ≤ 14.5km 1.4 km < R ≤ 14.5 km
1 2ms 684.4 µs 800 µs 29.5 km < R ≤ 77.3 km 29 .5km < R ≤ 77.3 km
2 2ms 203.1 µs
1,600
µs
14 .5km < R ≤ 29.5 km 14.5 km < R ≤ 29.5 km
3 3ms 684.4 µs
1,600
µs
77 .3km < R ≤ 100 km 77 .3km < R ≤ 100 km
4
167.9
µs
14.58 µs
133.33
µs
Not involved. R ≤ 1.4 km

11. LTE Access Fault Diagnosis
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12. Upon receiving the UE preamble, the eNodeB transmits an RA response over DL-SCH.
LTE Access Fault Diagnosis
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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13. With the grant ,the UE transmits uplink scheduled data over the UL-SCH. This message is
LTE Access Fault Diagnosis
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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14. After the UE sends message 3,the contention resolution timer starts. The UE monitors the
LTE Access Fault Diagnosis
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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15. Purpose of RRC connection
LTE Access Fault Diagnosis
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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16. LTE Access Fault Diagnosis
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17. After UE succeed attach to MME, MME initial the ERAB setup procedure, to setup
LTE Access Fault Diagnosis
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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18. LTE Access Fault Diagnosis
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19. LTE Access Fault Diagnosis
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20. LTE Access Fault Diagnosis
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21. Trace of UE capability
LTE Access Fault Diagnosis
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22. After SRB2 setup, all the NAS message on UU interface in carried by SRB2 with the
LTE Access Fault Diagnosis
message RRC_DL_INFO_TRANSF or RRC_UL_INFO_TRANSF
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23. LTE Access Fault Diagnosis
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24. LTE Access Fault Diagnosis
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25. NAS procedure is coming after RRC complete, including
LTE Access Fault Diagnosis
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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26. LTE Access Fault Diagnosis
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27. LTE Access Fault Diagnosis
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28. LTE Access Fault Diagnosis
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29. LTE Access Fault Diagnosis
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30. LTE Access Fault Diagnosis
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31. LTE Access Fault Diagnosis
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32. LTE Access Fault Diagnosis
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33. The barred cell only impacts on initial UE access, handover in is not affected.
LTE Access Fault Diagnosis
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34. LTE Access Fault Diagnosis
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35. LTE Access Fault Diagnosis
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36. LTE Access Fault Diagnosis
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37. LTE Access Fault Diagnosis
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38. LTE Access Fault Diagnosis
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39. LTE Access Fault Diagnosis
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40. LTE Access Fault Diagnosis
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41. LTE Access Fault Diagnosis
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42. LTE Access Fault Diagnosis
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43. LTE Access Fault Diagnosis
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44. LTE Access Fault Diagnosis
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45. LTE Access Fault Diagnosis
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46. This failure is caused by eNodeB admission failure. If PUCCH or SRS resource is limited,
LTE Access Fault Diagnosis
eNodeB should stop admit all services including RRC.
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47. LTE Access Fault Diagnosis
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48. Relevant RRC failure counter:
LTE Access Fault Diagnosis
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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

49. This NAS procedure refers to the procedure between UE initial message and Initial UE
LTE Access Fault Diagnosis
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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50. This failure refers the fault between “Initial context setup request” message and “Initial
LTE Access Fault Diagnosis
context setup response” message. If any step occur fault, then ERAB setup procedure fails.
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51. LTE Access Fault Diagnosis
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52. Scneario: the L.E-RAB.FailEst.NoReply counter is incremented each time the eNodeB
LTE Access Fault Diagnosis
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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53. LTE Access Fault Diagnosis
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54. LTE Access Fault Diagnosis
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55. LTE Access Fault Diagnosis
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56. LTE Access Fault Diagnosis
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57. LTE Access Fault Diagnosis
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58. LTE Access Fault Diagnosis
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59. LTE Access Fault Diagnosis
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60. Tracing message
LTE Access Fault Diagnosis
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61. Message tracing
LTE Access Fault Diagnosis
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62. LTE Access Fault Diagnosis
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63. LTE Access Fault Diagnosis
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64. LTE Access Fault Diagnosis
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65. LTE Access Fault Diagnosis
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66. LTE Access Fault Diagnosis
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67. Cautioned WordsCautioned WordsCautioned WordsCautioned Words
1
Tracing ( Signaling/
Message/Interface etc)
The privacy-related information may be anonymity for user's
privacy protection.
LTE Access Fault Diagnosis
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68. LTE Access Fault Diagnosis
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