III. METO DOLOGÍA
3.2. Operacionalización de variables,
This section provides information required to troubleshoot access faults due to radio environment abnormalities. The information includes fault descriptions, background information, possible causes, fault handling method and procedure, and typical cases.
Troubleshooting Guide 4 Troubleshooting Access Faults
4.1 Definitions of Access Faults
If an access fault occurs, UEs have difficulty accessing the network due to radio resource control (RRC) connection setup failures or E-UTRAN radio access bearer (E-RAB) setup failures.
4.2 Background Information
This section provides counters and alarms related to access faults, and methods for analyzing TopN cells.
In Long Term Evolution (LTE) networks, access faults occur either during radio resource control (RRC) connection setup or during E-UTRAN radio access bearer (E-RAB) setup. The access success rate is a key performance indicator (KPI) that quantifies end user experience. An excessively low access success rate indicates that end users have difficulty making mobile-originated or mobile-terminated calls.
Related Counters
l RRC Connection Setup Measurement (Cell)(RRC.Setup.Cell)
l RRC Connection Setup Failure Measurement (Cell)(RRC.SetupFail.Cell) l E-RAB Setup Measurement (Cell)(E-RAB.Est.Cell)
l E-RAB Setup Failure Measurement (Cell)(E-RAB.EstFail.Cell) For details, see eNodeB Performance Counter Reference.
Related Alarms
l Hardware-related alarms
– ALM-26104 Board Temperature Unacceptable – ALM-26106 Board Clock Input Unavailable – ALM-26107 Board Input Voltage Out of Range – ALM-26200 Board Hardware Fault
– ALM-26202 Board Overload
– ALM-26203 Board Software Program Error – ALM-26208 Board File System Damaged l Temperature-related alarms
– ALM-25650 Ambient Temperature Unacceptable – ALM-25651 Ambient Humidity Unacceptable – ALM-25652 Cabinet Temperature Unacceptable – ALM-25653 Cabinet Humidity Unacceptable
– ALM-25655 Cabinet Air Outlet Temperature Unacceptable – ALM-25656 Cabinet Air Inlet Temperature Unacceptable l Link-related alarms
– ALM-25880 Ethernet Link Fault
Troubleshooting Guide 4 Troubleshooting Access Faults
– ALM-25886 IP Path Fault – ALM-25888 SCTP Link Fault – ALM-25889 SCTP Link Congestion
– ALM-26233 BBU CPRI Optical Interface Performance Degraded – ALM-26234 BBU CPRI Interface Error
– ALM-29201 S1 Interface Fault
– ALM-29211 Excessive Packet Loss Rate in the Transmission Network – ALM-29212 Excessive Delay in the Transmission Network
– ALM-29213 Excessive Jitter in the Transmission Network l RF-related alarms
– ALM-26239 RX Channel RTWP/RSSI Unbalanced Between RF Units – ALM-26520 RF Unit TX Channel Gain Out of Range
– ALM-26521 RF Unit RX Channel RTWP/RSSI Too Low – ALM-26522 RF Unit RX Channel RTWP/RSSI Unbalanced l Configuration-related alarms
– ALM-26245 Configuration Data Inconsistency – ALM-26243 Board Configuration Data Ineffective
– ALM-26812 System Dynamic Traffic Exceeding Licensed Limit – ALM-26815 Licensed Feature Entering Keep-Alive Period – ALM-26818 No License Running in System
– ALM-26819 Data Configuration Exceeding Licensed Limit – ALM-29243 Cell Capability Degraded
– ALM-29247 Cell PCI Conflict For details, see eNodeB Alarm Reference.
TopN Cell Selection
TopN cells can be selected by analyzing the daily KPI file exported by the M2000.
l Top3 cells with the largest amounts of failed RRC connection setups
(L.RRC.ConnReq.Att - L.RRC.ConnReq.Succ) and lowest RRC connection setup success rates
l Top3 cells with the largest amounts of failed E-RAB setups and lowest E-RAB setup success rates
Tracing TopN Cells
After finding out topN cells and the periods when they have the lowest success rates, start Uu, S1, and X2 interface tracing tasks and check the exact point where the RRC connection or E-RAB setup fails.
In addition, after the Evolved Packet Core (EPC) obtains the international mobile subscriber identity (IMSI) of the UE with the lowest success rate based on the UE's temporary mobile subscriber identity (TMSI), you can start a task to trace the UE throughout the whole network.
Troubleshooting Guide 4 Troubleshooting Access Faults
Analyzing Environmental Interference to TopN Cells
Environmental interference to a cell consists of downlink (DL) interference and uplink (UL) interference to the cell. The following methods can be used to check the environmental interference:
l To check DL interference, use a spectral scanner. If both neighboring cells and external systems may cause DL interference to the cell, locate the exact source of the DL interference.
l To check UL interference, start a cell interference detection task and analyze the result.
4.3 Troubleshooting Method
This section describes how to identify and troubleshoot the possible cause.
Possible Causes
Scenario Fault Description Possible Causes
The RRC connection fails to be set up.
l The UE cannot search cells.
l Authentication fails.
l A fault occurs in radio interface processing.
l Parameters of the UE or eNodeB are incorrectly configured.
l The radio environment is abnormal.
l Parameters of the Evolved Packet Core (EPC) are incorrectly configured.
l The UE is abnormal.
The E-RAB fails to be set up. l Resources are insufficient.
l Parameters of the UE or eNodeB are incorrectly configured.
l The radio environment is abnormal.
l Parameters of the Evolved Packet Core (EPC) are incorrectly configured.
l The UE is abnormal.
Troubleshooting Flowchart
Figure 4-1 and Figure 4-2 show the troubleshooting flowcharts for handling low RRC connection setup rates and low E-RAB setup rates, respectively.
Troubleshooting Guide 4 Troubleshooting Access Faults
Figure 4-1 Troubleshooting flowchart for low RRC connection setup success rates
Troubleshooting Guide 4 Troubleshooting Access Faults
Figure 4-2 Troubleshooting flowchart for low E-RAB setup success rates
Troubleshooting Procedure
1. Select topN cells.
2. Check whether parameters of the UE or eNodeB are incorrectly configured.
l Yes: Correct the parameter configurations. Go to 3.
l No: Go to 4.
3. Check whether the fault is rectified.
l Yes: End.
l No: Go to 4.
4. Check whether the radio environment is abnormal.
l Yes: Handle abnormalities in the radio environment. Go to 5.
l No: Go to 6.
5. Check whether the fault is rectified.
l Yes: End.
Troubleshooting Guide 4 Troubleshooting Access Faults
l No: Go to 6.
6. Check whether parameters of the EPC are incorrectly configured.
l Yes: Correct the parameter configurations. Go to 7.
l No: Go to 8.
7. Check whether the fault is rectified.
l Yes: End.
l No: Go to 8.
8. Contact Huawei technical support.
4.4 Troubleshooting Access Faults Due to Incorrect Parameter Configurations
This section provides information required to troubleshoot access faults due to incorrect parameter configurations. The information includes fault descriptions, background information, possible causes, fault handling method and procedure, and typical cases.
Fault Description
l The UE cannot receive broadcast information from the cell.
l The UE cannot receive signals from the cell.
l The UE cannot camp on the cell.
l The end user complains about an access failure, and the value of the performance counter L.RRC.ConnReq.Att is 0.
l An RRC connection is successfully set up for the UE according to standard interface tracing results, but then the mobility management entity (MME) releases the UE because the authentication procedure fails.
l The end user complains that the UE can receive signals from the cell but is unable to access the cell.
l According to the values of the performance counters on the eNodeB side, the number of RRC connections that are successfully set up is much greater than the number of E-RABs that are successfully set up.
l According to the KPIs, the E-RAB setup success rate is relatively low, and among all cause values, the cause values indicated by L.E-RAB.FailEst.TNL and L.E-RAB.FailEst.RNL contribute a large proportion.
Background Information
None
Possible Causes
l Cell parameters are incorrectly configured. For example, the E-UTRA absolute radio frequency number (EARFCN), public land mobile network (PLMN) ID, threshold used in the evaluation of cell camping, pilot strength, and access class.
l The UE has special requirements for authentication and encryption.
Troubleshooting Guide 4 Troubleshooting Access Faults
l Parameters of the subscriber identity module (SIM) card or registration-related parameters on the home subscriber server (HSS) are incorrectly configured.
l The authentication and encryption algorithms are incorrectly configured on the Evolved Packet Core (EPC).
l The IPPATH or IPRT managed objects (MOs) are incorrectly configured.
Fault Handling Flowchart
Figure 4-3 Fault handling flowchart for access faults due to incorrect parameter configurations
Troubleshooting Guide 4 Troubleshooting Access Faults
Fault Handling Procedure
1. Check whether cell parameters are incorrectly configured. Pay special attention to the following parameter settings as they are often incorrectly configured: the EARFCN, PLMN ID, threshold used in the evaluation of cell camping, pilot strength, and access class.
Yes: Correct the cell parameter configurations. Go to 2.
No: Go to 3.
2. Check whether the fault is rectified.
Yes: End.
No: Go to 3.
3. Check the type and version of the UE and determine whether the authentication and encryption functions are required.
Yes: Enable the authentication and encryption functions. Go to 4.
No: Go to 5.
4. Check whether the fault is rectified.
Yes: End.
No: Go to 5.
5. Check whether parameters of the SIM card or registration-related parameters on the HSS are incorrectly configured. The parameters of the SIM card include the K value, originating point code (OPC), international mobile subscriber identity (IMSI), and whether this SIM card is a UMTS SIM (USIM) card.
Yes: Correct the parameter configurations. Go to 6.
No: Go to 7.
6. Check whether the fault is rectified.
Yes: End.
No: Go to 7.
7. Check whether the authentication and encryption algorithms are incorrectly configured on the EPC. For example, check whether the switches for the algorithms are turned off.
Yes: Modify the parameter configuration on the EPC. Go to 8.
No: Go to 9.
8. Check whether the fault is rectified.
Yes: End.
No: Go to 9.
9. Check whether the IPPATH or IPRT MOs are incorrectly configured.
Yes: Correct the MO configurations. Go to 10.
No: Go to 11.
10. Check whether the fault is rectified.
Yes: End.
No: Go to 11.
11. Check whether the fault can be diagnosed by tracing the access signaling procedure.
Yes: Handle the fault. Go to 12.
No: Go to 13.
12. Check whether the fault is rectified.
Troubleshooting Guide 4 Troubleshooting Access Faults
Yes: End.
No: Go to 13.
13. Contact Huawei technical support.
Typical Cases
l Case 1: An E398 UE failed to access the network despite the fact that the authentication and encryption functions were enabled on the EPC.
Fault Description
During a site test, an E398 UE failed to access a network where the authentication and encryption functions were enabled on the EPC.
Fault Diagnosis
1. The S1 interface was traced. According to the tracing result shown in Figure 4-4, the access attempt was rejected due to no-Sultable-Cells-In-tracking-area(15).
Figure 4-4 S1 tracing result
2. The signaling at the EPC side was traced. According to the tracing result shown in Figure 4-5, the access attempt was rejected by the HSS in the diameter-authorization-rejected(5003) message.
Figure 4-5 Tracing result of the signaling at the EPC side
3. The UE was checked. Specifically, the configuration, registration information, and the category of the SIM card were checked. Then, the cause of the fault was located, which was that the E398 UE used a SIM card. In response to the access request from a UE using a SIM card, the EPC would reply a diameter-authorization-rejected message. Figure 4-6 shows a snapshot of the related section in 3GPP TS 29.272.
Troubleshooting Guide 4 Troubleshooting Access Faults
Figure 4-6 Related section in the protocol
In conclusion, the E398 UE was unable to access the network because the UE used a SIM card. To access an LTE network, the UE must use a USIM card.
Fault Handling
The SIM card in the E398 UE was replaced by a USIM card. Then, the authentication procedure was successful and the UE successfully accessed the network.
l Case 2: The E-RAB setup success rate at a site deteriorated due to incorrect transport resource configurations.
Fault Description
According to the KPIs for a site, the E-RAB setup success rate deteriorated intermittently.
Fault Diagnosis
1. The cause value contained in the S1AP_INITIAL_CONTEXT_SETUP_FAIL message (that is, the initial context setup request message) was checked and was found to be transport resource unavailable(0), as shown in Figure 4-7.
Troubleshooting Guide 4 Troubleshooting Access Faults
Figure 4-7 Snapshot of the S1AP_INITIAL_CONTEXT_SETUP_FAIL message
This cause value indicates that the E-RAB failed to be set up due to faults related to transport resources, rather than faults related to radio resources.
2. The IP address contained in the S1AP_INITIAL_CONTEXT_SETUP_REQ message was checked and was found to be 8A:14:05:14. However, this IP address (8A:
14:05:14) was different from the peer IP address (8A 14 05 13) specified in the IPPATH MO. Figure 4-8 shows the details of the
S1AP_INITIAL_CONTEXT_SETUP_REQ message.
Figure 4-8 Snapshot of the S1AP_INITIAL_CONTEXT_SETUP_REQ message
3. This inconsistency was investigated. As the EPC maintenance personnel confirmed, multiple logical IP addresses were configured on the interface of the unified gateway (UGW), but only one IPPATH MO was configured on the eNodeB. As a result, the E-RAB failed to be set up.
Fault Handling
Troubleshooting Guide 4 Troubleshooting Access Faults
New IPPATH MOs were configured on the eNodeB based on the network plan. Then, the E-RAB setup success rate was observed for a while, during which the E-RAB setup success rate was normal all along.
4.5 Troubleshooting Access Faults Due to Radio Environment Abnormalities
This section provides information required to troubleshoot access faults due to radio environment abnormalities. The information includes fault descriptions, background information, possible causes, fault handling method and procedure, and typical cases.
Fault Description
l During a random access procedure, the UE cannot receive any random access responses.
l During an RRC connection setup process, the eNodeB has not received any RRC connection setup complete messages within the related timeout duration.
l During an E-RAB setup process, the response in security mode times out.
l The eNodeB has not received any RRC connection reconfiguration complete messages within the related timeout duration.
l At the eNodeB side, both the RRC connection setup success rate and the E-RAB setup success rate are low.
Background Information
Radio environment abnormalities include radio interference, imbalance between the uplink (UL) and downlink (DL) quality, weak coverage, and eNodeB hardware faults (such as distinct antenna configurations). The items to be investigated as well as the methods of investigating these items are described as follows:
l Investigating radio interference
DL interference from neighboring cells, DL interference from external systems, and UL interference need to be investigated. To investigate the DL interference, use a spectral scanner. To investigate the UL interference, start a cell interference detection task.
l Investigating weak coverage
The reference signal received power (RSRP) values reported by UEs during their access need to be investigated. If most of these values are relatively low, it is highly probable that the access difficulties lie in the weak coverage provided by the cell.
The actual radius of cell coverage as well as the signal quality variation need to be investigated so that users can determine whether wide coverage or cross-cell coverage occurs.
l Investigating the imbalance between UL and DL quality
The transmit power of the remote radio unit (RRU) and UE need to be investigated to check whether UL or DL limitations have occurred, because imbalance between UL and DL quality is caused by UL limitations or DL limitations.
The UL and DL radii of cell coverage need to be investigated using drive tests.
l Investigating eNodeB hardware
If two antennas are used, the tilt and azimuth of each antenna need to be investigated. If their tilts or azimuths are significantly different from each other, adjust them so that their tilts and azimuths are the same.
Troubleshooting Guide 4 Troubleshooting Access Faults
The jumper connection needs to be investigated by analyzing drive test results. If the jumper is reversely connected, the UL signal level will be much lower than the DL signal level in the cell, in which case UEs remote from the eNodeB will easily encounter access failures.
Therefore, if the jumper is reversely connected, rectify the jumper connection.
The physical conditions of feeders need to be investigated. If a feeder is damaged, water immersed, bending, or not securely connected, a large number of call drops will occur. If a voltage standing wave ratio (VSWR) alarm is reported, such problems exist and you need to replace the faulty feeder.
Figure 4-9 and Figure 4-10 show common causes of random access failures and E-RAB setup failures, respectively.
Figure 4-9 Common causes of random access failures
Figure 4-10 Common causes of E-RAB setup failures
Possible Causes
l The cell provides weak coverage.
l The UE does not use the maximum transmit power.
Troubleshooting Guide 4 Troubleshooting Access Faults
l Inter-modulation interference exists.
l The UE is located at cell edge.
Fault Diagnosis
To effectively diagnose access faults due to radio environment abnormalities, you are advised to firstly find out whether this fault is caused by radio interference or weak coverage. The following procedure is recommended:
Fault Handling Procedure
1. Check whether related alarms are reported.
Yes: Handle these alarms by referring to eNodeB Alarm Reference. Go to 2.
No: Go to 3.
2. Check whether the fault is rectified.
Yes: End.
No: Go to 3.
3. Check whether interference exists. By using a spectral scanner, check whether there is DL interference from neighboring cells or external systems. By analyzing the cell interference detection result, check whether there is UL interference.
Yes: Minimize the interference. Go to 4.
No: Go to 5.
4. Check whether the fault is rectified.
Yes: End.
No: Go to 5.
5. Check whether the transmit power of the RRU and UE falls beyond link budgets.
Yes: Adjust the UL and DL transmit power. Go to 6.
No: Go to 7.
6. Check whether the fault is rectified.
Yes: End.
No: Go to 7.
7. Check whether cell coverage is abnormal.
Yes: Based on the RSRP distribution of the UEs attempting to access the cell, investigate and handle possible coverage, interference, and imbalance between UL and DL quality by using drive tests. Go to 8.
No: Go to 9.
8. Check whether the fault is rectified.
Yes: End.
No: Go to 9.
9. Contact Huawei technical support.
Typical Cases
Fault Description
Troubleshooting Guide 4 Troubleshooting Access Faults
According to the KPIs for an eNodeB at a site, the RRC connection setup success rate fluctuated significantly within a period.
Fault Diagnosis
1. The KPIs were checked. For local cell 1, the daily RRC connection success rate was only 52%.
Figure 4-11 PRS KPI about RRC connection setups
2. The signaling over the Uu interface was traced. The result indicated that all RRC connection setup failures occurred because UEs do not respond. The following figure shows a snapshot of the signaling traced over the Uu interface.
Figure 4-12 Signaling traced over the Uu interface
3. Simulated load was added to the LTE side. The impact of the DL LTE signals on the DL GSM signals was tested, during which the call drop rate at the GSM side raised significantly.
As a result, it was highly probable that inter-modulation interference existed.
4. Online spectral scan was applied to the LTE side. Interference with a magnitude of 10 dB was found within the high-frequency resource blocks (RBs), which affected signaling transmission.
Troubleshooting Guide 4 Troubleshooting Access Faults
Figure 4-13 Online precise spectral scan result
5. The site was investigated and the cause of the fault was located. The LTE and GSM sides shared the same antennas. The antennas aged and induced inter-modulation interference.
Fault Handling
The antennas were replaced. Then, the access success rate was restored.
Troubleshooting Guide 4 Troubleshooting Access Faults
5 Troubleshooting Intra-RAT Handover Faults
About This Chapter
This chapter describes how to diagnose and handle intra-RAT handover faults. RAT is short for radio access technology.