Hello Community Members!
Today, I will share with you the possible causes of the following TDM Link fault alarms on BSC6900 and te solution to rectify them after some analysis:
ALM-20230 TDM Link Between TDM Switching Board and Service Board Faulty;
ALM-20235 Active TDM Link Fault Between TDM Switching Board and Service Board.
PROBLEM STATMENT
We observed the TDM-related alarms on one of our BSCs. These alarms keep appearing again and again.
ABOUT THE TNU BOARD
Before going into the details of the alarms and their handling procedure, I will first briefly describe the TNU board.
The TNU board is the TDM switching board. It provides the TDM switching and serves as the center of the circuit switched domain. This board can be called 'the TDM switching center'. The switching is
performed by the TNUa boards and the inter-TNUa cables.
The TNUa board is applicable to the BSC6900 GSM & BSC6900 GU. This board can be configured in board redundancy mode, as you may see in the below Device Panel view of a BSC. When two TNUa boards are configured to work in board redundancy or backup mode, one TNUa board is active and the other is on standby. The standby board synchronizes its data with that on the active board in real time.
The active and standby TNUa boards automatically perform a switchover called 'automatic switchover'. However, the manual swichover can also be performed by using the command SWP BRD, which will switch over the active and standby TNUa boards. However, it has some prerequisites that must be fulfilled before performing the manual switch over. The switchover between the active and standby TNUa boards does not affect the ongoing services.
ALARM DESCRIPTION
1. ALM-20230 TDM Link Between TDM Switching Board and Service Board Faulty
This alarm is generated When the TNU board or the service board detects that the TDM link between the TNU board and the service board is faulty. An alarm reporting a delay mechanism with a defult delay duration of 180s is applied to this alarm to avoid frequent reporting.
Alarm attributes
| Alarm ID | Alarm Severity | Alarm Type | Introduced in Version... |
|---|---|---|---|
| 20230 | Major | Fault | Version earlier than BSC6900 V900R017C10 |
Alarm impact
If this alarm is generated on the active board, the services that are carried on the faulty link are disrupted.
System actions
None.
Possible causes
The following list contains the possible hardware-related issues that may cause this alarm to be generated:
the local board is faulty;
the peer board is faulty.
the board is not securely inserted;
the peer board is not securely inserted;
the backplane is faulty;
the peer board is absent;
the clock signals transmitted by the SCU board to the service board are inaccurate.
2. ALM-20235 Active TDM Link Fault Between TDM Switching Board and Service Board
This alarm is generated when the TDM switching board or the service board detects that the active TDM link is faulty. An alarm reporting a delay mechanism with a defult delay duration of 180s is applied to this alarm to avoid frequent reporting.
Alarm attributes
| Alarm ID | Alarm Severity | Alarm Type | Introduced in Version... |
|---|---|---|---|
| 20235 | Major | Fault | Version earlier than BSC6900 V900R017C10 |
Alarm impact
If the faulty TDM link is carried on the active board, voice or data services carried on this link will be interrupted.
System actions
The system switches over the active and standby boards if the standby board allows the switchover when this alarm is generated on the active board.
This system takes no action if the alarm is generated on the standby board.
The system resets the board if the board works in independent mode.
Possible causes
The following list contains the possible hardware-related issues that may cause this alarm to be generated:
the peer board that carries the faulty link is uninstalled;
the clock signals transmitted to the service board from the SCU are faulty;
the local board is not securely inserted;
the peer board that carries the faulty link is not in position or not securely inserted;
the local board is faulty;
the peer board that carries the faulty link is faulty;
the backplane is faulty.
HANDLING
First we will focus of the MO Name and Location Information tabs in the alarm window to locate the local and peer boards.
Now we can check these two locations mentioned in the MO Name and Location Information in to the device panel:
Subrack 0 Slot 5;
Surack 0 Slot 19.
ANALYSIS CONCLUSION
After throughly analyzing the current alarm and the alarms logs, the following is the conclusion issue: the two boards in subrack 0 slot 19 and subrack 0 slot 5 positions are having FAULTS:
The LVDS chip of board in subrack 0 slot 19 & The TDM chip of board in subrack 0 slot 5 are faulty.
DETAILED ANALYSIS
TDM detection is used to detect the LVDS link between the service board and the TNU. It is used to check whether inter-board LVDS data frames are lost and whether the receive clock is lost. The possible causes of the fault include the local end fault, the peer end fault, the backplane pin fault and the clock exception. We need to locate the fault step by step.
We observed that after 19:52 on November 3rd, 2021, the OIUa board in slot 19 of subrack 0 and the TNUa board in slot 4/5 of subrack 0 repeatedly reported the TDM link fault alarms. The alarm did not recover after they were reported at 17:56 on November 21st.
The TDM links between slot 19 of subrack 0 and slot 4/5 of subrack 0 are faulty, which is caused by the LVDS chip fault of the OIUa board in subrack 0 slot 19.
After 18:26 on November 13th, 2021, the TNU in slot 5 of subrack 0 and the OIU in slot 14/15 of subrack 0 repeatedly reported the TDM link fault alarm. The alarm did not recover after being reported at 9:27 on November 26th.
The TDM link between slot 5 of subrack 0 and slot 14 or 15 of subrack 0 is faulty, which is caused by the TDM chip fault of TNU board in subrack 0 slot 5.
SOLUTION
Reset the OIUa board in subrack slot 19. If the alarm cannot be cleared or gets generated again, then replace the board.
Reset the TNUa board in subrack slot 5. If the alarm cannot be cleared or gets generated again, then replace the board.
Thank you for reading. You're welcome to leave your feedback about this post via the comment box below or via a private message!
