RFA Alarm Indicator Is On for a Port on the DTU Board Because CRC Verification Is Disabled

Publication Date:  2015-07-15 Views:  246 Downloads:  0
Issue Description
An office changes the network by replacing the original stored program control exchange (SPC) with the SoftCo9500. The change is as follows:
  • Original network: SPC–One pair of E1s–DDF-CC08
  • New network:Telecom gateway–DDF–E1–DTU board (port 2)–SoftCo9500–DTU board (port 3)–E1–DDF–CC08

Version: SoftCo9500 V100R003C01SPC600

Problem description:

Call services are normal on the CC08 before the change. The RFA indicator of port 3 on the DTU board is on. In addition, according to the output of the show pralink command, the PRA link on port 3 is in FAULT state. The LOS and RFA indicators for the port connected to the telecom network on the DTU board are off, and the PRA link works properly.
 

Handling Process
Step 1 Connect the TX and PX ports of the local E1 in short-circuit mode to form a self-loop. The LOS and RFA indicators are off, indicating that the DTU board and port 3 work properly.

Step 2 After the local DDF is connected, form a loop on the remote DDF. The LOS and RFA indicators are off, indicating that no crossed pair exists.

Step 3 Swap the TX and RX connectors on the local DDF. The LOS indicator is on, indicating that TX and RX connectors are correctly connected originally.

Step 4 Run the show system clocksource information command. It is found that no clock source is configured. Run the config system clocksource primaryslot 3 primaryport 3 command to add a clock source. The RFA indicator is still on.

Step 5 After confirmation with the peer end, CRC verification is enabled on the CC08. However, CRC verification is disabled by default at the local end according to output of the show board slot 3 command. Run the config modify board slot 3 type dtu trunkport 3 crcflag yes command to enable CRC verification. The RFA indicator is off.

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Root Cause
When encountering PRA trunk connection faults, first ensure that the underlying physical connection is normal, that is, the LOS and RFA indicators for the port on the DTU board are off.

If the PRA link is still faulty when physical transmission is normal, use the UCMaint or OMU to trace Q921 messages, and check whether the SoftCo has sent multi-frame operation SABME messages. If yes, check whether the peer end replies with the UA confirmation message.

Procedure for locating E1 physical transmission faults:

1. Connect the TX and PX ports of the local E1 in short-circuit mode to form a self-loop. Check whether the LOS and RFA indicators are off. If yes, the local board and port work properly.
2. After the local DDF is connected, form a loop on the remote DDF. Check whether the LOS and RFA indicators are off. If yes, the TX and RX cables are a normal pair of cables; if no, a crossed pair is selected.
3. Swap the TX and RX connectors on the local DDF to exclude the cause of incorrect TX and RX connections.
4. Run the show system clocksource information command to check whether the SoftCo synchronizes the clock from the peer office. If no, run the config system clocksource primaryslot <2-9> primaryport <0-3> command to add a clock source.
5. Run the show board slot <2-9> command to view information about the slot where the DTU board is installed. Verify that the CRC verification for the port is consistent with the peer end. To configure CRC verification, run the config modify board slot <2-9> type dtu trunkport <0-3> crcflag <yes|no> command.
6. Check whether the peer end is in balance or non-balance mode. The resistance for the balance mode is 120 ohms, and the resistance for the non-balance mode is 75 ohms. By default, the DTU board is in non-balance mode. To change the mode to balance, remove the DTU board and adjust the jumper near the ejector level to the end with exposed pins.
7. If the fault persists, contact the transmission and peer device engineers to locate the fault together.

Procedure for locating Layer 2 link establishment faults:

1. Check whether the SoftCo is on the user side or network side. The SoftCo and peer end cannot be on the same side.
2. If the SofCo is on the user side, trace Q921 messages and check whether the SoftCo has sent multi-frame operation SABME messages. If the SABME messages are sent but no UA response is received, contact the peer end engineers to locate the fault.
3. If the SofCo is on the network side, trace Q921 messages and check whether the SoftCo has received multi-frame operation SABME messages. If no SABME message is received, contact the peer end engineers to locate the fault.
4. If peer end sends Layer 2 messages properly but the local end cannot establish Layer 2 links, contact R&D engineers to locate the fault.

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