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MAC_FCS_EXC alarm in PTN cause BTS intermittent offline

Publication Date:  2018-05-02 Views:  1090 Downloads:  0
Issue Description
On 13/04/2018 around 4:00AM, it’s reported that BTS Clyde experiencing OML Fault alarms and intermittent offline:
It’s suspected that there was transmission issue which caused the BTS offline.
By checking alarms and logs for whole chain 5, it’s found poor signals between site 089 and 093 which was leading to packets loss. All PTN910s tunnels on this chain were affected by this poor signal issue as shown in below graphs:

Alarm Information

MAC_FCS_EXC alarm in PTN

Handling Process

1、After changing SFPs of site 089&093&095, bit error alarm (MAC_FCS_EXC) was still there on site 093 Carlingford. Then it was suspected that there was PTN910 hardware issue which was leading to the transmission bit error.

2、Field technician did a loopback by pigtail on site 089-Auburn, the MAC_FCS_EXC alarm couldn’t be cleared by loopback so it’s confirmed that the CXPH card was faulty on site 089 Auburn PTN910.

3、Self-loop test on site 089 Auburn proved this PTN910 had bit error in Tx signal of transmission.The root cause was MAC module of CXPH card in PTN910 got faulty which caused the bit error:

4、This was solved by replacing CXPH board on site 089 .

Root Cause

MAC module of CXPH card in PTN910 was faulty causing port 21 Tx signal having bit errors on Chain 5. 


This was solved by replacing CXPH board on site 089 


1、When “MAC_FCS_EXC” alarms was found, it’s suggested to check fibres and change SFPs of upstream or downstream PTNs.

2、If alarm still exists, reboot upstream or downstream PTNs. 

3、If step 2 can’t clear the alarm, replace upstream or downstream CXPH board.