Cause 81 error - no inbound calls - phone line issue?

Hi there,
Just wondering if anyone can help me with an ongoing problem I don’t seem any nearer to solving.
We are experiencing a problem on our asterisk based phone system. Every Monday we come in and we are having a problem with inbound calls. After setting up our phone system to log to a syslog server it has become clear that the issue is with a Cause 81 error. This builds up and eventually the inbound calls stop working until we manually restart the phone system.

We have already had BT out numerous times to investigate a possible fault on the line with no success.
I’ve had a look online to see what a Cause No. 81 error is - invalid call reference value.
This cause indicates that the equipment sending this cause has received a message with a call reference which is not currently in use on the user-network interface.

Is this definitely down to a fault with BT? Can anyone suggest how I can approach this with BT as we haven’t had much luck as yet!

In order to test the fault I have disconnected the phone system from the lines with the issue. All being well the phone system should be back up and running on Monday.

Thanks in advance

I’ve seen a couple of other people reporting something that could be the same, although they reported the immediate error message. I’m beginning to think there may be a local software problem. Which make of ISDN cards are you using?

Note, I would assume that this fault is in the signalling, so well above the level of a faulty cable.


Have you got access to a Trend ISDN simulator ? also can you post your dahdi conf files as we have asterisk connected to ISDN on customers sites using dahdi and zaptel and haven’t seen this.

You could as a work around you could cron a restart of asterisk and dahdi.

Twitter @cyberco


Thanks for the responses. On coming back into the office today we experienced the same issue. This time the fault was showing up on span 3 (i presume this is the 3rd port on the ISDN card as the 4th port was disconnected). I plugged the fourth cable back in and carried out an emergency stop and the system went back to operating normally.

David, I’m not sure what ISDN cards we are using but I will try and find out. When you talk about a fault in the signalling is this something I should be raising with BT or my phone system provider?

Ianplain, unfortunately I do not have access to a simulater and cannot access the conf files. I am not really up to speed on accessing the logs from the system other than via the web interface we have.

Anyone any suggestions on the way to progress the issue and any ideas as to why it is only on a Monday morning like clockwork?

Thanks for the help so far, much appreciated


[quote]Anyone any suggestions on the way to progress the issue and any ideas as to why it is only on a Monday morning like clockwork?

Without access to logfiles or conf files, you need to speak to the person who has. as these will have clues as to whats happening and even the answer.

You really need to go to who supplied it and speak to them, I doubt the problem is with BT and without a simulator or access to one they aren’t going to be too supportive.

Where r u based ?

Twitter @cyberco

Hi ian,

I will go and speak to the company that are supporting the phone system as they have access to the logs you talk about. I will keep this thread updated with my progress. I am thinking of disconnecting more lines next weekend to confirm that the issue isn’t related to a particular faulty line.

I am based in Liverpool.



This may be relevant

After giving up on the support from the supplier we are now going down the route of looking at a new phone system.

Anyone any recommendations for any companies who may be interested in swapping out or phone system, trying to diagnose our weird issue and handling the setup and switch over to ensure we migrate smoothly! We have approximately 40 users with existing SIP handsets

We are in Liverpool, UK. Drop me a message if anyone is interested