CUCM - Calls dropping after one ring

[Tyson Villeneuve]

Hi all. Having a strange problem with one of our locations and I wanted to see if anyone had any similar experiences before I open a TAC case, as this one seems to be really strange.

We're running a cluster of CUCM 8.6.2. One of our locations is having an issue where phones receiving calls are ringing once and then dropping.

-The problem is sporadic, with the issue seeming to happen several times to many phones during brief periods and certain times of the day, so that makes it somewhat difficult to pin down.

-It is only happening at one of our locations. -

-This location has a CUCM Sub on site, though I tried registering one of the phones to a different CUCM and the issue still came up a few times today.

-It happens on both internal calls and those originating on the PSTN.

This all points to some issue on the local LAN, though I can't imagine what. Does anyone have a suggestion on what I can check on the local network that might be causing this?

Thanks

[Ayodeji Okanlawon]

Tyson,

Issues like this are quite difficult to spot without detailed troubleshooting. I suggest you enabled detailed cucm logging. Then try and reproduce the issue. Collect cucm logs and post here. Please include calling and called number

[Iyad Musleh]

We're also having a very similar problem. We're running a CUCM 8.5.1 cluster with 7 subscribers.  Just like the original post, it's random and impacts only incoming calls regardless if the call originates from PSTN or intra-cluster.  It even happens between phones registered to the same sub and in the same physical office, connected to the same 3750 access switch.  Almost all phones that have experienced this problem are model 7962.  A total of about 45 phones have this issue. The only exception we've seen so far is one 7945.  The remaining few hundred 7965, 7945, 7925 and others don't seem to be impacted, or at least none of those users have noticed.

Resetting the phones doesn't make a difference. Upgraded the phone's firmware as well.  Sometimes the problem lasts just a few minutes. Sometimes over an hour.  End users are not CCX agents and do not use headsets of any kind. Sometime it happens with phones that have shared lines, sometime on phones that have only a unique DN configured. The only common thread among the groups of phones when there is a problem seems to be their pick-up groups.  So when there is a problem, it seems to impact just phones that are members of that particular group.  Only about 4 pickup groups, out of a few dozen, have reported this issue.

At first i thought it could be related to the issue in this thread:

https://supportforums.cisco.com/discussion/11498826/7942-weird-call-drops-after-one-ring-or-less

But then we also experienced this on a single 7945 phone as well. 

Any ideas?

[nalonsopresidio]

How do you have the codec relation between this site and the region where the other phones calling internally are on, as well as the SIP to CUBE/PSTN or PRI is under? If compression, how many codec sessions do you have available, and where is this transcoder residing, is it at the gateway local to the site? You could be running out of transcoder sessions during busy times.

Check CAC and make sure it's not limiting to that location, and resync the bandwidth. Also make sure RSVP is not mandatory for inter-locations under service parameters.

[Tyson Villeneuve]

Hi. Thanks for the reply.

This is happening on internal and external calls, even calls within the site. All calls there are g711 and not using a transcoder.

The calls ring once and then fail, so I don't think this is a CAC issue.

[nalonsopresidio]

If it is happening to intra-site calls then it is something else. Which phone model is this happening to? Are they 7962s?

[usamaahmed1]

If I remember correctly, I have resolved this issue before by increasing the bandwidth for the location in System -> Location configuration in CUCM. 

The issue arose in another site of mine yesterday and applying the same resolution. If it works the second time too, I will update this post. Just did not want to forget to share the resolution. 

I think the key is to ask them if the frequency of the calls has increased compared to the norm. If it has, this might be your fix.

Update:

It resolved the problem for another location/site too.