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New Member

VG350 SCCP Ports losing dial tone

This is an "answer" rather than a question, but I wanted to post it since it took a month or two to resolve this, even with the help of the TAC and I am hoping this post may benefit others who may hit this issue.

We had several VG350 gateways using SCCP to register to our 8.6.2 CallManager Cluster. We were finding that users would complain that at times they would go to use their analog phone and there would be no dial tone. By the time our tech reached the location (10-15 minutes later) the problem would be gone - everything would be working normally.

What we found was in our version of IOS (15.2(4)M4), the SCCP process would send the hello/keep alive packets to CallManager all at once, and all 144 replies would come back, all at once. In our rather fast network the 144 replies would hit so quickly it would overrun the input buffer on the port, resulting in drops. If the analog SCCP port experienced 3 consecutive drops (which some would), it would de-register from CallManager. This would result in no dial tone for the user. Usually the problem happened when there was also real (RTP) traffic in process on other ports, aggravating the port input queue issue. Typically in just a minute or two the SCCP keepalives would get processed correctly and the port would re-register.

Issues aggravating this issue were a high speed (LAN) network between the CallManager and the VG350 (a WAN connection likely would have slowed down the keepalives enough to have them processed correctly), the fact that we had all 144 ports configured (fewer ports in use would have helped the keepalive issue) and having ports with a good amount of activity (adding traffic to the input queues of the Gig ports, which is where the drops were being seen).

The solution was an easy one once the problem was fully understood: adding the "hold-queue 300 in" command to both interface GigabitEthernet0/0 and 0/1. This increased the queue from the default (70? 75? I think) to 300 and allowed the burst of keepalives to be held in queue until they could be processed.

Cisco stated they were investigating in a future IOS release of staggering the SCCP keepalives to avoid this issue, but the above solution worked perfectly at this point.

Rob.
 

1 ACCEPTED SOLUTION

Accepted Solutions
New Member

Hi Alex, Glad to hear it

Hi Alex,

 

Glad to hear it helped you - makes it worth posting it if it helped even one person.

 

How are you using RTMT to look at the ports? I am not an RTMT expert...if I use the "Device Search" feature they do not appear to be showing at all?

Rob.

10 REPLIES
New Member

Rob,If I knew where you are I

Rob,

If I knew where you are I would come and hug you!!!

Thanks 1000 times!!!

New Member

By the way Rob does RTMT

By the way Rob does RTMT count the registered analog phones for you? Mine shows 0 even thou they are registered. 

Thanks again,

Alex.

New Member

Hi Alex, Glad to hear it

Hi Alex,

 

Glad to hear it helped you - makes it worth posting it if it helped even one person.

 

How are you using RTMT to look at the ports? I am not an RTMT expert...if I use the "Device Search" feature they do not appear to be showing at all?

Rob.

Hall of Fame Super Red

Hi Rob, I couldn't rate your

Hi Rob,

 

I couldn't rate your original (excellent) post but here is the +5 it deserves. Nice work!

 

Cheers!

Rob

New Member

I am just looking at

I am just looking at registered devices screen in RTMT and there are 0 even thou I have 400+ analog phones registered via SCCP.

New Member

It looks like we have this

It looks like we have this problem also. We have been losing dial tone or getting one or two rings before the call drops. I noticed that the call manager never shows the registration drops, but when I did a "debug SCCP messages" I would see registrations rejected. My coworker changed the keepalive settings under the SCCP configuration on the VG 350 and it seems to have cleared the problem.

New Member

Re: Rob,If I knew where you are I

What is SCCP is bound to the loopback interface?
New Member

We have been having weird

We have been having weird problem with our VG350s since installation, this one included.

 

We get analog phones that can't receive or make calls (no dial tone).  However I have yet to see the phones de-register from CUCM or come back online by themselves.  We shut/no shut the voice ports on the VG.

I have applied the fix (TAC hasn't provided one yet) and I'll keep my fingers crossed.

Thanks.

 

 

New Member

Hi,Trying to remember, but I

Hi,

Trying to remember, but I don't think I actually ever saw the ports de-register from CallManager. I think that was something TAC found in the traces.

Let me know if this fixes the issue or if you find something else...we're up to about 15 VG350's now, so I'm always interested in any issues I may hit!

Thanks - Rob.

New Member

Did the problem get resolved

Did the problem get resolved with no dial tone from applying this fix?

 

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