[cisco-voip] multi-site conference call voice quality degrades overtime

[Scott Crosby]

It might be a transcoding issue. I encountered something very similar
with Cisco Conference Connection (CCC) and a 3640 using an HM-DHV farm
module for transcoding. It turned out the CCC wasn't sending uniform
G711 packet sizes to the 3640 for transcoding. We spotted this with a
packet trace. The packets kept varying in size from 20 ms to 10 ms and
back again coming from the CCC server to the router. The DSPs on the on
the router didn't know what to do with the 10ms packet samples it just
dropped them. It made the speech sound very muddy.  There wasn't a fix
for the CCC software; Cisco is very slow on updating it. But we were
able to upgrade the code on the router later and it seemed to help. 

 

In your case the PVDMs are a little different on the 1760V platform from
the PVDMs in the NM-HDV modules in the 26XX/36XX/37XX router platforms.
Also it's the software conference bridge on CM not CCC so it might not
be the same issue.

 

--Scott 

 

From: cisco-voip-bounces at puck.nether.net
[mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Kris Seraphine
Sent: Thursday, February 17, 2005 7:48 AM
To: cisco-voip at puck.nether.net
Subject: [cisco-voip] multi-site conference call voice quality degrades
overtime

 

Hi

 

I have a customer with a small two site cluster.  When they hold
conference calls, everything works fine for the first 15 - 20 minutes
but then the participant in the remote site will complain that the audio
becomes choppy or sounds like they're "under water".   These are meet-me
conferences initiated by a user at the central site (where the
callmanagers are) using the callmanager software conference bridge.  The
remote user calls across the WAN (g729) and uses a dsp resources in a
1760 for transcoding. 

 

After 15 minutes or so the call quality will degrade for the remote
participant but other participants are able to hear the remote user and
each other fine.  If the remote user hangs up and calls back into the
conference, it will sound fine but degrade again after 15 + minutes.
During one conference a user called in to the conference 4 times and the
call always degraded after 15 minutes.  

 

I don't think the WAN is an issue.  They have MPLS with guaranteed
realtime bandwidth for 3 concurrent calls.  Callmanager locations
enforce this limit and we've never had any call quality complaints
except for these conferences.  

 

I have a case open with TAC but we're not getting very far with them.
I'm wondering if anyone else has experienced a similar issue.    

 

Kris Seraphine
Senior Technology Specialist

Clifton Gunderson Technology Solutions
1111 Deming Way suite 101
Madison, WI  53717
Phone: 608.833.8638
Fax: 608.833.0194
Direct: 608.662.7640
Web: www.cliftoncpa.com <http://www.cliftoncpa.com/> 

 

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