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IP Telephony:  Echo using g711ulaw

Posted on 2004-04-05
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Last Modified: 2012-06-27
Our oganization has implemented a Cisco AVVID solution.  We are having echo problems with certain branch locations.  The problem exists for both internal and external calls.  We've got point-to-point T1s for each location and we're using codec g711ulaw which is uncompressed voice.  I've been troubleshooting the issue by applying echo-cancellation on the PRI interfaces which hasn't changed the performance.  Since the problem aslo exists for internal calls I believe the problem isn't with the PRI.  What steps can I take to troubleshoot this probem further?  Any suggestions on what the problem may be?

Call Manager version:  3.3(2)
Gateways:  H323
Phone type:  7960
Switch type:  Cisco 3550 with inline power

Thanks a lot!
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Question by:wendelina
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Expert Comment

by:shautayl
ID: 10759334
do you have the ability to ping another computer on the connection with the t1,  if you are, try to ping the other computer and see if you are getting repeating packets or packet loss.... that could be the cause of the issue or even latency... ping the ip phone server to see if that may be causing the issue.

shautayl
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Author Comment

by:wendelina
ID: 10759694
I've run extended ping scans using a 1500 MTU packet size.  The speed is less that 30 ms and the result is 100%.  The voice server (CCM) is designed to set-up the calls, not facilitate the conversation.  That is a peer-to-peer function.  That's what is confusing me.  Our network is a hub and spoke topolgy with plenty of bandwidth to handle the 80k voice-calls.  I can understand echo from a PRI, but internally?  All phones are set to 100/Full, so 80k is nothing.  Thanks for the reply!
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enkrypter earned 500 total points
ID: 10762228
Got any QoS or CoS turned on?  YOu might want to play with that.  Are you currently prioritizing voice packets.  Also, check out the statistics on your VLANs if you have any.  Make sure spanning tree is running properly or whatever other VLAN protocol you may have.  VLANs are sometimes a bottleneck for VOIP rather than a helper.

I'd play arround with compression, like G.729a, and some QoS.  What is your core switch?
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Expert Comment

by:public
ID: 10762981
Yes echo problems are usually due to QOS issues.
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Author Comment

by:wendelina
ID: 10766210
I have begun to play with qos a bit, am still awaiting the response from my customer.  I have a 4507 core switch.  Voice packets have priority over all other packets up to the full bandwidth to our sites.  Thanks for the responses, I'll see if the qos helps then award you your points if it does!
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