troubleshooting Question

Audio delay on incoming calls from certain numbers

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OAC TechnologyFlag for United States of America asked on
Voice Over IPTelecommunicationsIP Telephony
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We are having an issue with audio delay between both the caller and the called party on our phone system. For example, I pick up the phone and say "Hello" and after 2 seconds, they will receive this and respond "Hello" back which takes another two seconds to reach me. This seems to be happening only when certain numbers call our phone system. All of the numbers are from different providers (XO, Comcast, a cell phone, etc.) but the problem can be reproduced every time when they call our phone system. If we call them back, there is no delay in audio. If they call one of our cell phone numbers, there is also no delay. It is only when they call into our phone system that the problem is reproducible every time.

We currently are using Cbeyond as our SIP provider and we are sharing this line with another company in our building. Their phone system is a Trixbox 2.8 system running Asterisk 1.4 connected directly to Cbeyond's trunk using SIP. We have an IAX connection from their phone system to our FreePBX asterisk 1.8 system. When an incoming call comes in for our number, their Trixbox system passes the call over IAX into our system. When we make an outbound call, our FreePBX system uses a SIP extension to connect to the Trixbox phone system and then send out through the Cbeyond trunk. This has been working great for over a year and we have just started having problems this week.

I have restarted all of our equipment on our end including both phone systems, the ASA 5505 firewall, and Cbeyond's equipment with no luck. Could this be a problem with the IAX connection? I don't see any dropped packets between the phone systems or out to Cbeyond, so I don't believe it is a network issue (also because it is only with certain phone numbers).

Any ideas on where I should start?
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