CME 4.2 whit WAN calls

Unanswered Question
Sep 29th, 2008
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I have a CME directly connected to the Internet by a public IP address.

I have an ATA186 and elsewhere also connected to the Internet through a broadband phone with an analog. The ATA186 is registered without problems at the CME, but when a call is made the phone make ring but no audio traffic.

This topology is correct?

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CHRIS CHARLEBOIS Mon, 09/29/2008 - 14:00
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Sounds like you have the one way audio problem, possibly in both directions. If that's the case, here is what is happening.

The phone is registering using SCCP, which uses TCP. Call control also using TCP. The actual bear traffic, the voice, uses RTP which is a variant of UDP. UDP is not connection-oriented, like TCP, and because of these, many firwalls and NAT devices block it or just do not route it.

This would explain why the phone rings (that's the call control), but there is no audio and no errors; because UDP is connectionless, there is no error generated when a single packet, or every packet, gets lost en route.

So is there a NAT device on the ATA end? It is possible on some NAT/firewall devices to enable UDP traffic.


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