[asterisk-dev] RTP interop with Sonus: hack

Joshua Colp jcolp at digium.com
Mon Jan 5 13:42:32 CST 2009

----- "Kristian Kielhofner" <kristian.kielhofner at gmail.com> wrote:

> Hello everyone,
>   I'm dealing with some Sonus equipment and I've run into the
> infamous
> Sonus RTP timestamp problem.
>   A brief overview for those who might not be familiar:
>   Sonus gateways will discard ANY RTP packets that have the same
> timestamp, even if they are completely different and have the
> sequence
> number properly incremented.  This is in violation of various RFCs.
> Try to get Sonus to do anything about it...
>   This usually manifests itself as an RFC2833 DTMF problem. 
> Currently
> if a Sonus gateway receives an RFC2833 event with the same timestamp
> as a voice packet the event (quite possibly the voice packet too) is
> dropped even though technically, per the RFCs, this is legitimate and
> in some cases preferred behavior (sending two packets with the same
> timestamp).  Even if the sequence numbers are different and the
> duration changes (as is proper with RFC2833 events of variable
> length)
> Sonus will drop at least the non-voice packet on the floor.
>   I don't know how they expect variable length RFC2833 events to work
> with their implementation; by spec these events have the same
> timestamp and sequence number (only increasing the duration).  I
> suppose their RFC2833 handler could process subsequent duration
> updates for RFC2833 events only AFTER an RFC2833 event is handled
> with
> a unique timestamp.  Yeah, or something like that.

A few weeks ago I actually changed the RFC2833 code to do as mentioned and make it use a unique timestamp. In testing this seemed to solve the issue with a few providers (who could have been using Sonus equipment) and cause no issues with any other devices or providers. This should be in the next release of 1.4 and others so this thread may be a noop... would be nifty to test to confirm.

Joshua Colp
Digium, Inc. | Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at:  www.digium.com  & www.asterisk.org

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