Hi Andy -

I think:

1 - more not non-compliant, if you see what I mean;

2 - probably, given the change in SSRC

3 - nor could I

4 - I suspect that accepting packets with any sequence number immediately after a change of SSRC should be safe, and it looks like a reasonably straightforward change to handle_rfc2833 to cope with this situation.

--Dave

On Mon, Jan 18, 2021 at 12:02 PM Andy Newlands <andynewlands@gmail.com> wrote:

Hi,

A 3rd-party is sending each RFC2833  DTMF digit with a new SSRC and starts the packet sequence numbering at ZERO for each new digit.

I can see, in switch_rtp.c: handle_rfc2833(), that FS makes a note (in the session) of the last DTMF packet it processed, then drops any subsequent packets with a sequence number less than that.  

My questions are:

1. Is the remote-party compliant with relevant RFCs when they set a new SSRC for each DTMF digit?

2. Is the remote party compliant with relevant RFCs when they re-start packet sequence numbers from 0 for each DTMF digit?

3. Looking at the source for handle_rfc2833(), I can't see any setting which could be used to force FS to 'tolerate' the above behaviour

4. If I alter handle_rfc2833(), to cope with that behaviour, am I likely to run into problems with other remote systems (E.G. possibly ending up with duplicate digits)

Thanks,

Andy

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_________________________________________________________________________

The FreeSWITCH project is sponsored by SignalWire https://signalwire.com
Enhance your FreeSWITCH install with disruptive priced SMS and PSTN services.
Build your next product on our scalable cloud platform.

Join our online community to chat in real time https://signalwire.community

Professional FreeSWITCH Services
sales@freeswitch.com
https://freeswitch.com

Official FreeSWITCH Sites
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https://freeswitch.org/confluence
https://cluecon.com

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