[Freeswitch-dev] DTMF dropped due to remote party re-starting packet numbers from 0 for each digit

[David Knell]

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 at 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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