[SIPForum-discussion] Is "fmtp" line needed in 200 OK answer?

Thu Dec 13 02:05:15 UTC 2007

#any other settings that you can try with the sip phone? such as the
priority of the codec. adjust the g729 codec's priority.
#maybe there are still other reasons cause this issue. Who sends the BYE?
the AS or SBC?

On 12/12/07, Andrea Puddu <androjoker at hotmail.com> wrote:
>
>  Thanks for your analysis.
>
> By chance, I've just found a parameter on the phone that can help me  ->
> "Full SDP Answer" .... I've switched it to OFF.
> Now the phone sends only one codec in the 200 OK response (g729), but
> without the "fmtp" line.
> So the phone starts talking in G729 but AS (or SBC) sends a BYE to the
> phone!!!!!
>
> I'm starting to think that SBC does not like the lack of "fmtp" filed in
> the response .....
>
> Andrea
>
>
>
>  ------------------------------
> From: herve.jourdain at mstarsemi.com
> To: androjoker at hotmail.com; baolovebao at gmail.com
> CC: discussion at sipforum.org
> Subject: RE: [SIPForum-discussion] Is "fmtp" line needed in 200 OK answer?
> Date: Wed, 12 Dec 2007 11:25:55 +0100
>
>  Hi,
>
>
>
> As far as I remember of RFC 3264, the devices should be prepared to
> receive ANY of the codecs it sends in its offer/response…
>
> So basically, if you respond with 3 codecs, you should be able to receive
> at any time on any of those 3 codecs, and switch between them…
>
> That's why it seems customary on several phones to answer with only one
> codec…
>
>
>
> But even if it's stated this way in the specs, I still do think that
> before switching to another codec, the UAs should at least use the codec
> that was agreed for in the negotiation at first (the "highest priority" one,
> in your case G729).
>
> Experience shows, unfortunately, that even if it's usually the case, it's
> NOT ALWAYS the case…
>
> I think you might have an example here, and I know I've met several
> devices – phones or gateways usually – that would also behave in this way…
>
>
>
> So maybe try with only 1 codec in the response, to see if it works better…
>
>
>
> But if you do so, please switch to outband DTMF (RFC 2833 or RFC 4733),
> because once you give only G729 in the answer there should not be any
> possibility to switch to G711 for in-band DTMF.
>
> And your SDP suggests outband DTMF is not activated.
>
>
>
> Regards,
>
>
>
> Herve
>
>
>  ------------------------------
>
> *From:* discussion-bounces at sipforum.org [mailto:
> discussion-bounces at sipforum.org] *On Behalf Of *Andrea Puddu
> *Sent:* mercredi 12 décembre 2007 09:35
> *To:* Donald Lee
> *Cc:* discussion at sipforum.org
> *Subject:* Re: [SIPForum-discussion] Is "fmtp" line needed in 200 OK
> answer?
>
>
>
> I agree with your analysis. I've noticed that for example Cisco and
> Linksys phone sends only one codec in the 200 OK SDP envelope.
>
> But... Can the sending of multiple codec in the 200 OK response be an
> issue?
> I cannot complain with phone provider about this behaviour.
>
> Anyway why does the phone talk with G729 and AS talk with G711?  I'm
> wondering if the AS performs a check on  fmtp field in the 200 OK response
> .................
>
>
> Thanks,
>
> Andrea
>
>
>
>  ------------------------------
>
> Date: Wed, 12 Dec 2007 16:24:05 +0800
> From: baolovebao at gmail.com
> To: androjoker at hotmail.com
> Subject: Re: [SIPForum-discussion] Is "fmtp" line needed in 200 OK answer?
> CC: discussion at sipforum.org
>
> # the "g" and "G" have no difference. and the offer indicate that it's not
> G729B codec.
>
> # I don't think the lack of fmtp in answer is the reason for issue. Maybe
> the ip phone should reply only one codec in its SDP. Maybe the multi codec
> in answer make the offer confused.
>
>
>
> On 12/11/07, *Andrea Puddu* <androjoker at hotmail.com> wrote:
>
> Hello guys,
>
> I'm facing an issue when a mobile (common mobile 3G phone) tries to call
> an internal SIP phone through its geographical number.
> The issue is that when the SBC sends the INVITE to the IP phone,  in the
> SDP  enclosure it  suggests these codecs:
>
> m=audio 19570 RTP/AVP 18 8 0
> a=rtpmap:18 G729/8000
> a=fmtp:18 annexb=no
> a=rtpmap:8 PCMA/8000
> a=rtpmap:0 PCMU/8000
>
> The 200 OK of the phone (SDP part only) is:
>
> m=audio 57956 RTP/AVP 18 8 0
> a=rtpmap:18 g729/8000
> a=rtpmap:8 pcma/8000
> a=rtpmap:0 pcmu/8000
> a=sendrecv
>
> So the IP phone start to talk with G729 and SBC replies with G711A!!! So I
> can't hear the voice coming from mobile phone!!!!
>
> I have two questions:
>
> - Can the difference between the offer (G729) and the answer (g729) be
> significant? I mean the difference because the "g" is not capital in the
> answer
> - Can the lack of the "fmtp" line in the answer cause troubles?
>
>
> Thanks 1000,
>
> Andrea
>
>
>
>
>
>
>  ------------------------------
>
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>
> --
> BR
> Donald
>
>
>  ------------------------------
>
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-- 
BR
Donald
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