On Wed, Jul 23, 2008 at 12:51 PM, Ruud Klaver <ruud at ag-projects.com> wrote:
> Hi,
>
> I'm trying to use the SDP negotiation part of pjmedia to process SDP
> related to MSRP (RFC 4975), but ran into some issues when it tried to
> complete the negotiation procedure. The process_m_answer function
> assumes that the formats in the m= line are integers and starts
> looking for rtpmap attributes, while for MSRP the formats aren't
> actually used and are set to a single "*".
>
>
Actually it's not that bad, we have this in sdp_neg.c:618:
/* Find matching answer */
pt = pj_strtoul(fmt);
if (pt < 96) {
for (j=0; j<answer->desc.fmt_count; ++j) {
if (pj_strcmp(fmt, &answer->desc.fmt[j])==0)
break;
}
The idea is if pt is not a payload type number, pj_strtoul() should return 0
and the "if (pt<96)" checking above will be executed and it shouldn't need
to check for rtpmap.
But alas, there seems to be a bug in pj_strtoul(). Instead of stopping when
it finds a non-digit character, it continues to treat the input as digit,
causing it to return garbage value. I've just fixed this in the latest SVN.
> Maybe there should be a check to see if the protocol field (called
> transport in pjsip) starts with RTP, as RFC 4566 states:
>
>
I believe "proto" is shorthand for "transport protocol", so calling it
transport is not too far off . :)
> If the <proto> sub-field is "RTP/AVP" or "RTP/SAVP" the <fmt>
> sub-fields contain RTP payload type numbers.
>
> But also:
>
> If the <proto> sub-field is "udp" the <fmt> sub-fields MUST
> reference a media type describing the format under the "audio",
> "video", "text", "application", or "message" top-level media
> types.
>
> ...
>
> For media using other transport protocols, the <fmt> field is
> protocol specific.
>
> But then the question is, how would pjmedia declare the negotiation to
> have succeeded?
>
>
Currently, if both media type and transport protocol match, and there is
matching format. That's probably good enough for MSRP.
Cheers
Benny
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