That's very much true. It's a major issue for interoperatability. During the sip interop (SIPIT-12) event we observed that having the media attributes match (such as vif size, silence suppression etc.,) at both ends required a manual intervention several times (reconfiguring) due to the confusion with the current SDP definitions/implementations.
-Satya Telogy Networks A Texas Instruments Company -----Original Message----- From: Christer Holmberg [mailto:[EMAIL PROTECTED] Sent: Tuesday, March 25, 2003 1:21 AM To: Hearty, John Cc: Attila Sipos; [EMAIL PROTECTED]; link.xie; Christian Stredicke; [EMAIL PROTECTED] Subject: Re: [Sip-implementors] SDP packet times for muliple codecs Hi, I would suggest taking this question to the mmusic list. This could affect many codec related attributes, and not only ptime, so I think it is an important issue. Regards, Christer (lmfchh) "Hearty, John" wrote: > Christer, > > I believe Attila is correct. To do it the way you suggest would mean > each ptime attribute would need to be position sensitive to match up > with the appropriate codec. This behavior is not described anywhere > in RFC2327, and would need to be for implementations to be > interoperable. There are also some mentions of ptime handling in > RFC3264, and they do not suggest this behaviour. Those mentions > appear to indicate one ptime attribute associated with one stream. > > This issue has been discussed a few times before on mmusic, it may be > more appropriate to continue the discussion there if needed. I think > the bottom line is most implementations probabally associate one ptime > attribute to one m line. The only way to get different ptimes for a > stream is to omit the attribute completely when specifying multiple > codecs with different default times, such as G711 & G723. May have to > wait for sdpng to do this as desired. > > John Hearty > Level3 > > > -----Original Message----- > > From: Christer Holmberg [mailto:[EMAIL PROTECTED] > > Sent: Sunday, March 23, 2003 11:20 AM > > To: Attila Sipos > > Cc: [EMAIL PROTECTED]; link.xie; 'Christian Stredicke'; > > [EMAIL PROTECTED] > > Subject: Re: [Sip-implementors] SDP packet times for muliple codecs > > > > > > > > Hi, > > > > Which "rules" are you refering to? RFC2327 does say ptime is a media > > attribute, but I can't find anywhere said that you can't specify > > separate values for specific codecs (using it together with rtpmap). > > Please tell me if > > I'm wrong. > > > > Regards, > > > > Christer Holmberg > > Ericsson Finland > > > > > > > I think the problem is that (according to the rules) the ptime > > > attribute is not related to a specific profile but to a specific > > > media description: > > > > m=audio 10000 RTP/AVP 0 8 > > > > a=rtpmap: 0 PCMU/8000 > > > > a=ptime:20 > > > > a=rtpmap: 8 PCMA/8000 > > > > a=ptime:30 > > > > > > So I guess, officially, you can only really have one ptime > > > parameter associated with each "m=" line. Personally I can't see > > > why we couldn't use multiple packet times in the way you suggested > > > but maybe it'll break some implementations. I don't know. > > > > > > As a recap, I remember the various other proposals to > > handle the multiple > > > profiles: > > > m=audio 10000 RTP/AVP 0 8 > > > a=mptime:20 30 > > > a=rtpmap: 0 PCMU/8000 > > > a=rtpmap: 8 PCMA/8000 > > > > > > or: > > > m=audio 10000 RTP/AVP 0 8 > > > a=x-ptime:20 30 > > > a=rtpmap: 0 PCMU/8000 > > > a=rtpmap: 8 PCMA/8000 > > > > > > I have another idea: be explicit about the packet times used for > > > each profile (like with rtpmap): > > > > > > m=audio 10000 RTP/AVP 0 8 > > > a=rtpmap: 0 PCMU/8000 > > > a=rtpmap: 8 PCMA/8000 > > > a=ptimemap: 0 20 > > > a=ptimemap: 8 30 > > > > > > But, as you can see, it's less efficient that the mptime or > > > x-ptime parameters. > > > > > > Can anyone say how far away we are before all this "mulitple > > > packet time" stuff is standardised? > > > > > > Attila > > > > > > > -----Original Message----- > > > > From: Christer Holmberg > > > > [mailto:[EMAIL PROTECTED] > > > > Sent: 19 March 2003 22:43 > > > > To: [EMAIL PROTECTED] > > > > Cc: link.xie; Attila Sipos; 'Christian Stredicke'; > > > > [EMAIL PROTECTED] > > > > Subject: Re: [Sip-implementors] SDP packet times for > > muliple codecs > > > > > > > > > > > > > > > > Hi, > > > > > > > > Why don't you use normal RTPMAP stuff, without any extensions > > > > and/or x- parameters? > > > > > > > > Your SDP would look like: > > > > > > > > m=audio 10000 RTP/AVP 0 8 > > > > a=rtpmap: 0 PCMU/8000 > > > > a=ptime:20 > > > > a=rtpmap: 8 PCMA/8000 > > > > a=ptime:30 > > > > > > > > Or, have I missunderstood your issue? > > > > > > > > Regards, > > > > > > > > Christer Holmberg > > > > Ericsson Finland > > > > > > > > > > > > > > > > [EMAIL PROTECTED] wrote: > > > > > > > > > Hi all, > > > > > > > > > > I think Link.xie is right that till the attribute is > > > > > registered 'X-mptime' should be the attribute name used. > > > > > > > > > > Though, we should move towards standardizing this attribute in > > > > > a draft.... because chances are other implementations will not > > > > > understand this unregistered attribute and may lead to > > > > > inter-op issues later. PacketCable seems to have taken a step > > > > > forward already in this regard. > > > > > > > > > > PS: Some more digging into the archive shows that we did > > > > > agree to bring out a draft on the 'mptime' attrib > > > > > for exactly the same reason.... Perhaps Kevin and > > > > > Colin could tell if one is already on its way :) > > > > > Else we can prepare one now ? > > > > > > > > > > (ref: > > > > > > > > > http://www1.ietf.org/mail-archive/working-groups/mmusic/curren > > > > t/msg01030.ht > > > > > ml) > > > > > > > > > > Cheers, > > > > > Siddharth. > > > > > > > > > > -------------------------------------------------------- > > > > > Siddharth Toshniwal > > > > > Hughes Software Systems > > > > > Prestige Opal http://www.hssworld.com > > > > > 146, Infantry Road Ph (O): +91-80-2286390 (7094) > > > > > Bangalore-560001, India Mobile: +91-9845154068 > > > > > -------------------------------------------------------- > > > > > > > > > > "link.xie" <[EMAIL PROTECTED]> on 03/12/2003 04:49:12 PM > > > > > > > > > > To: "Attila Sipos" <[EMAIL PROTECTED]>, "'Christian > > > > Stredicke'" > > > > > <[EMAIL PROTECTED]> > > > > > cc: [EMAIL PROTECTED] (bcc: Siddharth J > > > > Toshniwal/HSSBLR) > > > > > > > > > > Subject: Re: [Sip-implementors] SDP packet times for > > muliple codecs > > > > > > > > > > I think X-mptime is better. Cause in rfc2327, "Unregistered > > > > > attributes should begin with "X-" to > > > > prevent inadvertent > > > > > collision with registered attributes" > > > > > > > > > > ----- Original Message ----- > > > > > From: "Attila Sipos" <[EMAIL PROTECTED]> > > > > > To: "'Christian Stredicke'" <[EMAIL PROTECTED]>; "'link.xie'" > > > > > <[EMAIL PROTECTED]>; "Attila Sipos" <[EMAIL PROTECTED]> > > > > > Cc: <[EMAIL PROTECTED]> > > > > > Sent: Wednesday, March 12, 2003 4:44 PM > > > > > Subject: RE: [Sip-implementors] SDP packet times for > > muliple codecs > > > > > > > > > > > > > > > > > Hello all, > > > > > > > > > > > > Link Xie, thanks for your response: > > > > > > > > m=audio 10000 RTP/AVP 0 8 > > > > > > > > a=X-ptime: 20 30 > > > > > > > > > > > > Following Siddharth's link > > > > > > > > > > > > > > > http://lists.cs.columbia.edu/pipermail/sip-implementors/2003-F > > > > ebruary/00455 > > > > > 6 > > > > > > .html > > > > > > > > > > > > It seems that from this link the answer is to use "mptime": > > > > > > > > > > > > >So instead of redefining ptime, create a new "mptime" > > > > parm that has a > > > > > > >construct similar to the m line: > > > > > > > > > > > > > >m=audio 49170 RTP/AVP 0 4 18 > > > > > > >A=mptime:10 30 30 > > > > > > > > > > > > > > > > > > > The packetcable spec (from > > > > http://www.packetcable.com/specifications/ ) > > > > > > > > > > http://www.packetcable.com/downloads/specs/PKT-SP-EC-MGCP-I06- > > > > 021127.pdf > > > > > > also seem to use mptime: > > > > > > > > > > > > (taken from PacketCable(tm) Network-Based Call > > Signaling Protocol > > > > > > Specification) > > > > > > > > > > > > m=audio 3456 RTP/AVP 96 97 0 > > > > > > a=rtpmap:96 G726-32/8000 > > > > > > a=rtpmap:97 telephone-event/8000 > > > > > > a=mptime: 10 - 10 > > > > > > > > > > > > Here, rfc2833 doesn't have a packet time so it's > > shown with a '-' > > > > > > (rfc2833 is supposed to have the same packet time as > > the selected > > > > > > audio codec). > > > > > > > > > > > > > > > > > > Which is correct mptime or X-ptime? > > > > > > > > > > > > > > > > > > Regards, > > > > > > > > > > > > Attila > > > > > > > > > > > > > > > > > > > -----Original Message----- > > > > > > > From: Christian Stredicke [mailto:[EMAIL PROTECTED] > > > > > > > Sent: 12 March 2003 08:31 > > > > > > > To: 'link.xie'; 'Attila Sipos' > > > > > > > Cc: [EMAIL PROTECTED] > > > > > > > Subject: AW: [Sip-implementors] SDP packet times for > > > > muliple codecs > > > > > > > > > > > > > > > > > > > > > The "X-" is a bad idea. We were using this in another > > > > > > > scenario and many SDP parsers complained about "x-" > > > > > > > headers. Better use something without > > > > > > > "x-" (e.g. "xptime"). > > > > > > > > > > > > > > Christian > > > > > > > > > > > > > > > -----Urspr > > > > > > > > > > > > > > -------------------------------------------------------------- > > > > ---------- > > > > > > > > > > �ngliche Nachricht----- > > > > > > > > Von: [EMAIL PROTECTED] > > > > > > > [mailto:sip-implementors- > > > > > > > > [EMAIL PROTECTED] Im Auftrag von link.xie > > > > > > > > Gesendet: Mittwoch, 12. M�rz 2003 03:46 > > > > > > > > An: Attila Sipos; [EMAIL PROTECTED] > > > > > > > > Betreff: Re: [Sip-implementors] SDP packet times for > > > > muliple codecs > > > > > > > > > > > > > > > > Hi,Attila > > > > > > > > I think your suggestion is wrong. We also use > > > > this solution > > > > > > > before. > > > > > > > > But we find that the meaning of 2 "m=" line repesent > > > > 2 media stream. > > > > > > > So > > > > > > > > it's not suitalbe for this case. > > > > > > > > Our solution is introducing a new attribut > > > > > > > > "X-mptime" > > > > > > > which means > > > > > > > > multiple ptime > > > > > > > > and the SDP would like: > > > > > > > > > > > > > > > > m=audio 10000 RTP/AVP 0 8 ----- 0 means g711u-law > > > > > > > and 8 means > > > > > > > > g711a-law > > > > > > > > a=X-ptime: 20 30 -----20 for > > > > > > > g711u 30 for > > > > > > > > g711a > > > > > > > > > > > > > > > > I think this can solve your problem > > > > > > > > > > > > > > > > Best Regard > > > > > > > > Link.Xie > > > > > > > > ----- Original Message ----- > > > > > > > > From: "Attila Sipos" <[EMAIL PROTECTED]> > > > > > > > > To: <[EMAIL PROTECTED]> > > > > > > > > Sent: Tuesday, March 11, 2003 7:33 PM > > > > > > > > Subject: [Sip-implementors] SDP packet times for > > > > muliple codecs > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hello everyone, > > > > > > > > > > > > > > > > > > For multiple codecs we can have an SDP like this: > > > > > > > > > m=audio 10000 RTP/AVP 0 8 ----- 0 means > > > > g711u-law and 8 means > > > > > > > > g711a-law > > > > > > > > > a=ptime:20 > > > > > > > > > But this is only correct if the packet times match for > > > > > > > > > u-law and a-law. > > > > > > > > > > > > > > > > > > > > > > > > > > > What if you have a system where, for some reason, the > > > > > > > > > codecs have different packet times? > > > > > > > > > > > > > > > > > > Can you do this? > > > > > > > > > m=audio 10000 RTP/AVP 0 - ---- g711-ulaw > > > > > > > > > a=ptime:20 > > > > > > > > > m=audio 10000 RTP/AVP 8 ---- g711 a-law > > > > > > > > > a=ptime:30 > > > > > > > > > > > > > > > > > > Regards, > > > > > > > > > > > > > > > > > > Attila > > > > > > > > > > > > > > > > > > <http://www.vegastream.com> > > > > > > > > > VegaStream : A World of difference for your Integrated > > > > > > > Communications > > > > > > > > _______________________________________________ > > Sip-implementors mailing list [EMAIL PROTECTED] > > http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors > > _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list [EMAIL PROTECTED] http://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
