Subject: RE: [MMUSIC] RFC3264: answer indicate a diff PT number

From: "Attila Sipos" <[email-masked]>
Date: Wed, 2 Mar 2005 16:03:49 -0000

Hi Kevin,

Fortunately, this has just been discussed in the SIP-implementors list.

Go to:
http://lists.cs.columbia.edu/pipermail/sip-implementors/2005-March/thread.html

And look at the e-mails with the title
"Negotiation of dynamic payloads using SDP".

Regards,

Attila

Attila Sipos
http://www.vegastream.com

> -----Original Message-----
> From: [email-masked] 
> [mailto:[email-masked]]On Behalf Of kkuei
> Sent: 02 March 2005 15:57
> To: [email-masked]
> Subject: [MMUSIC] RFC3264: answer indicate a diff PT number
> 
> 
> Hello all,
> 
> I'm a little bit confusing in rfc3264 (offer/answer model 
> with SDP) when 
> answer indicate a diff payload type number case. Is there 
> anybody can help 
> me?? 
> 
> 
> in 5.1, it says: 
>   For sendrecv RTP 
>   streams, the payload type numbers indicate the value of the payload 
>   type field the offerer expects to receive, and would prefer 
> to send. 
>   However, for sendonly and sendrecv streams, the answer 
> might indicate 
>   different payload type numbers for the same codecs, in which case, 
>   the offerer MUST send with the payload type numbers from 
> the answer. 
> 
> in 6.1, it says: 
>   In the case of RTP, if a particular codec was referenced with a 
>   specific payload type number in the offer, that same payload type 
>   number SHOULD be used for that codec in the answer.  Even 
> if the same 
>   payload type number is used, the answer MUST contain rtpmap 
>   attributes to define the payload type mappings for dynamic payload 
>   types, and SHOULD contain mappings for static payload types.  The 
>   media formats in the "m=" line MUST be listed in order of 
> preference, 
>   with the first format listed being preferred.  In this case, 
>   preferred means that the offerer SHOULD use the format with the 
>   highest preference from the answer. 
> 
> My question is, the payload type number in answer may be 
> different than in 
> offer. Here is the case: 
> 
> 1. Offer 
> PCM-WB: 98 
> ISAC: 101 
> iLBC: 102 
> 
> 2. Answer 
> iLBC: 98 
> 
> This means both parties agreed to use iLBC. 
> My questionis , what payload type number should be use in 
> constructing RTP 
> pkts. 
> 
> In sec5.1, (in my understanding) it says offerer MUST respect 
> the answer. It 
> MUST put "98" in 
> payload type number in RTP. 
> 
> But what about in the answerer?? should it respect the offer? 
> which payload 
> type 
> number (102 or 98) it should put in RTP?? 
> 
> 
> 
> --
> Kevin Kuei
> 
> 
> _______________________________________________
> mmusic mailing list
> [email-masked]
> https://www1.ietf.org/mailman/listinfo/mmusic
> 

_______________________________________________
mmusic mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/mmusic