[Freeswitch-users] enforcing RTP payload numbers for codecs

[Anthony Minessale]

The server is required to send the client on the payload it requested
regardless of what the server chooses.

RFC 3264:
   Once the answerer has sent the answer, it MUST be prepared to receive
   media for any recvonly streams described by that answer.  It MUST be
   prepared to send and receive media for any sendrecv streams in the
   answer, and it MAY send media immediately.  The answerer MUST be
   prepared to receive media for recvonly or sendrecv streams using any
   media formats listed for those streams in the answer, and it MAY send
   media immediately.  When sending media, it SHOULD use a packetization
   interval equal to the value of the ptime attribute in the offer, if
   any was present.  It SHOULD send media using a bandwidth no higher
   than the value of the bandwidth attribute in the offer, if any was
   present.  The answerer MUST send using a media format in the offer
   that is also listed in the answer, and SHOULD send using the most
   preferred media format in the offer that is also listed in the answer.
   In the case of RTP, it MUST use the payload type numbers
   from the offer, even if they differ from those in the answer.


What is pretty amusing though is from the same RFC:


   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.


So SHOULD means they have no nerve to enforce it because it's ambiguous and
we can choose not to do it.
The MUST in the first example is what we follow.

MAYBE its possible to find a way to prefer the callers pt like we SHOULD,
we'll have to think about it.






On Thu, Jul 8, 2010 at 9:28 AM, Tzury Bar Yochay
<tzury.by at reguluslabs.com>wrote:

> Brian and Anthony,
> Dears,
>
> I am afraid it is a bug in teh FS
> See, if during SDP the client declare on payload 98 and fs declare on 99.
> Then client expect receiving 99 while sending 98. That is fine.
> However, when both clients are the same (as in our case) since FS is not
> trans-coding
> clients receives 98 in
> given that same sip client cannot work with previous versions of FS
> where there Speex was 98 (and 97 in older)
>
>
> On Thu, Jul 8, 2010 at 5:08 PM, Anthony Minessale <
> anthony.minessale at gmail.com> wrote:
>
>> No, you can't force codecs in the dynamic range and if properly
>> implemented, it won't matter what number either side chooses.
>>
>> On Jul 8, 2010 8:34 AM, "Tzury Bar Yochay" <tzury.by at reguluslabs.com>
>> wrote:
>>
>> Hi,
>>
>> I just download the latest, build and brought up all is fine.
>> However, our clients are connected via IP over GPRS(UMTS) and thus we
>> are using Speex codec.
>>
>> Is there a way I can enforce speex to have 97 or 98 instead of 99?
>> Currently as it looks in the vars.xml speex is 99.
>> see dump (taken from default vars.xml)
>>
>> thanks
>> Tzury
>>       RTP Dynamic Payload Numbers currently used in FreeSWITCH and what
>> for.
>>
>>       96  - AMR
>>       97  - iLBC (30)
>>       98  - iLBC (20)
>>       99  - Speex 8kHz, 16kHz, 32kHz
>>       100 -
>>
>> _______________________________________________
>> FreeSWITCH-users mailing list
>> FreeSWITCH-users at lists.freeswitch.org
>> http://lists.freeswitch.org/mailman/listinfo/freeswitch-users
>> UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-users
>> http://www.freeswitch.org
>>
>>
>> _______________________________________________
>> FreeSWITCH-users mailing list
>> FreeSWITCH-users at lists.freeswitch.org
>> http://lists.freeswitch.org/mailman/listinfo/freeswitch-users
>> UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-users
>> http://www.freeswitch.org
>>
>>
>
>
> --
> Tzury Bar Yochay
>
> tzury.by at reguluslabs.com
> + 972 52 5133399
> twitter.com/tzury
>
> _______________________________________________
> FreeSWITCH-users mailing list
> FreeSWITCH-users at lists.freeswitch.org
> http://lists.freeswitch.org/mailman/listinfo/freeswitch-users
> UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-users
> http://www.freeswitch.org
>
>


-- 
Anthony Minessale II

FreeSWITCH http://www.freeswitch.org/
ClueCon http://www.cluecon.com/
Twitter: http://twitter.com/FreeSWITCH_wire

AIM: anthm
MSN:anthony_minessale at hotmail.com <MSN%3Aanthony_minessale at hotmail.com>
GTALK/JABBER/PAYPAL:anthony.minessale at gmail.com<PAYPAL%3Aanthony.minessale at gmail.com>
IRC: irc.freenode.net #freeswitch

FreeSWITCH Developer Conference
sip:888 at conference.freeswitch.org <sip%3A888 at conference.freeswitch.org>
googletalk:conf+888 at conference.freeswitch.org<googletalk%3Aconf%2B888 at conference.freeswitch.org>
pstn:+19193869900
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.freeswitch.org/pipermail/freeswitch-users/attachments/20100708/858c2e12/attachment.html