[Freeswitch-users] SDP with 2 m=audio lines

[Anthony Minessale]

In your case FS to FS, your FS will parse both m= lines in order they
are put in the sdp and choose the first stream it prefers based on
your codec prefs.  Its functionally identical to putting them all in
one m= line only they are grouped by ptime.





On Tue, Feb 14, 2012 at 12:40 PM, Sergey Okhapkin
<sos at sokhapkin.dyndns.org> wrote:
> But RFC 3388 says (in 1. Introduction):
>
>   An SDP session description typically contains one or more media lines
>   - they are commonly known as "m" lines.  When a session description
>   contains more than one "m" line, SDP does not provide any means to
>   express a particular relationship between two or more of them.  When
>   an application receives an SDP session description with more than one
>   "m" line, it is up to the application what to do with them.  SDP does
>   not carry any information about grouping media streams.
>
>
> On Tuesday 14 February 2012 11:40:40 Anthony Minessale wrote:
>> The word undefined does not even appear in that RFC.
>>
>> RFC 2327 (the one that actually describes SDP) is the relevant one:
>>
>> " A session description may contain a number of media descriptions.
>>    Each media description starts with an "m=" field, and is terminated
>>    by either the next "m=" field or by the end of the session
>>    description.  A media field also has several sub-fields: "
>>
>>
>> The ptime attribute cannot be applied to a single codec mentioned in a
>> m= line it must apply to all of them.
>> Once you have 2 different ptimes in the same description you have no
>> choice but to split it into different m= lines for each sep ptime.
>>
>> If you dislike this behavior then set:
>>
>> sdp_m_per_ptime=false
>>
>> either globally in vars.xml or in your dialplan on a per leg basis.
>>
>>
>>
>>
>>
>>
>>
>> On Tue, Feb 14, 2012 at 7:39 AM, Sergey Okhapkin
>>
>> <sos at sokhapkin.dyndns.org> wrote:
>> > I noticed that recent freeswitch versions could send SDP with 2 m=audio
>> > lines. Per RFC 3388, the behavior is undefined this case. I don't know
>> > how to reproduce the problem, I see such packets coming from my
>> > customers. Here is an example:
>> >
>> > INVITE sip:xxxxxxxxxxxx at sip.callwithus.com SIP/2.0
>> > ...
>> > User-Agent: FreeSWITCH-mod_sofia/1.0.head-git-eeeaf41 2012-02-10
>> > 17-27-50 -0600 ....
>> >
>> > v=0
>> > o=FreeSWITCH 1329167961 1329167962 IN IP4 xx.xx.xx.xx
>> > s=FreeSWITCH
>> > c=IN IP4 xx.xx.xx.xx
>> > t=0 0
>> > m=audio 24598 RTP/AVP 0 101 13
>> > a=rtpmap:101 telephone-event/8000
>> > a=fmtp:101 0-16
>> > a=ptime:30
>> > m=audio 24598 RTP/AVP 98 0 8 3 101 13
>> > a=rtpmap:98 SILK/8000
>> > a=fmtp:98 useinbandfec=1; usedtx=0
>> > a=rtpmap:101 telephone-event/8000
>> > a=fmtp:101 0-16
>> > a=ptime:20
>> >
>> >
>> > Hmm, I just realized that this SDP is buggy - 2 audio streams on the
>> > same
>> > port, with common codecs, but with different ptime :-)
>> >
>> > ________________________________________________________________________
>> > _
>> > Professional FreeSWITCH Consulting Services:
>> > consulting at freeswitch.org
>> > http://www.freeswitchsolutions.com
>> >
>> > 
>> > 
>> >
>> > Official FreeSWITCH Sites
>> > http://www.freeswitch.org
>> > http://wiki.freeswitch.org
>> > http://www.cluecon.com
>> >
>> > 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
>
> _________________________________________________________________________
> Professional FreeSWITCH Consulting Services:
> consulting at freeswitch.org
> http://www.freeswitchsolutions.com
>
> 
> 
>
> Official FreeSWITCH Sites
> http://www.freeswitch.org
> http://wiki.freeswitch.org
> http://www.cluecon.com
>
> 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
GTALK/JABBER/PAYPAL:anthony.minessale at gmail.com
IRC: irc.freenode.net #freeswitch

FreeSWITCH Developer Conference
sip:888 at conference.freeswitch.org
googletalk:conf+888 at conference.freeswitch.org
pstn:+19193869900