Re: [MMUSIC] Not fixing a=rtcp and rtcp-mux exclusive

[Christer Holmberg <[e-mail]>]

Hi,

>>> We can for sure define a new attribute, if people prefer that.
>>>
>>> But, it still wouldn't solve Paul's issue, that a non-ICE endpoint that doesn't support the attribute may
>>> start sending RTCP on RTP+1. But, at least the offerer would see from the answer that the answerer does 
>>> not support mux-exclusive, and can take proper actions.
>>>
>>> We can define new attribute that specifies address and port for both RTP and RTCP similar to ICE candidate 
>>> or a=rtcp attribute and set address in c= line to IN IP4 0.0.0.0. This way any end point that does not understand 
>>> this attribute will send no media.
>>
>> Another option would be to set the m- line port to zero, like we do for bundle-only. Then, if the answerer 
>> doesn't support the attribute, it won't use the m- line.
>>
>> Example:
>>
>> c=IN IP4 11.22.33.44
>> m=0 RTP/AVP 0 99
>> a=mux-exclusive: 12345  <------- 12345 is the port to be used for RTP and RTCP
>>
>> One problem with this solution is that an intermediary that doesn't support the attribute won't know where to 
>> forward the media, it the m- line port value is 0. It very likely will assume there will be no media to begin with.
>
> I always wondered what intermediary we are talking about which is supposed to know where to forward media. If 
> we are talking about firewalls which dynamically open ports, then, most of the time it has no access to signaling information 
> due to use of secure channels. If we are talking about something that does something to the media and forwards it (rtp proxy 
> in combination with sip proxy), then we actually want such proxy to support rtcp mux exclusive or fail the connection for 
> the same reason we want regular end points to fail during connection setup -- to prevent RTCP from being sent to 
> unexpected destination.

If such proxy only forwards what it receives, it doesn't need to support mux-exclusive. It only forwards what it gets. However, if it sees an m- line with port 0, it may not forward anything.

Regards,

Christer