Re: [Simple] COMEDIA vs MSRP Relays: Shared Connections

["Christer Holmberg" <christer.holmberg at ericsson.com>]

Hi,

More on this. 

>>>>I'm not sure I follow you - Comedia has a "connection:existing"  
>>>>attribute setting to re-use the same connection (e.g., in a new 
>>>>offer).  Or do you mean of two separate media m= lines?
>>>
>>>You are right of course. Brain fart on my part. However, the draft 
>>>should probably mention how to apply this--the only reference I see
to
>>>connection:existing is in the ICE section.
>>
>>Wait, I remember why I brought this up--if a peer is behind an MSRP 
>>relay, how is it to know whether a reuseable connection already exists
>>downstream of that relay?
>
>Even if it knows, how would it tell the relay whether to actually reuse
that connection? I guess that would require some 
>new information element.

We also need to think about the meaning of a=connection.

According to my understanding (I guess we can verify that with the
authors) of comedia, a=connection is not used to indicate that one can
use "any existing TCP connection" towards a specific destination.

My understanding is that a=connection is used during a session
modification, to indicate whether the existing TCP connection for that
specific session should be re-used (if possible) or not. So, for a
specific session, the change of address would always trigger a new TCP
connection - even if there exist TCP connections to the same address for
OTHER sessions.

Or?

>Note, however, that according to section 4.1.3, connection re-use is
not used for initial offer/answers, only for re-
>negotiations.

So, for session establishment, there is currently no difference between
ACM and 4975 - if there is a TCP connection to a specific address, then
use it. 

For 4975, I assume the same applies for session modifications
(eventhough 4975 doesn't explicitly says much about session
modifications)...

ACM currently specifies the usage of a=connection for session
modifications, in accordance with comedia.

So, IF we a=connection to work with relays, I guess we would need to
provide the information to the relay inside the MSRP message.

Again, I will add something about this to my presentation.

Regards,

Christer


>>> -----Original Message-----
>>> From: simple-bounces at ietf.org [mailto:simple-bounces at ietf.org] On 
>>> Behalf Of Ben Campbell
>>>
>>> How does the COMEDIA negotiation interact with the TCP-connection- 
>>> sharing features of MSRP? We negotiate sessions in the SDP offer/ 
>>> answer, not connections per se. COMEDIA implicitly assumes a one-to-

>>> one correspondence between these, but MSRP explicitly allows 
>>> multiple sessions to use the same TCP connection.
>>>
>>> I can see two approaches. One would be that the COMEDIA attributes 
>>> are only relevant if you have to create a new connection. If a 
>>> reusable connection already exists, you just use it. Alternatively, 
>>> we could state that a connection is only reuseable if it's direction

>>> matches the COMEDIA attributes, and if devices wanted to reuse an 
>>> existing connection, they would either omit COMEDIA entirely, or 
>>> choose COMEDIA attributes that match the connection.
>>>
>>> Neither of those approaches seems obviously wrong to me. I suspect 
>>> there may be some traps here, though--we should analyze this pretty 
>>> closely.
>>>
>>> _______________________________________________
>>> Simple mailing list
>>> Simple at ietf.org
>>> https://www.ietf.org/mailman/listinfo/simple
>
> _______________________________________________
> Simple mailing list
> Simple at ietf.org
> https://www.ietf.org/mailman/listinfo/simple

_______________________________________________
Simple mailing list
Simple at ietf.org
https://www.ietf.org/mailman/listinfo/simple
_______________________________________________
Simple mailing list
Simple at ietf.org
https://www.ietf.org/mailman/listinfo/simple