Re: [bfcpbis] Eric Rescorla's Discuss on draft-ietf-bfcpbis-rfc4583bis-26: (with DISCUSS and COMMENT)

[Christer Holmberg <[e-mail]>]

Hi,

>>>>>>> S 5.5.
>>>>>>>      'bfcpver' attribute in offers and answers.  The attribute value, if
>>>>>>>      present, MUST be in accordance with the definition of the Version
>>>>>>>      field in [I-D.ietf-bfcpbis-rfc4582bis].  If the attribute is not
>>>>>>>      present, endpoints MUST assume a default value in accordance with
>>>>>>>      [I-D.ietf-bfcpbis-rfc4582bis]: when used over a reliable transport
>>>>>>>      the default attribute value is "1", and when used over an unreliable
>>>>>>
>>>>>> Just for clarity: UDP over TURN-TCP is an unreliable transport, right?
>>>>>
>>>>> I would assume so, but I guess that question is not BFCP specific?
>>>>>
>>>>> Sorry, what I mean is "does BFCP count it as an unreliable transport". I agree it is unreliable.
>>>>
>>>> Do you think we need to add some text about it?
>>>>
>>>> Related to that, if ICE is used, if both UDP and TCP candidates are offered, endpoints might not know what kind of transport will eventually 
>>>> be selected. Perhaps there should be a note about that?
>>>>
>>>> Something like:
>>>>
>>>> "Note: When ICE is used, where the candidates represent both reliable and unreliable transports, the ICE process will determine what type of transport will eventually be used."
>>>
>>> Well, ICE can flip-flop the transport, so I think if you have anything other than ICE-TCP (which is to say anyone who uses ICE) then you have to assume it's unreliable
>>
>> My point was that when you send the offer, and set the 'bfcpver' attribute value, if you use ICE you may not yet know whether the transport will eventually be reliable 
>> or unreliable (if you offer candidates for both reliable and unreliable transports).
>> I guess we could say that the attribute value must match the transport indicated in the 'm' line. That way things will be correct if the remote peer does not support ICE.
>
> i don't really know what this attribute is used for so it's hard for me to say.
>
> Can you explain what it does?

It's used to negotiate the BFCP version. The default values are based on whether the transport is reliable or unreliable, which is a little strange, but 4583bis endpoints will always explicitly include it so there is no issues. I withdraw my comment :)

Regards,

Christer