Re: [MMUSIC] Draft new version: draft-holmberg-mmusic-sdp-dtls-01

[Christer Holmberg <[e-mail]>]

Hi Paul,

Thanks for your comments. See inline.


> * Section 2.1:
>
>    When a new DTLS association is established, an endpoint MUST use a
>    new set of transport parameters (IP address and port combination).
>
> The above seems slightly ambiguous: does "an endpoint" mean "each endpoint" or "one (of the two) endpoints"?
>
> IIUC we have established that the important point is that the 5-tuple must change. So at least one side must change the address or port. But if one > side is known to do so, then the other side need not do so. So I suggest changing the above to:
>
>    When a new DTLS association is established, one of the endpoints
>    MUST use a new set of transport parameters (IP address and port
>    combination).

The idea is that the endpoint(s) which does something the requires a new set of transport parameters needs to use a new set.

So, if e.g. endpoint A wants to change the fingerprint, which requires a new DTLS association, endpoint A needs to use a new set of transport parameters.

> But there may be more to sort out about the o/a protocol for guaranteeing this. I can see a few:
>
> - if the offer has connection:new then the offer must have new
>   transport parameters. Else, if the offer has connection:existing
>   but the answer has connection:new then the answer must have new
>   transport parameters.

Yes.

> - if the answer has connection:new and the offer didn't have new
>   transport parameters, then the answer must have new ones.

Yes.

> Something about the above should probably go into section 6.
>
> * Section 5.1
>
>    A 'connection' attribute value of 'new' indicates that a new DTLS
>    association MUST be established.  A 'connection' attribute value of
>    'existing' indicates that a new DTLS association MUST NOT be
>    established.
>
> I think this is wrong - that the answerer is permitted to answer with connection:new.

The was meant to say that an endpoint sending 'new' needs to use a new set of transport parameters.

However, if the offerer sends 'new', meaning it uses a new set of transport parameters, I am not sure we need to mandate the answerer to use a new set of transport parameters even if it sends 'new' in the answer.

> * Section 6.3
>
>    If an answerer receives an offer that contains an SDP 'connection'
>    attribute with a 'new' value, the answerer MUST insert a 'new' value
>    in the associated answer.  The same applies if the answerer receives
>    an offer that contains an SDP 'connection' attribute with a 'new'
>    value, but the answerer determines (based on the criteria for
>    establishing a new DTLS association) that a new DTLS association is
>   to be established.
>
> I think I previously commented on this: the 2nd sentence "The same applies if ... attribute with 'new' value ...". *That* 'new' should be 'existing' - it > is covering an alternative to the first sentence. And this aligns with my comment above about section 5.1.

I'll have a look at that.

Regards,

Christer