Re: [rtcweb] DTLS, DTLS-SRTP, and 5-tuples

["Makaraju, Maridi Raju (Raju)" <[e-mail]>]

> >>When was it agreed that DTLS ClientHello can be sent before the
> >> connectivity check succeeded? I understand >that this will increase the
> >> connection setup time, but I though that no data should be sent before
> the
> >> >connectivity check response (consent) from the remote party.
> >
> >
> >
> > And, if the ClientHello reaches the server BEFORE the connectivity check
> > STUN, how does the server know that it is associated with a given “virtual
> > connection”?
> 
> It just ignores it. Client retransmissions will fix that.
> 
> Anyhow, I'm sorry but I no longer remember whether DTLS (which is just
> media from the ICE point of view) can be sent before receiving the
> STUN response or not. From the point of view of the peer performing
> aggressive ICE nomination, it is sending USE-CANDIDATE Binding
> requests so I can understand that it assumes a "valid-pair" (even if
> it's not replied/confirmed yet by the remote) so media can begin (and
> DTLS is just media).

<Raju>
Aggressive nomination is to avoid 2nd round of checks with USE-CANDIDATE, but not to send media before the nomination is complete. Per [1], nomination is complete only when checks on all valid pairs are complete. A pair becomes "valid" only when you get response. That means, you can't send media (DTLS ClientHello) before you get STUN response.


[1] http://tools.ietf.org/html/rfc5245#section-8.1.1.2

8.1.1.2.  Aggressive Nomination

   With aggressive nomination, the controlling agent includes the USE-
   CANDIDATE attribute in every check it sends.  Once the first check
   for a component succeeds, it will be added to the valid list and have
   its nominated flag set.  When all components have a nominated pair in
   the valid list, media can begin to flow using the highest priority
   nominated pair.  However, because the agent included the USE-
   CANDIDATE attribute in all of its checks, another check may yet
   complete, causing another valid pair to have its nominated flag set.
   ICE always selects the highest-priority nominated candidate pair from
   the valid list as the one used for media.  Consequently, the selected
   pair may actually change briefly as ICE checks complete, resulting in
   a set of transient selections until it stabilizes.

</Raju>

BR
raju