Subject: Re: [sipcore] Outline of Happy Eyeballs for SIP

From: [email-masked] (Dale R. Worley)
Date: Tue, 01 Mar 2016 11:39:09 -0500

"Olle E. Johansson" <[email-masked]> writes:
>>    C. Two or more addresses may be contacted simultaneously rather than
>>    sequentially if provisions are made to avoid merged requests:
>
> Again, this only applies to UDP.

I don't see this as limited to UDP.  If Happy Eyeballs processing
decides to race two TCP connections to their targets (typically one IPv4
and one IPv6), ideally we don't want to have to wait a complete RTT
before a the request can be sent.  Better to send the request along with
the SYN packet on one connection, so if we don't have to fail over to
the other connection, we don't lose an RTT.

> The migration to IPv6 needs to be easy, and asking for dual simultaneous
> connections over TCP/TLS is big enough for many implementations. Implementing
> a whole new proxy merge scheme in the same document will in my view make it as
> ignored as SIP outbound currently is

I see the merge scheme as being *much easier* to implement than
Outbound, and probably simpler than dual simultaneous connections in
TCP.

> b) recommending server side DNS SRV separation, one prio per address family,
>     no dual stack hosts for UDP

If you use SRV to prioritize address families, then don't hosts that
can't access the destination with its preferred address family pay an
RTT penalty?  Or actually, a connection-timeout penalty?

Dale