Subject: [sipcore] Remaining Happy Eyeballs work, the hard part

From: [email-masked] (Dale R. Worley)
Date: Wed, 18 May 2016 15:52:27 -0400

A solution is needed for simple UDP, where "simple" means "without a
full implementation of SIP Outbound".

There are a number of decidedly different ways that this need might be
satisfied.  The ones that I can think of are:

- documenting a suitable subset of SIP Outbound (if one exists)

It's possible that the SIP Forum is already doing this in practice.  If
so, that would overcome the problem that Output implementations are not
ubiquitous.

- a lightweight SIP/DTLS (the cryptographic setup creates a flow)

- the registration message flow from the UA is sufficient to keep the
  cached reachability information up to date

This is really "client-side NAT compensation", where the SIP registrar
records the NAT-external address of the UA rather than its interface
address.  It seems like a lot of SIP systems do this, which means that
it works well in practice.  (Is it possible/reasonable to specify this
process?  Is that any simpler than specifying Outbound?)

- a mechanism to send simultaneous redundant requests to multiple
  addresses without causing problems with merged requests

This is largely agreed to be too large an extension for this work.

This is just a summary of where we are on this issue, as there has been
discussion pointing to possible solutions and the relationship with
other work (especially SIPConnect 2.0), but I don't have the time right
now to incorporate everything we've discussed into this list.

Dale

---

From: Paul Kyzivat <[email-masked]>
Date: Thu, 19 May 2016 15:55:31 -0400

> - documenting a suitable subset of SIP Outbound (if one exists)

I was thinking this was brought up because outbound wasn't defined for a 
single connection. But then I looked and think that it is. So what is 
needed here?

> - a lightweight SIP/DTLS (the cryptographic setup creates a flow)

ISTM this would be a good think on general principles, and if it helps 
with happy eyeballs then all the better.

Of course DTLS decreases the max sip message size before fragmentation, 
hence limiting further when it will be useful. Those who have carefully 
optimized to fit within UDP might find that they don't fit with DTLS.

The key is if there is interest in supporting this work. (Both a spec, 
and implementations of it.)

	Thanks,
	Paul

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