[sipcore] Happy Eyeballs for SIP

[[e-mail] (Dale R. Worley)]

This is the start of getting the Happy Eyeballs for SIP work going in
the working group.

The authors (Olle Johansson, Gonzalo Salgueiro, Dale Worley) are working
with the following strategy (at this time):  The first tranche is the
case where (1) alternative addresses are provided by A and AAAA records
based on one host name, i.e., we are not considering multiple SRV
records, and (2) all of the targets use connection-oriented protocols.
This case is the closest to the Happy Eyeballs for HTTP work that has
already been done, though it has some additional requirements (in
particular, the fact that connections can be idle for a considerable
time, but at unpredictable times, the client wants to use the connection
in a soft-real-time way).

The current draft is named draft-worley-sip-he-connection-01.  (We'll be
revising the name.)

Our idea is to start with an exposition that is not too far beyond the
work for HTTP, so that the discussion remains manageable.  In later
stages, we will produce successive expansions until the entire SIP
operational space is covered.  The expansions can be done by any of
several methods:

- Produce successive RFCs, each of which incorporates the preceding RFC
  but extends it to additional operational space.  Thus, each RFC
  obsoletes and extends its predecessor, so that an implementer only has
  to read the current RFC of the sequence.  (This is the method that we
  prefer at present.)

- Produce successive drafts, each of which covers a larger operational
  space and progress the last one to an RFC.  This will slow the
  standardization of the earlier tranches of the work but reduce the
  overhead of formalizing the drafts as RFCs.

- Produce a series of RFCs, each of which updates the preceding RFCs.
  This seems like the least desirable strategy, as it requires an
  implementer to read several RFCs and collate their provisions.

Let the discussion begin, both on the work and on the plan for the work!

Dale