[vwrap] VWRAP and IPv6

[Morgaine <[e-mail]>]

Despite exceedingly low takeup of IPv6 so far, it's coming, and in the
context of IETF WG rates of progress, it is really imminent.  Of special
relevance to us is that IPv4 addresses are projected to run out within
roughly the same time frame as VWRAP materializes.

There is little point in creating a new VW protocol today purely in the
context of IPv4 without thinking about tomorrow's IPv6 environment.  By the
time that VWRAP is fully defined, we should expect a substantial and rapidly
increasing proportion of VWRAP implementations to occur in IPv6-accessible
worlds.  This is a situation for which we need to plan now, otherwise the
protocol will be obsolete before it's even ready.

To get the ball rolling, here are a few IPv6-related issues that we could
usefully address in the group:


   - The 128-bit IP address of IPv6 is likely to become a common payload, so
   it should be supported natively.  LLSD already supports one 128-bit data
   type of course, the UUID.  IPv6 addresses should not be transported in UUID
   fields however, since their statistical properties and semantics are totally
   different.  In any case, the two spaces are disjoint so confusing them would
   be a mistake.  The IPv6 address seems a good candidate for its own defined
   type, in the absence of wide integers.


   - The extremely large address space of IPv6 has often been portrayed as
   allowing everything around us to have its own IP address.  In the context of
   virtual worlds, this idea can actually be put to good use, with each virtual
   object bearing its own IPv6 address.  One candidate application for this has
   already been described in earlier discussions --- for example, implementing
   virtual object simulation in two parts, one client-side and one world-side,
   the two parts communicating directly.  IPv6 addressing of objects makes this
   relatively easy to achieve efficiently, so its implementation in IPv6-based
   worlds is almost inevitable before long.  VWRAP should be ready for this.


   - The event queue in current implementations provides an indirect and
   highly inefficient way of achieving world-to-client communications.  IPv6
   offers opportunities for direct communication that can make the event queue
   approach obsolete, so it's worth examining IPv6-oriented alternatives.


   - We recently discussed feature and protocol negotiation within VWRAP.
   IPv6 provides much opportunity for new features and protocol pathways to be
   negotiated between endpoints, so it gives us a very real and imminent set of
   use cases for negotiation.


It would also be a feather in VWRAP's cap to be considered an "IPv6-capable
application protocol" in a stronger sense than just to be carried by IPv6
networks.  IPv6 does after all bring new abilities to the table, such as the
huge addressing, and it would be a mistake to ignore them.


Morgaine.