Heads up -- unifying of multipath options.

[Christian Huitema <[e-mail]>]

When we presented the work on QUIC multipath at the last IETF, we 
provided two options: one in which there is a packet number space for 
each path; and one in which there is a single number space. The high 
level summary is that the "number space per path" option allows for more 
precise management of packet loss recovery and congestion control, while 
the single number space option also works well if one of the peers use 
zero-length CID. The authors believe that we can "unify" the two 
options, as explained in the PR 
https://github.com/quicwg/multipath/pull/103.

The PR essentially proposes to use the "packet number space per path" 
option when both peers generate non-zero-length connection ID, but to 
fall back to the "number space per path" option for managing packets 
sent with a zero-length CID and their acks. That, plus a number of nice 
provision to control code complexity. The issue was discussed on this 
list, in WG meetings, and on Github. We know that many WG members care 
about multipath and have either preferences for one or the other option, 
or maybe opinions about how soon we need to converge. It would be very 
nice if we heard opinions quickly, and even better if those opinions 
came before the draft submission cut-off date!

-- Christian Huitema