Re: Spin bit as a negotiated option

[<[e-mail]>]

On 10/04/18 23:40, Kazuho Oku wrote:
> 2018年10月4日(木) 19:46 <[e-mail]>:
>>
>> Thanks Kazuho. Using version numbers directly was an obvious choice, but so far
>> I was discouraged by strong language in the spec, saying 0x00000001 was the
>> unavoidable point of convergence after all 0xFF0000XX experiments. So in essence
>> you're proposing to weaken that a bit, right ?
> 
> I am not sure if we have reached consensus that QUICv1 should use
> 0x00000001 as the one and only number for the version number field.
> 
> My understanding is that it is simply written as such because I-D is a
> draft of a RFC. A RFC needs to clarify the value of version number
> field it uses, and I-D needs to have a paragraph that amends on how
> the draft-versions uses the field.

OK, thanks for the clarification.

> I do not think we can segment the version number space, because IMO it
> essentially means making spin bits an invariant. My understanding is
> that spin bits is something specific to v1.
> 
> QUICv1 might use different values on the version number field to
> represent if spin bits is (or other signals are) available, but that
> does not mean that v2 will expose the same signals or they would use
> the version number field for indicating that.
> 
> If it is the case that the use of 0x1xx for V1 might give people the
> impression that the lower bits are used to indicate the availability
> of unencrypted signals across multiple versions, I think starting from
> 0x00000001 (i.e. the one you describe as "direct enumeration") would
> be preferable.

Crystal clear, and agreed:)

>> Also, are we sure that this explosion won't weigh on the new VN scheme, inducing
>> slower convergence due to longer lists on either side ?
> 
> I do not think that is an issue for v1, because what currently at
> stake is if we should assign one or two extra version numbers (i.e.
> one for spin bit, and possibly another for spin+vec as a separate
> draft).
> 
> If folks agree to expose other signals that requires a "configuration"
> to be exposed as well, then they can define a new version number that
> introduces a new field to the long header format for exposing the
> "configuration."

OK. So, wrapping up, and abstracting away for now the bit layout of the version 
number by using symbolic names, we'd start (right after Bangkok) with something 
like:

	- "v1"     = v1 without extensions
	- "v1s"    = v1 with spin bit only
	- "v1svv"  = v1 with spin bit and VEC
	- "v1sqr"  = v1 with spin bit and loss bits Q and R
	- etc (?)

One question though: what part of the version negotiation exchange is in clear ?
IOW, would the selected version always be exposed to the path, or should 
spin-consumers rely on heuristics to guess the variant in use ?




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