Re: Spin bit as a negotiated option

[<[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 ?

If so, how do you envision segmenting the version number space ?

  - direct enumeration:

	0x00000001 = v1dry
	0x00000002 = v1 + spinbit
	0x00000003 = v1 + spinbit + VEC
	
  - low order bits for options:

	0x000001XX = v1 + option XX
	0x000002YY = v2 + option YY

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 ?

On 10/04/18 11:50, Kazuho Oku wrote:
> Hi,
> 
> Thank you for starting the discussion specific to how we could
> possibly negotiate the use of spin bits.
> 
> Regarding the topic, my preference goes to using the version number
> field of the long header for negotiating the presence of spin bits, or
> any additional signal being exposed to the network.
> 
> For example, QUICv1 without spin bit could use version 0x101, and v1
> with spin bit could use 0x102. In the future, we can assign a
> different version number for QUICv1 with multiple spin + VEC (or
> people interested in testing the feature can designate a private
> version number even before that).
> 
> I see the following benefits to using the version field as a method to
> negotiate the use of spin bits.
> 
> 1. One of the concern regarding spin bits has been that they could
> lead to ossification. Spin bits are not part of the Invariants, but if
> the observation tools start looking at those bits without checking the
> version number field, we will have the pressure to not change how the
> bits are used. Using the version number to indicate the presence of
> spin bits is the best approach to resolve such concern.
> 
> 2. We have hoped to roll out multiple versions of QUIC in a small
> interval so that the version number field does not get ossified. The
> best solution is obviously to roll out two flavors of the protocol
> that uses different version numbers at the same time. We will have a
> real-world use of version negotiation from day one, because we are in
> a condition where implementors have different opinions on if they
> should support spin bit :-)
> 
> The blocker to this approach has been version negotiation requiring an
> additional round-trip, but that is going to be resolved by #1755.
> 
> 2018年10月3日(水) 19:06 <[e-mail]>:
>>
>> On 10/03/18 09:58, Brian Trammell (IETF) wrote:
>> > Backing off the MUST for now for such situations is IMO a good tradeoff,
>> > though, especially since we only need fractions of a percent of deployment to
>> > start seeing useful signal for baseline/anomaly measurement of large
>> > aggregates.
>>
>> If the consensus is that we must allow for such situations, then there are two
>> possibilities:
>>
>>   (a) weak spec language (MAY WISH TO or similar) => many implementations will
>> simply drop it
>>
>>   (b) negotiated option where the negotiation mechanism is mandatory
>>
>> In the vein of (b), Christian suggested offline to introduce negotiation to
>> allow for experimentation of the remaining two reserved bits. Then may be we can
>> synthesize both ideas by the following proposal:
>>
>>   - in the first few exchanges of the 5-tuple, use the three bits for option
>> negotiation
>>
>>   - then use them as defined by the selected option
>>
>> Example encodings:
>>
>>   000 : nothing
>>   001 : spin bit alone : S00
>>   010 : spin bit + VEC : SVV
>>   ... : other extensions
>>
>> The negotiation mechanism allows both endpoints to force 000.
>> And since it is in the clear first byte, it allows on-path observers to identify
>> the option without resorting to heuristics; this helps in the case of a small
>> support ratio.
>>
>>
>>
>>
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> 



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