Re: Spin bit decision

[<[e-mail]>]

On 10/02/18 08:51, Lars Eggert wrote:
> Hi,
> 
> On 2018-10-2, at 9:05, [e-mail] wrote:
>> After NYC, what are the remaining questions the WG is asking regarding the
>> spin bit to educate the upcoming decision (Bangkok):
>> 
>> (a) why is midpoint half-RTT measurement useful (in current practices) ? 
>> (b) is the spin bit up to the job ? >> (c) isn't there any other way ?
>> (d) other >> ?
> 
> the following is my personal feedback on this matter, i.e., I'm not speaking
> as chair:
> 
> I have little doubt that the single-bit spin bit variant is fit for purpose.
> I also think the DT has analyzed the privacy implications of the single-bit
> variant sufficiently for me to have no serious privacy concerns about the
> variant.
> 
> The key open question in my mind is this: on what fraction of the traffic
> would an operator need to see spinning and echoed bits in order to obtain
> useful network-wide or at least path specific latency information? In other
> words, how many browsers and servers-side deployments would need to opt in
> and spin or echo the bits? Would it be sufficient if one hyperscalar with a
> bowser and a server deployment opted in? Even if most of their traffic
> concentrated towards their peering links?

Experience with debugging our networks in several countries shows that (1) all
segments may misbehave, and (2) sample size is very often an issue, in that some
problems are triggered by a non-obvious conjunction of parameters that is
extremely sensitive to sampling bias. So, the more support for measurement, the
better. TCP shines because clear headers are ubiquitous, not an opt-in debug
mode, nor a randomly enabled feature in X% of flows.

May I ask why this question is key ? Are you envisioning a situation where v1
would allow for the spin bit as a negotiated option instead of just requiring it
? Added complexity and inferior outcome: what is the motivation ?


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