Re: Spin bit - semantics - rtt and loss

[<[e-mail]>]

Hi Igor,

Indeed packet loss is important to track.

Your proposal is an instance of the "square sequence" proposed earlier by 
Kazuho. He suggested a much longer period (hundreds); you're exploring lower 
values. Each range has issues: too long turns into a large temporal imprecision 
for sparse flows (like ACKs); too short blurs the signal in case of tail drops 
(many contiguous losses).

Also, these methods only give upstream losses (between the sender and the 
midpoint). For this reason we propose a more ambitious 7-bit solution here: Spin 
Counters

  http://snaggletooth.akam.ai/IETF-101-HotRFC/10-Ferrieux.pdf

Would that help ?

On 23/03/2018 01:12, Lubashev, Igor wrote:
> Since we decided to put some work into spin bit, albeit in a separate document
> from V1, here are some thoughts.
>
> It is nice that spin bit can be used to estimate rtt. I am sure that it is
> useful to many well-meaning people. It is not very useful to me, though.
>
> When I debug network problems, they are much more likely to be about lost
> packets. And I like to be able to know packet loss frequency and pattern very
> accurately. (I am assuming an encrypted packet number, or the problem would be
> trivial.)
>
> I would prefer, if we have a spin bit, for it to spin not every rtt but every,
> say, 10 packets that an endpoint sends. Client sends 10 packets with 0 and then
> 10 packets with 1, repeat. Sever does the same.
>
> So maybe two spin bits -- one for rtt and one for loss? I would assume that loss
> bit would assist in rtt estimation in case of loss.
>
> Thoughts?
>
> - Igor


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