Bona fide loss measurement bits

[<[e-mail]>]

On 04/04/2018 20:06, Ted Hardie wrote:
> it seems pretty clear that the passive measurement and diagnostic purposes would
> work with fairly small sequence numbers, maybe even down to sizes small enough
> to make the linkability problem less scary.  The other issues ("does this look
> like quic" and "does this look like a known flow") seem like they don't really
> require packet numbers or even deliberately exposed sequence numbers, just
> consistency.   In other words, if we do anything to expose sequences, the wire
> image we engineer does not have to simply re-use the packet numbers used for
> protocol mechanics. It can focus on the message we want to send to the path instead.

If we're to secure a few bits as a "message we want to send to the path", e.g. 
for loss measurement, please note that subsequence numbers are just one option 
among many, with known shortcomings (only losses between sender and observer; 
lack of robustness to strong loss and reordering).

Instead, building on top of the Spin Bit, we propose a 7-bit extension named 
"Spin Counters":

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

they give both up- and downstream losses, are robust to any level of loss and 
reordering, and leverage the Spin Bit's autoscaling to one congestion window.

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