Re: [Ecn-sane] IETF 110 quick summary

[Jonathan Morton <chromatix99@gmail.com>]

> On 9 Mar, 2021, at 4:13 am, Holland, Jake <jholland@akamai.com> wrote:
> 
> In the chat a person or 2 was surprised about the way
> L4S will impact NECT competing traffic when competing in a queue.

I think that was mostly Martin Duke.  I caught up with him in the IETF Gather space immediately afterwards and discussed this with him, one to one, and he now seems to understand more clearly what we were presenting.  I was pleased to hear that he's also familiar with the "risk matrix" formulation I presented.

> We also applied that to L4S by first explaining that risk is the
> product of severity and prevalence…

And also, crucially, the concept of "externalised risk", ie. the distinction between involved participants, interested observers, and innocent bystanders.  L4S has innocent bystanders (existing networks and their users, who have no idea that L4S even exists nor how to troubleshoot ECN related problems) incur most of the risk of Bad Things happening.  This is an "externalised risk" which is very difficult to manage after the fact, and must be minimised to a much greater extent than other risks.

SCE ensures that innocent bystanders incur virtually no risk, in that bad interactions only occur for poeple actually using SCE over an SCE-enabled path, which is where mitigations can actually be practical to employ - in the limit, by switching off SCE.  This is much easier to accept in a risk analysis.  We didn't get to that slide, however, due to shortage of time.

 - Jonathan Morton