Re: [ippm] QUIC concerns relating to draft-ietf-ippm-explicit-flow-measurements

[Christian Huitema <[e-mail]>]

On 5/11/2023 3:53 PM, Martin Thomson wrote:
> On Fri, May 12, 2023, at 01:21, Christian Huitema wrote:
>> Igor is right. In fact, the "square bit" that he describes is
>> implemented in Picoquic, under an option negotiation.
> 
> It's not about whether endpoints could negotiate something that allows the use of these bits, it's about whether measurement systems are able to rely on that happening.
> 
> It's quite possible that some extension could be negotiated that creates a signal in these bits.  OK, so now you can deploy a measurement system that relies on that.  Most bits will be random, but some proportion will have the signal.  Enter statistical methods and you can recover some signal.
> 
> Well...almost.  This works until someone else decides to negotiate the use of those bits for carrying a different signal.  Now you have a harder statistical problem to solve.  Maybe you can boost your adaptation by observing connection initiation and looking for clients that advertise a certain version and set of transport parameters.
> 
>> The probability that these measurement features be turned on by default
>> is extremely low, and the draft should be very explicit about it,
>> including a description of the privacy/measurement tradeoff.
> 
> This is really the point of all this.

That. Which means that at a minimum the IPPM draft should discuss the 
issue: needle of measurement in a haystack of noise. It might work 
sometimes, such as when debugging the end to end path between two well 
known IP addresses, or when knowing the specific connection IDs used by 
the system participating in the measurement. It might perhaps work if 
the connection last long enough to distinguish the IPPM pattern from a 
random pattern. But as you say, the general case is almost impossible.

-- Christian Huitema