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
