Re: [tsvwg] Scope of the L4S Experiment (was: Guard DSCP)

["Black, David" <[e-mail]>]

Mike,

> I had certainly understood the intended scope to be sets of cooperating/participating networks rather than the Internet as a whole.
> How could it possibly be otherwise, with a change in the semantics of CE that is incompatible with existing standards, without at the same time obsoleting those standards?

Short answer (as I understand it) – L4S was originally intended to be compatible.  For details of what compatible means in this context, see Section 4.3 of RFC 4774 (Option 3:  Friendly Coexistence with Competing Traffic, https://datatracker.ietf.org/doc/html/rfc4774#section-4.3).

> The evidence presented here strongly suggests to me that L4S is not benign to existing standards. If it is to be used experimentally, it must be contained.
> If it is to be used internet-wide, then existing incompatible uses should be obsoleted.

You're not the only person who has expressed the view that L4S is not able to proceed under RFC 4774 Option 3.

Everyone - when responding to this message, please keep in mind that RFC 4774 is a BCP (Best Current Practice) document, namely BCP 124.

Thanks, --David

From: C. M. Heard <[e-mail]>
Sent: Tuesday, May 4, 2021 12:40 AM
To: Black, David
Cc: TSVWG
Subject: Scope of the L4S Experiment (was: Guard DSCP)


[EXTERNAL EMAIL]
On Tue, Apr 27, 2021 at 3:57 PM Black, David wrote:
the appropriate L4S experiment scope may be sets of cooperating/participating networks rather than the (originally envisioned) Internet as a whole.

I had certainly understood the intended scope to be sets of cooperating/participating networks rather than the Internet as a whole. How could it possibly be otherwise, with a change in the semantics of CE that is incompatible with existing standards, without at the same time obsoleting those standards?

When Differentiated Services was introduced by RFC 2474, the existing TOS standard was obsoleted, based on good evidence that it was unused (there was only one implementation of TOS routing, IIRC, and negligible deployment). It didn't get introduced as an experiment.

When the original experimental incarnation of ECN was specified by RFC 2481, it could be introduced as an internet-wide experiment because prior standardized uses of the field had been obsoleted on good evidence of non-use, and there was good evidence that harm would not be caused to deployed systems.

The evidence presented here strongly suggests to me that L4S is not benign to existing standards. If it is to be used experimentally, it must be contained. If it is to be used internet-wide, then existing incompatible uses should be obsoleted.

One or the other, please. Don't deploy L4S internet-wide and call it experimental.

Mike Heard