Hi, Greg,
> On Feb 10, 2025, at 2:35 PM, Greg White <[email protected]> wrote:
>
> Joe,
>
> Thanks for pointing to that reference. I assume that is the most definitive
> guidance that the IETF has given to L2 networks on the topic, and any future
> changes to that guidance could take the form of updates to RFC3819.
>
> I agree with you that the sentence you quoted seems reasonable, but in the
> context of the rest of the text in that section in RFC3819, it seems to me
> that the warnings about TCP performance and header compression might undercut
> the recommendation.
The warnings are about compression - and still apply. If the compression
algorithm includes dependencies between sequences of packets, then those
sequences have to be restored for the compressor to work. Perhaps what isn’t
said is that if the compressor has such dependencies, then IT should perform
the needed reordering, rather than expecting the network to do so for it. The
prior section addresses the impact of loss on compression, but overlooked the
impact of reordering.
> I think many L2 designers consider TCP performance to be important (even if
> they don’t know the details of current implementations), and they also might
> not be willing to take the risk that their link would break someone’s header
> compression scheme (users do lots of different things!).
Yes, but again this argues for the compressor to reorder, not L2.
> Is there value in updating that section?
Certainly the entire doc could include more recent references and could be
subbed for omissions such as above, perhaps providing more comprehensive advice
up front, e.g.,:
- whatever you expect L2 to do, do at the ends of L3 in or in front of
protocols that depend on those features
- but do NOT engineer the entire L2 for any of those features
But in a sense that’s just reinforcing the advice in the E2E paper, which
doesn’t need (IMO) to be revised simply to refer to more recent examples.
> At a minimum we could point to RACK, L4S and the QUIC packet reordering
> threshold along with whatever consensus we can develop around the idea that
> transports that are interested in performance already (or at least can)
> implement reordering tolerance, and that the benefits of minimizing delay
> outweigh any slight benefits provided to older transport implementations.
> That said, this thread has seen several opinions (not all in agreement) so it
> might be challenging to get consensus.
And that’s part of the issue as well; to the extent that our docs lack clear,
direct advice, it can be the result of the consensus process.
I don’t particularly think an update is warranted - IMO, what’s needed is for
the advice that’s there to be heeded.
Joe
>
> -Greg
>
> From: Joe Touch <[email protected] <mailto:[email protected]>>
> Date: Friday, February 7, 2025 at 3:18 PM
> To: Ryan Hamilton <[email protected]
> <mailto:[email protected]>>
> Cc: Martin Thomson <[email protected] <mailto:[email protected]>>, Greg
> White <[email protected]
> <mailto:[email protected]>>, Ingemar Johansson S
> <[email protected]
> <mailto:[email protected]>>, "[email protected]
> <mailto:[email protected]>" <[email protected] <mailto:[email protected]>>,
> "[email protected] <mailto:[email protected]>" <[email protected]
> <mailto:[email protected]>>
> Subject: [tsvwg] Re: Robustness to packet reordering
>
>
>> On Feb 7, 2025, at 2:12 PM, Ryan Hamilton <[email protected]
>> <mailto:[email protected]>> wrote:
>>
> ….
>> Let's not hobble the performance of modern protocols in order to
>> *potentially* provide minimal improvements to the performance of obsolete
>> implementations.
>
> Agreed. As I noted, RFC3819 still has imo the best advice:
>
> This suggests that subnetwork implementers should try to avoid packet
> reordering whenever possible, but not if doing so compromises
> efficiency, impairs reliability, or increases average packet delay.
