Re: [tcpm] I-D Action: draft-nishida-tcpm-agg-syn-ext-01.txt

[Yoshifumi Nishida <[e-mail]>]

Hi Richard,

Thanks for the comments.

On Mon, Mar 27, 2023 at 1:34 AM <[e-mail]> wrote:

> Hi Yoshi,
>
> I just wanted to record my comment on list too:
>
> For the aggregated option I would like to also see some of the commonly
> used parameters (e.g. MSS, Window Scale) to be rolled into this.
> Ideally, in some not-too-distant future, all Hosts should be supporting
> this aggregated option, and retaining the additional space for those
> parameters and their tcp option encoding appears to be excessive.
>
> Especially as not the full range is used (window scale may receive a
> final boost to use 0..15 instead of 0..14 currently, thus a 4-bit field
> suffices; timestamp in the SYN could be abbreviated (no ECR field
> needed, as the proposal for granularity signalling never got much
> traction); MSS could be compressed to few commonly encountered values
> (e.g. 1200, 1300, 1460, 8960, 65535 (lo0), or some variant of an
> exponential encoding).
>

I see. I haven't thought about it, but it may make sense. One idea might be
to allocate GID for MSS or GID for window scale
If we need more GIDs, we can extend it to 3 bits.


> Martin's suggestion of adding in this early stage various competing
> proposals into the same draft, and working out the pro/cons over time
> also sounds appealing.
>
> Finally, there are (currently) more exotic options, which are heavy
> consumers of SYN tcp option space (MPTCP, TFO, MD5 / AO - with those two
> really having a limited applicability domain currently). A quick rundown
> of them all, and their requirements on the SYN and SYN,ACK space may be
> valuable to have in the draft for discussion purposes (avoid having to
> chase them when reading the draft).
>

Yes, I've thought about similar things. The tricky things are:
* MPTCP already pushes out some parameters to 3rd and 4th segments
* TFO and AO should carry large data in SYN otherwise their features will
be impaired.
I think I can add some discussions for them in the next version.

BTW, I wasn't aware that user timeout doesn't use SYN, but i think it's
because it doesn't require negotiation and it's a hint for the peer.
In my understanding , we cannot reliably negotiate features without using
SYN. If needed, I can add some texts for discussions.

--
Yoshi