Re: [tcpm] Issue with multiple option code points: Re: Early assignment of IANA TCP option number for AccECN

["Scheffenegger, Richard" <[e-mail]>]

Hi Joe,

It was our understanding, that there was an agreement among participants
in that discussion - which later focussed more on the perceived "covert
channel" issue - to go with an easier to implement and maintain
two-option approach.

The suggested other variants
* use the length field, and discard "fill bytes" for anything but
indicate ordering - convert channel issue above)
* use of a single bit from the first (or all) counter fields - special
handling of the wrap around situations for 23-bit and 24-bit wide
counters, making sure that the bit is properly masked out, potentially
issues with offloading into simple streamlined (small) code.

While the TCP option numbers are a scarce resource, the understanding
was this approach was still less wasteful (vs. length encoding) and more
straightforward to implement (vs. flag bit).  Although, tracking optimal
ordering and stuffing of the TCP options (sending only required/changed
counters rather than all counters all the time) is not that straight
forward.

However, a sender receiving the options in the ACK can have streamlined
logic to track this - lending to the possibility of doing this in
offload hardware.

The two-codepoint approach has been in the draft since -13. It was also
discussed in the IETF 109 meeting.

Bob can also provide more of the rationale that made us move from a
single, to two codepoints between -12 and -13.



Am 26.07.2022 um 16:20 schrieb [e-mail]:
> Hi, all,
>
> Whatever happened to the discussion from 1/27/21 where we all discussed
> a way that a single TCP option code point could suffice?
>
> I do not support any assignment of multiple code points for a single TCP
> option (multiple ExIDs are fine, though).
>
> This is especially true for early code points assignments, for which
> (IMO) the bar ought be higher.
> —
> Dr. Joe Touch, temporal epistemologist
> www.strayalpha.com <http://www.strayalpha.com>
>