[tcpm] Partial implementation of AccECN Option logic

[Bob Briscoe <[e-mail]>]

Yoshi (and tcpm)

Thanks for reminding me to get the AccECN draft finalized.

In the last tcpm meeting, I listed two things we're still planning to 
update:
https://datatracker.ietf.org/meeting/113/materials/slides-113-tcpm-draft-ietf-tcpm-accurate-ecn-18-00
I'll deal with each in a separate email:

This email is about switching round the recommendation on what is 'least 
worst' to leave out of an initial implementation in §3.2.3:
https://datatracker.ietf.org/doc/html/draft-ietf-tcpm-accurate-ecn#section-3.2.3
as below.

Current:

    Even if a developer does not implement sending of the AccECN Option,
    it is
    RECOMMENDED that they still implement logic to receive and
    understand any
    AccECN Options sent by remote peers.

Proposed:

    Even if a developer does not implement *logic to understand
    received* AccECN
    Option*s*, it is RECOMMENDED that they still implement logic to send
    AccECN
    Options *to provide richer feedback to those* remote peers *that do
    understand it.
    The logic to send AccECN Options is the simpler to implement of the
    two sides.
    *


Question for the list: Ought this to be a MUST, rather than just 
RECOMMENDED?
If there's disagreement, we won't make it a MUST.

____________
Rationale for the change: After Ilpo implemented the AccECN Option, he 
told me:
* the logic to receive an AccECN Option was more tricky, because it 
includes heuristics to estimate the counters if ACKs arrive without the 
option.
* whereas the logic to send them was fairly straightforward (now that 
the recommended default option size is constant). It essentially 
involves implementing:
    - the byte counters,
    - choosing the field order,
    - building and sending the option fields,
    - checking whether sending the option puts the connection into a 
black hole (and optionally caching this knowledge).



Bob

-- 
________________________________________________________________
Bob Briscoehttp://bobbriscoe.net/