Re: [tcpm] AccECN field order

Joseph Touch <> Wed, 27 January 2021 04:21 UTC

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From: Joseph Touch <>
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Date: Tue, 26 Jan 2021 20:21:42 -0800
Cc: tcpm IETF list <>, "Scheffenegger, Richard" <>, Michael Tuexen <>, Mirja Kuehlewind <>,
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To: Vidhi Goel <>
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Subject: Re: [tcpm] AccECN field order
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> On Jan 26, 2021, at 7:47 PM, Vidhi Goel <> wrote:
>> Please see my note from 12/3/20, which shows how a single codepoints would suffice without increasing length. 
> If the TCP option code points is not a scarce resource,

They are. Very much so.

> then why not just keep it simple with "two different codepoints”? Is there a reason that you think we should use only one code point?

That’s the core of the discussion we’ve been having.

> Regarding your suggestion of using 1 bit from the 24-bit counter field, do you mean specify ordering once before the first ECN counter field or specify before every counter field?
> For example, if all three counters are present, are you suggesting, a) or b)? To me b) would make more sense but that makes the implementation complex as the fields have different length.
> a) Kind | Length | 1-bit ordering | 23-bit EE1B | 1-bit ordering | 23-bit ECEB | 1-bit ordering | 23-bit EE0B
> b) Kind | Length | 1-bit ordering | 23-bit EE1B | 24-bit ECEB | 24-bit EE0B

The point of the bit is to encode the different kinds. (b) does this just fine. If we want all three counters to be the same length, simply do so and require the other two “first bits” to be zero.