Re: [tsvwg] Status of ECN encapsulation drafts (i.e., stuck)

["Holland, Jake" <[e-mail]>]

Hi Bob,

On 3/13/20, 9:42 AM, "Bob Briscoe" <[e-mail]> wrote:
>> But this does not jive with what I know about IP-layer fragmentation, in which TA1(ECT) TA2(ECT) always reassembles into TA(ECT), and TB1(CE) TB2(ECT) reassembles into TB, which is then CE marked by the RFC-3168 bitwise-OR rule.  We would then have A(ECT) and B(CE) transmitted onward, which seems to match the intent of the AQM - in particular, the number of CE marks is preserved, not doubled.
>>
>> What am I missing from the context of your objections?
>
> Well, I don't know, 'cos I don't know how you came to that 
> interpretation (you'll need to point to the sentence that made you think 
> that, if it's still not clear).

I'm also confused, so although I'm not speaking for Jonathan, I'll point to a sentence
that made me think the response raised an excellent and relevant point:
(From https://mailarchive.ietf.org/arch/msg/tsvwg/B2Gnb-jYPiZFYuA3YXNRhktKaT4/)

  'the "logical OR" reassembly process required in RFC3168 roughly doubles both the number
  and the proportion of CE marked packets and the number and proportion of CE-marked bytes
  (relative to a parallel flow with slightly smaller packets that is not fragmented).'

I thought the example succinctly suggested that one of the 4 things listed above can't be
doubled, namely:

- the number of CE-marked packets.

If there's a way for the number of CE packets to be doubled by the "logical OR" reassembly
process, I would like to see an example.  I haven't been able to think of one.

To me also, this seems a fundamental point worth clarifying.

(I do see that the other 3 metrics can be doubled under some specific assumptions about
the fragments and probabilities, as likewise demonstrated by the simple example.)

Best regards,
Jake