Re: [tcpm] Why draft-gomez-tcpm-ack-rate-request?

Bob Briscoe <ietf@bobbriscoe.net> Wed, 23 March 2022 16:18 UTC

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To: Jonathan Morton <chromatix99@gmail.com>, Gorry Fairhurst <gorry@erg.abdn.ac.uk>
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Subject: Re: [tcpm] Why draft-gomez-tcpm-ack-rate-request?
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Jonathan

On 23/03/2022 13:41, Jonathan Morton wrote:
>> On 23 Mar, 2022, at 3:25 pm, Gorry Fairhurst <gorry@erg.abdn.ac.uk> wrote:
>>
>> I would also note that ARR offers an alternative signalling method (to AccECN) for effectuating Generalised ECN, as applied to pure acks in particular.  I think ARR is conceptually and mechanically simpler for implementers than AccECN is.

[BB] If I read between the lines, I believe you are categorizing the 
combination of AccECN and generalized-ecn (ECN++) as just one very 
narrow application of them: ACK congestion control. Although the 
combination of AccECN and ECN++ makes ACK-CC possible, that wasn't one 
of the original motivations for either.*

Whatever, if we run with this narrow focus, TARR wouldn't be enough to 
deploy ACK CC. It solely gives the control signal, not the measurement 
in the other direction that would be needed to drive that control.

To be clear, I believe TARR is useful, I'm just saying it's not 
sufficient on its own for ACK CC, which seems to be what you are 
referring to here.


Bob

* Primary motivations:
     AccECN: robust feedback of the extent of ECN marking, not just its 
existence within one round trip, which is all RFC3168 feedback allows.
     ECN++: allowing TCP control packets and retransmissions to benefit 
from being ECN-capable.

>>
>>   - Jonathan Morton
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-- 
________________________________________________________________
Bob Briscoe                               http://bobbriscoe.net/