Re: [tcpm] [Fwd: New Version Notification for draft-gomez-tcpm-ack-pull-00.txt]

Michael Tuexen <michael.tuexen@lurchi.franken.de> Wed, 17 July 2019 13:40 UTC

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From: Michael Tuexen <michael.tuexen@lurchi.franken.de>
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Date: Wed, 17 Jul 2019 15:40:52 +0200
Cc: Carsten Bormann <cabo@tzi.org>, Yoshifumi Nishida <nsd.ietf@gmail.com>, "tcpm@ietf.org Extensions" <tcpm@ietf.org>, "jon.crowcroft@cl.cam.ac.uk" <jon.crowcroft@cl.cam.ac.uk>
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To: "Scharf, Michael" <Michael.Scharf@hs-esslingen.de>
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Subject: Re: [tcpm] [Fwd: New Version Notification for draft-gomez-tcpm-ack-pull-00.txt]
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> On 17. Jul 2019, at 14:44, Scharf, Michael <Michael.Scharf@hs-esslingen.de>; wrote:
> 
> Is my understanding correct that this could be formalized as follows:
>  
>   A TCP MAY not delay ACKs for data segments with the PSH flag.
I think this is what Carsten was referring to.

My point was: Is this already deployed?

The reason I'm asking is that I have heard several time that the semantic of the
PSH bit is to send out an ACK immediately. I could not find the source of this
statement...

Best regards
Michael
>  
> If that was the intention, I believe that the wording of RFC 1122 (and draft-ietf-tcpm-rfc793bis) would allow such a receiver-side heuristic already. Delayed ACKs are a SHOULD in RFC 1122 and the exact logic is not specified. Thus, taking the PSH flag into account inside a receiver-side delayed ACK heuristic may not even be a change of the TCP semantics…
>  
> Michael
>  
>  
> Von: Carsten Bormann
> Gesendet: Mittwoch, 17. Juli 2019 09:56
> An: Yoshifumi Nishida
> Cc: jon.crowcroft@cl.cam.ac.uk; tcpm@ietf.org Extensions
> Betreff: Re: [tcpm] [Fwd: New Version Notification for draft-gomez-tcpm-ack-pull-00.txt]
>  
> On Jul 17, 2019, at 08:58, Yoshifumi Nishida <nsd.ietf@gmail.com>; wrote:
> >
> >  using a reserved flag is a bit expensive
>  
> The option could simply redefine existing PSH as having the AKP semantics.
> (And possibly all packets having what used to be the PSH semantics.)
> They are close enough anyway…
>  
> Grüße, Carsten
>  
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