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Re: [6lo] recoverable fragments: should we allow the receiver to send asynchronous acks

Michael Richardson <mcr+ietf@sandelman.ca> Tue, 21 May 2019 13:47 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: "Pascal Thubert (pthubert)" <pthubert@cisco.com>
cc: "6lo@ietf.org" <6lo@ietf.org>, Laurent Toutain <laurent.toutain@imt-atlantique.fr>
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Date: Tue, 21 May 2019 09:47:05 -0400
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Archived-At: <https://mailarchive.ietf.org/arch/msg/6lo/FKdXJrlpEfJRYJ31TwrhF2CP6Mk>
Subject: Re: [6lo] recoverable fragments: should we allow the receiver to send asynchronous acks
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Pascal Thubert (pthubert) <pthubert@cisco.com> wrote:
    > During the review by Laurent, a question came up on whether the receiver
    > could asynchronously send RFRAG Acks e.g., to transport an ECN
    > indication.

So would the ACKs be out of order, acknoledging fragment n+2 while still
waiting for fragment n?  Or would the acks be repeat of a previous ack (n-1),
indicating congestion, and likely signaling that fragment n got lost?

    > At the moment, the sender is in full control and the ack is only sent if the
    > sender asks for it. Laurent indicates that asynchronous Ack could generate
    > more collisions and make the problem worse.

1) Not re-inventing TCP is important.
2) Perhaps the question is better turned around: what should the sender do if
   an ACK arrives without having been asked for?

--
Michael Richardson <mcr+IETF@sandelman.ca>, Sandelman Software Works
 -= IPv6 IoT consulting =-

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