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Re: [RTG-DIR] [Detnet] Review of draft-ietf-detnet-pof-04 for the RTGDIR

Henning Rogge <hrogge@gmail.com> Wed, 08 November 2023 08:24 UTC

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From: Henning Rogge <hrogge@gmail.com>
Date: Wed, 08 Nov 2023 09:24:04 +0100
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To: Balázs Varga A <balazs.a.varga@ericsson.com>
Cc: "detnet@ietf.org" <detnet@ietf.org>, "rtg-dir@ietf.org" <rtg-dir@ietf.org>, Daniam Henriques <daniam.henriques@liquid.tech>
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Subject: Re: [RTG-DIR] [Detnet] Review of draft-ietf-detnet-pof-04 for the RTGDIR
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On Tue, Nov 7, 2023 at 11:59 AM Balázs Varga A
<balazs.a.varga@ericsson.com> wrote:
>
> Hi Henning,
> 2, “why POFLastSent is always set to seq_num”
>
> Yes, this is an interesting question. Both POF algorithm assume, that the POFMaxDelay parameter applied on a
> buffered packet is correctly designed. It means, that a packet is removed from the buffer only if there is no chance
> anymore to receive an earlier (smaller SeqNum) packet over the slowest path. (In practice that means that
> POFMaxDelay > latency difference of the fastest and the slowest paths.) Therefore “if seq_num 10 already has
> been forwarded and now seq_num 5 is being forwarded” is a broken scenario, with correctly designed POFMaxDelay
> arrival of seq_num 5 is an invalid event or happened due to multiple network failures.
> State and initialization of the basic POF algorithm are described on page 7, so I would propose no change to the text.

Maybe a short "packages with a sequence number of less than
POFLastSent MUST/SHOULD be silently dropped" could be added to make
implementations more robust to these situations?

Henning Rogge

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