Re: [Detnet] Analysis of PREOF functions [was: detnet Digest, Vol 86, Issue 16]

Ludovic Thomas <ludovic.thomas@woolab.fr> Thu, 21 October 2021 09:43 UTC

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From: Ludovic Thomas <ludovic.thomas@woolab.fr>
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Date: Thu, 21 Oct 2021 11:42:51 +0200
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Subject: Re: [Detnet] Analysis of PREOF functions [was: detnet Digest, Vol 86, Issue 16]
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Hi Balázs,

thanks a lot for your feedback and for your suggestion.
I believe that we plan to share this with the TSN folks, but we haven't 
decided/found the best way to do it so far...

Cheers,
Ludovic

PS: I'm changing the subject for more clarity.
My previous mail was intended to follow your conversation with Toerless 
but I did not answer to the correct email.


Le 19/10/2021 à 20:05, Balázs Varga A a écrit :
>
> Hi Ludovic, Ahlem and Jean-Yves,
>
> Many thanks for the analysis. Very interesting reading.
>
> Helps definitely during DetNet network design (e.g.,
> proper placement of functionalities).
>
> ATS related findings may be interesting for IEEE folks as well.
>
> Cheers
>
> Bala’zs
>
> *From:* detnet <detnet-bounces@ietf.org> *On Behalf Of *Ludovic Thomas
> *Sent:* Thursday, October 14, 2021 7:29 PM
> *To:* detnet@ietf.org
> *Subject:* Re: [Detnet] detnet Digest, Vol 86, Issue 16
>
> Hi all,
>
> we have performed the worst-case delay analysis of the PREOF functions 
> and of their interactions with traffic regulators (either per-flow or 
> interleaved, as in TSN-ATS).
>
> Our main findings are:
>
> - The traffic profile at the output of the PEF depends on both the 
> traffic profile just before the PEF (on the paths to be merged) and on 
> the topology between the PRF (Packet-Replication Function) and the 
> PEF. We thus agree with Balázsthat both factors do play a role. If we 
> only consider the incoming traffic profiles before the PEF to compute 
> the output traffic profile (an approach denoted as "intuitive" in the 
> preprint), then the obtained latency bounds are much worse than the 
> tight model, as we illustrate on an industrial use-case. Delay bounds 
> can also be obtained in more complex networks with several duplication 
> locations (several PRFs) for a unique PEF, or the opposite.
>
> - Placing a POF (packet ordering function) after a PEF further 
> increases the burstiness of the flow.
>
> - Placing a regulator (per-flow or TSN-ATS) after the PEF such that 
> the regulator reinforces the source contract makes the redundancy 
> "transparent" to downstream nodes. But if the regulator is placed 
> directly after the PEF, then it incurs a delay penalty: PEF + PFR 
> (per-flow regulator) comes with a bounded delay penalty, however PEF + 
> ATS can induce unbounded latencies, unbounded backlogs and congestion 
> losses.
>
> - Placing a POF between the PEF and the regulator solves the above 
> issue (this gives the configuration "PEF + POF + regulator"). But, for 
> the case of ATS, it is not sufficient for the POFs to reorder each 
> flow independently (as written today in RFC8655). The POF must reorder 
> the whole aggregate as a unique flow in order to solve the above 
> issue, when using ATS.
>
>
> We hope that this provides additional insights on the possible 
> combinations for PEF, POF and the regulators.
> The results have been obtained using Network Calculus and if you are 
> interested, the following preprint contains more details: 
> https://arxiv.org/pdf/2110.05808.pdf 
> <https://arxiv.org/pdf/2110.05808.pdf>
> To obtain the results on PEF+POF, we have reused the results from 
> https://arxiv.org/pdf/2008.03075.pdf 
> <https://arxiv.org/pdf/2008.03075.pdf> regarding packet mis-ordering 
> in time-sensitive networks and their reordering using POF.
>
> Cheers,
>
> Ludovic, Ahlem and Jean-Yves
>
>
> (sorry moderators for the previous email with wrong sender address)
>
> Le 21/09/2021 à 21:00, detnet-request@ietf.org 
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>         1. Re: Policing/shaping and related calculus [was
>
>            draft-varga-detnet-pof (sorry, lot of input)] (Toerless Eckert)
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