Re: [Detnet] Packet Ordering Function (draft-varga-detnet-pof-00.txt)

Jeong-dong Ryoo <ryoo@etri.re.kr> Tue, 27 April 2021 09:34 UTC

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From: Jeong-dong Ryoo <ryoo@etri.re.kr>
To: Greg Mirsky <gregimirsky@gmail.com>, Stephan Kehrer <stephan.kehrer@belden.com>, =?UTF-8?Q?Bal=C3=A1zs_Varga_A?= <balazs.a.varga=40ericsson.com@dmarc.ietf.org>
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Subject: Re: [Detnet] Packet Ordering Function (draft-varga-detnet-pof-00.txt)
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Hi Bala'zs,

Thank you for your email.
Yes, it is the same operation.

Cheers,

Jeong-dong



-----Original Message-----
From: "Balázs Varga A" &lt;balazs.a.varga=40ericsson.com@dmarc.ietf.org&gt;
To: "Jeong-dong Ryoo" &lt;ryoo@etri.re.kr&gt;.re.kr&gt;; "Greg Mirsky" &lt;gregimirsky@gmail.com&gt;il.com&gt;; "Stephan Kehrer" &lt;stephan.kehrer@belden.com&gt;en.com&gt;;
Cc: "detnet@ietf.org" &lt;detnet@ietf.org&gt;tf.org&gt;;
Sent: 2021-04-27 (화) 18:15:10 (UTC+09:00)
Subject: Re: [Detnet] Packet Ordering Function (draft-varga-detnet-pof-00.txt)

Hi Greg/Stephan/Jeong-dong,
&nbsp;
Thanks for the question and the clarifications.
More clear definitions are always better, so we will update the text in the next version. :--)))
Thanks for the proposal, it is identical from operation perspective, but better structured.
&nbsp;
Cheers
Bala’zs
&nbsp;
&nbsp;
&nbsp;
From: detnet &lt;detnet-bounces@ietf.org&gt; On Behalf Of&nbsp;Jeong-dong RyooSent: Monday, April 26, 2021 11:51 AMTo: Greg Mirsky &lt;gregimirsky@gmail.com&gt;il.com&gt;; Stephan Kehrer &lt;stephan.kehrer@belden.com&gt;Cc.com&gt;Cc: detnet@ietf.orgSubject: Re: [Detnet] Packet Ordering Function (draft-varga-detnet-pof-00.txt)

&nbsp;
Hi,

&nbsp;

In order to describe the operation a little bit more clearly, how about the following modification:

OLD:

o If (seq_num &lt;= POFLastSent + 1)

&nbsp; &nbsp;* Then the packet is forwarded and "POFLastSent" is updated

&nbsp; &nbsp; &nbsp; (POFLastSent = seq_num).

&nbsp; * Else the received packet is buffered until a predefined time

&nbsp; &nbsp; &nbsp; ("POFMaxDelay") elapses OR its seq_num becomes equal to

&nbsp; &nbsp; &nbsp; "POFLastSent + 1".

NEW:

o If (seq_num &lt;= POFLastSent + 1)

&nbsp; &nbsp;* Then the packet is forwarded and "POFLastSent" is updated

&nbsp; &nbsp; &nbsp; (POFLastSent = seq_num).

&nbsp; * Else the received packet is buffered.

o &nbsp;A buffered packet is forwarded from the buffer&nbsp;

&nbsp; &nbsp; when its seq_num becomes equal to "POFLastSent +1," OR&nbsp;

&nbsp; &nbsp; a predefined time ("POFMaxDely") elapses.&nbsp;

&nbsp;

Best regards,

&nbsp;

Jeong-dong

&nbsp;

&nbsp;

&nbsp;

&nbsp;

&nbsp;

-----Original Message-----

From: "Stephan Kehrer" &lt;stephan.kehrer@belden.com mailto:stephan.kehrer@belden.com&gt;

To: "Greg Mirsky" &lt;gregimirsky@gmail.com mailto:gregimirsky@gmail.com&gt;;

Cc: "detnet@ietf.org mailto:detnet@ietf.org" &lt;detnet@ietf.org mailto:detnet@ietf.org&gt;;

Sent: 2021-04-26 (월) 18:26:05 (UTC+09:00)

Subject: Re: [Detnet] Packet Ordering Function (draft-varga-detnet-pof-00.txt)

&nbsp;

Hi Greg,
&nbsp;
Looking at the scenario you describe I think packets arriving in the order 100, 103, 102, 101 cannot happen due to an error on the transmission path if you are using only two paths. They might happen if the sender is failing and sends out the packets in the wrong order to begin with or if you are using more than two paths for redundancy and have failures on multiple transmission paths in a very specific order.
That being said, even then the transmission order 100, 101, 103, 102 should not be something you get from the POF in my opinion. If the packets are arriving and are buffered the way you describe, I think the following is what should happen (changes to what you had in your mail marked in red):
POFLastSent = 100a packet&nbsp;with&nbsp;seq_num = 103 is received and placed into the buffer for the duration of&nbsp;POFMaxDelaynext received packet has seq_num = 102. It is also moved into the buffer for the duration of&nbsp;POFMaxDelayfinally, before all delayed packets transmitted out of the buffer, a packet with seq_num = 101 is received and is forwarded right away. This sets POFLastSent = 101.the packet with seq_num=102 is forwarded because it now fulfills the condition ‘OR its seq_num becomes equal to"POFLastSent + 1"’. This sets POFLastSent = 102.the packet with seq_num=103 is forwarded because it now fulfills the condition ‘OR its seq_num becomes equal to"POFLastSent + 1"’. This set POFLastSent = 103.Packets arriving after that are forwarded without delay if they are next in sequence, and delayed if they are out of sequence as described in the POF algorithm.Regards,
Stephan
--
Mit freundlichen Grüßen | With kind regards
&nbsp;
Stephan Kehrer&nbsp;| Senior Architect –&nbsp;CTO Office&nbsp;| Hirschmann Automation and Control GmbH
Stuttgarter Straße 45-51 | 72654 Neckartenzlingen | Germany
Phone: +49 7127 14 - 1035 | Mobile: +49 152 28813002 | Fax: +49 7127 14 - 1600
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&nbsp;
Hirschmann Automation and Control GmbH, Neckartenzlingen
Register Court: Stuttgart, Trade Register No.: HRB 225927
VAT No.: DE 814 212 604
Managing Director: Brian Anderson, Wolfgang Schenk, Brian Lieser
&nbsp;
&nbsp;
&nbsp;
Von: detnet &lt;detnet-bounces@ietf.org mailto:detnet-bounces@ietf.org&gt; Im Auftrag von&nbsp;Greg MirskyGesendet: Samstag, 24. April 2021 03:04An: Balázs Varga A &lt;balazs.a.varga=40ericsson.com@dmarc.ietf.org mailto:balazs.a.varga=40ericsson.com@dmarc.ietf.org&gt;Cc: &nbsp;detnet@ietf.org mailto:detnet@ietf.orgBetreff: [EXTERNAL] Re: [Detnet] Packet Ordering Function (draft-varga-detnet-pof-00.txt)

&nbsp;
External Message:Use caution before opening links or attachments

Hi Balazs,
thank you for the well-designed mechanism of one of the key DetNet functions.

I have a scenario and would appreciate your consideration if you think it is a plausible one:

assume that&nbsp;POFLastSent = 100a packet&nbsp;with&nbsp;seq_num = 103 is received and placed into the buffer for the duration of&nbsp;POFMaxDelaynext received packet has seq_num = 102. It is also moved into the buffer for the duration of&nbsp;POFMaxDelayfinally, before all delayed packets transmitted out of the buffer, a packet with seq_num = 101 is received and is forwarded right awaythe delay timer expires on the packet with seq_num=103. It is forwarded and &nbsp;POFLastSent = 103next, the delay timer expires on the packet with seq_num=102. It, in turn, is forwarded and &nbsp;POFLastSent = 102from now, based on my understanding of the described POF algorithm, every packet will be delayed even if there are no re-ordered packets. For example, the sequence of arriving packets is as 104, 105, 106, ...Much appreciate your opinion if the scenario, i.e., a&nbsp;sequence like 100, 103, 102, 101, is a realistic one.


&nbsp;

Regards,

Greg


&nbsp;
On Mon, Apr 19, 2021 at 10:39 PM Balázs Varga A &lt;balazs.a.varga=40ericsson.com@dmarc.ietf.org mailto:40ericsson.com@dmarc.ietf.org&gt; wrote:

Hi,A draft on Packet Ordering Function (POF) algorithms were uploaded.Comments and views are highly appreciated.ThanksBala'zs (and the authors)



-----Original Message-----
From: internet-drafts@ietf.org mailto:internet-drafts@ietf.org &lt;internet-drafts@ietf.org mailto:internet-drafts@ietf.org&gt;
Sent: Tuesday, April 20, 2021 7:14 AM
To: Balázs Varga A &lt;balazs.a.varga@ericsson.com mailto:balazs.a.varga@ericsson.com&gt;; Janos Farkas &lt;Janos.Farkas@ericsson.com mailto:Janos.Farkas@ericsson.com&gt;; Balázs Varga A &lt;balazs.a.varga@ericsson.com mailto:balazs.a.varga@ericsson.com&gt;;
 Janos Farkas &lt;Janos.Farkas@ericsson.com mailto:Janos.Farkas@ericsson.com&gt;; Stephan Kehrer &lt;Stephan.Kehrer@belden.com mailto:Stephan.Kehrer@belden.com&gt;; Stephan Kehrer &lt;stephan.kehrer@belden.com mailto:stephan.kehrer@belden.com&gt;;
 Tobias Heer &lt;Tobias.Heer@belden.com mailto:Tobias.Heer@belden.com&gt;; Tobias Heer &lt;tobias.heer@belden.com mailto:tobias.heer@belden.com&gt;
Subject: New Version Notification for draft-varga-detnet-pof-00.txt


A new version of I-D, draft-varga-detnet-pof-00.txt has been successfully submitted by =?utf-8?q?Bal=C3=A1zs_Varga?= and posted to the IETF repository.

Name: draft-varga-detnet-pof
Revision: 00
Title: Deterministic Networking (DetNet): Packet Ordering Function
Document date: 2021-04-19
Group: Individual Submission
Pages: 10
URL: 
&nbsp;https://www.ietf.org/archive/id/draft-varga-detnet-pof-00.txt https://protect2.fireeye.com/v1/url?k=42292fb7-1db216b7-42296f2c-86fc6812c361-b79213ba824e6d93&amp;q=1&amp;e=5dd3eaf7-6baf-4f90-b030-71c3c708325b&amp;u=https://urldefense.com/v3/__https:/www.ietf.org/archive/id/draft-varga-detnet-pof-00.txt__;!!B_EDKQmmvsU!7vmDpLfsfmmLuG9tQHwCrsPqlNqL_fA88lGK7awH9s4iu2A-gZ-KVq6uPhKWdzZ8c98$
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Abstract:
Replication and Elimination functions of DetNet [RFC8655] may result
in out-of-order packets, which may not be acceptable for some time-
sensitive applications. The Packet Ordering Function (POF) algorithm
described herein enables to restore the correct packet order when
replication and elimination functions are used in DetNet networks.




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