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

Jeong-dong Ryoo <ryoo@etri.re.kr> Mon, 26 April 2021 09:51 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>
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Subject: Re: [Detnet] Packet Ordering Function (draft-varga-detnet-pof-00.txt)
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Hi,

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;

Best regards,

Jeong-dong

&nbsp;



-----Original Message-----
From: "Stephan Kehrer" &lt;stephan.kehrer@belden.com&gt;
To: "Greg Mirsky" &lt;gregimirsky@gmail.com&gt;il.com&gt;;
Cc: "detnet@ietf.org" &lt;detnet@ietf.org&gt;tf.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)

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.&nbsp;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
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&nbsp;
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Von: detnet &lt;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&gt;Cc.org&gt;Cc: 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 AMTo: 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.txtA 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-pofRevision:       00Title:          Deterministic Networking (DetNet): Packet Ordering FunctionDocument date:  2021-04-19Group:          Individual SubmissionPages:          10URL:            &nbsp;https://www.ietf.org/archive/id/draft-varga-detnet-pof-00.txt https://urldefense.com/v3/__https:/www.ietf.org/archive/id/draft-varga-detnet-pof-00.txt__;!!B_EDKQmmvsU!7vmDpLfsfmmLuG9tQHwCrsPqlNqL_fA88lGK7awH9s4iu2A-gZ-KVq6uPhKWdzZ8c98$Status:         https://datatracker.ietf.org/doc/draft-varga-detnet-pof/ https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-varga-detnet-pof/__;!!B_EDKQmmvsU!7vmDpLfsfmmLuG9tQHwCrsPqlNqL_fA88lGK7awH9s4iu2A-gZ-KVq6uPhKWJABOkBc$Htmlized:       https://datatracker.ietf.org/doc/html/draft-varga-detnet-pof https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/html/draft-varga-detnet-pof__;!!B_EDKQmmvsU!7vmDpLfsfmmLuG9tQHwCrsPqlNqL_fA88lGK7awH9s4iu2A-gZ-KVq6uPhKWE_vUf0k$Htmlized:       https://tools.ietf.org/html/draft-varga-detnet-pof-00 https://urldefense.com/v3/__https:/tools.ietf.org/html/draft-varga-detnet-pof-00__;!!B_EDKQmmvsU!7vmDpLfsfmmLuG9tQHwCrsPqlNqL_fA88lGK7awH9s4iu2A-gZ-KVq6uPhKW2P84vhs$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.Please note that it may take a couple of minutes from the time of submission until the htmlized version and diff are available at &nbsp;tools.ietf.org https://urldefense.com/v3/__http:/tools.ietf.org__;!!B_EDKQmmvsU!7vmDpLfsfmmLuG9tQHwCrsPqlNqL_fA88lGK7awH9s4iu2A-gZ-KVq6uPhKWhEGXwQU$.The IETF Secretariat_______________________________________________detnet mailing listdetnet@ietf.org mailto:detnet@ietf.orghttps://www.ietf.org/mailman/listinfo/detnet https://urldefense.com/v3/__https:/www.ietf.org/mailman/listinfo/detnet__;!!B_EDKQmmvsU!7vmDpLfsfmmLuG9tQHwCrsPqlNqL_fA88lGK7awH9s4iu2A-gZ-KVq6uPhKWTJ53qCw$


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