[Detnet] draft-varga-detnet-pof (sorry, lot of input)

Toerless Eckert <tte@cs.fau.de> Fri, 30 July 2021 22:41 UTC

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Date: Sat, 31 Jul 2021 00:40:49 +0200
From: Toerless Eckert <tte@cs.fau.de>
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Subject: [Detnet] draft-varga-detnet-pof (sorry, lot of input)
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Balazs, *:

I very much support work on POF, however:

I think we should aim higher than informational guidelines

I think we can build a normative document on two interfaces:

a) "per hop behavior"

   We can stanardize the externally observable behavior
   between arriving and sent packets on the node.

   This was regularily done for DiffServ Traffic Classes in
   TSVWG, where it is calle Per Hop Behavior. When i tried
   to apply this term to the input vs. outbut timing for
   traffic from what today is an IntServ flow (DetNet),
   David Black was somewhat concerned about re-use of the
   term, which is why i wrote "per hop behavior". IMHO,
   it is perfectly valid to also call this PHB, but i will
   leave it up to David to recommend appropriate terminology.

   I am only interested to be able to get as little as possible
   unexpecte behavior of DetNet products, and we can only 
   arrive that if we standardize the behavior.

b) Management interface

   Yang module specifying what the operator 
   can observe about the function about the POF function, e.g: 

   "static" parameters such as how many buffers there are available,
     algorithm (you do have algorithm in the draft)
    - maybe read/write if configurable.

   "dynamic parameters" - read-only for monitoring, troubleshooting:
     - buffers dynamically used,
     - latency between first and further copies
     - missing packets
     - ...

Now wrt to other content:

c) It would be lovely to have a section summarizing what if anythng
   TSN did standardize about their ordering function for all those
   IETF participants too lazy to read all that documentation
   and/or rejecting the notion of having to pay money to read a document.

   (informational, appendix).

d) I think it would be great to have anoher algorithm option
   by which one could configure for every packet copy path
   (assuming we can identify that in the forwardin plane)
   a fixed time delay.
  
   The reason for this, and why i think it was not an issue in
   TSN (with its typical topologies) is that in DetNets
   we much more likely will have rings with significant path 
   latency differences between A and B path,
   and whenever the A (shorter) path looses a packet, we would wait
   until the B path packet arrives, resulting in a lot of
   jitter. If the DetNet controller could configure 
   the B-A pah lateny difference as a delay, we could get rid
   of this problem.

Still have to dig deeper into the algo details you proposed
for more comments.

Cheers
    Toerless