Re: [Lsr] Zaheduzzaman Sarker's Discuss on draft-ietf-lsr-isis-fast-flooding-08: (with DISCUSS and COMMENT)

["Les Ginsberg (ginsberg)" <[e-mail]>]

John/Zahed –

In regards to Algorithm 2, note that older versions used the term “Flow Control”, but based on the discussion with Mirja (not that I am blaming her…) we changed that section to use the term “Congestion Control”.

This seems proper to me. If one looks at Section 6.1 – and in particular paragraphs 2 and 3 – congestion control seems like the correct choice.


Zahed – I would appreciate your updated response after rereading those paragraphs.

John – I am not entirely clear on what would address your comment. Would replacing “algorithm” with “approach” in Section 6.3.2 be satisfactory?

  Les


From: John Scudder <[e-mail]>
Sent: Thursday, April 4, 2024 6:59 AM
To: Zaheduzzaman Sarker <[e-mail]>
Cc: The IESG <[e-mail]>; [e-mail]; [e-mail]; [e-mail]; [e-mail]; [e-mail]
Subject: Re: Zaheduzzaman Sarker's Discuss on draft-ietf-lsr-isis-fast-flooding-08: (with DISCUSS and COMMENT)

Hi Zahed,

I guess the authors should respond comprehensively. I do have one response to your comments on algorithm 2, though. They seem to boil down to your first comment, "Can we really call congestion control algorithm 2 a congestion control algorithm?” It seems to me, on looking at the document again, that the answer is probably “no”. From §6.3.2, with emphasis added:

"When congestion control is necessary, it can be implemented based on knowledge of the current flooding rate and the current acknowledgement rate. **Such an algorithm is a local matter and there is no requirement or intent to standardize an algorithm.** There are a number of aspects which serve as guidelines which can be described."

I wonder if it’s both necessary and sufficient to reword “algorithm” 2 to be called something else, and to remove the RFC 2119 keywords from 6.3.x. As I read the quoted text, it’s not an algorithm, it’s hints towards an algorithm.

Looking forward to your comments and those of the authors.

—John


On Apr 4, 2024, at 6:16 AM, Zaheduzzaman Sarker via Datatracker <[e-mail]<mailto:[e-mail]>> wrote:

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----------------------------------------------------------------------
DISCUSS:
----------------------------------------------------------------------

Thanks for working on this specification. Thanks for Mirja for the TSVART
review.

I would like to discuss the following points as I believe some clarifications
would help -

- Does the flow and congestion control algorithm 1 assume that there is only on
(input)queue in a particular link? I understand that the motivation for
congestion control algorithm 2 is that there are multiple input queues and
defining rwin is difficult. Why is that easy for the case of algorithm 1?

- Can we really call congestion control algorithm 2 a congestion control
algorithm? We are are really solving the problem of flow control, it sounded
more like a emergency break ( aka circuit breaker ) to me where you reduce or
even stop sending LSPs. My point is I am not sure how to interpret the
congestion control algorithm 2 with any sort of details. If I replace section
6.3.2 with - "if the routing architecture does not support deterministic rwin,
the transmitter MUST adapts the transmission rate based on measurement of the
actual rate of acknowledgments received." what harm would it cause?

- For the congestion control algorithm 2, I am missing when the transmitter
should reduce or when it should stop sending as I am not sure reducing the
transmission rate would solve the problem of not. This comes from lack of
details on the particular algorithm that will be implemented eventually.

- Section 6.3.2. says -

   The congestion control algorithm MUST NOT assume the receive performance of
   a neighbor is static, i.e., it MUST handle transient conditions which
   result in a slower or faster receive rate on the part of a neighbor.

 How to separate the persistent congestion from transient slower receive rate?
 I am not sure how to fulfill the "MUST".


----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------

I have some further questions or comments -

- How does the implementers select between congestion control (CC) algorithm 1
and 2? or is the intention that both gets implemented and after experiments we
pick one? As in my discuss point I am not sure about the CC algorithm 2 on how
to conclude on the experiments.

- It already says flow control and congestion control is a Layer-4
responsibility, it would be great if we can say why that is not the preferred
layer for fast flooding even if it may be obvious for some of us.

- Section 6.3.2 says -

   When congestion control is necessary, it can be implemented based on
   knowledge of the current flooding rate and the current acknowledgement rate.

 So, how do we know when the congestion control is necessary?