Re: [Lsr] New draft on Flex-Algorithm Bandwidth Constraints

Robert Raszuk <robert@raszuk.net> Wed, 03 March 2021 10:42 UTC

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In-Reply-To: <42fbaa46-7434-39fb-b5a1-97fe0c7866d3@cisco.com>
From: Robert Raszuk <robert@raszuk.net>
Date: Wed, 3 Mar 2021 11:41:47 +0100
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To: Peter Psenak <ppsenak@cisco.com>
Cc: Tony Li <tony.li@tony.li>, Gyan Mishra <hayabusagsm@gmail.com>, "DECRAENE Bruno IMT/OLN" <bruno.decraene@orange.com>, Shraddha Hegde <shraddha@juniper.net>, Rajesh M <mrajesh@juniper.net>, "lsr@ietf.org" <lsr@ietf.org>, William Britto A J <bwilliam=40juniper.net@dmarc.ietf.org>
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Subject: Re: [Lsr] New draft on Flex-Algorithm Bandwidth Constraints
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Sorry but to me the draft is very clear that it does not care about min
delay, but possible maximum delay of a link  ...

After all for time sensitive applications we do care how long it will take
to actually traverse a path in practice not what would be the theoretical
min amount of time needed for this path to be traversed.

And it does define it here as brand new metric.

Just read this paragraph as well as sections 3.1.2 and 3.2.2.:

   Similarly, exclude maximum link delay constraint is also defined in
   this document.  Links may have the link delay measured dynamically
   and advertised in delay metric in IGP.  For usecases that deploy low
   latency flex-algo, may want to exclude links that have delay more
   than a defined threshold.

Thx,
R.


On Wed, Mar 3, 2021 at 11:31 AM Peter Psenak <ppsenak@cisco.com> wrote:

> On 03/03/2021 11:27, Robert Raszuk wrote:
> >
> > I am not sure I follow your logic here ...
> >
> > If we are already advertising "Min Unidirectional link delay" as
> > described in https://tools.ietf.org/html/draft-ietf-lsr-flex-algo-13
> why
> > would we need to define it again here in this draft ?
>
> we are not defining the metric here, we are defining the constraint that
> says what is the maximum value of that metric that can be used.
>
> thanks,
> Peter
> >
> > Also does it really make sense to advertise maximum value of
> > minimum value ?
> >
> > Thx,
> > R.
> >
> > On Wed, Mar 3, 2021 at 11:22 AM Peter Psenak <ppsenak@cisco.com
> > <mailto:ppsenak@cisco.com>> wrote:
> >
> >     Robert,
> >
> >     On 03/03/2021 11:10, Robert Raszuk wrote:
> >      > Hey Peter,
> >      >
> >      >      > Authors stated: "Whether egress queueing delay is included
> >     in the
> >      >     link
> >      >      > delay depends on the measuring mechanism."
> >      >
> >      >     I disagree with that statement - the Min Unidirectional Link
> >     Delay is
> >      >     the value that does not include the queueing delay - that's
> >     why it is
> >      >     called Min.
> >      >
> >      >
> >      >
> >      > But draft we are discussing here does not talk about "Min" delay.
> >      > Contrary it talks about "Max"
> >      >
> >      > *Maximum*  Delay sub-TLV
> >      >
> >      > That is also I asked that very question up front.
> >
> >     I'm afraid you misunderstood it. FA uses "Min Unidirectional Link
> >     Delay"
> >     as one of its metrics. The "Maximum Delay sub-TLV"  is used to
> >     advertise
> >     the maximum value of the "Min Unidirectional Link Delay" that is
> >     allowed
> >     for the particular FA.
> >
> >     The text should be improved in that regard though, it's not obvious,
> >     but
> >     I believe that's what it is.
> >
> >     thanks,
> >     Peter
> >
> >      >
> >      > Thx,
> >      > R.
> >      >
> >      >
> >      >
> >      >
> >
>
>