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

Peter Psenak <ppsenak@cisco.com> Wed, 03 March 2021 10:47 UTC

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To: Robert Raszuk <robert@raszuk.net>
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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From: Peter Psenak <ppsenak@cisco.com>
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Date: Wed, 3 Mar 2021 11:47:18 +0100
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Subject: Re: [Lsr] New draft on Flex-Algorithm Bandwidth Constraints
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Robert,

On 03/03/2021 11:41, Robert Raszuk wrote:
> 
> Sorry but to me the draft is very clear that it does not care about min 
> delay, but possible maximum delay of a link  ...

"maximum link delay constraint" !=  "max link delay"

You are not listening.

Peter

> 
> 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. 
> <http://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 
> <mailto: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>
>      > <mailto: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.
>      >      >
>      >      >
>      >      >
>      >      >
>      >
>