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

[Tony Li <[e-mail]>]

Hi William, Gyan, Robert, Tony, et. al.,

Please permit me to wax a bit philosophic here.

William is exactly correct that the goal is not to make FlexAlgo deal with reservations like RSVP does.  Without some kind of setup protocol or global computation, that’s simply not possible. Moreover that’s not the real problem that we’re out to solve.

Reservations are just a first order approximation to a traffic flow in any case. We characterize them as having a fixed constant bandwidth, but we all know that that is far from the truth. Each flow is diurnal and fractally bursty. Every user who ever clicks on a link creates bandwidth demand and while the Law of Large Numbers helps us out with some averages we all know that we have no good way of characterizing the traffic that we’re trying to carry. Claiming that it is a single 12Gbps LSP is truly a huge over simplification and a good step towards solving the real problem.

So what is the real problem that we’re trying to solve?

We are trying to not drop packets.

Dropping packets is bad because it forces retransmissions and impacts someone’s Internet experience. Dropping packets is our response to congestion events. If we could manage to have a network that never congested and always delivered packets without giant latency, all would be good.

To date, we have created traffic engineering mechanisms to help us steer traffic so that we could delivery traffic without congesting. It has been a means to an end. The mechanisms that we’ve created have a non-trivial overhead and approximate our goals, but they do NOT preclude, anticipate, or avoid congestion. They do not react when we have unexpected inputs. We do extensive pre-computation to deal with even single failures and have no serious mechanisms that handle multiple failures.

Right now, FlexAlgo does nothing to help with bandwidth management. Wiilliam et. al., are proposing some first steps, which are to be encouraged. Much more will be needed, not to recreate legacy mechanisms but because we should be striving for a more sophisticated, real-time approach to bandwidth management and congestion avoidance.

Regards,
Tony


> On Mar 1, 2021, at 2:24 AM, William Britto A J <bwilliam=[e-mail]> wrote:
> 
> Hi Gyan, 
>  
> This draft aims to provide the protocol constructs to define a flex-algorithm which is suitable for sending high bandwidth traffic. Flex-Algo is a very useful feature for network consolidation use-cases which requires different metric-types for SPF. We are trying introduce the protocol constructs to simplify the use of metric based on bandwidth via Flex-Algo.
>  
> This draft does not attempt to do bandwidth management nor reservation like what RSVP does. For LDP based networks that use igp metric relative to bandwidth, Flex-Algo provides an easy alternate.
>  
> Thanks,
> William
>  
> From: Gyan Mishra <[e-mail] <mailto:[e-mail]>>
> Date: Saturday, 27 February 2021 at 9:40 PM
> To: Robert Raszuk <[e-mail] <mailto:[e-mail]>>
> Cc: DECRAENE Bruno IMT/OLN <[e-mail] <mailto:[e-mail]>>, Rajesh M <[e-mail] <mailto:[e-mail]>>, Shraddha Hegde <[e-mail] <mailto:[e-mail]>>, William Britto A J <[e-mail] <mailto:[e-mail]>>, [e-mail] <mailto:[e-mail]> <[e-mail] <mailto:[e-mail]>>
> Subject: Re: [Lsr] New draft on Flex-Algorithm Bandwidth Constraints
> 
> [External Email. Be cautious of content]
>  
>  
> Hi William & Co-authors 
>  
> From first read of the draft it does appear your are trying to apply RSVP TE PCALC path and reserve message link attributes constraints such as concept of affinity bits to exclude low bandwidth or delay of individual links without taking into account all of what RSVP TE is reserving of bandwidth in the end to end path with the Path and Reserve message.  As mentioned Looking at individual links will not provide the end to end path view or bandwidth requirements for the entire path to be reserved as accomplished by RSVP TE.  
>  
> As Tony and Robert have mentioned I agree this is a good first step but does need more refinement to make useful.
>  
> Kind Regards 
>  
> Gyan
>  
> On Sat, Feb 27, 2021 at 7:24 AM Robert Raszuk <[e-mail] <mailto:[e-mail]>> wrote:
> Hi William & co-authors, 
>  
> I read the draft and have two basic questions. 
>  
> 1. 
> Both bw & delay can be used as defined in the draft to construct new forwarding topologies. But how practical such topologies would be in the real life when 40GB links may be heavily occupied with bursty traffic and 10G links can sit idle ? I suppose you are trying to address the case where say 12 gbps holographic stream needs to be sent across a network.. But then I don't think if sending it in a single flow instead of spreading into many sub-flows and use as much as possible ecmp would not be a better option. 
>  
> 2. 
> Likewise how good is my accumulated link delay value if in between there are deep buffer network elements and say egress queuing to each link (which max is unaccounted for in your draft) can significantly alter the end to end delay ? Have you consider to add MAX_EGRESS_QUEUE_DELAY on a per link basis (still as static value).  So if some traffic is delay sensitive we will have a much better accuracy not to get into a trap of queuing related delays. 
>  
> Thx a lot,
> Robert.
>  
>  
> On Fri, Feb 26, 2021 at 8:37 AM William Britto A J <bwilliam=[e-mail] <mailto:[e-mail]>> wrote:
> All,
>  
> We would like to draw your attention to a new ID: https://datatracker.ietf.org/doc/html/draft-hegde-lsr-flex-algo-bw-con-00 <https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/html/draft-hegde-lsr-flex-algo-bw-con-00__;!!NEt6yMaO-gk!U3HBQwaZL7T4mjz-MUHE7VjFtnOyNghGDh5vwJXUXkHdMxlravmRvJwdZ8sz2YPxkw$>
>  
> The draft talks about introducing link bandwidth related constraints in Flex-Algorithm which can be used to define a Flex-Algorithm based on bandwidth based metric.
>  
> Please review. Any questions and comments are welcome.
>  
> Thanks,
> William
>  
>  
> From: [e-mail] <mailto:[e-mail]> <[e-mail] <mailto:[e-mail]>>
> Date: Monday, 22 February 2021 at 10:56 PM
> To: Bruno Decraene <[e-mail] <mailto:[e-mail]>>, Rajesh M <[e-mail] <mailto:[e-mail]>>, Rajesh M <[e-mail] <mailto:[e-mail]>>, Shraddha Hegde <[e-mail] <mailto:[e-mail]>>, William Britto A J <[e-mail] <mailto:[e-mail]>>, William Britto A J <[e-mail] <mailto:[e-mail]>>
> Subject: New Version Notification for draft-hegde-lsr-flex-algo-bw-con-00.txt
> 
> [External Email. Be cautious of content]
> 
> 
> A new version of I-D, draft-hegde-lsr-flex-algo-bw-con-00.txt
> has been successfully submitted by Shraddha Hegde and posted to the
> IETF repository.
> 
> Name:           draft-hegde-lsr-flex-algo-bw-con
> Revision:       00
> Title:          Flexible Algorithms Bandwidth Constraints
> Document date:  2021-02-22
> Group:          Individual Submission
> Pages:          21
> URL:            https://urldefense.com/v3/__https://www.ietf.org/archive/id/draft-hegde-lsr-flex-algo-bw-con-00.txt__;!!NEt6yMaO-gk!QGg36p91zPfVMznYY91xs-zx70Qp5BE1nJx-Thnl14sTCkvwgOjEzjGBtD3v6TruoA$ <https://urldefense.com/v3/__https:/www.ietf.org/archive/id/draft-hegde-lsr-flex-algo-bw-con-00.txt__;!!NEt6yMaO-gk!QGg36p91zPfVMznYY91xs-zx70Qp5BE1nJx-Thnl14sTCkvwgOjEzjGBtD3v6TruoA$>
> Status:         https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-hegde-lsr-flex-algo-bw-con/__;!!NEt6yMaO-gk!QGg36p91zPfVMznYY91xs-zx70Qp5BE1nJx-Thnl14sTCkvwgOjEzjGBtD1VexjHPQ$ <https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/draft-hegde-lsr-flex-algo-bw-con/__;!!NEt6yMaO-gk!QGg36p91zPfVMznYY91xs-zx70Qp5BE1nJx-Thnl14sTCkvwgOjEzjGBtD1VexjHPQ$>
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> 
> 
> Abstract:
>    Many networks configure the link metric relative to the link
>    capacity.  High bandwidth traffic gets routed as per the link
>    capacity.  Flexible algorithms provides mechanisms to create
>    constraint based paths in IGP.  This draft documents a set of
>    bandwidth related constraints to be used in Flexible Algorithms.
> 
> 
> 
> 
> 
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