Subject: Re: [Lsr] Looking for feedback of using Flex Algo to advertise the 5G edge computing associated metrics

From: Peter Psenak <[email-masked]>
Date: Wed, 3 Nov 2021 13:42:44 +0100

Hi Linda,

I went through your document and here are my comments:

1. the section 1, 2, and 3 can probably be summarized in a single 
paragraph stating the problem you are trying to solve. The 5G details 
are redundant, you may just want to add reference to the parent document.

2. FAD is used to advertise how to compute the flex-algo paths, not to 
advertise metrics. What I believe you need to define for FAD is a new 
bit in the ISIS/OSPF Flexible Algorithm Definition Flags Sub-TLV to 
indicate that the calculation should use the new application prefix 
metric that you define and how exactly that metric will be used during 
calculation:

a) does it replace the regular prefix metric, is added on top, only used 
as tiebreaker, etc,.
b) what happens if the metric is not present with prefix advertisement, 
is the prefix considered unreachable for the flex-algo or do you 
fallback to regular prefix metric, etc,.
c) how is the propagation of the new metric done between areas/domains

3. The new application metric should be advertised in the IP prefix 
reachability TLV associated with the (anycast) prefix.

4. How the application metric is calculated, using load, preference, 
etc, should be hidden from IGPs. I believe the application metric should 
be calculated at the egress router, associated with the 
prefix/Server-address and advertised in a form of the resulting value. 
If you need to consider Network Delay, you can combine the new app. 
metric (for prefixes) with the existing delay metric support (for links) 
in the flex-algo, no need to include network delay in the application 
metric itself. Advertising all the metadata and asking IGP at each node 
to derive the app metric seems sub-optimal, unless there is an 
unavoidable reason to do so.

5. I don't see any reason to define a new application in SABM as you do 
in section 7. The existing flex-algo app is sufficient.

thanks,
Peter

On 14/10/2021 00:50, Linda Dunbar wrote:
> LSR experts:
> 
> We have updated the draft to reflect the suggestions from LSR WG to use 
> Flex Algo to advertise the metrics associated with the environment where 
> 5G edge computer servers are running.
> 
> https://datatracker.ietf.org/doc/draft-dunbar-lsr-5g-edge-compute/
> 
> In a nutshell, the draft proposes some new values in the Flex Algo 
> Definition Sub-TLV
> 
>   * A new Metric-Type is introduced to indicate the Aggregated Cost
>     AppMetaData Metrics included in computing the constrained SPF.
>   * Additional subsub-TLVs to be included in the Flex Algo Definition
>     Sub-TLV to carry the detailed metrics for the constrained SPF. 
> 
> We are looking for feedback of our revised approach.
> 
> Thank you.
> 
> Linda Dunbar
>

---

From: "Acee Lindem (acee)" <[email-masked]>
Date: Wed, 3 Nov 2021 13:27:16 +0000

Hi Linda,

On 11/3/21, 8:43 AM, "Lsr on behalf of Peter Psenak" <[email-masked] on behalf of ppsenak=[email-masked]> wrote:

    Hi Linda,

Please consider this comment when preparing your presentation for the LSR meeting. Since you have a 10 minute slot, there won't be time for another 5G application tutorial. 

Thanks,
Acee

    thanks,
    Peter

    > We are looking for feedback of our revised approach.

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