[spring] Re: Follow-up on IETF 124 Presentation of draft-liu-spring-sr-policy-flexible-path-selection and draft clarification

[Alvaro Retana <[e-mail]>]

 On November 18, 2025 at 8:26:51 PM, Yisong Liu wrote:


Yisong:

Hi!  How are you?

> Thank you for the valuable feedback following our presentation at
> IETF 124. We would like to offer some clarification to ensure our
> draft's purpose is properly understood.
>
> In our latest revision, we have referenced
> draft-karboubi-spring-sr-policy-eligibility, though we wish to
> emphasize that the two drafts serve distinctly different purposes.
> The eligibility draft introduces new concepts for path qualification,
> while our draft focuses specifically on defining a mechanism for path
> selection and switching based on forwarding performance metrics such
> as latency, jitter, and bandwidth. Our approach predefines quality
> requirements for SR policies and enables rapid path selection or
> switching when real-time monitoring indicates these requirements are
> no longer met. The reference to eligibility is included to maintain
> compatibility with the SR Policy architecture defined in RFC 9256.
>
> We believe there is no significant overlap between our draft and
> eligibility draft and see value in advancing them independently.

I understand what you're saying, but I am having a hard time seeing that
reflected in the document.

(1) From §4:

      When a candidate path fails to meet forwarding quality
      requirements, its Eligibility attribute SHOULD be set to false,
      thereby excluding it from active candidate path selection.

   This text is effectively the same as what
   draft-karboubi-spring-sr-policy-eligibility says in §3.2 (Example 2:
   Delay sensitive paths):

       ...the policy could have a constraint to not use a path when its
       end-end delay exceeds a given value D1. ... In this case, a
       system could set the eligibility as false when it detects that
       path delay exceeds D1 (e.g. using STAMP) rendering path
       ineligible for selection...

   The main difference I see is that
   draft-karboubi-spring-sr-policy-eligibility focuses the example on
   delay, while your document mentions other possible "threshold
   parameters" (§4.1). Your document also includes examples in §4.1 and
   §5. If I may go further, the document is a more detailed version of
   the example in §3.2/draft-karboubi-spring-sr-policy-eligibility.

   The comments at the meeting in Montreal also mentioned a "high
   amount of overlap" (even from one of the authors of this document).


(2) From above: "our draft focuses specifically on defining a mechanism for
path selection and switching based on forwarding performance metrics".

   A mechanism is described in §4.3 (Flexible Candidate Path Selection
   Process):

    1) The document mentions that a "headend may be informed about the
    forwarding quality requirements...through various means", and
    points at BGP and PCEP drafts (§4).

    2) Examples of how the path can be monitored are listed in §4.3,
    but I see no specification...only examples.

    3) The Rules for Setting the Eligibility Attribute (§4.2) are
    basically the same as what is defined in
    draft-karboubi-spring-sr-policy-eligibility: if the constraints are
    met, set the Eligibility to True; otherwise, it can be set to False.

    4) Finally, "whether to revert to the previous active candidate
    path can be specified by the configuration" is mentioned as a
    possibility, but no explicit specification.


   In summary, if the intent is to define/specify a mechanism, there's
   significant work to be done, given that the document only mentions
   examples at this point. The current content does not justify the
   Intended Status of putting this document in the Standards Track.



> We would appreciate if the chairs can give the guidance on how to
> proceed with our draft. Additionally, we have formally requested an
> adoption call during our presentation and would be grateful if the
> chairs can help to schedule this.

In addition to the comments above, the main action item at this time is to
build WG engagement and interest. I only found comments from one other
non-author in the archive (Joel) [1]. We need to see explicit engagement
and interest [2] before moving forward.

Thanks!

Alvaro.


[1]
https://mailarchive.ietf.org/arch/search/?q=%22draft-liu-spring-sr-policy-flexible-path-selection%22&f_list=spring


[2] https://wiki.ietf.org/en/group/spring/WG_Policies