Re: [Teas] Default NRP definition [Was: Repeated call for last call on draft-ietf-teas-ietf-network-slices]

[John E Drake <[e-mail]>]

Hi,

I hope this email doesn’t cause anyone’s head to explode (https://en.wikipedia.org/wiki/Scanners), but existing IP/MPLS networks can support multiple NRPs without requiring an NRP ID in either the control or data plane.

I.e., all that is needed is a way to communicate to the ingress PEs what subset of the underlay  network topology (an NRP) they are to use for a given IETF network slice service, and after that RSVP-TE or SR is used to constrain the packets to that topology.  There are at least three ways, configuration, PCE, or  https://www.ietf.org/archive/id/draft-drake-bess-enhanced-vpn-07.html, to accomplish this.  (As an aside, several years ago Joel Halpern and I developed a scheme for adding NRP support to flex-algo.)

Yours Irrespectively,

John



Juniper Business Use Only
From: Adrian Farrel <[e-mail]>
Sent: Monday, September 26, 2022 5:27 PM
To: 'Krzysztof Szarkowicz' <[e-mail]>
Cc: John E Drake <[e-mail]>; 'Greg Mirsky' <[e-mail]>; [e-mail]
Subject: RE: [Teas] Default NRP definition [Was: Repeated call for last call on draft-ietf-teas-ietf-network-slices]

[External Email. Be cautious of content]

Thanks Krzysztof,

But are today’s networks delivering network slice services?
If they are not (they can deliver services with SLOs without having to call them slices) then we won’t have to worry about any NRPs.

But, of course, it is reasonable to want to be able to show a mapping between existing services and this slicing framework. In this mapping you can talk about mapping the entire set of network resources to a single NRP. You can even say this mapping is implicit.

I think it is more healthy to talk about mapping one system to another than it is to try to force them to be the same thing. We can robustly continue to describe the systems we have and deploy, and we can say how if you want to consider one system as equivalent to another you can make the mapping.

Cheers,
Adrian


From: Krzysztof Szarkowicz <[e-mail]<mailto:[e-mail]>>
Sent: 26 September 2022 19:36
To: Adrian Farrel <[e-mail]<mailto:[e-mail]>>
Cc: John E Drake <[e-mail]<mailto:[e-mail]>>; Greg Mirsky <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: Re: [Teas] Default NRP definition [Was: Repeated call for last call on draft-ietf-teas-ietf-network-slices]

Adrian,

In today’s operator’s network, where services with SLOs are delivered, NRP is not (explicitly) defined.

Are we saying, that today’s network are providing these services without NRP (a) at all, or with implicit (default) NRP (b) that uses all resources in the network.

—
Krzysztof


On 2022 -Sep-26, at 18:48, Adrian Farrel <[e-mail]<mailto:[e-mail]>> wrote:

I would add that Krzysztof’s default NRP *is* explicitly defined. That it, the system is operated with the simple instruction “all resources are in the single NRP”. That is, it is not default and this is a policy operational decision. It may be that the operational decision is made at purchase time (this equipment supports only having a single NRP that contains all of the resources of the underlay network), but it is still an active decision. I see know benefit in referring to it as “default” since (as was pointed out way up this thread) the concept of defaulting becomes unclear when a second NRP is defined.

But shouldn’t we step back from the naming and talk about what function we need to achieve?

Adrian

From: John E Drake <[e-mail]<mailto:[e-mail]>>
Sent: 26 September 2022 17:33
To: Greg Mirsky <[e-mail]<mailto:[e-mail]>>
Cc: Krzysztof Szarkowicz <[e-mail]<mailto:[e-mail]>>; Adrian Farrel <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: Re: [Teas] Default NRP definition [Was: Repeated call for last call on draft-ietf-teas-ietf-network-slices]

Greg,

A most excellent point.  All attempts to describe a transition from a single NRP to a default NRP have foundered on this distinction.
Sent from my iPhone

On Sep 26, 2022, at 12:29 PM, Greg Mirsky <[e-mail]<mailto:[e-mail]>> wrote:

[External Email. Be cautious of content]

Hi Krzysztof,
I would note that the meaning of "default", as defined in, for example, Merriam-Webster dictionary<https://urldefense.com/v3/__https:/www.merriam-webster.com/dictionary/default__;!!NEt6yMaO-gk!H1gH-SvWJAhAijZq1KDgW_aaVA0pN9BVcWY3L4Fti4wjpwvCpYxtvhBWeBCAWTUSowUsDZ2Ur17W1aoiW-wt$>, is not the same as "single":
computers : a selection automatically used by a program in the absence of a choice made by the user
As I understand it, "default" exists and might be used in the presence of other alternatives, NPRs, in our case. Hence, it appears that by equating "single NPR" with "default NPR" we'll limit the applicability of the latter. WDYT?

Regards,
Greg


On Sun, Sep 25, 2022 at 8:07 AM Krzysztof Szarkowicz <[e-mail]<mailto:[e-mail]>> wrote:
Thanks John,

Please see inline.

//Krzysztof

On 2022 -Sep-25, at 16:51, John E Drake <[e-mail]<mailto:[e-mail]>> wrote:

Hi,

Comments inline below

Yours Irrespectively,

John


Juniper Business Use Only
From: Krzysztof Szarkowicz <[e-mail]<mailto:[e-mail]>>
Sent: Sunday, September 25, 2022 10:36 AM
To: Adrian Farrel <[e-mail]<mailto:[e-mail]>>
Cc: John E Drake <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Subject: Re: [Teas] Default NRP definition [Was: Repeated call for last call on draft-ietf-teas-ietf-network-slices]

[External Email. Be cautious of content]

Adrian,

I have couple of questions here:


1. Taking into consideration typical SP network today, where we have:

a) differentiated services realized via mapping of DCSP and/or MPLS TC values to buffers, and deploying some differentiated scheduling
b) running services (L3VPN, L2VPN, ...) over such network
c) possibly (but not necessarily) deploying some TE

Do we refere to typical current SP deployment as using ’single NRP’ or not using NRP at all?

[JD]  A single NRP

[Krzysztof] So, isn’t it wise to call this single NRP as ‘default’ NRP, as it is not explicitly defined? Adrian mentioned: "NRPs should be explicit. Sure, you can have a single one that includes all resources on all links, but that is still an active choice." I can assure you, that these operators have no idea, they operate the network using single NRP. Wording proposed by Adrian (and commented by Jie) for default NRP looks good to me.


2. If I have in my network two set of tunnels between PE nodes, using different link metric types (e.g. one set of tunnels uses IGP link metric to determine the path through the network, another set of tunnels using TE link metric to determine the path through the network), and these two sets of tunnels use exactly the same resources: entire topology, i.e. all links and nodes in the network, and the PHB is exactly the same (i.e., packet with QoS marking ‘X’ get exactly the same treatment in terms of buffering/scheduling, regardless if forwarded over tunnel from 1st tunnel set, or tunnel from 2nd tunnel set) are we talking about one NRP or two NRPs?

[JD]  A single NRP.  You are using different path computations on the same NRP

[Krzysztof] If we are changing the framework text, might be some clarification wording for this point would be needed, as I heard opinions that this constitute two NRPs.


//Krzysztof

On 2022 -Sep-22, at 18:30, Adrian Farrel <[e-mail]<mailto:[e-mail]>> wrote:

John makes some good points.


  1.  Adding a definition of a term that is only used in parentheses in one (early) individual draft where one of the authors says it was a mistake to use it, seems excessive. Perhaps we should all just stop using the term?
  2.  The idea of “default” seems wrong in any case. NRPs should be explicit. Sure, you can have a single one that includes all resources on all links, but that is still an active choice.

Adrian

From: Teas <[e-mail]<mailto:[e-mail]>> On Behalf Of John E Drake
Sent: 22 September 2022 14:55
To: John E Drake <jdrake=[e-mail]<mailto:jdrake=[e-mail]>>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: Re: [Teas] Default NRP definition [Was: Repeated call for last call on draft-ietf-teas-ietf-network-slices]

Adrian,

Upon reflection, the revised wording changes the meaning.  We start by observing that “The connected set of links can be the entire set of links in the underlay network” and then continue with “ *and in this case there
can be a single NRP* and it has all of the buffer/queuing/scheduling resources for each of the links in the underlay network”.  I.e.,  We can define one or more NRPs that use the entire underlay network topology but we can also define, in this case, a single NRP that uses all of the underlay network resources – the underlay network has a topology and it has resources.

Yours Irrespectively,

John


Juniper Business Use Only
From: Teas <[e-mail]<mailto:[e-mail]>> On Behalf Of John E Drake
Sent: Thursday, September 22, 2022 9:01 AM
To: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: Re: [Teas] Default NRP definition [Was: Repeated call for last call on draft-ietf-teas-ietf-network-slices]

[External Email. Be cautious of content]

Adrian,

I am okay with your revised wording for single NRP, but I don’t agree that we need to define a ‘default NRP’ because it is attempting to detail how a given service provider *might* operate its underlay network.  I.e., it is pure speculation.

Yours Irrespectively,

John


Juniper Business Use Only
From: Teas <[e-mail]<mailto:[e-mail]>> On Behalf Of Adrian Farrel
Sent: Thursday, September 22, 2022 6:19 AM
To: [e-mail]<mailto:[e-mail]>
Subject: [Teas] Default NRP definition [Was: Repeated call for last call on draft-ietf-teas-ietf-network-slices]

[External Email. Be cautious of content]

Hi all, again.

Jumping in at the top of the thread, yet again, to try to dig into two pieces of terminology. Picking up particularly on Greg, Jie, and Pavan’s points.

“Single” does, indeed, mean “just one”. But it’s usage is very deterministic, meaning “one of (potentially) many” in some cases, and meaning “there is exactly one” in other cases. Perhaps it would help if:
OLD
   The connected set of links can be the
   entire set of links in the underlay network and in this case there
   can be a single NRP and it has all of the buffer/queuing/scheduling
   resources for each of the links in the underlay network.
NEW
   The connected set of links can be the
   entire set of links in the underlay network and in this case there
   can be precisely one NRP supported in the underlay network where
   that NRP has all of the buffer/queuing/scheduling resources for
   each of the links in the underlay network.
END

“Default” has, of course, a clear meaning in English (although there are several different meanings). As engineers, we should be careful not to introduce terms without also writing a clear definition. If we want to use the term “default NRP” then we should define it and, in that case, this document seems like a fine place to include it. But we are definitely fishing around for what “we” mean by the term. I think we are getting to…

Default NRP:
   The default NRP is constructed from all of the buffer/queuing/scheduling
   resources on all of the links in the underlay network that have not been
   assigned for use by any other NRP.  That is, it consists of the residue
   resources.  If no other NRP has been defined, the default NRP comprises
   all of the buffer/queuing/scheduling resources of the underlay network.
   If a further NRP is subsequently defined, the default NRP will be reduced
   by the resources assigned to the new NRP.  If an NRP is deleted, its
   resources are released back into the default NRP.

Commensurate with that, the text quoted above could can become…
   In the case where there is just the default NRP and no other NRPs
   have been defined, the connected set of links can be the entire set
   of links in the underlay network, and in this case there is precisely
   one NRP (the default NRP) supported in the underlay network where
   that NRP has all of the buffer/queuing/scheduling resources for
   each of the links in the underlay network.

Thoughts?

Cheers,
Adrian

From: Vishnu Pavan Beeram <[e-mail]<mailto:[e-mail]>>
Sent: 22 September 2022 06:34
To: [e-mail]<mailto:[e-mail]>
Cc: Krzysztof Szarkowicz <[e-mail]<mailto:[e-mail]>>; Joel Halpern <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>; John E Drake <jdrake=[e-mail]<mailto:jdrake=[e-mail]>>
Subject: Re: [Teas] Repeated call for last call on draft-ietf-teas-ietf-network-slices

Adrian, Hi!

Thanks for the top-post. Please see inline (prefixed VPB).

Regards,
-Pavan


On Thu, Sep 22, 2022 at 3:46 AM Adrian Farrel <[e-mail]<mailto:[e-mail]>> wrote:
Hi,

Sort of top-posting on the thread, and speaking as editor.

Krzysztof >>
> I see that the current text is clear and precisely describes the
> intent of single (default) NRP, so it doesn’t need any change/correction.

Well, it was certainly the intent that the text would be clear, but if some people are confused or unclear, we should seek to make things clearer.

Note well that the term "default NRP" is not one that is used in the document, and any lack of clarity about the term must be laid at the feet of the people using the term!
I *think* the term is being used to describe the limiting case where there is just one NRP that is all of the resources in the network.

Joel >>
 > Does that single NRP admit multiple diffserv code points / queueing behaviors?
[JD]  That is at the discretion of the underlay network operator

I think John and Joel may be at cross-purposes with the same conclusion.
To Joel: Yes, the single NRP admits the possibility of multiple diffserv code points / queueing behaviors.
To John: Yes, the underlay network operator is free to make the default NRP have multiple or fewer codepoints / queueing behaviors.

Joel >>
> If so, then the notion of NRP is itself purely an arbitrary collection of
> behaviors, and thus not helpful or particularly meaningful.

"Arbitrary" and "helpful" are possibly a bit loaded.
Recall that the NRP is an internal mechanism for the underlay network operator. It is not exposed to the customer, but is a tool for the operator.
It allows the operator to partition their network in a way that they find useful for the rapid construction of network slices.
What that amounts to is that the operator may profile the resources of the network into collections (NRPs) to enable the support of particular types of network slice service.
The way that an operator does this is entirely up to them (it's a policy), so it could be arbitrary or highly logical.

But some people think that it won't be necessary to build NRPs and so we have the concept of "the default NRP" which is essentially all of the resources of the network.
It's a null-op in the process, but we keep it there to have a consistent picture.

Joel >>
> One way out is to declare that relative to any given device, the collection of behaviors in
> an NRP may be different diffserv code points but may not be further differentiated.
> Another way out is to declare that the collection referred to in the definition refers to
> the collection across devices, but within a device an NRP has only one queueing
> behavior / resource.

But I wonder if there is a confusion between resources and behaviors? The text in the draft is clear that it is describing resources. How the resources are used is surely a different matter, or is it?

As a quick reference, the text we're talking about is...

   A Network Resource Partition (NRP) is a collection of resources
   (bufferage, queuing, scheduling, etc.) in the underlay network.  The
   amount and granularity of resources allocated in an NRP is flexible
   and depends on the operator's policy.  Some NRP realizations may
   build NRPs with dedicated topologies, while some other realizations
   may use a shared topology for multiple NRPs; one possible realization
   is of a single NRP using all of the resources of the entire underlay
   network topology.  Thus, an NRP consists of a subset of the
   buffer/queuing/scheduling resources on each of a connected set of
   links in the underlay network.  The connected set of links can be the
   entire set of links in the underlay network and in this case there
   can be a single NRP and it has all of the buffer/queuing/scheduling
   resources for each of the links in the underlay network.

Pavan and Lou >>
> This thread does seem to suggest there are some loose ends with
> respect to the notion of a default NRP that need to be tied before
> publication. There are some open questions on how resources in
> the default NRP get impacted when you start adding resource
> partitions in the underlay network.

We do have to return to ask, "What is this default NRP that you are talking about?" If it is, as I assume, the "single NRP" that "has all of the buffer/queuing/scheduling resources for each of the links in the underlay network" then it should be fairly obvious that adding other NRPs does change the definition of the "default NRP." This happens because the default NRP stops being the only NRP and so stops being the default NRP.

I believe you have yourself wrapped around the definition of a term that doesn't exist.

[VPB] You are right -- draft-ietf-teas-ietf-network-slices does not use the term "default NRP".  draft-ietf-teas-ns-ip-mpls, which extensively discusses the notion of one or more network resource partitions, also does not use this term (yet). But, we are starting to discuss slicing realization documents in the WG that are building on this notion of a "default/single/only NRP" as framed in draft-ietf-teas-ietf-network-slices (see draft-srld-teas-5g-slicing which does use this term) and for that purpose it may be useful to discuss what this entails (now rather than later).  As Jie has pointed out in this thread, there is an interpretation here that you may start with a default NRP (no explicit resource partitioning) to realize slicing, but you may end up having the default NRP co-exist with non-default NRPs as they get gradually added to the network. The default NRP in this interpretation may simply translate to the set of resources that don't meet the selection criteria of any explicit user-specified NRP (if there are no user-specified NRPs, then the default NRP includes all the resources in the underlay network). Another interpretation of the default NRP is (like you said) that it ceases to exist when the first resource partition is made (two explicit NRPs get created).

[VPB] We (the WG) may end up saying that we don't need to discuss "default NRP" or its semantics in draft-ietf-teas-ietf-network-slices, but rather have it discussed in draft-ietf-teas-ns-ip-mpls (which does talk about slicing realization using one or more resource partitions) instead. But it is a loose end that needs to be tied at some point.


Pavan and Lou >>
> We are hoping that the WGLC (the process for which has just begun)
> would be a forcing function for those of you (chairs included) who
> intend to suggest text/edits to clear this up.

It would be great if exactly that happened. That is, text suggestions.

Cheers,
Adrian
_______________________________________________
Teas mailing list
[e-mail]<mailto:[e-mail]>
https://www.ietf.org/mailman/listinfo/teas<https://urldefense.com/v3/__https:/www.ietf.org/mailman/listinfo/teas__;!!NEt6yMaO-gk!C0Cbp6e6wcOCIVeA1aT1n44Wf96-VKMA8tnK1DUNPN_0pNkp0OBouxUGsaaZCen03sfeMUmURWIB-wW6HCBj$>

_______________________________________________
Teas mailing list
[e-mail]<mailto:[e-mail]>
https://www.ietf.org/mailman/listinfo/teas<https://urldefense.com/v3/__https:/www.ietf.org/mailman/listinfo/teas__;!!NEt6yMaO-gk!H1gH-SvWJAhAijZq1KDgW_aaVA0pN9BVcWY3L4Fti4wjpwvCpYxtvhBWeBCAWTUSowUsDZ2Ur17W1QCegxMj$>