Re: [Teas] WG adoption - draft-nsdt-teas-transport-slice-definition - Appendix

["Gengxuesong (Geng Xuesong)" <[e-mail]>]

Hi Greg,

Thank you for directing the discussion to the technical nature of isolation. Please find comments below:
I assume that the term "isolation" is not simply a replacement for "dedicated" and is intended to apply to cases when transport slices share underlying infrastructure.
I agree about your description of isolation. Although there may be other kinds of understanding which will broaden the scope of this concept. I will leave it to the authors and WG. The discussions below based on the assumption that “isolation is intended to apply to cases when transport slices share underlying infrastructure ”.
There is a number of performance metrics that may indicate the lack of isolation but that, in my view, can be attributed to under-isolation (for the lack of better term at the moment) between slices as the result of root cause analysis of increased latency and/or packet loss.
I think here hides some basic logic behind the debate: if the isolation could be described indirectly by other SLO attribute, whether we still need it as an independent concept. My answer is: the hypothetical part of the question is incorrect, because isolation can’t be described by other attributes, although it influences other attributes. A further conclusion is that : Deterioration of other SLO metrics is neither sufficient nor necessary for isolation absence. Two simple examples to defense this:

1.       When isolation is perfectly executed that there is no interfere among different slices, the performance could still be very terrible if the resource inside the slice is exhausted.

2.       When there is no isolation among slices and all the resource is shared, the performance could still be very great if the resource is sufficient for all the slices.
So the trick here is: other SLO attributes (delay, jitter, loss…) depend on whether there is enough cake to make everybody happy, and isolation prevents other guys to touch my cake. They're relevant, but they're different, and not interchangeable.
That is why I agree that isolation should be clearly defined in draft-nsdt-teas-transport-slice-definition, not in Appendix.

Regards,
Xuesong


From: Greg Mirsky [mailto:[e-mail]]
Sent: Sunday, August 30, 2020 5:38 AM
To: Gengxuesong (Geng Xuesong) <[e-mail]>
Cc: Jeff Tantsura <[e-mail]>; TEAS WG <[e-mail]>; Jari Arkko <[e-mail]>; Vishnu Pavan Beeram <[e-mail]>
Subject: Re: [Teas] WG adoption - draft-nsdt-teas-transport-slice-definition - Appendix

Hi Xuesong,
I assume that the term "isolation" is not simply a replacement for "dedicated" and is intended to apply to cases when transport slices share underlying infrastructure. If that is the case,  I think there's a sort of contradiction between statements "isolation is SLO" and "isolation is not directly measurable [calculable GIM]". I wonder, What is the opposite of isolation as a TS characteristic? I imagine that one example of that would be a case when the flow from one slice is using resources from another, i.e., interference between slices. There is a number of performance metrics that may indicate the lack of isolation but that, in my view, can be attributed to under-isolation (for the lack of better term at the moment) between slices as the result of root cause analysis of increased latency and/or packet loss. And even if interference from another slice doesn't result in observable quality degradation, an operator can compare the offered load from the customer with the available BW. And that information doesn't have to be measured by the client but reported by the operator in the agreed intervals and aggregated on an hourly and daily basis. Certainly, we can have more cases that constitute the un-isolationism of slices but that, I suspect, still will be observable, measurable, calculable through other SLOs and only the analysis will point to the inadequate isolation of resources.
But back to the isolation. I believe that the proposal from WG Chairs is the best way forward. Let us explore our interpretations of the term and work on formulating one we can build consensus (rough) around. And if so happens that there is none, then we all get a better understanding of the problem and may get it in the new document.

Regards,
Greg

On Tue, Aug 25, 2020 at 7:40 PM Gengxuesong (Geng Xuesong) <[e-mail]<mailto:[e-mail]>> wrote:
+1
And one more supplementary comment about “Isolation is not a directly measurable SLO”. Maybe here is some fog about what is measurable. Isolation could not described by number/value. But it doesn’t mean that it is an abstract concept that could not be defined precisely. People are asking whether TE link is isolated or not. It could be clarified by some deep analysis, good discussions and clear text. There is no conclusion yet just because we don’t even allow it to be existing in an WG document. And I don’t think the definition of other SDOs really matter. Because isolation in mobile network is different from isolation in IETF. If there is requirement in IETF, define it in IETF. We can’t say we could not get to somewhere because there is no path. Build the path by ourselves.

Xuesong

From: Teas [mailto:[e-mail]<mailto:[e-mail]>] On Behalf Of Jeff Tantsura
Sent: Wednesday, August 26, 2020 6:32 AM
To: TEAS WG <[e-mail]<mailto:[e-mail]>>; Jari Arkko <[e-mail]<mailto:[e-mail]>>
Cc: Vishnu Pavan Beeram <[e-mail]<mailto:[e-mail]>>
Subject: Re: [Teas] WG adoption - draft-nsdt-teas-transport-slice-definition - Appendix

I find Pavan and Lou proposal reasonable and a good/working way forward.
While isolation is not a directly measurable SLO, it is often a legally binding requirement wrt service provided, could be expressed as a physical SRLG or disjointness.
It is also a viable constrain to be used in  a path computation logic.
There are connectivity RFIs that explciteily require full physical separation/isolation - finance for security reasons,  DCI for resiliency, etc.

We could pretend it doesn’t exist (which is the complete removal) or find an appropriate and acceptable to the WG description as the document evolves.

Cheers,
Jeff
On Aug 25, 2020, 12:59 PM -0700, Jari Arkko <[e-mail]<mailto:[e-mail]>>, wrote:
High-level bit: I would like to see the document adopted. With changes if needed. Let the WG decide. Design teams are there just for preparing proposals. Authority to do stuff is entirely in the WG now.

When it comes to the isolation topic, however, FWIW, I wanted to provide both a context from design team discussions and my personal perspective on this.

Design team discussions:

We’ve had variants of this discussion on almost all of the calls we’ve had for the last year. One one side there was our shared observation that industry uses the term isolation, and (perhaps less widely shared conclusion) that it is important to be able to relate to this. On the other side, there was our shared agreement that what matters from a requirement perspective is the bandwidth and other requirements, and that there are several techniques that can provide the desired characteristic of not having your neighbour affect the bandwidth the service provider has agreed to give you.

The text that we had was in an appendix precisely because we felt that the top-level SLOs should be the requirement and are sufficient by themselves. The appendix only attempts to say that “there’s multiple ways to achieve this, and by the way, this term in the industry relates to our work in this indirect way”..

I can appreciate that we may have failed in the task of writing that. Delete and move on, no biggie :-)

Personal perspective:

My impression of customer requirements and how they get represented matches with what Joel has been saying in this thread.

I’m fine removing the appendix.

If I had my way, I would write the document based entirely on the primary characteristics — such as that we promise you n GB/s. Then I would write a footnote or appendix somewhere that explains that this notion isolation has also been discussed elsewhere, and that it can be represented using the primary characteristics, and hence need not be discussed further in this document. One could perhaps also point out that there are multiple ways to implement the primary characteristics promises, so that those promises can be kept despite what’s happening with your neighbour’s traffic. And leave it at that. But I understand from this thread that people are reluctant to do that, and may even be reluctant to write anything about isolation. I’m fine with that, too.

Jari

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