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

Shunsuke Homma <s.homma0718@gmail.com> Wed, 02 September 2020 16:21 UTC

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From: Shunsuke Homma <s.homma0718@gmail.com>
Date: Thu, 3 Sep 2020 01:21:43 +0900
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To: adrian@olddog.co.uk
Cc: Vishnu Pavan Beeram <vishnupavan@gmail.com>, TEAS WG <teas@ietf.org>, TEAS WG Chairs <teas-chairs@ietf.org>
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Subject: Re: [Teas] WG adoption - draft-nsdt-teas-transport-slice-definition
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Hi Adrian,

Thank you for your detailed review and valuable feedback.

Regarding the necessity of this work, in my understanding, there are mainly
two reasons:
- Unifying understanding about network slicing and scope of design team's
work. As you know, network slice have wide meaning and the definition is
very ambiguous.  There are many drafts and some RFCs which mention network
slicing, but the terms and definitions seem not unified. For example, RFC
8578 describes what network slicing is. Is it completely the same with one
defined in RFC 8453? For designing the framework and NBI, we need to be on
the same page, and documentation is an approach to do this. At least, we
found there is a gap between understanding between DT and WG by this draft,
and this was help at that point, isn't it?
- Showing IETF's understanding on network slicing to externals such as
other SDOs. Currently, several SDOs are discussing network slicing, but the
scopes are based on their ranges of responsibility. For example, the main
scope of 3GPP is standardizing specification of radio communication and
user plane for mobility management of UE's.  Transport network is out of
their scope, and TN slicing is not discussed enough. This work is expected
to fill the lack. For realizing E2E network slices which includes not only
transport network but other slices and network functions, it is needed to
harmonize technologies of several SDOs including IETF, and it would be
important to show thought of IETF on network slices. Actually, some SDOs
are interested in IETF technologies for network slicing usage, but wondered
which documents they should refer to.

If they are achieved, I personally think we can select other ways, for
example, as Deborah recommended, moving the essences to other related
drafts such as framework or  NBI drafts.

Best regards,

Shunsuke

2020年9月2日(水) 6:36 Adrian Farrel <adrian@olddog.co.uk>uk>:

> Hi,
>
>
>
> I've reviewed this document as part of the adoption poll. My review has
>
> been partially overtaken by threads on the list. Sorry about that, but
>
> it is a lengthy review.
>
>
>
> I'd like to start by thanking the design team for tackling the thorny
>
> subject of terminology, and the authors of this draft for pulling
>
> together the various opinions of the team so that we, the working group,
>
> can do the easier task of reviewing the material.
>
>
>
> I'm aware that the conditions for WG adoption specifically do not
>
> include that the document should be perfect. But it is important that
>
> the work is clear enough and sufficiently on message that we can work
>
> out what it is for and why we might adopt it.
>
>
>
> In my review, below, I raise a number of points that I think are quite
>
> serious and need to be addressed before we can look at the document
>
> properly and decide whether or not to adopt it. These points call into
>
> question what is actually being defined. That is, I am reserving
>
> judgement and not saying "adopt once these issues are fixed."
>
>
>
> Above all, I see no benefit to a document that defines a term that seems
>
> to have no particular benefit or use. We know that underlay networks
>
> carry traffic for overlay networks. We know that virtualisation can be
>
> done at different technology levels and that networks can be arranged
>
> hierarchically or stitched together with abstraction and adaptation.
>
> We know that an underlay network can be sliced. What additional benefit
>
> is the definition of the term "Transport Slice" bring? It looks that the
>
> composed end-to-end transport slice is another term for a virtual
>
> network, where at the lowest level a transport slide seems to be a
>
> network slice. This question has to be answered before I can support
>
> adoption.
>
>
>
> Finally, I want to say that we often decide to adopt a document on the
>
> understanding that we can fix it up later. But in this case I am very
>
> concerned that adopting this document would be interpreted as the
>
> acceptance of the concept of a transport slice without agreement on
>
> what it is or why we want it. That would surely lead us into a very
>
> difficult place where debate about the document would be hard to
>
> progress.
>
>
>
> Thanks,
>
> Adrian
>
>
>
> ===
>
>
>
> I brought up my concern about the use of the term "Transport" around
>
> IETF-106 and it still bothers me. The Abstract says "...the definition
>
> of a slice in the transport networks" but since that term is not common
>
> in the IETF (or rather, it has two very specific meanings neither of
>
> which is intended here) the Abstract fails in its goal "to bring
>
> clarity".
>
>
>
> A more accurate Abstract might be:
>
>
>
>    This document provides a definition of the term "Transport Slice" for
>
>    use within the IETF and specifically within other IETF documents that
>
>    describe aspects of network slicing.
>
>
>
>    The document also describes the characteristics of a transport slice,
>
>    describes related terms and their meanings, and explains how
>
>    transport slices can be used in combination with end to end network
>
>    slices or independent of them.
>
>
>
> Section 3 goes on to reference RFC 5921 to give basis for use of the
>
> word "transport". In view of this, it might be interesting to examine
>
> how any network slice can be anything other than a transport slice. That
>
> will lead to a discussion about why this document needs to be separate
>
> from the slicing framework draft. The answers to these questions would
>
> usefully be placed in the document.
>
>
>
> ---
>
>
>
> Section 1
>
>
>
>    A number of use cases benefit from establishing network connectivity
>
>    providing transport and assurance of a specific set of network
>
>    resources.
>
>
>
> I cannot understand this sentence. What does it mean to "provide
>
> transport"? Transport of what? And, is there a punctuation issue or does
>
> the text mean "transport of network resources"?
>
>
>
> What does "assurance of network resources" mean?
>
>
>
> ---
>
>
>
> Section 1
>
>
>
>
>
>    In this document, as detailed in the subsequent sections,
>
>    we refer to this connectivity and resource commitment as the
>
>    transport slice.
>
>
>
> It is unhelpful to include this text here. Is this the normative
>
> definition of a transport slice or just a passing comment?
>
>
>
> ---
>
>
>
> Section 1
>
>
>
>    Services that might benefit from the transport
>
>    slices include but not limited to:
>
>
>
> Since this assertion is unsubstantiated and expressed as a speculation
>
> it reads like marketing! I suspect we don't need it or the list of
>
> bullets, but maybe you could insert forward references to the sections
>
> that describe the use cases and how a transport slice might be
>
> beneficial in those cases (those would be sections yet to be written).
>
> If, as you seem to imply, the reason for this document is to describe
>
> a term for a concept that has value in certain deployments, I think it
>
> is incumbent on you to describe those cases.
>
>
>
> I would recommend throwing out the whole of Section 1 as currently
>
> written and replacing it with an Introduction that expands upon the
>
> Abstract as well as describing what the document will do. You would
>
> still want to add the use case descriptions.
>
>
>
> ---
>
>
>
> Section 1.1
>
>
>
> This section launches into a discussion of why we want a transport
>
> slice, but it does so before defining (section 3) what a transport slice
>
> actually is. The later paragraphs of this section are descriptive about
>
> transport slices, but are presumably not normative definitions.
>
>
>
> You may find it helpful to re-write this section in abstract terms. What
>
> behaviors are needed from the network? How is the network operated? How
>
> does this compare with "traditional" VPNs? In other words, don't mention
>
> Transport Slice in this section at all, but use this section to
>
> establish the need.
>
>
>
> ---
>
>
>
> Section 1.1
>
>
>
>    Transport slice is described as a construct that specifies
>
>    connectivity requirements, emphasizing on assurance of those
>
>    requirements.  Transport slice is unaware of the underlying
>
>    infrastructure connectivity (hence, the term "transport").
>
>
>
> Firstly, please avoid using passive voice. I think you are defining (in
>
> this not document) not running a commentary on the fact that someone
>
> somewhere describes "transport slice" in a particular way.
>
>
>
> More important, however, is what is going on here. It appears that you
>
> are describing a "transport slice as a service". This would be really
>
> helpful to state up front. That is, you are not describing how the
>
> transport slice is delivered by the network, nor any visibility that
>
> the client has of that network. Hence, "[the] transport slice if unaware
>
> of the underlying infrastructure connectivity".
>
>
>
> But this view as a "service" seems at odds with the quote in Section 3
>
> where you state that
>
>
>
>    "A transport slice is a logical network topology connecting a number
>
>    of endpoints with a set of shared or dedicated network resources,
>
>    that are used to satisfy specific Service Level Objectives (SLOs)".
>
>
>
> ...If the transport slice is unaware of the underlying infrastructure
>
> connectivity, how can the slice be a set of shared or dedicated network
>
> resources?
>
>
>
> I don't understand how you get to 'hence the term "transport"' from the
>
> lack of awareness of underlying infrastructure.
>
>
>
> ---
>
>
>
> Section 1.1
>
>
>
> Relation to Enhanced VPN. As you know, VPN+ is adopted TEAS work. I see
>
> that you have an Informative reference to draft-ietf-teas-enhanced-vpn,
>
> but I also see that you never make use of this reference until the
>
> appendix. I think you need to discuss VPN+ in Section 1.1 to provide
>
> sufficient contrast and to explain why you need your new concept.
>
>
>
> ---
>
>
>
> Section 1.1.
>
>
>
> The final paragraph in this section says "Transport slices relate to a
>
> more general topic of network slicing." It is hard to evaluate this
>
> without a more detailed description of network slicing than is provided
>
> in the single next sentence. In particular, we need to understand why
>
> you need the term "transport slice" instead of simply "network slice."
>
>
>
> I'd say you could go one of three ways:
>
> 1. Provide a more detailed description of network slicing in this
>
>    document
>
> 2. Make a normative reference to some other document that defines a
>
>    network slice
>
> 3. Remove this paragraph and clean the document so that the focus is
>
>    entirely on the definition of "transport slice" and no mention is
>
>    made of "network slicing".
>
>
>
> ---
>
>
>
> Section 2
>
>
>
> Trying to not nit-pick this section (it can be worked on later), but
>
> the terms SLI, SLO, and SLA seem to be fairly important within this
>
> document. These three brief paragraphs are not very much information
>
> for such key terms.
>
>
>
> You probably either need a section to go into more details of these
>
> definitions or you need external references to where these concepts are
>
> defined.
>
>
>
> ---
>
>
>
> Section 3
>
>
>
> Why is the definition of a transport slice in quotes? Is it a definition
>
> taken from somewhere else?
>
>
>
> ---
>
>
>
> Section 3
>
>
>
>    "Slice" refers to a set of characteristics that separate
>
>    one type of user-traffic from other types.
>
>
>
> Is "separation" a different term from "isolation"? They are often used
>
> as synonyms. If you mean them to be the same, it may help to use only
>
> one term in this document, but if you mean them to be different, it may
>
> help to provide some statement of contrast.
>
>
>
> ---
>
>
>
> Section 4
>
>
>
>    The following subsections describe the characteristics needed for
>
>    support of transport slices.
>
>
>
> "Characteristics" of what? "Needed" by whom?
>
>
>
> ---
>
>
>
> Section 4.1 (and elsewhere)
>
>
>
> The use of the term "end user" may not convey the message you intend.
>
> (Or maybe it does!) An end user is usually conceived to be a person or
>
> machine that it the ultimate source or sink of packet data. Do you
>
> define that the consumer/customer/client of a transport slice is such an
>
> individual person/component? Or is a transport slice provided as a
>
> service to support another network (like a pseudowire, VLAN, VPN, etc.)?
>
>
>
> If you plan to continue using "end user" you might include it in Section
>
> 5.1.
>
>
>
> ---
>
>
>
> Section 4.1
>
>
>
>    If for
>
>    example the range of latencies a network can provide is 50ms-100ms,
>
>    then this would be the range of values the end user should be able to
>
>    request, it would be as low as 50ms or as high as 100ms or anything
>
>    in between.
>
>
>
> Is this just a bad example, or is there something I am not seeing?
>
> Surely no one request a latency. They may indicate that they can
>
> tolerate a latency: that is, they may request an upper bound to the
>
> latency they will receive. If so, just because the network "can provide"
>
> latency of 50-100ms, does not restrict the user from giving a higher
>
> value.
>
>
>
> There is also some question of who asks and who provides. As you have it
>
> phrased, the network must tell the end user what is available, and the
>
> end user can then select. Is that really how it works? Doesn't latency
>
> in a network depend on many factors (including where the sources and
>
> destinations are, and what other service parameters are being
>
> delivered)? If so, wouldn't the end user make a request with a set of
>
> SLIs and the network would respond yes/no/negotiate?
>
>
>
> ---
>
>
>
> Section 4.1.1
>
>
>
> I'm not sure what this paragraph is doing here. If it were illustrative
>
> it might be acceptable but currently it has:
>
>
>
>    This document defines a minimal set of SLOs and later systems or
>
>    standards could extend this set and define more SLOs.  For example,
>
>    we included Guaranteed bandwidth which is the minimum requested
>
>    bandwidth for the transport slice.  The later standard might define
>
>    other SLOs related to bandwidth if needed.
>
>
>
> This document is not positioned as Standards Track, so this text looks
>
> very out of place.
>
>
>
> I do understand that is a transport slice is to be viewed as a service
>
> then it is important to qualify the service parameters. Is this the
>
> same list of service requirements as we find in section 3 of
>
> draft-ietf-teas-enhanced-vpn? Are any differences the clue to
>
> understanding the difference between an enhanced VPN and a transport
>
> slice?
>
>
>
> ---
>
>
>
> Section 4.1.1
>
>
>
>    o  Availability: is defined as the ratio of uptime to
>
>       total_time(uptime+downtime), where uptime is the time the
>
>       transport slice is available in accordance with the SLOs
>
>       associated with it.
>
>
>
> There is some circuitous definition here since an SLO is "A target value
>
> or range of values for a service level that is measured by an SLI."
>
> You also need to indicate what you mean by "the transport slice is
>
> available"? Does the disconnection of one TSE from a slice mean the
>
> slice is not available, or just downgraded?
>
>
>
> (This may be a comment too far! It is probably off in the details that
>
> the WG might discuss if/when the document is adopted.)
>
>
>
> ---
>
>
>
> Section 4.1.1
>
>
>
> Security : really?
>
>
>
> draft-ietf-teas-enhanced-vpn has:
>
>
>
>    While an enhanced VPN service may be sold as offering encryption and
>
>    other security features as part of the service, customers would be
>
>    well advised to take responsibility for their own security
>
>    requirements themselves possibly by encrypting traffic before
>
>    handing it off to the service provider.
>
>
>
> Do you really believe that "encrypted connectivity" is likely to be an
>
> SLI of a transport slice?
>
>
>
> ---
>
>
>
> Section 4.1.2
>
>
>
>    With these objectives incorporated, a customer sees transport slice
>
>    as a dedicated network for its exclusive use.
>
>
>
> Do you mean like a VPN? A sort of VPN with enhanced attributes? Like a
>
> sort of enhanced VPN?
>
>
>
> ---
>
>
>
> Sections 4.2 and 4.3
>
>
>
> I didn't really understand how/why we need another decomposition of
>
> network services, network virtualisation, and hierarchical networks
>
> that is essentially functionally the same as many of the ones we have
>
> worked n before but which has a different set of names for things. Is
>
> there really a big difference between this and work we have done before?
>
>
>
> ---
>
>
>
> Section 5.1
>
>
>
> I'm a bit confused by your statement (in the TSC definition) that there
>
> are different types of orchestrators and different types of TSC. There
>
> is no explanation of this and the definitions appear to be generic.
>
>
>
> If it is OK to have "slice operator for short" why is it not OK to
>
> have "slice" for short?
>
>
>
> ---
>
>
>
> The only mention of the "e2e network slice orchestrator" is in Section
>
> 5.2.
>
>
>
> This seems to be related to some text in 5.1
>
>
>
>       A user may either directly manage its service
>
>       by interfacing with the transport slice controller or indirectly
>
>       through an orchestrator.
>
>
>
>    Orchestrator:  An orchestrator is an entity that composes different
>
>       services, resource and network requirements.  It interfaces with
>
>       the transport slice controllers.
>
>
>
> ...which is slightly in conflict with text in 5.
>
>
>
>    A transport slice is requested from an entity (such as an
>
>    orchestrator or a system-wide controller) performing broader service
>
>    or application specific functions.
>
>
>
> There is probably some unspoken meaning to these differences, but it is
>
> hard to guess.
>
>
>
> ---
>
>
>
> I consider the distinction in Section 6 between "end-to-end slice",
>
> "other slice", and "transport slice" to be somewhat bogus. The customer
>
> of an end-to-end slice might be directly using the "transport network".
>
> The IETF only deals with IETF technologies.
>
>
>
> ---
>
>
>
> Section 7 will need to filled in at some stage. At the least, you have a
>
> suggestion that security is an SLI. But probably, there are plenty of
>
> security and privacy concerns with all aspects of network slicing.
>
>
>
> *From:* Teas <teas-bounces@ietf.org> *On Behalf Of *Vishnu Pavan Beeram
> *Sent:* 19 August 2020 16:50
> *To:* TEAS WG <teas@ietf.org>
> *Cc:* TEAS WG Chairs <teas-chairs@ietf.org>
> *Subject:* [Teas] WG adoption - draft-nsdt-teas-transport-slice-definition
>
>
>
> All,
>
> This is start of a *three* week poll on making
> draft-nsdt-teas-transport-slice-definition-03 a TEAS working group
> document.
> Please send email to the list indicating "yes/support" or "no/do not
> support". If indicating no, please state your reservations with the
> document. If yes, please also feel free to provide comments you'd
> like to see addressed once the document is a WG document.
>
> The poll ends September 9th (extra week to account for vacation season).
>
> Thanks,
> Pavan and Lou
> _______________________________________________
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>