Re: [Teas] Network slicing framework : Issue #2 : How many connectivity matrices in a slice?

[Xufeng Liu <[e-mail]>]

Hi John,
The equivalence is right, except that there is a need to have the
connectivity-metrix-id if multiple connectivity matrices are allowed. More
comments in-line below.
Thanks,
- Xufeng

On Thu, Oct 7, 2021 at 4:56 PM John E Drake <[e-mail]> wrote:

> Hi,
>
>
>
> Comment inline
>
>
>
> Yours Irrespectively,
>
>
>
> John
>
>
>
>
>
> Juniper Business Use Only
>
> *From:* Teas <[e-mail]> *On Behalf Of * Xufeng Liu
> *Sent:* Thursday, October 7, 2021 4:43 PM
> *To:* Joel M. Halpern <[e-mail]>
> *Cc:* TEAS WG <[e-mail]>
> *Subject:* Re: [Teas] Network slicing framework : Issue #2 : How many
> connectivity matrices in a slice?
>
>
>
> *[External Email. Be cautious of content]*
>
>
>
> In this case, there is slice-a for traffic class A with slo-A, and slice-b
> for traffic class B with slo-B. There is another base slice-c under both
> slice-a and slice-b. The slo-C on slice-c limits the total traffic.
>
> Thanks,
>
>
>
> *[JD]  If you replace ‘slice-a’ with ‘connectivity matrix a’,  ‘slice-b’
> with ‘connectivity matrix b’, and ‘slice-c’ with ‘IETF network slice c’,
> you have the current architecture. *
>
[Xufeng] This is an exact equivalence. There is still a need for nested
slice hierarchy since the connectivity matrices are not hierarchically
structured.

>
>
> - Xufeng
>
>
>
> On Thu, Oct 7, 2021 at 3:27 PM Joel M. Halpern <[e-mail]>
> wrote:
>
> Do you consider the use case where there is a ingress limit on the total
> traffic thata a consumer can send across a set of traffic classes, and
> there are separate SLOs for those separate classes, to be a case we need
> to address?
>
> It seems legitimate to me.  And multiple connectivity matrices in a
> slice seems the natural way to address it.
>
> Yours,
> Joel
>
> On 10/7/2021 3:19 PM, Xufeng Liu wrote:
> > I would like to have:
> > - Support of one connectivity matrix per slice is mandatory
> >
> > But not have:
> > - Support of more than one connectivity matrix per slice is in the
> > architecture
> >    but is optional to implement
> >
> > Allowing the second option would unnecessarily complicate the user
> > experience, without providing any additional capabilities, as commented
> > below in-line.
> >
> > Thanks,
> > - Xufeng
> >
> > On Tue, Sep 28, 2021 at 1:17 PM Adrian Farrel <[e-mail]
> > <mailto:[e-mail]>> wrote:
> >
> >     Hi Tarek, ____
> >
> >     __ __
> >
> >     You’ve called out some good cases for consideration.____
> >
> >     __ __
> >
> >     >> For example, a consumer may want a slice that is ultra-low
> latency,
> >     and they may know that they want to send traffic from A to B, from A
> >     to C and multicast from D to A, B, and C.____
> >
> >     [TS]: I agree that creating multiple matrices (per service type) to
> >     address the above usecase makes sense and makes it simpler for the
> >     IETF slice service consumer to reference a single ultra-low latency
> >     slice. ____
> >
> >       * In such case, wouldn’t the service type (unicast/multicast) be
> >         enough to differentiate what connectivity matrix the traffic
> >         would pick – as opposed to requiring an additional ID (one for
> >         identifying slice, and one for identifying the connectivity
> >         matrix).____
> >
> >     [AF] There are two points to consider:____
> >
> >       * How the customer specifies the connectivity supported by the
> >         slice____
> >       * How the implementation identifies the connectivity matrix and
> >         places traffic on the matrix____
> >
> >     So, in this case, there is no traffic flow anticipated from A to D
> >     or from B to C, etc. Thus, it is not good enough to specify the set
> >     of endpoints, it is also important to specify the connectivity
> >     between those endpoints so that the provider knows that there is no
> >     need to provision resources for connectivity that will not be
> used.____
> >
> >     How the connectivity is actually implemented in the network (and
> >     even how traffic is policed, and how SLIs are measured) is up to the
> >     provider/implementer. If (this may be a big if) the traffic is
> >     simply routed, then it would not be necessary for the provider to
> >     match traffic to a connectivity matrix – they would simply route it,
> >     and in this case the provider’s network is unaware of the
> >     connectivity matrix. On the other hand, if some form of
> >     connection-oriented approach is taken then while the traffic is
> >     simply routed/classified at the ingress endpoint, there is some
> >     relationship between connection matrix and reserved resources (think
> >     of MPLS-TE). ____
> >
> >     If, in all this, there is no policing at the ingress endpoint, then
> >     admission control or use of resources in the transit network may
> >     need to be more carefully associated with the “flow” i.e. the
> >     connectivity matrix.____
> >
> >     __ __
> >
> >       * Does it make sense to have two “same type” connectivity matrices
> >         (for example, two p2p connectivity matrices for two connections
> >         between A and B)? I can see two cases:____
> >           o If the two parallel connections (between A and B) have same
> >             SLOs, then why not aggregate into 1 connection/connectivity
> >             matrix?____
> >
> >     [AF] I think that if they have the same SLOs and the same
> >     connectivity, then you would probably have them as a single matrix
> >     (summing the bandwidth, but keeping the latency constant, for
> >     example). But you would not be required to do that. Again, it might
> >     depend on policing and how you want to manage the SLOs. For example,
> >     two parallel connectivity matrices from A to B each with a required
> >     throughput of X Mbps is not the same as one matrix from A to B with
> >     throughput 2X – this is because A is not the traffic source: traffic
> >     comes from upstream of the slice endpoint and may originate at
> >     different applications, hosts, or sites.____
> >
> >     __ __
> >
> >     Again consider MPLS-TE LSPs. You might, for convenience and
> >     scalability tunnel two parallel LSPs down one hierarchical LSP. The
> >     capacity of the H-LSP is the sum of the children, but the children
> >     have their own rights!____
> >
> >     __ __
> >
> >     Of course, in this case, the SLOs might only be identical today.
> >     They might be available to change tomorrow, and in that case it is a
> >     lot easier to have two separate (“parallel”) matrices.____
> >
> >     __ __
> >
> >           o If the two parallel connections (between A and B) have
> >             different SLOs, then are they still same slice? wouldn’t it
> >             be better to just have them in two different slices?____
> >
> >     [AF] This is the nub of the question. It is a multi-dimensional
> >     problem (because of the many SLOs) with a hierarchy of ownership.
> >     Customer àslice àmatrix. You end up with the same number of leaves
> >     in the tree, but the branches are at different places. And, further,
> >     you could hang the SLOs at any point in the tree (for example at the
> >     matrix as currently proposed, or at the slice).
> >
> > [Xufeng]: If the slices can be organized hierarchically, the original
> > desired behavior can be achieved:  in addition to the three separate
> > slices described earlier, we can have a base (underlay) slice that
> > supports all these three slices. The base slice can serve as a construct
> > containing all three connectivity matrices, without introducing
> > additional connectivity-matrix-id.
> >
> >     ____
> >
> >     __ __
> >
> >     A part of this debate is: suppose two connectivity matrices have 98%
> >     agreement on their SLOs, but one SLO is fractionally different. Does
> >     that require two slices?____
> >
> >     __ __
> >
> >     But please be aware that describing the architecture is not
> >     engineering the YANG model! With the current proposal, I would
> >     probably still write a YANG model that had default SLOs per
> >     customer, with variations per slice, with additional variations per
> >     matrix.____
> >
> >     __ __
> >
> >     And also recall that how the network protocol implementations choose
> >     to implement adherence to SLOs is open for discussion. If they need
> >     some form of indicator/index to tell them what to do, this value
> >     will be “mapped” from {customer, slice, matrix} and it is not
> >     important (to the architecture) how that mapping is performed.____
> >
> >     __ __
> >
> >           o it is not clear in such case what creating two matrices “of
> >             same type” is solving? Is it loadbalance, redundancy, ?____
> >
> >     [AF] It is not clear to me that anyone (except for you :-) has
> >     raised the case of two parallel matrices with identical SLOs.  I am
> >     not convinced that they would be used (although my throughput
> >     example, above) is a possible case. But equally important to me is
> >     the question: why would we prevent this when it comes for free?____
> >
> >     __ __
> >
> >     Cheers,____
> >
> >     Adrian____
> >
> >     __ __
> >
> >     *From: *Teas <[e-mail] <mailto:[e-mail]>>
> >     on behalf of Adrian Farrel <[e-mail]
> >     <mailto:[e-mail]>>
> >     *Date: *Monday, September 27, 2021 at 12:29 PM
> >     *To: *'TEAS WG' <[e-mail] <mailto:[e-mail]>>
> >     *Subject: *[Teas] Network slicing framework : Issue #2 : How many
> >     connectivity matrices in a slice?____
> >
> >     Hi,
> >
> >     Igor raised this especially in the context of how traffic is
> >     identified for association with a connectivity matrix that belongs
> >     to a slice.
> >
> >     Consider the definition of connectivity matrix in the current draft
> >     and as discussed in issue #1.
> >
> >     A consumer may want multiple connectivity matrices in their
> >     "contract" with the provider. In the example with four edge nodes
> >     (A, B, C, D), their may be traffic that flows between some edges,
> >     but not between others.
> >
> >     For example, a consumer may want a slice that is ultra-low latency,
> >     and they may know that they want to send traffic from A to B, from A
> >     to C and multicast from D to A, B, and C.
> >
> >     It is, of course, possible to express this as three separate slices.
> >     And this is perfectly acceptable. We must not make any definitions
> >     that prevent this from being the case.
> >
> >     However, it seems likely that the consumer (and the operator) would
> >     prefer to talk about "the consumer's low latency slice". That is, to
> >     bundle these three connections into one construct. However, they are
> >     distinctly different connections and must be understood as such.
> >     Indeed, they may have some different SLOs associated (for example,
> >     A-B may require more bandwidth than A-C).
> >
> >     By allowing (but not mandating) multiple connectivity matrices in a
> >     single slice service, we facilitate this administrative group.
> >
> >     One could also imagine (but I do not pre-judge the network slice
> >     service YANG model definition) a default set of SLOs that apply to
> >     all connectivity matrices in a slice, and specific modified SLOs per
> >     connectivity matrix.
> >
> >     Now, to Igor's point. This is about how traffic arriving at an edge
> >     (say a PE) is mapped to the correct connection. I promised a Venn
> >     diagram, but words are easier 😊
> >
> >     If we take the model of a port-based VPN, then one approach might be
> >     to map the (virtual or physical) port number or VLAN ID to the
> >     network slice. But clearly (and this was Igor's point) this doesn't
> >     identify the connectivity matrix if there is more than one matric
> >     per slice.
> >
> >     A solution I offered is that the VLAN ID could identify {slice,
> >     connectivity matrix}. At that PE, for a given AC to a CE, it is
> >     necessary to expose with a separate VLAN ID for each {slice,
> >     connectivity matrix}. That does not mean:
> >     - we need a global unique identifier for each connectivity matrix
> >     - we need a per-PE unique identifier for each connectivity matrix
> >
> >     I am *very* cautious about discussing potential technology solutions
> >     because they are just that. It is not the business of a framework to
> >     direct solutions work. But I provide this example solution just to
> >     show that it is possible.
> >
> >     Consider also, how traffic is placed on LSPs or on SFCs. The answer
> >     is that there is some form of classification performed at the head
> >     end. In many cases, this is as simple as examination of the
> >     destination address (traffic is "routed" onto the LSP). In other
> >     cases there is deeper analysis of the 5-tuple and even other packet
> >     parameters. Often this will be enough, but when there are multiple
> >     "parallel" connections to the same destination, some form of choice
> >     must be made: how that choice is made can be configured in an
> >     implementation, and may include looking at additional information
> >     (such as a VLAN ID) passed from the consumer.
> >
> >     Note that the identity of the connectivity matrix is not needed
> >     anywhere except at the ingress edge node. It may be that the
> >     connectivity matrix is mapped to some internal network structure
> >     (such as an LSP) and that that provides an implicit identification
> >     of the connectivity matrix, and it may be that a solution technology
> >     chooses to keep an identifier of the connectivity matrix with each
> >     packet, but that is not a requirement of the architecture.
> >
> >     I think what I have said is:
> >     - Support of one connectivity matrix per slice is mandatory
> >     - Support of more than one connectivity matrix per slice is in the
> >     architecture
> >        but is optional to implement
> >     - There are ways that a protocol solution could achieve this function
> >     - I have heard some voices asking for the association of multiple
> >     connectivity
> >        matrices with a single slice
> >     - I have not heard anyone providing examples of harm this would cause
> >
> >     Please discuss.
> >
> >     Adrian
> >
> >
> >
> >
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