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

["Joel M. Halpern" <[e-mail]>]

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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