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

[t petch <[e-mail]>]

On 07/10/2021 22:54, Xufeng Liu wrote:
> Hi John,
>
> To me, "connectivity matric ID" is a term and concept that I have not seen
> before, inside IETF and outside of IETF. My preference is to avoid it if it
> is not something that we must have.

Mmmm, assuming that matrix, being the singular of matrices, is intended, 
then I see that used widely in the IETF as in RFC7448, RFC7579 and in 
most of the current I-D in the TEAS or CCAMP WG that include a YANG 
module.  I would agree that it is usually accompanied by 'MatrixID' 
rather than being written as 'matrix id' but would assume that the 
meaning of those two phrases is the same.

Tom Petch

>
> Thanks,
> - Xufeng
>
>
> On Thu, Oct 7, 2021 at 5:38 PM John E Drake <[e-mail]> wrote:
>
>> What is the difference between having N connectivity matrix IDs and having
>> N IETF network slice IDs?
>>
>>
>>
>> Yours Irrespectively,
>>
>>
>>
>> John
>>
>>
>>
>>
>>
>> Juniper Business Use Only
>>
>> *From:* Xufeng Liu <[e-mail]>
>> *Sent:* Thursday, October 7, 2021 5:17 PM
>> *To:* John E Drake <[e-mail]>
>> *Cc:* Joel M. Halpern <[e-mail]>; 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]*
>>
>>
>>
>> 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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>>>      [e-mail] <mailto:[e-mail]>
>>>      https://www.ietf.org/mailman/listinfo/teas
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