[Bier] What is Slice-Flow Aggregate?

Lizhenbin <lizhenbin@huawei.com> Thu, 25 November 2021 16:14 UTC

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From: Lizhenbin <lizhenbin@huawei.com>
To: "draft-bestbar-teas-ns-packet@ietf.org" <draft-bestbar-teas-ns-packet@ietf.org>, "teas@ietf.org" <teas@ietf.org>
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Thread-Topic: What is Slice-Flow Aggregate?
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Date: Thu, 25 Nov 2021 16:14:28 +0000
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Subject: [Bier] What is Slice-Flow Aggregate?
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Hi authors of draft-bestbar-teas-ns-packet,

Thanks for updating the terminologies based on the comments and suggestions made during the meeting and the mail list.  While there are still several thing which are not clear to me:


1.       The term Slice Aggregate is now changed to Slice Flow Aggregate to reflect that it is the aggregation of a set of network flows. This term may help the description of the mapping of network slice services to the underlay network resource partition. However, it is not clear whether this concept is needed or related to the realization of the network resource partition. Also it is not clear whether the identifier of Slice Flow Aggregate in data packet is needed.



2.       If the Slice-Flow Aggregate is the aggregation of network flows, what is the meaning of the term "Slice-Flow Aggregate Topology" in section 3.4? Is it the topology associated with the underlay network construct? Or is it something related to the connectivity matrix?


IMHO this updated terminology is still confusing about what is the attribute of the service flows, and what is the attribute of the underlay network construct. They are still mixed up.

Moreover, based on the mail list discussion, the consensus is to use general terms instead of slice specific terms in the network slice realization, please consider to follow that


Best regards,
Robin




From: Adrian Farrel [mailto:adrian@olddog.co.uk]
Sent: Wednesday, November 10, 2021 3:41 AM
To: Lizhenbin <lizhenbin@huawei.com>om>; teas@ietf.org
Cc: bier@ietf.org; apn@ietf.org
Subject: RE: What is Slice Aggregate?

Hi Robin,

Answering as pen-holder for draft-ietf-teas-ietf-network-slices, but providing a definitive answer for something that might need WG consensus...

In line...

From: BIER <bier-bounces@ietf.org<mailto:bier-bounces@ietf.org>> On Behalf Of Lizhenbin
Sent: 09 November 2021 13:35
To: teas@ietf.org<mailto:teas@ietf.org>; apn@ietf.org<mailto:apn@ietf.org>
Cc: bier@ietf.org<mailto:bier@ietf.org>
Subject: [Bier] What is Slice Aggregate?

Hi authors of draft-ietf-teas-ietf-network-slices,

The authors of the draft draft-zzhang-bier-slicing-and-differentiation-00 mentioned in the draft:
"
   [I-D.bestbar-teas-ns-packet] introduces the notion of Slice Aggregate
   which comprises of one of more IETF network slice traffic streams.  A
   Slice Aggregate is identified by a Slice Selector (SS), and packets
   carry the SS so that associated forwarding treatment or S-PHB (Slice
   policy Per Hop Behavior - the externally observable forwarding
   behavior applied to a specific packet belonging to a slice aggregate)
   - can be applied along the path.
"
"
   The authors of this document believe that the IETF Network Slicing
   framework, when augmented by the Slice Aggregate, addresses the APN
   problem domain very well.
"

According to the past discussion, we think the slice aggregate means the underlay slice, that is the new terminology "network resource partition".
If so, the Slice Selector should be the identifier of the network resource partition. But according to the draft-zzhang-bier-slicing-and-differentiation-00,
the slice aggregate can be augmented to address the APN problem. In the recently published draft draft-li-apn-header-00, the APN attribute is defined
including the APN ID (user group/application group) the packet belongs to , the Intent and APN parameters applied to the packet. It is apparent these
attributes are totally different from the identifier of the underlay slice.

Can you clarify the following about the slice aggregate:

1.       What is slice aggregate? Is it the underlay network slice, the APN attribute-like parameters, both or other identifier? Or can it be all possible identifiers to identify a flow?

I have no specific definition for a "slice aggregate." There is some text on the concept of "aggregating slices" in Section 6.5 of draft-ietf-teas-ietf-network-slices-05. But this is fairly high-level and conceptual acknowledgement that there may be some form of scaling required so that a network is not required to maintain state on every slice service it supports.

As far as "identifiers in the underlay network" is concerned, I think that is entirely a choice for the solution. The solution mechanism needs to be able to deliver the high-level functionality that results in the slice service. I think it is likely that some form of "grouping" is needed, but that is not a requirement. If the designers of the solution believe that they have enough identifiers to handle the number of slices, and if they believe that the network can be provisioned and managed, then the solution is practical.

In short, the framework does not force the solutions, but the solutions have to be able to deliver the function described in the framework.


2.       What is the usage of the slice aggregate in the draft-ietf-teas-ietf-network-slices if it is not the network resource partition any more? Is it introduced a new identifier to identify a flow?

As above, the concept of "slice aggregation" is only that: a concept. The text reads...

   These approaches are also sensitive to the scaling concerns of
   supporting a large number of IETF Network Slices within a single IP
   or MPLS network, and so offer ways to aggregate the slices so that
   the packet markings indicate an aggregate or grouping of IETF Network
   Slices where all of the packets are subject to the same routing and
   forwarding behavior.

So, in this context, I think you can consider a slice aggregate to be equivalent to a "group" as described in the following text from 6.1

   For scalability reasons, IETF Network Slices may be grouped together
   according to characteristics (including SLOs and SLEs).  This
   grouping allows an operator to host a number of slices on a
   particular set of resources and so reduce the amount of state
   information needed in the network.  The NSC is responsible for
   grouping the IETF Network Slice requests.

3. What is the scope of the slice aggregate work in the TEAS WG if it is a new identifier other than the resource partition? Will you go on to define the encapsulation and the protocol extensions for the new identifier or augment it to address the APN problem?

I can't answer this question as editor of the framework document. It is a wider question for the working group, I think.

Best,
Adrian