Subject: Re: [Teas-ns-dt] Suggested new text for the isolation part and related characteristics

From: Jari Arkko <[email-masked]>
Date: Mon, 9 Mar 2020 15:35:26 +0000

Take 2, per discussions on the call:

4.1.  Service Level Objectives on Transport Slice

   A transport slice is defined ...

   A non-exhaustive list of characteristics types for transport slice is
   described below:

   o  Guaranteed Bandwidth: assurance of minimum or range of the
      bandwidth requirement.  Requested unidirectionally.

   o ...

   o  Packet loss rate: To specify permissible packet loss rate between
      two endpoints.  For critical networks, this number may be very
      close to zero.  See [RFC7680].
      Bandwidth guarantees come in two variants:

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   o Hardness of a guarantee. The above characteristics can be
      specified as hard guarantees and not affected by other traffic,
      or as soft guarantees. In a soft guarantee, a violation of the
      guarantee may occur in rare cases due to resource interference.  In
      such cases, the guarantee will be maintained by the controller
      within a certain tolerance level of that objective.
      Note that specifying a hard guarantee will not prevent failures --
      such as losing a node -- from affecting the transport slice. Protection
      against such issues is possible, but needs to be specified separately
      (see item "resource redundancy" below).

      Note also that the hard and soft guarantees do not say anything
      about the specific implementation of how these guarantees are
      achieved. Different implementations might use different
      techniques, from avoiding oversubsription to dedicating
      particular links or their virtual fractions to particular
      transport slices.

   o Resource isolation. In some cases it may be necessary to dedicate
      specific resources to the slice, for instance, for security reasons.

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   o ...

   o  etc.

   The framework may further specify ...

4.1.1.  Isolation

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   Providing a hard guarantee for the characteristics of a transport slice
   means that the behavior and performance of other transport slices
   should not impact that slice, even if they run over the same underlying
   infrastructure or use logically shared network resources.

   Since the transport slices are logically partitioned over the
   shared resources, a certain degree of commitment to the guarantee
   is expected even when it is not hard.  When the shared resource
   pools begin to become saturated, SLO violations can happen,
   however, impacting the performance or operation of service
   associated with the transport slice.

   The degree of isolation can be derived from availability
   characteristics requested, such as whether a hard or soft guarantee was
   requested. Requesting a hard guarantee may commit more resources
   than would be required for a softer limit. In addition, resource isolation
   may be applied to ensure dedicated access to a particular node, for instance.

   When realizing a transport slice, the network controller should be
   responsible for allocating and providing resources according to the specified
   characteristics.

   SLO violations can occur for two reasons and corresponding statements
   apply

   o  Shared resource interference: i.e. multiple transport slices
      simultaneously share the same resource, and one of them consume
      the resource in surplus.  If the SLO guarantees are strictly
      required, then the network controller can be informed of this by
      requesting a hard guarantee. Note that the terms hard and soft
      limit are requirement oriented and different from what is
      specified in, for instance, [I-D.ietf-teas-enhanced-vpn]).

   o  Resource failure or fault occurs, such as a link or node failure.

       Where it is important to defend against these, the relevant
       characteristics on resoure redundancy (and perhaps some
       other characteristics on restoration speed and other factors) need to be specified.
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