Network Working Group                                         I. Bryskin
Internet-Draft                                       Huawei Technologies
Intended status: Informational                                    X. Liu
Expires: December 31, 2017                                         Jabil
                                                             J. Guichard
                                                                  Y. Lee
                                                     Huawei Technologies
                                                           June 29, 2017

                 Use Cases for SF Aware Topology Models


   This document describes some use cases that benefit from the network
   topology models that are service and network function aware.

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   the Trust Legal Provisions and are provided without warranty as
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Exporting SF/NF Information to Network Clients and Other
       Network SDN Controllers . . . . . . . . . . . . . . . . . . .   3
   3.  Flat End-to-end SFCs Managed on  Multi-domain Networks  . . .   3
   4.  Managing SFCs with TE Constrains  . . . . . . . . . . . . . .   4
   5.  SFC Protection and Load Balancing . . . . . . . . . . . . . .   5
   6.  Network Clock Synchronization . . . . . . . . . . . . . . . .   5
   7.  Client - Provider Network Slicing Interface . . . . . . . . .   6
   8.  Dynamic Assignment of Regenerators for L0 Services  . . . . .   6
   9.  Dynamic Assignment of OAM Functions for L1 Services . . . . .   7
   10. SFC Abstraction and Scaling . . . . . . . . . . . . . . . . .   7
   11. Dynamic Compute/VM/Storage Resource Assignment  . . . . . . .   8
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   13. Security Considerations . . . . . . . . . . . . . . . . . . .   8
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     15.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     15.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Normally network connectivity services are discussed as a means to
   interconnect various abstract or physical network topological
   elements, such as ports, link termination points and nodes
   [I-D.ietf-teas-yang-te-topo] [I-D.ietf-teas-yang-te].  However, the
   connectivity services, strictly speaking, interconnect not the
   network topology elements per-se, rather, located on/associated with
   the various network and service functions [RFC7498] [RFC7665].  In
   many scenarios it is beneficial to decouple the service/network
   functions from the network topology elements hosting them, describe
   them in some unambiguous and identifiable way (so that it would be
   possible, for example, to auto-discover on the network topology
   service/network functions with identical or similar functionality and
   characteristics) and engineer the connectivity between the service/
   network functions, rather than between their current topological
   locations.  The purpose of this document is to describe some use
   cases that could benefit from such an approach.

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2.  Exporting SF/NF Information to Network Clients and Other Network SDN

   In the context of Service Function Chain (SFC) orchestration one
   existing problem is that there is no way to formally describe a
   Service or Network Function in a standard way (recognizable/
   understood by a third party) as a resource of a network topology

   One implication of this is that there is no way for the orchestrator
   to give a network client even a ball-park idea as to which network's
   SFs/NFs are available for the client's use/control and where they are
   located in the network even in terms of abstract topologies/virtual
   networks configured and managed specifically for the client.
   Consequently the client has no say on how the SFCs provided for the
   client by the network should be set up and managed (which SFs are to
   be used and how they should be chained together, optimized,
   manipulated, protected, etc.).

   Likewise, there is no way for the orchestrator to export SF/NF
   information to other network controllers.  The SFC orchestrator may
   serve, for example, a higher level controller (such as Network
   Slicing Orchestrator), with the latter wanting at least some level of
   control as to which SFs/NFs it wants on its SFCs and how the Service
   Function Paths (SFPs) are to be routed and provisioned, especially,
   if it uses services of more than one SFC orchestrator.

   The issue of exporting of SF/NF information could be addressed by
   defining a model, in which formally described/recognizable SF/NF
   instances are presented as topological elements, for example, hosted
   by (associated with) TE, L3 or L2 topology nodes.  The model could
   describe whether, how and at what costs the SFs/NFs hosted by a given
   node could be chained together, how these intra-node SFCs could be
   connected to the node's Service Function Forwarders (SFFs, entities
   dealing with SFC NSHs and metadata), and how the SFFs could be
   connected to the node's Tunnel and Link Termination Points (TTPs and
   LTPs) to chain the intra-node SFCs across the network topology.

3.  Flat End-to-end SFCs Managed on Multi-domain Networks

   SFCs may span multiple administrative domains, each of which
   controlled by a separate SFC controller.  The usual solution for such
   q scenario is the Hierarchical SFCs (H-SFCs), in which the higher
   level orchestrator controls only SFs located on domain border nodes.
   Said higher level SFs are chained together into higher level SFCs via
   lower level (intra-domain) SFCs provisioned and controlled
   independently by respective domain controllers.  The decision as to
   which higher level SFCs are connected to which lower level SFCs is

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   driven by packet re- classification every time the packet enters a
   given domain.  Said packet re-classification is very time-consuming
   operation.  Furthermore, the independent nature of higher and lower
   level SFC control is prone to configuration errors, which may lead to
   long lasting loops and congestions.  It is highly desirable to be
   able to set up and manage SFCs spanning multiple domains in a flat
   way as far as the data plane is concerned (i.e. with a single packet
   classification at the ingress into the multi-domain network but
   without re-classifications on domain ingress nodes).

   One way to achieve this is to have the domain controllers expose SF/
   NF- aware topologies, and have the higher level orchestrator operate
   on the network-wide topology, the product of merging of the
   topologies catered by the domain controllers.  This is similar in
   spirit to setting up, coordinating and managing the transport
   connectivity (TE tunnels) on a multi-domain multi-vendor transport

4.  Managing SFCs with TE Constrains

   Some SFCs require per SFC link/element and end-to-end TE constrains
   (bandwidth, delay/jitter, fate sharing/diversity. etc.).  Said
   constraints could be ensured via carrying SFPs inside overlays that
   are traffic engineered with the constrains in mind.  A good analogy
   would be orchestrating delay constrained L3 VPNs.  One way to support
   such L3 VPNs is to carry MPLS LSPs interconnecting per-VPN VRFs
   inside delay constrained TE tunnels interconnecting the PEs hosting
   the VRFs.

   Planning, computing and provisioning of TE overlays to constrain
   arbitrary SFCs, especially those that span multiple administrative
   domains with each domain controlled by a separate controller, is a
   very difficult challenge.  Currently it is addressed by pre-
   provisioning on the network of multiple TE tunnels with various TE
   characteristics, and "nailing down" SFs/NFs to "strategic" locations
   (e.g. nodes terminating many of such tunnels) in a hope that an
   adequate set of tunnels could be found to carry the SFP of a given
   TE-constrained SFC.  Such an approach is especially awkward in the
   case when some or all of the SFs/NFs are VNFs (i.e. could be
   instantiated at multiple network locations).

   SF/NF-aware TE topology model in combination with TE tunnel model
   will allow for the network orchestrator (or a client controller) to
   compute, set up and manipulate the TE overlays in the form of TE
   tunnel chains.  Said chains could be duel-optimized compromising on
   optimal SF/NF locations with optimal TE tunnels interconnecting them.
   The TE tunnel chains (carrying multiple similarly constrained SFPs)

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   could be adequately constrained both at individual TE tunnel level
   and at the chain end-to-end level.

5.  SFC Protection and Load Balancing

   Currently the combination of TE topology & tunnel models offers to a
   network controller various capabilities to recover an individual TE
   tunnel from network failures occurred on one or more network links or
   transit nodes on the TE paths taken by the TE tunnel's connection(s).
   However, there is no simple way to recover a TE tunnel from a failure
   affecting its source or destination node.  SF/NF-aware TE topology
   model can decouple the association of a given SF/NF with its location
   on the network topology by presenting multiple, identifiable as
   mutually substitutable SFs/NFs hosted by different TE topology nodes.
   So, for example, if it is detected that a given TE tunnel destination
   node is malfunctioning or has gone out of service, the TE tunnel
   could be re- routed to terminate on a different node hosting
   functionally the same SFs/NFs as ones hosted by the failed node.
   This is in line with the ACTN edge migration and function mobility
   concepts.  It is important to note that the described strategy works
   much better for the stateless SFs/NFs.  This is because getting the
   alternative stateful SFs/MFs into the same respective states as the
   current (i.e. active, affected by failure) are is a very difficult

   At the SFC level the SF/NF-aware TE topology model can offer SFC
   dynamic restoration capabilities against failed/malfunctioning SFs/
   NFs by identifying and provisioning detours to a TE tunnel chain, so
   that it starts carrying the SFC's SFPs towards healthy SFs/NFs that
   are functionally the same as the failed ones.  Furthermore, multiple
   parallel TE tunnel chains could be pre-provisioned for the purpose of
   SFC load balancing and end-to-end protection.  In the latter case
   said parallel TE tunnel chains could be placed to be sufficiently
   disjoint from each other.

6.  Network Clock Synchronization

   Many current and future network applications (including 5g and IoT
   applications) require very accurate time services (PTP level, ns
   resolution).  One way to implement the adequate network clock
   synchronization for such services is via describing network clocks as
   NFs on an NF-aware TE topology optimized to have best possible delay
   variation characteristics.  Because such a topology will contain
   delay/delay variation metrics of topology links and node cross-
   connects, as well as costs in terms of delay/delay variation of
   connecting clocks to hosting them node link and tunnel termination
   points, it will be possible to dynamically select and provision bi-
   directional time-constrained deterministic paths or trees connecting

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   clocks (e.g. grand master and boundary clocks) for the purpose of
   exchange of clock synchronization information.  Note that network
   clock aware TE topologies separately provided by domain controllers
   will enable multi-domain network orchestrator to set up and
   manipulate the clock synchronization paths/trees spanning multiple
   network domains.

7.  Client - Provider Network Slicing Interface

   3GPP defines network slice as "a set of network functions and the
   resources for these network functions which are arranged and
   configured, forming a complete logical network to meet certain
   network characteristics.".  Network slice could be also defined as a
   logical partition of a provider's network that is owned and managed
   by a tenant.  SF/NF-aware TE topology model has a potential to
   support a very important interface between network slicing clients
   and providers because, on the one hand, the model can describe
   holistically and hierarchically the client's requirements and
   preferences with respect to a network slice functional, topological
   and traffic engineering aspects, as well as of the degree of resource
   separation/ sharing between the slices, thus allowing for the client
   (up to agreed upon extent) to dynamically (re-)configure the slice or
   (re-)schedule said (re-)configurations in time, while, on the other
   hand, allowing for the provider to convey to the client the slice's
   operational state information and telemetry the client has expressed
   interest in.

8.  Dynamic Assignment of Regenerators for L0 Services

   On large optical networks some of provided to their clients L0
   services could not be provisioned as single Och trails, rather, as
   chains of such trails interconnected via regenerators, such as 3R
   regenerators.  Current practice of the provisioning of such services
   requires configuration of explicit paths (EROs) describing identity
   and location of regenerators to be used.  A solution is highly
   desirable that could:

   o  Identify such services based, for example, on optical impairment

   o  Assign adequate for the services regenerators dynamically out of
      the regenerators that are grouped together in pools and
      strategically scattered over the network topology nodes;

   o  Compute and provision supporting the services chains of optical
      trails interconnected via so selected regenerators, optimizing the
      chains to use minimal number of regenerators, their optimal

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      locations, as well as optimality of optical paths interconnecting

   o  Ensure recovery of such chains from any failures that could happen
      on links, nodes or regenerators along the chain path.

   NF-aware TE topology model (in this case L1 NF-aware L0 topology
   model) is just the model that could provide a network controller (or
   even a client controller operating on abstract NF-aware topologies
   provided by the network) to realize described above computations and
   orchestrate the service provisioning and network failure recovery

9.  Dynamic Assignment of OAM Functions for L1 Services

   OAM functionality is normally managed by configuring and manipulating
   TCM/MEP functions on network ports terminating connections or their
   segments over which OAM operations, such as performance monitoring,
   are required to be performed.  In some layer networks (e.g.
   Ethernet) said TCMs/MEPs could be configured on any network ports.
   In others (e.g.  OTN/ODUk) the TCMs/MEPs could be configured on some
   (but not all network ports) due to the fact that the OAM
   functionality (i.e. recognizing and processing of OAM messages,
   supporting OAM protocols and FSMs) requires in these layer networks
   certain support in the data plane, which is not available on all
   network nodes.  This makes TCMs/MEPs good candidates to be modeled as
   NFs.  This also makes TCM/MEP aware topology model a good basis for
   placing dynamically an ODUk connection to pass through optimal OAM
   locations without mandating the client to specify said locations

10.  SFC Abstraction and Scaling

   SF/NF-aware topology may contain information on native SFs/NFs (i.e.
   SFs/NFs as known to the provider itself) and/or abstract SFs/NFs
   (i.e.  logical/macro SFs/NFs representing one or more SFCs each made
   of native and/or lower level abstract SFs/NFs).  As in the case of
   abstracting topology nodes, abstracting SFs/NFs is hierarchical in
   nature - the higher level of SF/NF-aware topology, the "larger"
   abstract SFs/NFs are, i.e. the larger data plane SFCs they represent.
   This allows for managing large scale networks with great number of
   SFs/NFs (such as Data Center interconnects) in a hierarchical, highly
   scalable manner resulting in control of very large number of flat in
   the data plane SFCs that span multiple domains.

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11.  Dynamic Compute/VM/Storage Resource Assignment

   In a distributed data center networks, virtual machines for compute
   resources may need to be dynamically re-allocated due to various
   reasons such as DCI network failure, compute resource load balancing,
   etc.  In many cases, the DCI connectivity for the source and the
   destination is not predetermined.  There may be a pool of sources and
   a pool of destination data centers associated with re-allocation of
   compute/VM/storage resources.  There is no good mechanism to date to
   capture this dynamicity nature of compute/VM/storage resource
   reallocation.  Generic Compute/VM/Storage resources can be described
   and announced as a SF where a DC hosting these resources can be
   modeled as an abstract node.  Topology interconnecting these abstract
   nodes (DCs) in general is of multi-domain nature.  Thus, SF-aware
   topology model can facilitate a joint optimization of TE network
   resources and Compute/VM/Storage resources and solve Compute/VM/
   Storage mobility problem within and between DCs.

12.  IANA Considerations

   This document has no actions for IANA.

13.  Security Considerations

   This document does not define networking protocols and data, hence
   are not directly responsible for security risks.

14.  Acknowledgements

   The authors would like to thank Maarten Vissers, Joel Halpern, and
   Greg Mirsky for their helpful comments and valuable contributions.

15.  References

15.1.  Normative References

   [RFC7498]  Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for
              Service Function Chaining", RFC 7498,
              DOI 10.17487/RFC7498, April 2015,

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,

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              Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and
              O. Dios, "YANG Data Model for TE Topologies", draft-ietf-
              teas-yang-te-topo-09 (work in progress), June 2017.

              Saad, T., Gandhi, R., Liu, X., Beeram, V., Shah, H., and
              I. Bryskin, "A YANG Data Model for Traffic Engineering
              Tunnels and Interfaces", draft-ietf-teas-yang-te-06 (work
              in progress), March 2017.

15.2.  Informative References

              Dolson, D., Homma, S., Lopez, D., Boucadair, M., Liu, D.,
              Ao, T., and V. Vu, "Hierarchical Service Function Chaining
              (hSFC)", draft-ietf-sfc-hierarchical-02 (work in
              progress), January 2017.

Authors' Addresses

   Igor Bryskin
   Huawei Technologies


   Xufeng Liu


   Jim Guichard
   Huawei Technologies


   Young Lee
   Huawei Technologies


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