IRTF                                                        M. Boucadair
Internet-Draft                                                    Orange
Intended status: Informational                                D. Trossen
Expires: 6 August 2022                                            Huawei
                                                               A. Farrel
                                                      Old Dog Consulting
                                                         2 February 2022


     Considerations for the use of SDN in Semantic Routing Networks
            draft-boucadair-irtf-sdn-and-semantic-routing-00

Abstract

   Semantic Routing is the process of making routing and forwarding
   decisions based, not only on the destination IP address, but on other
   information carried in an IP packet.  The intent is to facilitate
   enhanced routing decisions based on this information in order to
   provide differentiated forwarding paths for specific packet flows.

   Software Defined Networking (SDN) places control of network elements
   (including all or some of their forwarding decisions) within external
   software components called controllers and orchestrators.  This
   approach differs from conventional approaches that solely rely upon
   distributed routing protocols for the delivery of advanced
   connectivity services.  By doing so, SDN aims to enable network
   elements to be simplified while still performing (some high level)
   forwarding function.

   This document examines the applicability of SDN techniques to
   Semantic Routing and provides considerations for the development of
   Semantic Routing solutions in the context of SDN.

Status of This Memo

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   This Internet-Draft will expire on 6 August 2022.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Software Defined Networking (SDN): An Overview  . . . . . . .   3
   3.  Semantic Routing: Summary of Required Technical Elements  . .   5
   4.  Programmable Forwarding . . . . . . . . . . . . . . . . . . .   5
     4.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  SDN for Semantic Routing: The Intended Behavior . . . . .   8
   5.  Policy-Based Semantic Routing . . . . . . . . . . . . . . . .  10
   6.  Network-Wide Coordination . . . . . . . . . . . . . . . . . .  10
   7.  Applying Semantic Information to Packets  . . . . . . . . . .  10
   8.  Benefits and Concerns with the Use of SDN for Semantic
           Routing . . . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   12. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  12
   13. Informative References  . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Service differentiation in the network can be enforced by
   manipulating a set of parameters that belong to distinct dimensions
   (e.g., forwarding, routing, traffic classification, resource
   partitioning).  Among the techniques to achieve such differentiation,
   this document focuses on Semantic Routing, which refers to a process
   that is meant to provide differentiated forwarding paths for specific
   packet flows distinct from simple shortest path first routing and,
   thus, satisfy specific service/application requirements.





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   More concretely, Semantic Routing is the process of making routing
   and forwarding decisions based, not only on the destination IP
   address of a packet, but also by taking into account other
   information that is carried in the packet such as (but not limited
   to):

   *  Other fields of the IP header, e.g., DSCP/Traffic Class.

   *  The transport header, e.g., transport port numbers [RFC7597] or
      subflows [RFC8803].

   *  Specific transport encapsulation shims, e.g., [RFC8926].

   *  Specific service headers, e.g., [RFC8300].

   *  Specific metadata.

   Section 3 provides more details about Semantic Routing.

   Software Defined Networking (SDN) places (partial or full) control of
   network elements and their forwarding decisions within dedicated
   software components called controllers and orchestrators.  This
   approach differs from those that solely rely upon distributed routing
   protocols.  An ambition of SDN is to enable network elements to be
   simplified while the network is optimized to deliver value-added
   connectivity services.  Refer to Section 2 for an overview of SDN.

   This document examines the applicability of SDN to Semantic Routing
   (Section 4) and provides considerations for the development of
   Semantic Routing solutions in the context of SDN.

   This version of the document does not elaborate on specific SDN
   protocols.

2.  Software Defined Networking (SDN): An Overview

   SDN refers to an approach for network programmability, that is, the
   capacity to initialize, control, and manage network behavior
   dynamically via open interfaces.  Such programmability should
   facilitate the delivery of services in a deterministic, dynamic, and
   scalable manner.










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   SDN emphasizes the role of software in running networks by endorsing
   the separation between data and control planes.  Even if such a
   separation has been adopted by most routing processes for decades
   (Section 2.1 of [RFC7149]), SDN focuses more on the power of
   "central" controllers to optimize route computation within a network
   before populating the Forwarding Information Base (FIB) of involved
   network elements.

   The separation between control and data planes allows faster
   innovation in both planes, and enables a dynamic and flexible
   approach to implementing new network behaviors and reacting to
   changes in network state and traffic demands.

   SDN has been discussed in many places during the last decade.  For
   example, within the IRTF, [RFC7426] provides a concise reference for
   the SDN research community to address the questions of what SDN is,
   what the layer structure of an SDN architecture is, and how layers
   interface with each other within that architecture.  [RFC7149]
   (published in the IETF stream) offers a service provider's
   perspective of the SDN landscape by describing requirements, issues,
   and other considerations about SDN.  In particular, [RFC7149]
   classifies SDN techniques into the following functional domains:

   *  Techniques for the dynamic discovery of network topology, devices,
      and capabilities, along with relevant information and data models
      that are meant to precisely document such topology, devices, and
      their capabilities.

   *  Techniques for exposing network services and their characteristics
      and for dynamically capturing the set of service parameters that
      will be used to measure the level of quality associated with the
      delivery of a given service or a combination thereof.

   *  Techniques used by service-requirement-derived dynamic resource
      allocation and policy enforcement schemes, so that networks can be
      programmed accordingly.

   *  Dynamic feedback mechanisms that are meant to assess how
      efficiently a set of policies are enforced from a service
      fulfillment and assurance perspective.

   SDN can be deployed following a recursive model that involves
   dedicated interfaces for both network and service optimization.
   Indeed, [RFC8597] differentiates the control functions associated
   with transport from those related to services in an approach called
   Cooperating Layered Architecture for Software-Defined Networking
   (CLAS).




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   In an SDN context, domain-specific controllers can be deployed with
   specific interactions between them as discussed in Section 4 of
   [RFC8309].

3.  Semantic Routing: Summary of Required Technical Elements

   As described in [I-D.farrel-irtf-introduction-to-semantic-routing],
   Semantic Routing is the process of achieving enhanced routing
   decisions based on semantics added to IP headers to provide
   differentiated paths for different packet flows distinct from simple
   shortest path first routing.  The additional information or
   "semantics" may be placed in existing header fields (such as the IPv6
   Traffic Class field or the destination address) or may be achieved by
   adding fields to the header.  Furthermore, it may be encoded in the
   payload or additional headers (such as in the port number fields or
   in an IPv6 Extension Header).

   The application of Semantic Routing allows packets from different
   flows (even between the same applications on the same devices) to be
   marked for different treatment in the network.  The packets may then
   be routed onto different paths according to the capabilities and
   states of the network links in order to meet the requirements of the
   flows.  For example, one flow may need low latency, while another may
   require ultra low jitter, and a third may demand very high bandwidth.

   Three elements are needed to achieve Semantic Routing:

   *  The capabilities and state of the network must be discovered.

   *  The packets must be marked (with semantic information) according
      to their required delivery characteristics.

   *  The routers must be programmed to forward the traffic according to
      how the packets are marked.

   All these elements can be matched to the SDN functional domains
   listed in Section 2.  From that standpoint, this document provides
   more details on how SDN can be used to satisfy specific Semantic
   Routing needs.

4.  Programmable Forwarding

   Programmable Forwarding is the term applied to the use of control
   techniques to instruct network devices how to forward packets in a
   programmatic way.






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4.1.  Motivation

   Modern networks are designed to carry traffic that belongs to a
   variety of services/applications that have distinct traffic
   performance requirements, reliability and robustness expectations,
   and service-specific needs [RFC7665][RFC8517].  Such expectations,
   and other forwarding requirements that can be captured in a Service
   Level Agreement (SLA) [RFC7297], can be considered by providers when
   designing their networks in order to be able to deliver
   differentiated forwarding behaviors.  However, conventional routing
   and forwarding procedures do not always offer the required
   functionalities for such differentiated service delivery.  Thus,
   additional means have to be enabled in these networks for the sake of
   innovative service delivery while minimizing the induced complexity
   to operate such networks.  Also, these means should be tweaked to
   ensure consistent forwarding behaviors network-wide.

   The aforementioned means are not only extensions to routing
   protocols, but include other mechanisms that affect the forwarding
   behaviors within a network.  An non-exhaustive list of sample
   capabilities that can be offered by appropriately controlling
   forwarding elements is provided below:

   Resource Pooling:  A network may host dedicated functions that
      implement resource pooling among many available paths or control
      which path is used to steer traffic as a function of the observed
      RTT (e.g., enable MPTCP converters [RFC8803] in specific network
      segments, including data centers as detailed in Section 2.1 of
      [RFC8041]).

      There is a need to interact with the underlying forwarding
      elements to communicate a set forwarding policies that will ensure
      that such a differentiated service is provided to the specific
      flows.  These forwarding policies include, for example, a set of
      rules that characterize the flows that are eligible to the
      resource pooling service or the scheduling policies (maximize link
      utilization, grab extra resources only when needed, etc.).

      These polices are then enforced by programmable forwarders.

   Performance-based Route Selection:  Some applications may have strict
      traffic performance requirements (e.g., a low one-way delay
      [RFC7679]), however the underlying network elements may not
      support a mechanism to disseminate performance metrics associated
      with specific paths and/or perform performance-based route
      selection (e.g., [I-D.ietf-idr-performance-routing]).





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      As an alternative, an off-line Semantic Routing approach can be
      used to collect measurement data to reach a given content (e.g.,
      one-way delay to reach specific data centers), perform route
      selection based on this data, and then program the appropriate
      forwarding elements accordingly.

   Energy-efficient Forwarding:  An important effort was made in the
      past to optimize the energy consumption of network elements.
      However, such optimization is node-specific and no standard means
      are supported to optimize the energy consumption at the scale of
      the network.  For example, many nodes (also, service cards) are
      deployed as backups.

      A controller-based approach can be implemented so that the route
      selection process optimizes the overall energy consumption of a
      path.  Such a process takes into account the current load, avoids
      waking nodes/cards for handling "few" traffic (i.e., minor portion
      of traffic), considers node-specific data (e.g., [RFC7460]), etc.
      This off-line Semantic Routing approach will transition specific
      cards/nodes to "idle", wake them, etc., without breaking service
      objectives.  Moreover, such an approach will have to maintain an
      up-to-date topology even if a node is in an "idle" state (such
      nodes may be removed from adjacency tables if they don't
      participate to routing advertisements).

   Network Partitioning:  In order to rationalize the delivery of
      advanced connectivity services, a network may need to be
      partitioned in order to address specific forwarding requirements
      of groups of services/applications.  Network slicing
      [I-D.ietf-teas-ietf-network-slices] can be considered to deliver
      these services.  However, an intelligence is needed to decide the
      criteria to be used to partition the available resources, filter
      them, decide whether network extensions are needed, ensure
      whether/how resource preemption is adequately implemented, etc.

      These tasks are better achieved using a central intelligence that
      has direct visibility into the intents of applications, underlying
      network capabilities, local policies and guidelines, etc.  As an
      output of processing these various inputs, a set of node-specific
      policies are generated, and then pushed using available SDN
      interface.

   Alternative Forwarding:  The programmability of SDN in the form of
      forwarding actions defined on packet header fields allows for
      realizing forwarding techniques beyond the typical longest-prefix
      match used for IP-based reachability.  Solutions like those in
      [ICC2016], for instance, use a binary representation of links in a
      network to realize a path-based forwarding action that purely acts



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      on node-local state, independent from the nature of the path or
      the communications traversing over it.  As discussed in Section 7,
      the limitation of forwarding actions to only apply to defined (IP)
      packet header fields results, however, in issues that need special
      consideration when realizing such solutions in real-world
      deployments.

   The next subsection further details which elements are needed when
   interacting with programmable forwarders in an SDN context.

4.2.  SDN for Semantic Routing: The Intended Behavior

   SDN minimizes the required changes to legacy (interior) routing
   protocols.  More concretely, SDN can be used to provide the intended
   Semantic Routing behavior, especially:

   *  Identify the forwarding elements that can be safely involved in
      providing the intended Semantic Routing features.

   *  Maintain abstract topologies that involve these elements and their
      capabilities.

   *  Capture application-specific intents and derive the corresponding
      forwarding requirements and, then, forwarding policies.

   *  Map these abstract topologies to (groups of) applications with
      specific Semantic Routing needs.

   *  Program a subset of nodes (called boundary nodes) with the
      required classification and marking policies to bind flows with
      their intended Semantic Routing behavior.

      In order to adequately process the application flows that require
      specific differentiated forwarding, SDN controllers maintain a
      table that allows to unambiguously identify such flows.  The
      content of that table is used to derive the appropriate
      classification/match rules that are then communicated by an SDN
      controller to a set of forwarding elements.

      When volatile data (e.g., dynamic IP addresses) is used to build
      such rules, it is the responsibility of the SDN controllers to
      update the rules whenever a new identifier is used.  Failure to
      maintain "fresh" classification rules will lead to service
      failure/degradation.







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   *  Supply intermediate nodes (that is, nodes that are not boundary
      nodes) with the appropriate rules to locate and interpret the bits
      within the packet to proceed with forwarding actions that comprise
      Semantic Routing.

   *  Automatically adjust, if possible, the network MTU to accommodate
      the overhead that is required by any extra bits to signal semantic
      routing behavior.

   *  Instruct egress boundary nodes about the required actions such as
      stripping or setting any Semantic Routing bits.

   *  Interact with the underlying nodes to maintain, retrieve, and
      disseminate the appropriate data that is used for assuring that
      Semantic Routing policies are appropriately fulfilled.

   *  Configure OAM policies to measure the experience and adjust the
      forwarding behavior.

   *  Monitor the network and detect parts of the network where such
      policies are broken.

   *  Automate the overall procedure [RFC8969].

   At least three approaches can be considered by an SDN controller to
   accomplish the above tasks:

   *  Compute (centrally) the differentiated paths and install the
      required forwarding rules in involved nodes.  Strict or loose
      paths may be installed.  This approach has the merit of
      implementing new path selection algorithms without requiring them
      to be supported by every involved node.

   *  Assign (centrally) differentiated link information and install the
      required forwarding rules in the involved nodes.  End-to-end paths
      are constructed without involvement of the SDN controller,
      utilizing the link information to establish path identification
      information on which installed forwarding rules can act upon
      without additional path-specific knowledge being required.  See
      [ICC2016] for an example of such approach.

   *  Rely upon a distributed routing protocol to customize the route
      selection process ([I-D.ietf-lsr-flex-algo], for example).  In
      such case, the SDN controller is responsible for communicating the
      parameters to be used for route selection process, select the
      nodes that will participate in a given topology, and configure any
      tunnels to interconnect these nodes.




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   A hierarchical SDN design can also be considered, where specific
   controllers are enabled in each domain with dedicated interfaces to
   share data (e.g., radio bottleneck, expectations).  These domains do
   not need to support the same technological implementation.  The
   interaction between the SDN controllers eases the delivery of
   consistent Semantic Routing behaviors without requiring common domain
   configuration.

5.  Policy-Based Semantic Routing

   TBD

   **SDN techniques as a whole are an instantiation of the policy-based
   management framework.***

6.  Network-Wide Coordination

   TBD

7.  Applying Semantic Information to Packets

   Given the focus of SDN is the use within IP networks, semantic
   information that can be used in SDN-based semantic routing is limited
   to those fields being defined in related SDN specifications; see
   Section 2 for more information.

   With this, SDN aligns with the concept of semantic routing
   [I-D.farrel-irtf-introduction-to-semantic-routing] in that it allows
   for range of packet header fields beyond mere IP addresses to be used
   in forwarding actions.

   However, solutions have also been devised that "overwrite" existing
   protocol fields in order for them to be used in an SDN forwarding
   action outside their original semantics.  [POINT2015][POINT2016]
   outline an example for such solution in which SDN is used for a path-
   based forwarding decision; while no "path" information is foreseen as
   an actionable packet header field in IPv6.

   Here, the path is constructed by a path-computation element (PCE)
   that matches a given service name against previously announced
   locations where said service name is located.  The path is
   represented as a concatenation of individual link information, which
   in turn is used to SDN node locally forward the packet after arrival.
   Given the binary structure of the end-to-end path information, the
   SDN forwarding operation can be implemented in a standard-compliant
   manner with its realization described in [ICC2016] as a arbitrary
   wildcard matching operation.




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   However, the constraint of acting only on limited packet fields
   requires that the path information needs transfer in one of those
   standard-defined packet header fields; thereby overwriting any
   existing packet header field.  As described in [POINT2016], the IPv6
   address fields are used for this purpose, representing the longest
   continuous binary field in the IPv6 header (256 bit in total),
   thereby allowing for representing topologies with up to 256 links.

   Given the approach chosen in [POINT2016], any IPv6 address
   information, if needed, is provided in the encapsulated payload,
   leading to repetitive encapsulation overhead by carrying two IP
   headers in a single packet, one used for path-based forwarding and
   one for the operations in arriving endpoint.  Only newer forwarding
   plane architectures, such as P4, would allow for removing such
   overhead by placing the path information into another packet header
   field (or even the payload as an extended header of sort) to act
   upon.

8.  Benefits and Concerns with the Use of SDN for Semantic Routing

   The programmability of SDN provides a fertile ground for forwarding
   decision that go beyond the reachability information provided through
   IPv4/v6 addresses, e.g., by using other packet header fields.  This
   not only allows for extending the simple reachability-driven
   forwarding decision with richer, e.g., policy-based, decisions (as
   discussed in Section 5), it may also enable new forwarding paradigms
   per se, such as those in [POINT2016], which in turn may realize
   forwarding behaviours like multicast at much lower cost points and
   higher efficiency (see [ICC2016]).

   However, SDN specifications have limited capabilities when it comes
   to the additional packet header fields that may be used for
   forwarding actions.  As a consequence, "true" semantic routing on any
   semantic enhancement, which is included in the packet, is only
   possible in a manner limited to those fields.

   Solutions such as those in [POINT2016], using methods outlined in
   [ICC2016], attempt to break this limitation albeit by overwriting
   standard-defined packet header fields, thereby changing the semantics
   of those fields within the realm of where the "re-defined" semantics
   are defined.

   This limits any solution to a limited domain [RFC8799].  More
   importantly, the redefinition of packet fields poses the danger of
   exposing this (non standard compliant) semantic to elements outside
   the limited domain; semantic leakage may occur, requiring appropriate
   methods such as dedicated gateways for preventing such leakage.  This
   can be seen in [POINT2016], where the boundaries to IP-compliant end



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   devices and other domains alike are delimited by dedicated gateway
   elements.  Those gateways usually act at higher layers than the SDN
   forwarding layer, thereby incurring complexity and often delay.

   See also [I-D.king-irtf-challenges-in-routing] for a discussion of
   issues and concerns that need to be examined when applying a new
   routing or forwarding paradigm to a self-contained network or
   Internet.

9.  Security Considerations

   SDN-related considerations are discussed in Section 5 of [RFC7149].

10.  IANA Considerations

   This document makes no requests for IANA action.

11.  Acknowledgements

   Thanks to George Polyzos for helpful comments on this work.

12.  Contributors

   George Xylomenos
   Email: xgeorge@aueb.gr

13.  Informative References

   [I-D.farrel-irtf-introduction-to-semantic-routing]
              Farrel, A. and D. King, "An Introduction to Semantic
              Routing", Work in Progress, Internet-Draft, draft-farrel-
              irtf-introduction-to-semantic-routing-03, 22 January 2022,
              <https://www.ietf.org/archive/id/draft-farrel-irtf-
              introduction-to-semantic-routing-03.txt>.

   [I-D.ietf-idr-performance-routing]
              Xu, X., Hegde, S., Talaulikar, K., Boucadair, M., and C.
              Jacquenet, "Performance-based BGP Routing Mechanism", Work
              in Progress, Internet-Draft, draft-ietf-idr-performance-
              routing-03, 22 December 2020,
              <https://www.ietf.org/archive/id/draft-ietf-idr-
              performance-routing-03.txt>.









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   [I-D.ietf-lsr-flex-algo]
              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", Work in Progress,
              Internet-Draft, draft-ietf-lsr-flex-algo-18, 25 October
              2021, <https://www.ietf.org/archive/id/draft-ietf-lsr-
              flex-algo-18.txt>.

   [I-D.ietf-teas-ietf-network-slices]
              Farrel, A., Gray, E., Drake, J., Rokui, R., Homma, S.,
              Makhijani, K., Contreras, L. M., and J. Tantsura,
              "Framework for IETF Network Slices", Work in Progress,
              Internet-Draft, draft-ietf-teas-ietf-network-slices-05, 25
              October 2021, <https://www.ietf.org/archive/id/draft-ietf-
              teas-ietf-network-slices-05.txt>.

   [I-D.king-irtf-challenges-in-routing]
              King, D., Farrel, A., and C. Jacquenet, "Challenges for
              the Internet Routing Infrastructure Introduced by Semantic
              Routing", Work in Progress, Internet-Draft, draft-king-
              irtf-challenges-in-routing-06, 22 January 2022,
              <https://www.ietf.org/archive/id/draft-king-irtf-
              challenges-in-routing-06.txt>.

   [ICC2016]  Reed, M., Al-Naday, M., Thomos, N., Trossen, D.,
              Petropoulos, G., and S. Spirou, "Stateless multicast
              switching in software defined networks", Paper IEEE ICC
              2016, 2016.

   [POINT2015]
              Trossen, D., Reed, M., Riihijarvi, J., Georgiades, M.,
              Xylomenos, G., and S. Fotiou, "IP Over ICN: The Better
              IP?", Paper EuCNC (European Conference on Networks and
              Communications), Paris, France, 2015.

   [POINT2016]
              Kim, S.-Y.., Robitzsch, S., Trossen, D., Reed, M., Al-
              Naday, M., and J. Riihijarvi, "Realizing IP-based Services
              over an Information-Centric Networking Transport Network",
              Paper Proceedings of the 3rd ACM Conference on
              Information-Centric Networking, Pages 215-216, 2016.

   [RFC7149]  Boucadair, M. and C. Jacquenet, "Software-Defined
              Networking: A Perspective from within a Service Provider
              Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,
              <https://www.rfc-editor.org/info/rfc7149>.






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   [RFC7297]  Boucadair, M., Jacquenet, C., and N. Wang, "IP
              Connectivity Provisioning Profile (CPP)", RFC 7297,
              DOI 10.17487/RFC7297, July 2014,
              <https://www.rfc-editor.org/info/rfc7297>.

   [RFC7426]  Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S.,
              Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software-
              Defined Networking (SDN): Layers and Architecture
              Terminology", RFC 7426, DOI 10.17487/RFC7426, January
              2015, <https://www.rfc-editor.org/info/rfc7426>.

   [RFC7460]  Chandramouli, M., Claise, B., Schoening, B., Quittek, J.,
              and T. Dietz, "Monitoring and Control MIB for Power and
              Energy", RFC 7460, DOI 10.17487/RFC7460, March 2015,
              <https://www.rfc-editor.org/info/rfc7460>.

   [RFC7597]  Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
              Murakami, T., and T. Taylor, Ed., "Mapping of Address and
              Port with Encapsulation (MAP-E)", RFC 7597,
              DOI 10.17487/RFC7597, July 2015,
              <https://www.rfc-editor.org/info/rfc7597>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <https://www.rfc-editor.org/info/rfc7665>.

   [RFC7679]  Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
              Ed., "A One-Way Delay Metric for IP Performance Metrics
              (IPPM)", STD 81, RFC 7679, DOI 10.17487/RFC7679, January
              2016, <https://www.rfc-editor.org/info/rfc7679>.

   [RFC8041]  Bonaventure, O., Paasch, C., and G. Detal, "Use Cases and
              Operational Experience with Multipath TCP", RFC 8041,
              DOI 10.17487/RFC8041, January 2017,
              <https://www.rfc-editor.org/info/rfc8041>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.

   [RFC8309]  Wu, Q., Liu, W., and A. Farrel, "Service Models
              Explained", RFC 8309, DOI 10.17487/RFC8309, January 2018,
              <https://www.rfc-editor.org/info/rfc8309>.






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   [RFC8517]  Dolson, D., Ed., Snellman, J., Boucadair, M., Ed., and C.
              Jacquenet, "An Inventory of Transport-Centric Functions
              Provided by Middleboxes: An Operator Perspective",
              RFC 8517, DOI 10.17487/RFC8517, February 2019,
              <https://www.rfc-editor.org/info/rfc8517>.

   [RFC8597]  Contreras, LM., Bernardos, CJ., Lopez, D., Boucadair, M.,
              and P. Iovanna, "Cooperating Layered Architecture for
              Software-Defined Networking (CLAS)", RFC 8597,
              DOI 10.17487/RFC8597, May 2019,
              <https://www.rfc-editor.org/info/rfc8597>.

   [RFC8799]  Carpenter, B. and B. Liu, "Limited Domains and Internet
              Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
              <https://www.rfc-editor.org/info/rfc8799>.

   [RFC8803]  Bonaventure, O., Ed., Boucadair, M., Ed., Gundavelli, S.,
              Seo, S., and B. Hesmans, "0-RTT TCP Convert Protocol",
              RFC 8803, DOI 10.17487/RFC8803, July 2020,
              <https://www.rfc-editor.org/info/rfc8803>.

   [RFC8926]  Gross, J., Ed., Ganga, I., Ed., and T. Sridhar, Ed.,
              "Geneve: Generic Network Virtualization Encapsulation",
              RFC 8926, DOI 10.17487/RFC8926, November 2020,
              <https://www.rfc-editor.org/info/rfc8926>.

   [RFC8969]  Wu, Q., Ed., Boucadair, M., Ed., Lopez, D., Xie, C., and
              L. Geng, "A Framework for Automating Service and Network
              Management with YANG", RFC 8969, DOI 10.17487/RFC8969,
              January 2021, <https://www.rfc-editor.org/info/rfc8969>.

Authors' Addresses

   Mohamed Boucadair
   Orange
   Rennes
   France

   Email: mohamed.boucadair@orange.com


   Dirk Trossen
   Huawei
   Munich
   Germany

   Email: dirk.trossen@huawei.com




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   Adrian Farrel
   Old Dog Consulting
   United Kingdom

   Email: adrian@olddog.co.uk














































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