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Versions: (draft-ietf-detnet-dp-sol-mpls) 00 01

DetNet                                                     B. Varga, Ed.
Internet-Draft                                                 J. Farkas
Intended status: Informational                                  Ericsson
Expires: January 2, 2020                                       L. Berger
                                                                D. Fedyk
                                                 LabN Consulting, L.L.C.
                                                                A. Malis
                                                               S. Bryant
                                                  Futurewei Technologies
                                                             J. Korhonen
                                                            July 1, 2019


                      DetNet Data Plane Framework
               draft-ietf-detnet-data-plane-framework-01

Abstract

   This document provides an overall framework for the Deterministic
   Networking data plane.  It covers concepts and considerations that
   are generally common to any Deterministic Networking data plane
   specification.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 2, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Terms Used in This Document . . . . . . . . . . . . . . .   3
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   4
   3.  DetNet Data Plane Overview  . . . . . . . . . . . . . . . . .   4
     3.1.  Data Plane Characteristics  . . . . . . . . . . . . . . .   6
     3.2.  Encapsulation . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  DetNet Specific Metadata  . . . . . . . . . . . . . . . .   7
     3.4.  DetNet IP Data Plane  . . . . . . . . . . . . . . . . . .   8
     3.5.  DetNet MPLS Data Plane  . . . . . . . . . . . . . . . . .   8
     3.6.  Further DetNet Data Plane Considerations  . . . . . . . .   9
       3.6.1.  Service Protection  . . . . . . . . . . . . . . . . .  11
       3.6.2.  Aggregation Considerations  . . . . . . . . . . . . .  13
       3.6.3.  End-System Specific Considerations  . . . . . . . . .  14
       3.6.4.  Sub-Network Considerations  . . . . . . . . . . . . .  14
   4.  Controller Plane (Management and Control)
       Considerations  . . . . . . . . . . . . . . . . . . . . . . .  15
     4.1.  DetNet Controller Plane Requirements  . . . . . . . . . .  15
     4.2.  Generic Controller Plane Considerations . . . . . . . . .  16
       4.2.1.  Flow Aggregation Control  . . . . . . . . . . . . . .  17
       4.2.2.  Explicit Routes . . . . . . . . . . . . . . . . . . .  18
       4.2.3.  Contention Loss and Jitter Reduction  . . . . . . . .  19
       4.2.4.  Bidirectional Traffic . . . . . . . . . . . . . . . .  19
     4.3.  Packet Replication, Elimination, and Ordering (PREOF) . .  20
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  21
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

1.  Introduction

   Deterministic Networking (DetNet) provides a capability to carry
   specified unicast or multicast data flows for real-time applications
   with extremely low packet loss rates and assured maximum end-to-end
   delivery latency.  A description of the general background and
   concepts of DetNet can be found in [I-D.ietf-detnet-architecture].



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   This document describes the concepts needed by any DetNet data plane
   specification and provides considerations for any corresponding
   implementation.  It covers the building blocks that provide the
   DetNet service, the DetNet service sub-layer and the DetNet
   forwarding sub-layer functions as described in the DetNet
   Architecture.

   The DetNet Architecture models the DetNet related data plane
   functions decomposed into two sub-layers: a service sub-layer and a
   forwarding sub-layer.  The service sub-layer is used to provide
   DetNet service protection and reordering.  The forwarding sub-layer
   is used to provide congestion protection (low loss, assured latency,
   and limited out-of-order delivery) and leverages Traffic Engineering
   mechanisms.

   As part of the service sub-layer functions, this document describes
   typical DetNet node data plane operation.  It describes the function
   and operation of the Packet Replication (PRF) Packet Elimination
   (PEF) and the Packet Ordering (POF) functions within the service sub-
   layer.  It also describes the forwarding sub-layer that is used to
   eliminate (or reduce) contention loss and provide bounded latency for
   DetNet flows.

   DetNet flows may be carried over network technologies that can
   provide the DetNet required service characteristics.  For example,
   DetNet MPLS flows can be carried over IEEE 802.1 Time Sensitive
   Network (TSN) [IEEE802.1TSNTG] sub-networks.  However, IEEE 802.1 TSN
   support is not required and some of the DetNet benefits can be gained
   by running over a data link layer that has not been specifically
   enhanced to support TSN.

   Different traffic types, or application flows, can be mapped on top
   of DetNet.  DetNet can optionally reuse header information provided
   by, or shared with, applications.  An example of shared header fields
   can be found in [I-D.ietf-detnet-ip].

   This document also covers concepts related to the controller plane
   and Operations, Administration, and Maintenance (OAM) functions
   related to the control plane.  Data plane OAM specifics are out of
   scope for this docuement.

2.  Terminology

2.1.  Terms Used in This Document

   This document uses the terminology established in the DetNet
   architecture [I-D.ietf-detnet-architecture], and the reader is
   assumed to be familiar with that document and its terminology.



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2.2.  Abbreviations

   The following abbreviations are used in this document:

   CW            Control Word.

   DetNet        Deterministic Networking.

   GRE           Generic Routing Encapsulation.

   IPSec         IP Security.

   L2            Layer 2.

   LSR           Label Switching Router.

   MPLS          Multiprotocol Label Switching.

   MPLS-TE       Multiprotocol Label Switching - Traffic Engineering.

   OAM           Operations, Administration, and Maintenance.

   PEF           Packet Elimination Function.

   PRF           Packet Replication Function.

   PREOF         Packet Replication, Elimination and Ordering Functions.

   POF           Packet Ordering Function.

   PSN           Packet Switched Network.

   PW            PseudoWire.

   QoS           Quality of Service.

   TSN           Time-Sensitive Network.

3.  DetNet Data Plane Overview

   This document describes how application flows, or app-flows, are
   carried over DetNet networks.  The DetNet Architecture,
   [I-D.ietf-detnet-architecture], models the DetNet related data plane
   functions decomposed into two sub-layers: a service sub-layer and a
   forwarding sub-layer.

   Figure 1 reproduced from the [I-D.ietf-detnet-architecture],shows a
   logical DetNet service with the two sub-layers.



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              |  packets going  |        ^  packets coming   ^
              v down the stack  v        |   up the stack    |
           +-----------------------+   +-----------------------+
           |        Source         |   |      Destination      |
           +-----------------------+   +-----------------------+
           |   Service sub-layer:  |   |   Service sub-layer:  |
           |   Packet sequencing   |   | Duplicate elimination |
           |    Flow replication   |   |      Flow merging     |
           |    Packet encoding    |   |    Packet decoding    |
           +-----------------------+   +-----------------------+
           | Forwarding sub-layer: |   | Forwarding sub-layer: |
           |  Resource allocation  |   |  Resource allocation  |
           |    Explicit routes    |   |    Explicit routes    |
           +-----------------------+   +-----------------------+
           |     Lower layers      |   |     Lower layers      |
           +-----------------------+   +-----------------------+
                       v                           ^
                        \_________________________/

                Figure 1: DetNet data plane protocol stack

   The DetNet forwarding sub-layer may be directly provided by the
   DetNet service sub-layer, for example by IP tunnels or MPLS.
   Alternatively, an overlay approach may be used in which the packet is
   natively carried between key nodes within the DetNet network (say
   between PREOF nodes) and a sub-layer is used to provide the
   information needed to reach the next hop in the overlay.

   The forwarding sub-layer provides the quality underpin needed by the
   DetNet flow.  It may do this directly through the use of queuing
   techniques and traffic engineering methods, or it may do this through
   the assistance of its underlying connectivity.  For example it may
   call upon Ethernet TSN capabilities defined in IEEE 802.1 TSN
   [IEEE802.1TSNTG].

   The service sub-layer provides additional support beyond the
   connectivity function of the forwarding sub-layer.  An example of
   this is Packet Replication, Elimination, and Ordering (PREOF)
   functions see Section 4.3.

   The method of instantiating each of the layers is specific to the
   particular DetNet data plane method.  There may be more than one
   approach that is applicable to a given bearer network type.








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3.1.  Data Plane Characteristics

   There are two major characteristics to the data plane:

   1.  Data plane technology: The DetNet data plane is provided by the
       DetNet service and forwarding sub layers.  The DetNet service
       sub-layer generally provides its functions for the DetNet
       application flows by using or applying existing standardized
       headers and/or encapsulations.  The Detnet forwarding sub-layer
       may provide capabilities leveraging that same header or
       encapsulation technology e.g.  Figure 2 or it may be achieved by
       other technologies e.g.  Figure 3.  DetNet is currently defined
       for operation over packet switched (IP) networks or label
       switched (MPLS) networks.

   2.  Encapsulation format: DetNet encodes specific flow attributes
       (namely flow identity and sequence number) in packets.  For
       example, in DetNet IP, zero encapsulation may be used and no
       sequence number is available, and in DetNet MPLS, DetNet specific
       information may be added explicitly to the packets in the format
       of S-label and d-CW.



                           +-------+  +---------+
                           | DN IP |  | DN MPLS |
                           +-------+  +---------+


                         Figure 2: DetNet Services


                                             +-----+
                                             | TSN |
                        +-------+          +-+-----+-+
                        | DN IP |          | DN MPLS |
                     +--+--+----+----+   +-+---+-----+-+
                     | TSN | DN MPLS |   | TSN | DN IP |
                     +-----+---------+   +-----+-------+


                     Figure 3: DetNet Service Examples

3.2.  Encapsulation

   The encapsulation of the DetNet flows allows them to be sent over a
   data plane technology other than their native type.  Encapsulation is
   essential if, for example, it is required to send Ethernet TSN stream



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   as a DetNet Application over a data plane such as MPLS.  Figure 3
   illustrates some relationships between the components.

   The use of encapsulation is also required if additional information
   (meta-data) is needed by the DetNet data plane and there is either no
   ability to include it in the client data packet, or the specification
   of the client data plane does not permit the modification of the
   packet to include additional data.  An example of such meta-data is
   the inclusion of a sequence number required by the PREOF function.

   Encapsulation may also be used to carry or aggregate flows for
   equipment with limited DetNet capability.

3.3.  DetNet Specific Metadata

   The DetNet data plane can provide or carry meta-data:

   1.  Flow-ID

   2.  Sequence Number

   Both of these metadata are required for DetNet service sub-layer
   specific functions (e.g., PREOF).  DetNet forwarding sub-layer
   related functions require only Flow-ID.

   Metadata can be a useful way of identifying packets that need to be
   treated as a flow or flow aggregate.  It is also useful as a way of
   including a sequence number the packet for use by the PREOF function
   or as a place to carry OAM indications or OAM information to
   instrument DetNet data plane operation.

   Explicit inclusion of metadata is possible through the use of IP
   options or IP extension headers.  New IP options are almost
   impossible to get standardized or to deploy in an operational network
   and will not be discussed further in this text.  IPv6 extensions
   headers are finding popularity in current IPv6 development work,
   particularly in connection with Segment Routing of IPv6 (SRv6) and IP
   OAM.  The design of a new IPv6 extension header or the modification
   of an existing one is a technique available in the tool box of the
   DetNet IP data plane designer.

   Explicit inclusion of metadata in an IP packet is also possible
   through the inclusion of an MPLS label stack and the MPLS DetNet
   Control Word using one of the methods for carrying MPLS over IP
   [I-D.ietf-detnet-mpls-over-udp-ip].  This is described in more detail
   in Section 3.6.4.





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   Implicit metadata in IP can be included through the use of the
   network programming paradigm
   [I-D.ietf-spring-srv6-network-programming] in which the suffix of an
   IPv6 address is used to encode additional information for use by the
   network of the receiving host.

   Some MPLS examples of implicit metadata include the sequence number
   for use by the PREOF function, or even all the essential information
   being included into the DetNet over MPLS label stack (the DetNet
   Control Word and the DetNet Service label).

3.4.  DetNet IP Data Plane

   An IP data plane may operate natively or through the use of an
   encapsulation.  Many types of IP encapsulation can satisfy DetNet
   requirements and it is anticipated that more than one encapsulation
   may be deployed for example GRE, IPSec etc.

   One method of operating an IP DetNet data plane without encapsulation
   is to use "6-tuple" based flow identification, where "6-tuple" refers
   to information carried in IP and higher layer protocol headers.
   General background on the use of IP headers, and "6-tuples", to
   identify flows and support Quality of Service (QoS) can be found in
   [RFC3670].  [RFC7657] also provides useful background on the delivery
   differentiated services (DiffServ) and "tuple" based flow
   identification.  DetNet flow aggregation may be enabled via the use
   of wildcards, masks, prefixes and ranges.  The operation of this
   method is described in detail in [I-D.ietf-detnet-ip].

   The DetNet forwarding plane may use explicit route capabilities and
   traffic engineering capabilities to provide a forwarding sub-layer
   that is responsible for providing resource allocation and explicit
   routes.  It is possible to include such information in a native IP
   packet explicitly, or implicitly.

3.5.  DetNet MPLS Data Plane

   MPLS provides the ability to forward traffic over implicit and
   explicit paths to the point in the network where the next DetNet
   service sub-layer action needs to take place.  It does this through
   the use of a stack of one or more labels with various forwarding
   semantics.

   MPLS also provides the ability to identify a service instance that is
   used to process the packet through the use of a label that maps the
   packet to a service instance.





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   In cases where metadata is needed to process an MPLS encapsulated
   packet at the service sub-layer, a shim layer also called a control
   word (CW) [RFC4385] can be used.  Although such CWs are frequently 32
   bits long, there is no architectural constraint on its size of this
   structure, only the requirement that it is fully understood by all
   parties operating on it in the DetNet service sub-layer.  The
   operation of this method is described in detail in
   [I-D.ietf-detnet-mpls].

3.6.  Further DetNet Data Plane Considerations

   This section provides informative considerations related to providing
   DetNet service to flows which are identified based on their header
   information.  At a high level, the following are provided on a per
   flow basis:

   Reservation and Allocation of resources:

      Reservation of resources can allocate resources to specific DetNet
      flows.  This can eliminate packet contention and loss for DetNet
      traffic.  This also can reduce jitter for the DetNet traffic.
      DetNet flows are assumed to behave with respect to the reserved
      traffic profile.  If other traffic shares the link resources, the
      use of (queuing, policing, shaping) policies can be used to ensure
      that the allocation of resources reserved for DetNet is met.
      Queuing and shaping of DetNet traffic could be required to ensure
      that DetNet traffic does not exceed its reserved profile but this
      would impact the DetNet service characteristics.

   Explicit routes:

      Use of a specific path for a flow.  This allows control of the
      network delay by steering the packet with the ability to influence
      the physical path.  Explicit routes complement reservation by
      ensuring that a consistent path can be associated with its
      resources for the duration of that path.  Coupled with the traffic
      mechanism, this limits misordering and bounds latency.  Explicit
      route computation can encompass a wide set of constraints and
      optimize the path for a certain characteristic e.g. highest
      bandwidth or lowest jitter.  In these cases the "best" path for
      any set of characteristics may not be a shortest path.  The
      selection of path can take into account multiple network metrics.
      Some of these metrics are measured and distributed by the routing
      system as traffic engineering metrics.

   Service protection:





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      Use of multiple packet streams using multiple paths, for example
      1+1 or 1:1 linear protection.  For DetNet this primarily relates
      to packet replication and elimination capabilities.  MPLS offers a
      number of protection schemes.  MPLS hitless protection can be used
      to switch traffic to an already established path in order to
      restore delivery rapidly after a failure.  Path changes, even in
      the case of failure recovery, can lead to the out of order
      delivery of data requiring packet ordering functions either within
      the DetNet service or at a high layer in the application traffic.
      Establishment of new paths after a failure is out of scope for
      DetNet services.

   Network Coding:

      Network Coding, not to be confused with network programming,
      comprises several techniques where multiple data flows are
      encoded.  These resulting flows can then be sent on different
      paths.  The encoding operation can combine flows and error
      recovery information.  When the encoded flows are decoded and
      recombined the original flows can be recovered.  Note that Network
      coding uses an alternative to packet by packet PREOF.  Therefore,
      for certain network topologies and traffic loads, Network Coding
      can be used to improve a network's throughput, efficiency,
      latency, and scalability, as well as resilience to partition,
      attacks, and eavesdropping, as compared to traditional methods.
      DetNet could utilized Network coding as an alternative to other
      protection means.  Network coding is often applied in wireless
      networks and is being explored for other network types.

   Load sharing:

      Use of packet by packet distribution of the same DetNet flow over
      multiple paths is not recommended except for the cases listed
      above where PREOF is utilized to improve protection of traffic and
      maintain order.  Packet by packet load sharing, e.g., via ECMP or
      UCMP, impacts ordering and possibly jitter.

   Troubleshooting:

      Since Detnet leverages many different forwarding sub-layers, those
      technologies also support a number of tools to troubleshoot
      connectivity for example, to support identification of misbehaving
      flows.  At the service layer again there are existing mechanisms
      to troubleshoot or monitor flows.  Many of these mechanisms exist
      for IP and MPLS networks.  A client of a DetNet service can
      introduce any monitoring applications which can detect and monitor
      delay and loss.




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   Recognize flow(s) for analytics:

      To a large degree this follows the logic in the previous section.
      Analytics can be inherited from the two sub-layers.  At the DetNet
      service edge packet and bit counters e.g. sent, received, dropped,
      and out of sequence are maintained.

   Correlate events with flows:

      The provider of a DetNet service may allow other capabilities to
      monitor flows such as more detail loss statistics and time
      stamping of events.  The details of these capabilities are
      currently out of scope for this document.

   Several of these capabilities are expanded upon in more detail below.

3.6.1.  Service Protection

   Service protection allow DetNet services to increase reliability and
   maintain a DetNet Service Assurance in the case of network congestion
   or some failures.  Detnet relies on the underlying technology
   capabilities for various protection schemes.  Protection schemes
   enable partial or complete coverage of the network paths and active
   protection with combinations of PRF, PRE, and POF.

3.6.1.1.  Linear Service Protection

   An example DetNet MPLS network fragment and packet flow is
   illustrated in Figure 4.



            1      1.1       1.1      1.2.1    1.2.1      1.2.2
         CE1----EN1--------R1-------R2-------R3--------EN2-----CE2
                  \           1.2.1 /                   /
                   \1.2     /-----+                   /
                    +------R4------------------------+
                              1.2.2

         Figure 4: Example Packet Flow in DetNet protected Network

   In Figure 4 the numbers are used to identify the instance of a
   packet.  Packet 1 is the original packet, and packets 1.1, and 1.2
   are two first generation copies of packet 1.  Packet 1.2.1 is a
   second generation copy of packet 1.2 etc.  Note that these numbers
   never appear in the packet, and are not to be confused with sequence
   numbers, labels or any other identifier that appears in the packet.
   They simply indicate the generation number of the original packet so



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   that its passage through the network fragment can be identified to
   the reader.

   Customer Equipment CE1 sends a packet into the DetNet enabled
   network.  This is packet (1).  Edge Node EN1 encapsulates the packet
   as a DetNet Packet and sends it to Relay node R1 (packet 1.1).  EN1
   makes a copy of the packet (1.2), encapsulates it and sends this copy
   to Relay node R4.

   Note that along the path from EN1 to R1 there may be zero or more
   nodes which, for clarity, are not shown.  The same is true for any
   other path between two DetNet entities shown in Figure 4 .

   Relay node R4 has been configured to send one copy of the packet to
   Relay Node R2 (packet 1.2.1) and one copy to Edge Node EN2 (packet
   1.2.2).

   R2 receives packet copy 1.2.1 before packet copy 1.1 arrives, and,
   having been configured to perform packet elimination on this DetNet
   flow, forwards packet 1.2.1 to Relay Node R3.  Packet copy 1.1 is of
   no further use and so is discarded by R2.

   Edge Node EN2 receives packet copy 1.2.2 from R4 before it receives
   packet copy 1.2.1 from R2 via relay Node R3.  EN2 therefore strips
   any DetNet encapsulation from packet copy 1.2.2 and forwards the
   packet to CE2.  When EN2 receives the later packet copy 1.2.1 this is
   discarded.

   The above is of course illustrative of many network scenarios that
   can be configured.

   This example also illustrates 1:1 protection scheme meaning there is
   traffic and path for each segment of the end to end path.  Local
   DetNet relay nodes determine which packets are eliminated and which
   packets are forwarded.  A 1+1 scheme where only one path is used for
   traffic at a time, could use the same topology.  In this case there
   is no PRF function and traffic is switched upon detection of failure.
   An OAM scheme that monitors the paths detects the loss of path or
   traffic is required to initiate the switch.  A POF may still be used
   in this case to prevent misordering of packets.  In both cases the
   protection paths are established and maintained for the duration of
   the DetNet service.

3.6.1.2.  Ring Service Protection

   Ring protection may also be supported if the underlying technology
   supports it.  Many of the same concepts apply however Rings are




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   normally 1+1 protection for data efficiency reasons.  [RFC8227] is an
   example of MPLS-TP data plane that supports Ring protection.

3.6.2.  Aggregation Considerations

   The DetNet data plane also allows for the aggregation of DetNet
   flows, to improved scaling by reducing the state per hop.  How this
   is accomplished is data plane or control plane dependent.  When
   DetNet flows are aggregated, transit nodes provide service to the
   aggregate and not on a per-DetNet flow basis.  When aggregating
   DetNet flows the flows should be compatible i.e. the same or very
   similar QoS and CoS characteristics.  In this case, nodes performing
   aggregation will ensure that per-flow service requirements are
   achieved.

   If bandwidth reservations are used, the sum of the reservations
   should be the sum of all the individual reservations, in other words,
   the reservations should not create an over subscription of bandwidth
   reservation.  If maximum delay bounds are used the system should
   ensure that the aggregate does not exceed the delay bounds of the
   individual flows.

   DetNet encapsulation is a data plane mechanism that can be used to
   aggregate traffic.  Encapsulation can either be in the same service
   type or in a different service type see Figure 3 for example.  When
   an encapsulation is used the choice of reserving a maximum resource
   level and then tracking the services in the aggregated service or
   adjusting the aggregated resources as the services are added is
   implementation and technology specific.

   DetNet flows at edges must be able to handle rejection to an
   aggregation group due to lack of resources as well as conditions
   where general requirements are not satisfied.

3.6.2.1.  IP Aggregation

   IP aggregation has both data plane and controller plane aspects.  For
   the data plane flows may be aggregated for treatment based on shared
   characteristics such as 6-tuple.  Alternatively, an IP encapsulation
   may be used to tunnel an aggregate number of DetNet Flows between
   relay nodes.

3.6.2.2.  MPLS Aggregation

   MPLS aggregation similarly has data plane and controller plane
   aspects.  In the case of MPLS flows are often tunneled in a
   forwarding sub-layer and reservation is associated with that MPLS
   tunnel.



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3.6.3.  End-System Specific Considerations

   Data-flows requiring DetNet service are generated and terminated on
   end-systems.  Encapsulation depends on the application and its
   preferences.  For example, a DetNet MPLS domain the DN functions use
   the d-CWs, S-Labels and F-Labels to provide DetNet services.
   However, an application may exchange further flow related parameters
   (e.g., time-stamp), which are not provided by DN functions.

   As a general rule, DetNet domains are capable of forwarding any
   DetNet flows and the DetNet domain does not mandate the end-system or
   edge system encapsulation format.  Unless there is a proxy of some
   form present, end-systems peer with similar end-systems using the
   same application encapsulation format.  For example, as shown in
   Figure 5, IP applications peer with IP applications and Ethernet
   applications peer with Ethernet applications.

             +-----+
             |  X  |                               +-----+
             +-----+                               |  X  |
             | Eth |               ________        +-----+
             +-----+     _____    /        \       | Eth |
                    \   /     \__/          \___   +-----+
                     \ /                        \ /
                      0======== tunnel-1 ========0_
                      |                             \
                       \                             |
                       0========= tunnel-2 =========0
                      / \                        __/ \
               +-----+   \__ DetNet MPLS domain /     \
               |  X  |      \         __       /       +-----+
               +-----+       \_______/  \_____/        |  X  |
               |  IP |                                 +-----+
               +-----+                                 |  IP |
                                                       +-----+


             Figure 5: End-Systems and The DetNet MPLS Domain

3.6.4.  Sub-Network Considerations

   Any of the DetNet service types may be transported by another DetNet
   service.  MPLS nodes may interconnected by different sub-network
   technologies, which may include point-to-point links.  Each of these
   sub-network technologies need to provide appropriate service to
   DetNet flows.  In some cases, e.g., on dedicated point-to-point links
   or TDM technologies, all that is required is for a DetNet node to
   appropriately queue its output traffic.  In other cases, DetNet nodes



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   will need to map DetNet flows to the flow semantics (i.e.,
   identifiers) and mechanisms used by an underlying sub-network
   technology.  Figure 6 shows several examples of header formats that
   can be used to carry DetNet MPLS flows over different sub-network
   technologies.  L2 represent a generic layer-2 encapsulation that
   might be used on a point-to-point link.  TSN represents the
   encapsulation used on an IEEE 802.1 TSN network, as described in
   [I-D.ietf-detnet-mpls-over-tsn].  UDP/IP represents the encapsulation
   used on a DetNet IP PSN, as described in
   [I-D.ietf-detnet-mpls-over-udp-ip].


                              +------+  +------+  +------+
           App-Flow           |  X   |  |  X   |  |  X   |
                        +-----+======+--+======+--+======+-----+
           DetNet-MPLS        | d-CW |  | d-CW |  | d-CW |
                              +------+  +------+  +------+
                              |Labels|  |Labels|  |Labels|
                        +-----+======+--+======+--+======+-----+
           Sub-Network        |  L2  |  | TSN  |  | UDP  |
                              +------+  +------+  +------+
                                                  |  IP  |
                                                  +------+
                                                  |  L2  |
                                                  +------+


             Figure 6: Example DetNet MPLS Sub-Network Formats

4.  Controller Plane (Management and Control) Considerations

4.1.  DetNet Controller Plane Requirements

   While the definition of controller plane for DetNet is out of the
   scope of this document, there are particular considerations and
   requirements for such that result from the unique characteristics of
   the DetNet architecture [I-D.ietf-detnet-architecture] and data plane
   as defined herein.

   The primary requirements of the DetNet controller plane are that it
   must be able to:

   o  Instantiate DetNet flows in a DetNet domain (which may include
      some or all of explicit path determination, link bandwidth
      reservations, restricting flows to IEEE 802.1 TSN links, node
      buffer and other resource reservations, specification of required
      queuing disciplines along the path, ability to manage
      bidirectional flows, etc.) as needed for a flow.



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   o  In the case of MPLS, manage DetNet S-Label and F-Label allocation
      and distribution, where the DetNet MPLS encapsulation is in use
      see [I-D.ietf-detnet-mpls].

   o  Support DetNet flow aggregation.

   o  Advertise static and dynamic node and link resources such as
      capabilities and adjacencies to other network nodes (for dynamic
      signaling approaches) or to network controllers (for centralized
      approaches).

   o  Scale to handle the number of DetNet flows expected in a domain
      (which may require per-flow signaling or provisioning).

   o  Provision flow identification information at each of the nodes
      along the path.  Flow identification may differ depending on the
      location in the network and the DetNet functionality (e.g. transit
      node vs. relay node).

   These requirements, as stated earlier, could be satisfied using
   distributed control protocol signaling (such as RSVP-TE), centralized
   network management provisioning mechanisms (such as BGP, PCEP, YANG
   [I-D.ietf-detnet-flow-information-model], etc.) or hybrid
   combinations of the two, and could also make use of MPLS-based
   segment routing.

   In the abstract, the results of either distributed signaling or
   centralized provisioning are equivalent from a DetNet data plane
   perspective - flows are instantiated, explicit routes are determined,
   resources are reserved, and packets are forwarded through the domain
   using the DetNet data plane.

   However, from a practical and implementation standpoint, they are not
   equivalent at all.  Some approaches are more scalable than others in
   terms of signaling load on the network.  Some can take advantage of
   global tracking of resources in the DetNet domain for better overall
   network resource optimization.  Some are more resilient than others
   if link, node, or management equipment failures occur.  While a
   detailed analysis of the control plane alternatives is out of the
   scope of this document, the requirements from this document can be
   used as the basis of a later analysis of the alternatives.

4.2.  Generic Controller Plane Considerations

   This section covers control plane considerations that are independent
   of the data plane technology used for DetNet service delivery.





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   While management plane and control planes are traditionally
   considered separately, from the Data Plane perspective there is no
   practical difference based on the origin of flow provisioning
   information, and the DetNet architecture
   [I-D.ietf-detnet-architecture] refers to these collectively as the
   'Controller Plane'.  This document therefore does not distinguish
   between information provided by distributed control plane protocols,
   e.g., RSVP-TE [RFC3209] and [RFC3473], or by centralized network
   management mechanisms, e.g., RestConf [RFC8040], YANG [RFC7950], and
   the Path Computation Element Communication Protocol (PCEP)
   [I-D.ietf-pce-pcep-extension-for-pce-controller] or any combination
   thereof.  Specific considerations and requirements for the DetNet
   Controller Plane are discussed in Section 4.1.

   Each respective data plane document also covers the control plane
   considerations for that technology.  For example [I-D.ietf-detnet-ip]
   covers IP control plane normative considerations and
   [I-D.ietf-detnet-mpls] covers MPLS control plane normative
   considerations.

4.2.1.  Flow Aggregation Control

   Flow aggregation includes aggregation accomplished through the use of
   hierarchical LSPs in MPLS and tunnels, in the case of IP, MPLS and
   TSN, all of which aggregate multiple DetNet flows into a single new
   DetNet flow.  Aggregation can also be grouping of IP flows that share
   6-tuple attributes or flow identifiers at the DetNet sub-layer.

   Control of aggregation involves a set of procedures listed here.
   Aggregation may use some or all of these capabilities and the order
   may vary:

   o  Traffic engineering resource collection and distribution:

         Available resources are tracked through control plane or
         management plane databases and distributed amongst controllers
         or nodes that can manage resources.

   o  Path computation and resource allocation:

         When DetNet services are provisioned or requested one or more
         paths meeting the requirements are selected and the resources
         verified and recorded.

   o  Resource assignment and data plane co-ordination:

         The assignment of resources along the path depends on the
         technology and it includes assignment of specific links and



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         coordination of the queuing and other traffic management
         capabilities such as policing and shaping.

   o  Assigned Resource recording and updating:

         Depending on the specific technology the assigned resources are
         updated and distributed in the databases preventing over
         subscription.

4.2.2.  Explicit Routes

   Explicit routes are used to ensure that packets are routed through
   the resources that have been reserved for them, and hence provide the
   DetNet application with the required service.  A requirement for the
   DetNet Controller Plane will be the ability to assign a particular
   identified DetNet IP flow to a path through the DetNet domain that
   has been assigned the required nodal resources.  This provides the
   appropriate traffic treatment for the flow and also includes
   particular links as a part of the path that are able to support the
   DetNet flow.  For example, by using IEEE 802.1 TSN links (as
   discussed in [I-D.ietf-detnet-mpls-over-tsn] ) DetNet parameters can
   be maintained.  Further considerations and requirements for the
   DetNet Controller Plane are discussed in Section 4.1.

   Whether configuring, calculating and instantiating these routes is a
   single-stage or multi-stage process, or in a centralized or
   distributed manner, is out of scope of this document.

   There are several approaches that could be used to provide explicit
   routes and resource allocation in the DetNet forwarding sub-layer.
   For example:

   o  The path could be explicitly set up by a controller which
      calculates the path and explicitly configures each node along that
      path with the appropriate forwarding and resource allocation
      information.

   o  The path could use a distributed control plane such as RSVP
      [RFC2205] or RSVP-TE [RFC3473] extended to support DetNet IP
      flows.

   o  The path could be implemented using IPv6-based segment routing
      when extended to support resource allocation.

   See Section 4.1 for further discussion of these alternatives.  In
   addition, [RFC2386] contains useful background information on QoS-
   based routing, and [RFC5575] discusses a specific mechanism used by
   BGP for traffic flow specification and policy-based routing.



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4.2.3.  Contention Loss and Jitter Reduction

   As discussed in Section 1, this document does not specify the
   mechanisms needed to eliminate packet contention, packet loss or
   reduce jitter for DetNet flows at the DetNet forwarding sub-layer.
   The ability to manage node and link resources to be able to provide
   these functions is a necessary part of the DetNet controller plane.
   It is also necessary to be able to control the required queuing
   mechanisms used to provide these functions along a flow's path
   through the network.  See [I-D.ietf-detnet-ip] and Section 4.1 for
   further discussion of these requirements.

4.2.4.  Bidirectional Traffic

   DetNet applications typically generate bidirectional traffic.  IP and
   MPLS typically treat each direction separately and do not force
   interdependence of each direction.  MPLS has considered bidirectional
   traffic requirements and the MPLS definitions from [RFC5654] are
   useful to illustrate terms such as associated bidirectional flows and
   co-routed bidirectional flows.  MPLS defines a point-to-point
   associated bidirectional LSP as consisting of two unidirectional
   point-to-point LSPs, one from A to B and the other from B to A, which
   are regarded as providing a single logical bidirectional forwarding
   path.  This is analogous to standard IP routing.  MPLS defines a
   point-to-point co-routed bidirectional LSP as an associated
   bidirectional LSP which satisfies the additional constraint that its
   two unidirectional component LSPs follow the same path (in terms of
   both nodes and links) in both directions.  An important property of
   co-routed bidirectional LSPs is that their unidirectional component
   LSPs share fate.  In both types of bidirectional LSPs, resource
   reservations may differ in each direction.  The concepts of
   associated bidirectional flows and co-routed bidirectional flows can
   also be applied to DetNet IP flows.

   While the DetNet IP data plane must support bidirectional DetNet
   flows, there are no special bidirectional features with respect to
   the data plane other than the need for the two directions of a co-
   routed bidirectional flow to take the same path.  That is to say that
   bidirectional DetNet flows are solely represented at the management
   and control plane levels, without specific support or knowledge
   within the DetNet data plane.  Fate sharing and associated or co-
   routed bidirectional flows, can be managed at the control level.

   DetNet's use of PREOF may increase the complexity of using co-routing
   bidirectional flows, since if PREOF is used, then the replication
   points in one direction would have to match the elimination points in
   the other direction, and vice versa, and the optimal points for these
   functions in one direction may not match the optimal points in the



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   other subsequent to the network and traffic constraints.
   Furthermore, due to the per packet service protection nature,
   bidirectional forwarding per packet may not be ensured.  The first
   packet of received member flows is selected by the elimination
   function independently of which path it has taken through the
   network.

   Control and management mechanisms need to support bidirectional
   flows, but the specification of such mechanisms are out of scope of
   this document.  An example control plane solution for MPLS can be
   found in [RFC3473] , [RFC6387] and [RFC7551].  These requirements are
   included in Section 4.1.

4.3.  Packet Replication, Elimination, and Ordering (PREOF)

   The controller plane protocol solution required for managing the
   PREOF processing is outside the scope of this document.  That said,
   it should be noted that the ability to determine, for a particular
   flow, optimal packet replication and elimination points in the DetNet
   domain requires explicit support.  There may be capabilities that can
   be used, or extended, for example GMPLS end-to-end recovery [RFC4872]
   and GMPLS segment recovery [RFC4873].

5.  Security Considerations

   Security considerations for DetNet are described in detail in
   [I-D.ietf-detnet-security].  General security considerations are
   described in [I-D.ietf-detnet-architecture].  This section considers
   general security considerations applicable to all data planes.

   Security aspects which are unique to DetNet are those whose aim is to
   provide the specific quality of service aspects of DetNet, which are
   primarily to deliver data flows with extremely low packet loss rates
   and bounded end-to-end delivery latency.

   The primary considerations for the data plane is to maintain
   integrity of data and delivery of the associated DetNet service
   traversing the DetNet network.  Application flows can be protected
   through whatever means is provided by the underlying technology.  For
   example, encryption may be used, such as that provided by IPSec
   [RFC4301] for IP flows and/or by an underlying sub-net using MACSec
   [IEEE802.1AE-2018] for Ethernet (Layer-2) flows.

   From a data plane perspective DetNet does not add or modify any
   header information.

   At the management and control level DetNet flows are identified on a
   per-flow basis, which may provide controller plane attackers with



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   additional information about the data flows (when compared to
   controller planes that do not include per-flow identification).  This
   is an inherent property of DetNet which has security implications
   that should be considered when determining if DetNet is a suitable
   technology for any given use case.

   To provide uninterrupted availability of the DetNet service,
   provisions can be made against DOS attacks and delay attacks.  To
   protect against DOS attacks, excess traffic due to malicious or
   malfunctioning devices can be prevented or mitigated, for example
   through the use of existing mechanism such as policing and shaping
   applied at the input of a DetNet domain.  To prevent DetNet packets
   from being delayed by an entity external to a DetNet domain, DetNet
   technology definition can allow for the mitigation of Man-In-The-
   Middle attacks, for example through use of authentication and
   authorization of devices within the DetNet domain.

6.  IANA Considerations

   This document makes no IANA requests.

7.  Acknowledgements

   The authors wish to thank Pat Thaler, Norman Finn, Loa Anderson,
   David Black, Rodney Cummings, Ethan Grossman, Tal Mizrahi, David
   Mozes, Craig Gunther, George Swallow, Yuanlong Jiang and Carlos J.
   Bernardos for their various contributions to this work.

8.  References

8.1.  Normative References

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Resource ReserVation Protocol-
              Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
              DOI 10.17487/RFC3473, January 2003,
              <https://www.rfc-editor.org/info/rfc3473>.

   [RFC4385]  Bryant, S., Swallow, G., Martini, L., and D. McPherson,
              "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
              Use over an MPLS PSN", RFC 4385, DOI 10.17487/RFC4385,
              February 2006, <https://www.rfc-editor.org/info/rfc4385>.




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8.2.  Informative References

   [I-D.ietf-detnet-architecture]
              Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", draft-ietf-
              detnet-architecture-13 (work in progress), May 2019.

   [I-D.ietf-detnet-flow-information-model]
              Farkas, J., Varga, B., Cummings, R., and Y. Jiang, "DetNet
              Flow Information Model", draft-ietf-detnet-flow-
              information-model-03 (work in progress), March 2019.

   [I-D.ietf-detnet-ip]
              Varga, B., Farkas, J., Berger, L., Fedyk, D., Malis, A.,
              Bryant, S., and J. Korhonen, "DetNet Data Plane: IP",
              draft-ietf-detnet-ip-00 (work in progress), May 2019.

   [I-D.ietf-detnet-mpls]
              Varga, B., Farkas, J., Berger, L., Fedyk, D., Malis, A.,
              Bryant, S., and J. Korhonen, "DetNet Data Plane: MPLS",
              draft-ietf-detnet-mpls-00 (work in progress), May 2019.

   [I-D.ietf-detnet-mpls-over-tsn]
              Varga, B., Farkas, J., Malis, A., Bryant, S., and J.
              Korhonen, "DetNet Data Plane: MPLS over IEEE 802.1 Time
              Sensitive Networking (TSN)", draft-ietf-detnet-mpls-over-
              tsn-00 (work in progress), May 2019.

   [I-D.ietf-detnet-mpls-over-udp-ip]
              Varga, B., Farkas, J., Berger, L., Malis, A., Bryant, S.,
              and J. Korhonen, "DetNet Data Plane: MPLS over IP", draft-
              ietf-detnet-mpls-over-udp-ip-00 (work in progress), May
              2019.

   [I-D.ietf-detnet-security]
              Mizrahi, T., Grossman, E., Hacker, A., Das, S., Dowdell,
              J., Austad, H., Stanton, K., and N. Finn, "Deterministic
              Networking (DetNet) Security Considerations", draft-ietf-
              detnet-security-04 (work in progress), March 2019.

   [I-D.ietf-pce-pcep-extension-for-pce-controller]
              Zhao, Q., Li, Z., Negi, M., and C. Zhou, "PCEP Procedures
              and Protocol Extensions for Using PCE as a Central
              Controller (PCECC) of LSPs", draft-ietf-pce-pcep-
              extension-for-pce-controller-01 (work in progress),
              February 2019.





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   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J.,
              daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
              Network Programming", draft-ietf-spring-srv6-network-
              programming-00 (work in progress), April 2019.

   [IEEE802.1AE-2018]
              IEEE Standards Association, "IEEE Std 802.1AE-2018 MAC
              Security (MACsec)", 2018,
              <https://ieeexplore.ieee.org/document/8585421>.

   [IEEE802.1TSNTG]
              IEEE Standards Association, "IEEE 802.1 Time-Sensitive
              Networking Task Group", <http://www.ieee802.org/1/tsn>.

   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
              September 1997, <https://www.rfc-editor.org/info/rfc2205>.

   [RFC2386]  Crawley, E., Nair, R., Rajagopalan, B., and H. Sandick, "A
              Framework for QoS-based Routing in the Internet",
              RFC 2386, DOI 10.17487/RFC2386, August 1998,
              <https://www.rfc-editor.org/info/rfc2386>.

   [RFC3670]  Moore, B., Durham, D., Strassner, J., Westerinen, A., and
              W. Weiss, "Information Model for Describing Network Device
              QoS Datapath Mechanisms", RFC 3670, DOI 10.17487/RFC3670,
              January 2004, <https://www.rfc-editor.org/info/rfc3670>.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <https://www.rfc-editor.org/info/rfc4301>.

   [RFC4872]  Lang, J., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
              Ed., "RSVP-TE Extensions in Support of End-to-End
              Generalized Multi-Protocol Label Switching (GMPLS)
              Recovery", RFC 4872, DOI 10.17487/RFC4872, May 2007,
              <https://www.rfc-editor.org/info/rfc4872>.

   [RFC4873]  Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
              "GMPLS Segment Recovery", RFC 4873, DOI 10.17487/RFC4873,
              May 2007, <https://www.rfc-editor.org/info/rfc4873>.

   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
              and D. McPherson, "Dissemination of Flow Specification
              Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
              <https://www.rfc-editor.org/info/rfc5575>.



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   [RFC5654]  Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
              Sprecher, N., and S. Ueno, "Requirements of an MPLS
              Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
              September 2009, <https://www.rfc-editor.org/info/rfc5654>.

   [RFC6387]  Takacs, A., Berger, L., Caviglia, D., Fedyk, D., and J.
              Meuric, "GMPLS Asymmetric Bandwidth Bidirectional Label
              Switched Paths (LSPs)", RFC 6387, DOI 10.17487/RFC6387,
              September 2011, <https://www.rfc-editor.org/info/rfc6387>.

   [RFC7551]  Zhang, F., Ed., Jing, R., and R. Gandhi, Ed., "RSVP-TE
              Extensions for Associated Bidirectional Label Switched
              Paths (LSPs)", RFC 7551, DOI 10.17487/RFC7551, May 2015,
              <https://www.rfc-editor.org/info/rfc7551>.

   [RFC7657]  Black, D., Ed. and P. Jones, "Differentiated Services
              (Diffserv) and Real-Time Communication", RFC 7657,
              DOI 10.17487/RFC7657, November 2015,
              <https://www.rfc-editor.org/info/rfc7657>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8227]  Cheng, W., Wang, L., Li, H., van Helvoort, H., and J.
              Dong, "MPLS-TP Shared-Ring Protection (MSRP) Mechanism for
              Ring Topology", RFC 8227, DOI 10.17487/RFC8227, August
              2017, <https://www.rfc-editor.org/info/rfc8227>.

Authors' Addresses

   Balazs Varga (editor)
   Ericsson
   Magyar Tudosok krt. 11.
   Budapest  1117
   Hungary

   Email: balazs.a.varga@ericsson.com









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   Janos Farkas
   Ericsson
   Magyar Tudosok krt. 11.
   Budapest  1117
   Hungary

   Email: janos.farkas@ericsson.com


   Lou Berger
   LabN Consulting, L.L.C.

   Email: lberger@labn.net


   Don Fedyk
   LabN Consulting, L.L.C.

   Email: dfedyk@labn.net


   Andrew G. Malis
   Futurewei Technologies

   Email: agmalis@gmail.com


   Stewart Bryant
   Futurewei Technologies

   Email: stewart.bryant@gmail.com


   Jouni Korhonen

   Email: jouni.nospam@gmail.com















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