



Internet Engineering Task Force (IETF)                     B. Varga, Ed.
Request for Comments: 9023                                     J. Farkas
Category: Informational                                         Ericsson
ISSN: 2070-1721                                                 A. Malis
                                                        Malis Consulting
                                                               S. Bryant
                                                  Futurewei Technologies
                                                               June 2021


    Deterministic Networking (DetNet) Data Plane: IP over IEEE 802.1
                    Time-Sensitive Networking (TSN)

Abstract

   This document specifies the Deterministic Networking IP data plane
   when operating over a Time-Sensitive Networking (TSN) sub-network.
   This document does not define new procedures or processes.  Whenever
   this document makes statements or recommendations, these are taken
   from normative text in the referenced RFCs.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9023.

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Table of Contents

   1.  Introduction
   2.  Terminology
     2.1.  Terms Used in This Document
     2.2.  Abbreviations
   3.  DetNet IP Data Plane Overview
   4.  DetNet IP Flows over an IEEE 802.1 TSN Sub-network
     4.1.  Functions for DetNet Flow to TSN Stream Mapping
     4.2.  TSN Requirements of IP DetNet Nodes
     4.3.  Service Protection within the TSN Sub-network
     4.4.  Aggregation during DetNet Flow to TSN Stream Mapping
   5.  Management and Control Implications
   6.  Security Considerations
   7.  IANA Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   Deterministic Networking (DetNet) is a service that can be offered by
   a network to DetNet flows.  DetNet provides these flows extremely low
   packet-loss rates and assured maximum end-to-end delivery latency.
   General background and concepts of DetNet can be found in the DetNet
   Architecture [RFC8655].

   [RFC8939] specifies the DetNet data plane operation for IP hosts and
   routers that provide DetNet service to IP-encapsulated data.  This
   document focuses on the scenario where DetNet IP nodes are
   interconnected by a Time-Sensitive Networking (TSN) sub-network.

   The DetNet Architecture decomposes the DetNet-related data plane
   functions 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
   reordering).  As described in [RFC8939], no DetNet-specific headers
   are added to support DetNet IP flows.  So, only the forwarding sub-
   layer functions can be supported inside the DetNet IP domain.
   Service protection can be provided on a per-sub-network basis as
   shown here for the IEEE 802.1 TSN sub-network scenario.

2.  Terminology

2.1.  Terms Used in This Document

   This document uses the terminology and concepts established in the
   DetNet Architecture [RFC8655].  TSN-specific terms are defined by the
   TSN Task Group of the IEEE 802.1 Working Group.  The reader is
   assumed to be familiar with these documents and their terminology.

2.2.  Abbreviations

   The following abbreviations are used in this document:

   DetNet        Deterministic Networking

   FRER          Frame Replication and Elimination for Redundancy (TSN
                 function)

   L2            Layer 2

   L3            Layer 3

   TSN           Time-Sensitive Networking; TSN is a Task Group of the
                 IEEE 802.1 Working Group.

3.  DetNet IP Data Plane Overview

   [RFC8939] describes how IP is used by DetNet nodes, i.e., hosts and
   routers, to identify DetNet flows and provide a DetNet service.  From
   a data plane perspective, an end-to-end IP model is followed.  DetNet
   uses flow identification based on a "6-tuple", where "6-tuple" refers
   to information carried in IP- and higher-layer protocol headers as
   defined in [RFC8939].

   DetNet flow aggregation may be enabled via the use of wildcards,
   masks, prefixes, and ranges.  IP tunnels may also be used to support
   flow aggregation.  In these cases, it is expected that DetNet-aware
   intermediate nodes will provide DetNet service assurance on the
   aggregate through resource allocation and congestion control
   mechanisms.

   Congestion protection, latency control, and the resource allocation
   (queuing, policing, and shaping) are supported using the underlying
   link / sub-net-specific mechanisms.  Service protections (packet-
   replication and packet-elimination functions) are not provided at the
   IP DetNet layer end to end due to the lack of unified end-to-end
   sequencing information that would be available for intermediate
   nodes.  However, such service protection can be provided per
   underlying L2 link and per sub-network.

   DetNet routers ensure that DetNet service requirements are met per
   hop by allocating local resources, by both receiving and
   transmitting, and by mapping the service requirements of each flow to
   appropriate sub-network mechanisms.  Such mappings are sub-network
   technology specific.  DetNet nodes interconnected by a TSN sub-
   network are the primary focus of this document.  The mapping of
   DetNet IP flows to TSN Streams and TSN protection mechanisms are
   covered in Section 4.

4.  DetNet IP Flows over an IEEE 802.1 TSN Sub-network

   This section covers how DetNet IP flows operate over an IEEE 802.1
   TSN sub-network.  Figure 1 illustrates such a scenario where two IP
   (DetNet) nodes are interconnected by a TSN sub-network.  Dotted lines
   around the Service components of the IP (DetNet) nodes indicate that
   they are DetNet service aware but do not perform any DetNet service
   sub-layer function.  Node-1 is single homed and Node-2 is dual homed
   to the TSN sub-network, and they are treated as Talker or Listener
   inside the TSN sub-network.  Note that from the TSN perspective,
   dual-homed characteristics of Talker or Listener nodes are
   transparent to the IP Layer.

       IP (DetNet)                   IP (DetNet)
         Node-1                        Node-2

      ............                  ............
   <--: Service  :-- DetNet flow ---: Service  :-->
      +----------+                  +----------+
      |Forwarding|                  |Forwarding|
      +--------.-+    <-TSN Str->   +-.-----.--+
                \      ,-------.     /     /
                 +----[ TSN Sub-]---+     /
                      [ Network ]--------+
                       `-------'
   <----------------- DetNet IP ----------------->

         Figure 1: DetNet-Enabled IP Network over a TSN Sub-network

   At the time of this writing, the Time-Sensitive Networking (TSN) Task
   Group of the IEEE 802.1 Working Group have defined (and are defining)
   a number of amendments to [IEEE8021Q] that provide zero congestion
   loss and bounded latency in bridged networks.  Furthermore,
   [IEEE8021CB] defines frame replication and elimination functions for
   reliability that should prove both compatible with and useful to
   DetNet networks.  All these functions have to identify flows that
   require TSN treatment.

   TSN capabilities of the TSN sub-network are made available for IP
   (DetNet) flows via the protocol interworking function described in
   Annex C.5 of [IEEE8021CB].  For example, applied on the TSN edge port
   it can convert an ingress unicast IP (DetNet) flow to use a specific
   L2 multicast destination Media Access Control (MAC) address and a
   VLAN in order to forward the packet through a specific path inside
   the bridged network.  A similar interworking function pair at the
   other end of the TSN sub-network would restore the packet to its
   original L2 destination MAC address and VLAN.

   Placement of TSN functions depends on the TSN capabilities of nodes.
   IP (DetNet) nodes may or may not support TSN functions.  For a given
   TSN Stream (i.e., a mapped DetNet flow), an IP (DetNet) node is
   treated as a Talker or a Listener inside the TSN sub-network.

4.1.  Functions for DetNet Flow to TSN Stream Mapping

   Mapping of a DetNet IP flow to a TSN Stream is provided via the
   combination of a passive and an active Stream identification function
   that operate at the frame level (Layer 2).  The passive Stream
   identification function is used to catch the 6-tuple of a DetNet IP
   flow, and the active Stream identification function is used to modify
   the Ethernet header according to the ID of the mapped TSN Stream.

   Clause 6.7 of [IEEE8021CB] defines an IP Stream identification
   function that can be used as a passive function for IP DetNet flows
   using UDP or TCP.  Clause 6.8 of [IEEEP8021CBdb] defines a Mask-and-
   Match Stream identification function that can be used as a passive
   function for any IP DetNet flows.

   Clause 6.6 of [IEEE8021CB] defines an Active Destination MAC and VLAN
   Stream identification function that can replace some Ethernet header
   fields: (1) the destination MAC address, (2) the VLAN-ID, and (3)
   priority parameters with alternate values.  Replacement is provided
   for the frame passed down the stack from the upper layers or up the
   stack from the lower layers.

   Active Destination MAC and VLAN Stream identification can be used
   within a Talker to set flow identity or within a Listener to recover
   the original addressing information.  It can be used also in a TSN
   bridge that is providing translation as a proxy service for an End
   System.

4.2.  TSN Requirements of IP DetNet Nodes

   This section covers the required behavior of a TSN-aware DetNet node
   using a TSN sub-network.  The implementation of TSN packet-processing
   functions must be compliant with the relevant IEEE 802.1 standards.

   From the TSN sub-network perspective, DetNet IP nodes are treated as
   a Talker or Listener that may be (1) TSN unaware or (2) TSN aware.

   In cases of TSN-unaware IP DetNet nodes, the TSN relay nodes within
   the TSN sub-network must modify the Ethernet encapsulation of the
   DetNet IP flow (e.g., MAC translation, VLAN-ID setting, sequence
   number addition, etc.) to allow proper TSN-specific handling inside
   the sub-network.  There are no requirements defined for TSN-unaware
   IP DetNet nodes in this document.

   IP (DetNet) nodes being TSN aware can be treated as a combination of
   a TSN-unaware Talker/Listener and a TSN relay, as shown in Figure 2.
   In such cases, the IP (DetNet) node must provide the TSN sub-network-
   specific Ethernet encapsulation over the link(s) towards the sub-
   network.

                  IP (DetNet)
                     Node
      <---------------------------------->

      ............
   <--: Service  :-- DetNet flow ------------------
      +----------+
      |Forwarding|
      +----------+    +---------------+
      |    L2    |    | L2 Relay with |<--- TSN ---
      |          |    | TSN function  |    Stream
      +-----.----+    +--.------.---.-+
             \__________/        \   \______
                                  \_________
       TSN-unaware
        Talker /          TSN Bridge
        Listener             Relay
                                          <----- TSN Sub-network -----
      <------- TSN-aware Tlk/Lstn ------->

               Figure 2: IP (DetNet) Node with TSN Functions

   A TSN-aware IP (DetNet) node implementation must support the Stream
   identification TSN component for recognizing flows.

   A Stream identification component must be able to instantiate the
   following: (1) Active Destination MAC and VLAN Stream identification,
   (2) IP Stream identification, (3) Mask-and-Match Stream
   identification, and (4) the related managed objects in Clause 9 of
   [IEEE8021CB] and [IEEEP8021CBdb].

   A TSN-aware IP (DetNet) node implementation must support the
   Sequencing function and the Sequence encode/decode function as
   defined in Clauses 7.4 and 7.6 of [IEEE8021CB] if FRER is used inside
   the TSN sub-network.

   The Sequence encode/decode function must support the Redundancy tag
   (R-TAG) format as per Clause 7.8 of [IEEE8021CB].

   A TSN-aware IP (DetNet) node implementation must support the Stream
   splitting function and the Individual recovery function as defined in
   Clauses 7.7 and 7.5 of [IEEE8021CB] when the node is a replication or
   elimination point for FRER.

4.3.  Service Protection within the TSN Sub-network

   TSN Streams supporting DetNet flows may use FRER as defined in Clause
   8 of [IEEE8021CB] based on the loss service requirements of the TSN
   Stream, which is derived from the DetNet service requirements of the
   DetNet mapped flow.  The specific operation of FRER is not modified
   by the use of DetNet and follows [IEEE8021CB].

   The FRER function and the provided service recovery are available
   only within the TSN sub-network, as the TSN Stream ID and the TSN
   sequence number are not valid outside the sub-network.  An IP
   (DetNet) node represents an L3 border and as such, it terminates all
   related information elements encoded in the L2 frames.

4.4.  Aggregation during DetNet Flow to TSN Stream Mapping

   Implementations of this document shall use management and control
   information to map a DetNet flow to a TSN Stream.  N:1 mapping
   (aggregating DetNet flows in a single TSN Stream) shall be supported.
   The management or control function that provisions flow mapping shall
   ensure that adequate resources are allocated and configured to
   provide proper service requirements of the mapped flows.

5.  Management and Control Implications

   DetNet flows and TSN Stream-mapping-related information are required
   only for TSN-aware IP (DetNet) nodes.  From the data plane
   perspective, there is no practical difference based on the origin of
   flow-mapping-related information (management plane or control plane).

   The following summarizes the set of information that is needed to
   configure DetNet IP over TSN:

   *  DetNet-IP-related configuration information according to the
      DetNet role of the DetNet IP node, as per [RFC8939].

   *  TSN-related configuration information according to the TSN role of
      the DetNet IP node, as per [IEEE8021Q], [IEEE8021CB], and
      [IEEEP8021CBdb].

   *  Mapping between DetNet IP flow(s) and TSN Stream(s).  DetNet IP
      flow identification is summarized in Section 5.1 of [RFC8939] and
      includes all wildcards, port ranges, and the ability to ignore
      specific IP fields.  Information on TSN Stream identification
      information is defined in [IEEE8021CB] and [IEEEP8021CBdb].  Note
      that managed objects for TSN Stream identification can be found in
      [IEEEP8021CBcv].

   This information must be provisioned per DetNet flow.

   Mappings between DetNet and TSN management and control planes are out
   of scope of this document.  Some of the challenges are highlighted
   below.

   TSN-aware IP DetNet nodes are members of both the DetNet domain and
   the TSN sub-network.  Within the TSN sub-network, the TSN-aware IP
   (DetNet) node has a TSN-aware Talker/Listener role, so TSN-specific
   management and control plane functionalities must be implemented.
   There are many similarities in the management plane techniques used
   in DetNet and TSN, but that is not the case for the control plane
   protocols.  For example, RSVP-TE and the Multiple Stream Registration
   Protocol (MSRP) of IEEE 802.1 behave differently.  Therefore,
   management and control plane design is an important aspect of
   scenarios where mapping between DetNet and TSN is required.

   In order to use a TSN sub-network between DetNet nodes, DetNet-
   specific information must be converted to TSN sub-network-specific
   information.  DetNet flow ID and flow-related parameters/requirements
   must be converted to a TSN Stream ID and stream-related parameters/
   requirements.  Note that, as the TSN sub-network is just a portion of
   the end-to-end DetNet path (i.e., single hop from an IP perspective),
   some parameters (e.g., delay) may differ significantly.  Other
   parameters (like bandwidth) also may have to be tuned due to the L2
   encapsulation used within the TSN sub-network.

   In some cases, it may be challenging to determine some TSN Stream-
   related information.  For example, on a TSN-aware IP (DetNet) node
   that acts as a Talker, it is quite obvious which DetNet node is the
   Listener of the mapped TSN Stream (i.e., the IP next-hop).  However,
   it may not be trivial to locate the point/interface where that
   Listener is connected to the TSN sub-network.  Such attributes may
   require interaction between control and management plane functions
   and between DetNet and TSN domains.

   Mapping between DetNet flow identifiers and TSN Stream identifiers,
   if not provided explicitly, can be done by a TSN-aware IP (DetNet)
   node locally based on information provided for configuration of the
   TSN Stream identification functions (IP Stream identification, Mask-
   and-Match Stream identification, and the active Stream identification
   function).

   Triggering the setup/modification of a TSN Stream in the TSN sub-
   network is an example where management and/or control plane
   interactions are required between the DetNet and TSN sub-network.
   TSN-unaware IP (DetNet) nodes make such a triggering even more
   complicated, as they are fully unaware of the sub-network and run
   independently.

   Configuration of TSN-specific functions (e.g., FRER) inside the TSN
   sub-network is a TSN-domain-specific decision and may not be visible
   in the DetNet domain.

6.  Security Considerations

   Security considerations for DetNet are described in detail in
   [DETNET-SECURITY].  General security considerations are described in
   [RFC8655].  Considerations specific to the DetNet IP data plane are
   summarized in [RFC8939].  This section discusses security
   considerations that are specific to the DetNet IP-over-TSN sub-
   network scenario.

   The sub-network between DetNet nodes needs to be subject to
   appropriate confidentiality.  Additionally, knowledge of what DetNet/
   TSN services are provided by a sub-network may supply information
   that can be used in a variety of security attacks.  The ability to
   modify information exchanges between connected DetNet nodes may
   result in bogus operations.  Therefore, it is important that the
   interface between DetNet nodes and the TSN sub-network are subject to
   authorization, authentication, and encryption.

   The TSN sub-network operates at Layer 2, so various security
   mechanisms defined by IEEE can be used to secure the connection
   between the DetNet nodes (e.g., encryption may be provided using
   MACsec [IEEE802.1AE-2018]).

7.  IANA Considerations

   This document has no IANA actions.

8.  References

8.1.  Normative References

   [IEEE8021CB]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks--Frame Replication and Elimination for
              Reliability", IEEE 802.1CB-2017,
              DOI 10.1109/IEEESTD.2017.8091139, October 2017,
              <https://standards.ieee.org/standard/802_1CB-2017.html>.

   [IEEEP8021CBdb]
              IEEE, "Draft Standard for Local and metropolitan area
              networks -- Frame Replication and Elimination for
              Reliability -- Amendment: Extended Stream Identification
              Functions", IEEE P802.1CBdb / D1.3, April 2021,
              <https://1.ieee802.org/tsn/802-1cbdb/>.

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,
              <https://www.rfc-editor.org/info/rfc8655>.

   [RFC8939]  Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S.
              Bryant, "Deterministic Networking (DetNet) Data Plane:
              IP", RFC 8939, DOI 10.17487/RFC8939, November 2020,
              <https://www.rfc-editor.org/info/rfc8939>.

8.2.  Informative References

   [DETNET-SECURITY]
              Grossman, E., Ed., Mizrahi, T., and A. Hacker,
              "Deterministic Networking (DetNet) Security
              Considerations", Work in Progress, Internet-Draft, draft-
              ietf-detnet-security-16, March 2021,
              <https://tools.ietf.org/html/draft-ietf-detnet-security-
              16>.

   [IEEE802.1AE-2018]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks--Media Access Control (MAC) Security", IEEE
              802.1AE-2018, DOI 10.1109/IEEESTD.2018.8585421, December
              2018, <https://ieeexplore.ieee.org/document/8585421>.

   [IEEE8021Q]
              IEEE, "IEEE Standard for Local and Metropolitan Area
              Network--Bridges and Bridged Networks", IEEE Std 802.1Q-
              2018, DOI 10.1109/IEEESTD.2018.8403927, July 2018,
              <https://ieeexplore.ieee.org/document/8403927>.

   [IEEEP8021CBcv]
              IEEE 802.1, "Draft Standard for Local and metropolitan
              area networks--Frame Replication and Elimination for
              Reliability--Amendment: Information Model, YANG Data Model
              and Management Information Base Module", IEEE P802.1CBcv,
              Draft 1.1, February 2021,
              <https://1.ieee802.org/tsn/802-1cbcv/>.

Acknowledgements

   The authors wish to thank Norman Finn, Lou Berger, Craig Gunther,
   Christophe Mangin, and Jouni Korhonen for their various contributions
   to this work.

Authors' Addresses

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

   Email: balazs.a.varga@ericsson.com


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

   Email: janos.farkas@ericsson.com


   Andrew G. Malis
   Malis Consulting

   Email: agmalis@gmail.com


   Stewart Bryant
   Futurewei Technologies

   Email: sb@stewartbryant.com
