DetNet                                                     B. Varga, Ed.
Internet-Draft                                                 J. Farkas
Intended status: Informational                                  Ericsson
Expires: August 16, 23, 2021                                        A. Malis
                                                        Malis Consulting
                                                               S. Bryant
                                                  Futurewei Technologies
                                                       February 12, 19, 2021

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


   This document specifies the Deterministic Networking MPLS data plane
   when operating over an IEEE 802.1 Time-Sensitive Networking (TSN)
   sub-network.  This document does not define new procedures or
   processes.  Whenever this document makes requirements statements or
   recommendations, these are taken from normative text in the
   referenced RFCs.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Terms Used in This Document . . . . . . . . . . . . . . .   3
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   3
   3.  DetNet MPLS Data Plane Overview . . . . . . . . . . . . . . .   4   3
   4.  DetNet MPLS Operation Over IEEE 802.1 TSN Sub-Networks  . . .   4
     4.1.  Functions for DetNet Flow to TSN Stream Mapping . . . . .   6
     4.2.  TSN requirements of MPLS DetNet nodes . . . . . . . . . .   6
     4.3.  Service protection within the TSN sub-network . . . . . .   8
     4.4.  Aggregation during DetNet flow to TSN Stream mapping  . .   8
   5.  Management and Control Implications . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

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

   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) leveraging MPLS Traffic Engineering mechanisms.

   [RFC8964] specifies the DetNet data plane operation for MPLS-based
   Packet Switched Network (PSN).  MPLS encapsulated DetNet flows can be
   carried over network technologies that can provide the DetNet
   required level of service.  This document focuses on the scenario
   where MPLS (DetNet) nodes are interconnected by a IEEE 802.1 TSN sub-
   network.  There is close cooperation between the IETF DetNet WG and
   the IEEE 802.1 TSN TG.

2.  Terminology

2.1.  Terms Used in This Document

   This document uses the terminology established in the DetNet
   architecture [RFC8655] and [RFC8964].  TSN specific terms are defined
   in the TSN TG of 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:

   A-Label       Aggregation label, a special case of an S-Label.


   d-CW          DetNet Control Word.

   DetNet        Deterministic Networking.

   DF            DetNet Flow.

   F-Label       Forwarding label that identifies the LSP used by a
                 DetNet flow.

   FRER          Frame Replication and Elimination for Redundancy (TSN

   L2            Layer 2.

   L3            Layer 3.

   LSR           Label Switching Router.

   MPLS          Multiprotocol Label Switching.

   PE            Provider Edge.

   PREOF         Packet Replication, Elimination and Ordering Functions.

   PSN           Packet Switched Network.

   PW            PseudoWire.

   S-PE          Switching Provider Edge.

   RSVP-TE       Resource Reservation Protocol - Traffic Engineering.

   S-Label       Service label.

   T-PE          Terminating Provider Edge.

   TSN           Time-Sensitive Network.

3.  DetNet MPLS Data Plane Overview

   The basic approach defined in [RFC8964] supports the DetNet service
   sub-layer based on existing pseudowire (PW) encapsulations and
   mechanisms, and supports the DetNet forwarding sub-layer based on
   existing MPLS Traffic Engineering encapsulations and mechanisms.

   A node operating on a DetNet flow in the Detnet service sub-layer,
   i.e.  a node processing a DetNet packet which has the S-Label as top
   of stack uses the local context associated with that service label
   (S-Label), for example a received forwarding label (F-Label), to
   determine what local DetNet operation(s) are applied to that packet.
   An S-Label may be unique when taken from the platform label space
   [RFC3031], which would enable correct DetNet flow identification
   regardless of which input interface or LSP the packet arrives on.
   The service sub-layer functions (i.e., PREOF) use a DetNet control
   word (d-CW).

   The DetNet MPLS data plane builds on MPLS Traffic Engineering
   encapsulations and mechanisms to provide a forwarding sub-layer that
   is responsible for providing resource allocation and explicit routes.
   The forwarding sub-layer is supported by one or more F-Labels.

   DetNet edge/relay nodes are DetNet service sub-layer aware,
   understand the particular needs of DetNet flows and provide both
   DetNet service and forwarding sub-layer functions.  They add, remove
   and process d-CWs, S-Labels and F-labels as needed.  MPLS DetNet
   nodes and transit nodes include DetNet forwarding sub-layer
   functions, notably support for notably explicit routes, and resources
   allocation to eliminate (or reduce) congestion loss and jitter.
   Unlike other DetNet node types, transit nodes provide no service sub-
   layer processing.

   MPLS (DetNet) nodes and transit nodes interconnected by a TSN sub-
   network are the primary focus of this document.  The mapping of
   DetNet MPLS flows to TSN streams and TSN protection mechanisms are
   covered in Section 4.

4.  DetNet MPLS Operation Over IEEE 802.1 TSN Sub-Networks

   The DetNet WG collaborates with IEEE 802.1 TSN in order to define a
   common architecture for both Layer 2 and Layer 3, that maintains
   consistency across diverse networks.  Both DetNet MPLS and TSN use
   the same techniques to provide their deterministic service:

   o  Service protection.

   o  Resource allocation.

   o  Explicit routes.

   As described in the DetNet architecture [RFC8655] a sub-network
   provides from MPLS perspective a single hop connection between MPLS
   (DetNet) nodes.  Functions used for resource allocation and explicit
   routes are treated as domain internal functions and does do not require
   function interworking across the DetNet MPLS network and the TSN sub-

   In the case of the service protection function due to the
   similarities of the DetNet PREOF and TSN FRER functions some level of
   interworking is possible.  However, such interworking is out-of-scope
   in this document and left for further study.

   Figure 1 illustrates a scenario, where two MPLS (DetNet) nodes are
   interconnected by a TSN sub-network.  Node-1 is single homed and
   Node-2 is dual-homed to the TSN sub-network.

      MPLS (DetNet)                 MPLS (DetNet)
         Node-1                        Node-2

      +----------+                  +----------+
   <--| Service* |-- DetNet flow ---| Service* |-->
      +----------+                  +----------+
      |Forwarding|                  |Forwarding|
      +--------.-+    <-TSN Str->   +-.-----.--+
                \      ,-------.     /     /
                 +----[ TSN-Sub ]---+     /
                      [ Network ]--------+
   <---------------- DetNet MPLS --------------->

   Note: * no service sub-layer required for transit nodes

       Figure 1: DetNet Enabled MPLS 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 IEEE 802.1Q [IEEE8021Q] that provide zero congestion
   loss and bounded latency in bridged networks.  Furthermore IEEE 802.1CB
   [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 those
   require TSN treatment (i.e., applying TSN functions during

   TSN capabilities of the TSN sub-network are made available for MPLS
   (DetNet) flows via the protocol interworking function defined in
   Annex C.5 of IEEE 802.1CB [IEEE8021CB].  For example, applied on the TSN edge port
   it can convert an ingress unicast MPLS (DetNet) flow to use a
   specific Layer-2 multicast destination MAC address and a VLAN, in
   order to direct 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 Layer-2
   destination MAC address and VLAN.

   Placement of TSN functions depends on the TSN capabilities of the
   nodes along the path.  MPLS (DetNet) Nodes may or may not support TSN
   functions.  For a given TSN Stream (i.e., DetNet flow) an MPLS
   (DetNet) node is treated as a Talker or a Listener inside the TSN

4.1.  Functions for DetNet Flow to TSN Stream Mapping

   Mapping of a DetNet MPLS 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.  The passive stream identification
   function is used to catch the MPLS label(s) of a DetNet MPLS flow and
   the active stream identification function is used to modify the
   Ethernet header according to the ID of the mapped TSN Stream.

   Clause 6.8 of IEEE P802.1CBdb [IEEEP8021CBdb] defines a Mask-and-
   Match Mask-and-Match Stream
   identification function that can be used as a passive function for
   MPLS DetNet flows.

   Clause 6.6 of IEEE 802.1CB [IEEE8021CB] defines an Active Destination MAC and VLAN
   Stream identification function, what can replace some Ethernet header
   fields namely (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 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 MPLS DetNet nodes

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

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

   In cases of TSN-unaware MPLS DetNet nodes the TSN relay nodes within
   the TSN sub-network must modify the Ethernet encapsulation of the
   DetNet MPLS 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
   MPLS DetNet nodes in this document.

   MPLS (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 MPLS (DetNet) node must provide the TSN
   sub-network specific Ethernet encapsulation over the link(s) towards
   the sub-network.

                 MPLS (DetNet)

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

   Note: * no service sub-layer required for transit nodes

              Figure 2: MPLS (DetNet) Node with TSN Functions

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

   A Stream identification component must be able to instantiate the
   following functions (1) Active Destination MAC and VLAN Stream
   identification function, (2) Mask-and-Match Stream identification
   function and (3) the related managed objects in Clause 9 of IEEE
   [IEEE8021CB] and IEEE P802.1CBdb [IEEEP8021CBdb].

   A TSN-aware MPLS (DetNet) node implementation must support the
   Sequencing function and the Sequence encode/decode function as
   defined in Clause 7.4 and 7.6 of IEEE 802.1CB [IEEE8021CB] if in order for FRER is to be
   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 IEEE 802.1CB [IEEE8021CB].

   A TSN-aware MPLS (DetNet) node implementation must support the Stream
   splitting function and the Individual recovery function as defined in
   Clause 7.7 and 7.5 of IEEE 802.1CB [IEEE8021CB] when the in order for that node is to be a
   replication or elimination point for FRER.

4.3.  Service protection within the TSN sub-network

   TSN Streams supporting DetNet flows may use Frame Replication and
   Elimination for Redundancy (FRER) as defined in Clause 8. of IEEE
   [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 IEEE 802.1CB [IEEE8021CB].

   FRER function and the provided service recovery is 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 MPLS (DetNet) node
   represents a L3 border and as such it terminates all related
   information elements encoded in the L2 frames.

   As the Stream-ID and the TSN sequence number are paired with the
   similar MPLS flow parameters, FRER can be combined with PREOF
   functions.  Such service protection interworking scenarios may
   require to move sequence number fields among TSN (L2) and PW (MPLS)
   encapsulations and they are left for further study.

4.4.  Aggregation during DetNet flow to TSN Stream mapping


   Implementation 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 flow and TSN Stream mapping related information are required
   only for TSN-aware MPLS (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 MPLS over TSN:

   o  DetNet MPLS related configuration information according to the
      DetNet role of the DetNet MPLS node, as per [RFC8964].

   o  TSN related configuration information according to the TSN role of
      the DetNet MPLS node, as per [IEEE8021Q], [IEEE8021CB] and

   o  Mapping between DetNet MPLS flow(s) (label information: A-labels,
      S-labels and F-labels as defined in [RFC8964]) and TSN Stream(s)
      (as stream identification information defined in [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 the document.  Some of the challenges are highlighted

   TSN-aware MPLS DetNet nodes are member members of both the DetNet domain and
   the TSN sub-network.  Within the TSN sub-network the TSN-aware MPLS
   (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 MSRP (Multiple Stream
   Registration Protocol) behaves 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
   ones.  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 end2end end-2-end DetNet path (i.e., a single hop from MPLS 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 case cases it may be challenging to determine some TSN Stream
   related information.  For example, on a TSN-aware MPLS (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 MPLS Next-Hop).  However
   it may be not 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 MPLS (DetNet)
   node locally based on information provided for configuration of the
   TSN Stream identification functions (Mask-and-match Stream
   identification and 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 MPLS (DetNet) nodes make such a triggering even more
   complicated as they are fully unaware of the sub-network and run

   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.  Service protection interworking scenarios are
   left for further study.

6.  Security Considerations

   Security considerations for DetNet are described in detail in
   [I-D.ietf-detnet-security].  General security considerations are
   described in [RFC8655].  DetNet MPLS data plane specific
   considerations are summarized in [RFC8964].  This section considers
   exclusively security considerations which are specific to the DetNet
   MPLS 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 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 makes no IANA requests.

8.  Acknowledgements

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

9.  References

9.1.  Normative References

              IEEE 802.1, "Standard for Local and metropolitan area
              networks - Frame Replication and Elimination for
              Reliability (IEEE Std 802.1CB-2017)", 2017,

              Mangin, C., "Extended Stream identification functions",
              IEEE P802.1CBdb /D1.0 P802.1CBdb, September 2020,

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,

   [RFC8964]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., Bryant,
              S., and J. Korhonen, "Deterministic Networking (DetNet)
              Data Plane: MPLS", RFC 8964, DOI 10.17487/RFC8964, January
              2021, <>.

9.2.  Informative References

              Grossman, E., Mizrahi, T., and A. Hacker, "Deterministic
              Networking (DetNet) Security Considerations", draft-ietf-
              detnet-security-13 (work in progress), December 2020.

              IEEE Standards Association, "IEEE Std 802.1AE-2018 MAC
              Security (MACsec)", 2018,

              IEEE 802.1, "Standard for Local and metropolitan area
              networks--Bridges and Bridged Networks (IEEE Std 802.1Q-
              2018)", 2018, <>.

              Kehrer, S., "FRER YANG Data Model and Management
              Information Base Module", IEEE P802.1CBcv
              /D0.4 P802.1CBcv, August 2020,

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,

Authors' Addresses

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


   Janos Farkas
   Magyar Tudosok krt. 11.
   Budapest  1117


   Andrew G. Malis
   Malis Consulting


   Stewart Bryant
   Futurewei Technologies