DetNet                                                     B. Varga, Ed.
Internet-Draft                                                 J. Farkas
Intended status: Standards Track                                Ericsson
Expires: September 7, December 10, 2020                                      A. Malis
                                                        Malis Consulting
                                                               S. Bryant
                                                  Futurewei Technologies
                                                           March 6,
                                                            June 8, 2020

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


   This document specifies the Deterministic Networking MPLS data plane
   when operating over a TSN sub-network.

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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
     2.3.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  DetNet MPLS Data Plane Overview . . . . . . . . . . . . . . .   4
   4.  DetNet MPLS Operation Over IEEE 802.1 TSN Sub-Networks  . . .   5
     4.1.  Functions for DetNet Flow to TSN Stream Mapping . . . . .   7
     4.2.  TSN requirements of MPLS DetNet nodes . . . . . . . . . .   7
     4.3.  Service protection within the TSN sub-network . . . . . .   9
     4.4.  Aggregation during DetNet flow to TSN Stream mapping  . .   9
   5.  Management and Control Implications . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12  13

1.  Introduction

   Deterministic Networking (DetNet) is a service that can be offered by
   a network to DetNet flows.  DetNet provides these flows with a low
   packet loss rates 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
   provides congestion protection (low loss, assured latency, and
   limited reordering) leveraging MPLS Traffic Engineering mechanisms.

   [I-D.ietf-detnet-mpls] 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.

2.  Terminology

2.1.  Terms Used in This Document

   This document uses the terminology established in the DetNet
   architecture [RFC8655] and [I-D.ietf-detnet-mpls], and the reader is
   assumed to be familiar with that document and its terminology.

2.2.  Abbreviations

   The following abbreviations are used in this document:

   CW            Control Word.

   DetNet        Deterministic Networking.

   DF            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.

   T-PE          Terminating Provider Edge.

   TSN           Time-Sensitive Network.

2.3.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  DetNet MPLS Data Plane Overview

   The basic approach defined in [I-D.ietf-detnet-mpls] 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 S-Label, for
   example a received 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 forwarding
   labels (F-Labels).

         Edge          Transit        Relay
         Node           Node           Node
        (T-PE)          (LSR)         (S-PE)
   <--|Svc Proxy|-- End to End Service ----------->
      +---------+                   +---------+
      |IP | |Svc|<-- DetNet flow ---| Service |--->
      +---+ +---+    +---------+    +---------+
      |Fwd| |Fwd|    |   Fwd   |    |Fwd| |Fwd|
      +-.-+ +-.-+    +--.----.-+    +-.-+ +-.-+
        :    /  ,-----.  \   :  Link  :     :
   .....+    +-[TSN Sub]-+   +........+     +.....
           |<----------- LSP ---------->| |<--- LSP -->|
           |<------------- DetNet MPLS ------------

    Figure 1: Part of a Simple DetNet MPLS Network using a TSN sub-net

   Figure 1 illustrates an extract of a DetNet enabled MPLS network.
   Edge/relay nodes sit at MPLS LSP boundaries and transit nodes are
   LSRs.  In this figure, two MPLS nodes (the edge node and the transit
   node) are interconnected by a TSN sub-network.

   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 enabled
   DetNet nodes can enhance the reliability of delivery by enabling the
   replication of packets where multiple copies, possibly over multiple
   paths, are forwarded through the DetNet domain.  They can also
   eliminate surplus previously replicated copies of DetNet packets.
   MPLS (DetNet) nodes also include DetNet forwarding sub-layer
   functions, support for notably explicit routes, and resources
   allocation to eliminate (or reduce) congestion loss and jitter.

   DetNet transit nodes reside wholly within a DetNet domain, and also
   provide DetNet forwarding sub-layer functions in accordance with the
   performance required by a DetNet flow carried over an LSP.  Unlike
   other DetNet node types, transit nodes provide no service sub-layer

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, what 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] and also
   illustrated here in Figure 1 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 not require function
   interworking across the DetNet MPLS network and the TSN sub-network.

   In 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 2 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 2: DetNet Enabled MPLS Network Over a TSN Sub-Network

   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.

   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 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 nodes.
   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 sub-network.

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 3.  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 3: MPLS (DetNet) Node with TSN Functions

   A TSN-aware MPLS (DetNet) node impementations 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
   802.1CB [IEEE8021CB] and IEEE P802.1CBdb [IEEEP8021CBdb].

   A TSN-aware MPLS (DetNet) node implementations 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 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 IEEE 802.1CB [IEEE8021CB].

   A TSN-aware MPLS (DetNet) node implementations 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
   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 Frame Replication and
   Elimination for Redundancy (FRER) as defined in Clause 8. of IEEE
   802.1CB [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

   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 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

   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 [I-D.ietf-detnet-mpls]) 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.

   TSN-aware MPLS DetNet nodes are member 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 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 DetNet path (i.e., 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 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

   The security

   Security considerations of for DetNet in general are discussed described in detail in
   [RFC8655] and
   [I-D.ietf-detnet-security].  General security considerations are
   described in [RFC8655].  DetNet IP MPLS data plane specific
   considerations are summarized in [I-D.ietf-detnet-ip].
   Encryption may [I-D.ietf-detnet-mpls].  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 an underlying sub-net using MACSec
   [IEEE802.1AE-2018] for 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 IP over nodes may
   result in bogus operations.  Therefore, it is important that the
   interface between DetNet nodes and TSN flows. 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

              Varga, B., Farkas, J., Berger, L., Fedyk, D., Malis, A., Bryant, S.,
              and J. Korhonen, "DetNet Data Plane: MPLS",
              draft-ietf-detnet-mpls-05 draft-ietf-
              detnet-mpls-06 (work in progress), February April 2020.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

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

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

9.2.  Informative References

              Varga, B., Farkas, J., Berger, L., Fedyk, D., Malis, A., and S.
              Bryant, "DetNet Data Plane: IP", draft-ietf-detnet-
              ip-05 draft-ietf-detnet-ip-06
              (work in progress), February April 2020.

              Mizrahi, T., Grossman, E., Hacker, A., Das, S., Dowdell,
              J., Austad, H., T. and N. Finn, E. Grossman, "Deterministic Networking
              (DetNet) Security Considerations", draft-ietf-detnet-
              security-10 (work in progress), February May 2020.

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

              Finn, N., "Draft Standard for Local and metropolitan area
              networks - Seamless Redundancy", IEEE P802.1CB
              /D2.1 P802.1CB, December 2015,

              IEEE 802.1, "Standard for Local and metropolitan area
              networks--Bridges and Bridged Networks (IEEE Std 802.1Q-
              2014)", 2014, <>.

              Kehrer, S., "FRER YANG Data Model and Management
              Information Base Module", IEEE P802.1CBcv
              /D0.3 P802.1CBcv, May 2020,

              Mangin, C., "Extended Stream identification functions",
              IEEE P802.1CBdb /D0.2 P802.1CBdb, August 2019,

   [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