Original text:
Abstract This document specifies the Deterministic Networking MPLS data plane <del> when operating over a TSN network. </del>  1. <del> [Editor's note: Introduction to be made specific to DetNet MPLS over TSN scenario.  May be similar to intro of DetNet IP over TSN.]. </del> 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. provides congestion protection (low loss, assured latency, and limited reordering) leveraging MPLS Traffic Engineering mechanisms. <del> This document specifies the DetNet data plane operation and the on- wire encapsulation of DetNet flows over an MPLS-based Packet Switched Network (PSN).  The specified encapsulation provides the building blocks to enable the DetNet service and forwarding sub-layer functions and supports flow identification as described in the DetNet Architecture.  As part of the service sub-layer functions, this document describes DetNet node data plane operation.  It also describes the function and operation of the Packet Replication (PRF) Packet Elimination (PEF) and Packet Ordering (POF) functions with an MPLS data plane.  It also describes an MPLS-based DetNet forwarding sub-layer that eliminates (or reduces) contention loss and provides bounded latency for DetNet flows. MPLS encapsulated DetNet flows can be carried over network technologies that can provide the DetNet required level of service. This document defines examples of such, specifically carrying DetNet MPLS flows over IEEE 802.1 TSN sub-networks, and over DetNet IP PSN. The intent is for this document to support different traffic types being mapped over DetNet MPLS, but this is out side the scope of this document.  An example of such can be found in I-D.ietf-detnet-dp-sol- ip.  This document also allows for, but does not define, associated controller plane and Operations, Administration, and Maintenance (OAM) functions. </del>  2. 2.1. This document uses the terminology established in the DetNet <del> architecture I-D.ietf-detnet-architecture, and the reader is assumed to be familiar with that document and its terminology. The following terminology is introduced in this document: A Detnet "forwarding" label that identifies the LSP used to forward a DetNet flow across an MPLS PSN, e.g., a hop-by-hop label used between label switching routers (LSR). A DetNet "service" label that is used between DetNet nodes that implement also the DetNet service sub-layer functions.  An S-Label is also used to identify a DetNet flow at DetNet service sub- layer. A DetNet Control Word (d-CW) is used for sequencing and identifying duplicate packets of a DetNet flow at the DetNet service sub-layer. </del>  2.2. The following abbreviations are used in this document: <del> Attachment Circuit. Customer Edge equipment. Class of Service. </del> Control Word. Deterministic Networking. DetNet Flow. <del> DetNet Inter-Working Function. </del>  Layer 2. <del> Layer 2 Virtual Private Network. </del> Layer 3. Label Switching Router. Multiprotocol Label Switching. <del> Multiprotocol Label Switching - Traffic Engineering. Multiprotocol Label Switching - Transport Profile. Multi-Segment PseudoWire (MS-PW). Native Service Processing. Operations, Administration, and Maintenance. </del> Provider Edge. <del> Packet Elimination Function. Packet Replication Function. </del> Packet Replication, Elimination and Ordering Functions. <del> Packet Ordering Function. </del> Packet Switched Network. PseudoWire. <del> Quality of Service. </del> Switching Provider Edge. Terminating Provider Edge. Time-Sensitive Network. <del> 3. </del>  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 14 RFC2119 RFC8174 when, and only when, they appear in all capitals, as shown here. <del> 4. [Editor's note: simplify this section and highlight DetNet MPLS over subnets scenario being the focus in the remaining part of the document.]. 4.1. </del>  <del> This document describes how DetNet flows are carried over MPLS networks.  The DetNet Architecture, I-D.ietf-detnet-architecture, decomposes the DetNet data plane into two sub-layers: a service sub- layer and a forwarding sub-layer.  The basic approach defined in this document 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.  Background on PWs can be found in RFC3985 and RFC3031.  Background on MPLS Traffic Engineering can be found in RFC3272 and RFC3209. The DetNet MPLS data plane approach defined in this document is shown in dn_mpls_dp_approach.  The service sub-layer is supported by a DetNet control word (d-CW) which conforms to the Generic PW MPLS Control Word (PWMCW) defined in RFC4385.  A d-CW identifying service label (S-Label) is also used. </del>  A node operating on a DetNet flow in the Detnet service sub-layer, <del> i.e. a node processing a DetNet packet which has the S-Label as top </del>  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 <del> interface or LSP the packet arrives on. </del>  The DetNet MPLS data plane builds on MPLS Traffic Engineering encapsulations and mechanisms to provide a forwarding sub-layer that The forwarding sub-layer is supported by one or more forwarding labels (F-Labels). <del> 4.2. [Editor's note: simplify this section and highlight DetNet MPLS over subnets scenario being the focus in the remaining part of the document.]. </del>  <del> fig_dn_mpls_detnet illustrates a hypothetical DetNet MPLS-only network composed of DetNet aware MPLS enabled end systems, operating over a DetNet aware MPLS network.  In this figure, relay nodes sit at MPLS LSP boundaries and transit nodes are LSRs. DetNet end system and relay nodes are DetNet service sub-layer aware, </del>  understand the particular needs of DetNet flows and provide both DetNet service and forwarding sub-layer functions.  They add, remove <del> and process d-CWs, S-Labels and F-labels as needed.  MPLS enabled end system and relay 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.  DetNet MPLS nodes provide functionality similar to T-PEs when they sit at the edge of an MPLS domain, and functionality similar to S-PEs when they are in the middle of an MPLS domain, see RFC6073.  End system and relay nodes also include DetNet forwarding sub-layer functions, support for notably explicit routes, and resources allocation to eliminate (or reduce) congestion loss and jitter. </del>  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 <del> processing.  In a DetNet MPLS network, transit nodes may be DetNet service aware or may be DetNet unaware MPLS Label Switching Routers (LSRs).  In this latter case, such LSRs would be unaware of the special requirements of the DetNet service sub-layer, but would still provide traffic engineering services and the QoS need to ensure that the (TE) LSPs meet the service requirements of the carried DetNet flows. The LSPs may be provided by any MPLS controller method.  For example they may be provisioned via a management plane, RSVP-TE, MPLS-TP, or MPLS Segment Routing (when extended to support resource allocation). [Editor's note: Figure 3. and surrunding text are candidates to delete from this document.]. fig_pw_detnet illustrates how an end to end MPLS-based DetNet service is provided in a more detail.  In this figure, the end systems, CE1 and CE2, are able to send and receive MPLS encapsulated DetNet flows, and R1, R2 and R3 are relay nodes as they sit in the middle of a DetNet network.  The 'X' in the end systems, and relay nodes represents potential DetNet compound flow packet replication and elimination points.  In this example, service protection is supported over four DetNet member flows and TE LSPs.  For a unidirectional flow, R1 supports PRF, R2 supports PREOF and R3 supports PEF and POF. Note that the relay nodes may change the underlying forwarding sub- layer, for example tunneling MPLS over IEEE 802.1 TSN mpls-over-tsn, or simply over interconnect network links. As previously mentioned, this document specifies how MPLS is used to support DetNet flows using an MPLS data plane as well as how such can be mapped to IEEE 802.1 TSN and IP DetNet PSNs.  An equally import scenario is when IP is supported over DetNet MPLS and this is covered in I-D.ietf-detnet-dp-sol-ip.  Another important scenario is where an Ethernet Layer 2 service is supported over DetNet MPLS and this is covered in [TBD-TSN-OVER-DETNET]. 4.3. [Editor's note: this text might be relevant for the discussion of FRER within the TSN sub-network.  Needs revision.]. An example DetNet MPLS network fragment and packet flow is illustrated in fig_mpls_example. In fig_mpls_example 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 that its passage through the network fragment can be identified to the reader. Customer Equipment CE1 sends a packet into the DetNet enabled MPLS 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 MPLS path from EN1 to R1 there may be zero or more LSRs which, for clarity, are not shown.  The same is true for any other path between two DetNet entities shown in fig_mpls_example. 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.  Between a pair of relay nodes there may be one or more transit nodes that simply forward the DetNet traffic, but these are omitted for clarity. 5. [Editor's note: Sort out what data plane considerations are relevant for sub-net scenarios.]. 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: Use of allocated resources (queuing, policing, shaping) to ensure that the congestion-related loss and latency/jitter requirements of a DetNet flow are met. </del>  <del> Use of a specific path for a flow.  This limits misordering and bounds latency. Which in the case of this document primarily relates to replication and elimination.  Changing the explicit path after a failure is detected in order to restore delivery of the required DetNet service characteristics is also possible.  Path changes, even in the case of failure recovery, can lead to the out of order delivery of data. Generally, distributing packets of the same DetNet flow over multiple paths is not recommended.  Such load sharing, e.g., via ECMP or UCMP, impacts ordering and possibly jitter. For example, to support identification of misbehaving flows. For example, increase counters. For example, unexpected loss. The DetNet data plane also allows for the aggregation of DetNet flows, e.g., via MPLS hierarchical LSPs, to improved scaling.  When DetNet flows are aggregated, transit nodes provide service to the aggregate and not on a per-DetNet flow basis.  In this case, nodes performing aggregation will ensure that per-flow service requirements are achieved. 5.1. </del>  <del> As shown in fig_dn_mpls_detnet, MPLS nodes are interconnected by different sub-network technologies, which may include point-to-point links.  Each of these 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 will need to map DetNet flows to the flow semantics (i.e., identifiers) and mechanisms used by an underlying sub-network technology.  fig_dn_mpls_sn_ex 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 mpls-over-tsn.  UDP/IP represents the encapsulation used on a DetNet IP PSN. </del>  <del> 6. </del>  <del> [Editor's note: this is a place holder section.  A standalone section on MPLS over IEEE 802.1 TSN.  Includes RFC2119 Language.] </del>  <del> This section covers how DetNet MPLS flows operate over an IEEE 802.1 TSN sub-network.  fig_mpls_detnet_to_tsn illustrates such 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.  MPLS nodes can be (1) DetNet MPLS End System, (2) DetNet MPLS Edge or Relay node or (3) MPLS Transit node. </del>  <del> Note: in case of MPLS Transit node there is no DetNet Service sub- layer processing. </del>  The Time-Sensitive Networking (TSN) Task Group of the IEEE 802.1 Working Group have defined (and are defining) a number of amendments compatible with and useful to, DetNet networks.  All these functions have to identify flows those require TSN treatment. <del> As is the case for DetNet, a Layer 2 network node such as a bridge may need to identify the specific DetNet flow to which a packet belongs in order to provide the TSN/DetNet QoS for that packet.  It also may need a CoS marking, such as the priority field of an IEEE Std 802.1Q VLAN tag, to give the packet proper service. </del>  <del> The challange for MPLS DeNet flows is that the protocol interworking function defined in IEEE8021CB works only for IP flows.  The aim of the protocol interworking function is to convert an ingress flow to use a specific multicast destination MAC address and VLAN, for example to direct the packets through a specific path inside the bridged network.  A similar interworking pair at the other end of the TSN sub-network would restore the packet to its original destination MAC address and VLAN. As protocol interworking function defined in IEEE8021CB does not work for MPLS labeled flows, the DetNet MPLS nodes MUST ensure proper TSN sub-network specific Ethernet encapsulation of the DetNet MPLS packets.  For a given TSN Stream (i.e., DetNet flow) an MPLS (DetNet) node MUST behave as a TSN-aware Talker or a Listener inside the TSN sub-network. 6.1. TSN capable MPLS (DetNet) nodes are TSN-aware Talker/Listener as shown in fig_mpls_with_tsn.  MPLS (DetNet) node MUST provide the TSN sub-network specific Ethernet encapsulation over the link(s) towards the sub-network.  An TSN-aware MPLS (DetNet) node MUST support the following TSN components: </del>  <del> For recognizing flows: </del>  <del> Stream Identification (MPLS-flow-aware) </del>  <del> For FRER used inside the TSN domain, additonaly: </del>  <del> Sequencing function (MPLS-flow-aware) </del>  <del> Sequence encode/decode function </del>  <del> For FRER when the node is a TSN replication or elimination point, additionally: </del>  <del> Stream splitting function </del>  <del> Individual recovery function </del>  <del> [Editor's note: Should we added here requirements regarding IEEE 802.1Q C-VLAN component?] </del>  <del> The Stream Identification and The Sequencing functions are slightly modified for frames passed down the protocol stack from the upper layers. </del>  <del> Stream Identification MUST pair MPLS flows and TSN Streams and encode that in data plane formats as well.  The packet's stream_handle subparameter (see IEEE8021CB) inside the Talker/Listener is defined based on the Flow-ID used in the upper DetNet MPLS layer.  Stream Identification function MUST encode Ethernet header fields namely (1) the destination MAC-address, (2) the VLAN-ID and (3) priority parameters with TSN sub-network specific values.  Encoding is provided for the frame passed down the stack from the upper layers. </del>  <del> The sequence generation function resides in the Sequencing function. It generates a sequence_number subparameter for each packet of a Stream passed down to the lower layers.  Sequencing function MUST copy sequence information from the MPLS d-CW of the packet to the sequence_number subparameter for the frame passed down the stack from the upper layers. </del>  The Sequence encode/decode function MUST support the Redundancy tag (R-TAG) format as per Clause 7.8 of IEEE8021CB. <del> 6.2. </del>  TSN Streams supporting DetNet flows may use Frame Replication and <del> Elimination for Redundancy (FRER) [802.1CB] 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. </del>  FRER function and the provided service recovery is available only <del> within the TSN sub-network however as the Stream-ID and the TSN sequence number are paired with the MPLS flow parameters they can be combined with PREOF functions. 6.3. [Editor's note: This section is TBD - covers required behavior of a TSN-aware DetNet node using a TSN underlay.] </del>  <del> 6.4. [Editor's NOTE: review and simplify this section.  May overlap with previous sections.] 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.  IEEE8021CB defines packet replication and elimination functions that should prove both compatible with and useful to, DetNet networks. As is the case for DetNet, a Layer 2 network node such as a bridge may need to identify the specific DetNet flow to which a packet belongs in order to provide the TSN/DetNet QoS for that packet.  It also will likely need a CoS marking, such as the priority field of an IEEE Std 802.1Q VLAN tag, to give the packet proper service. Although the flow identification methods described in IEEE8021CB are flexible, and in fact, include IP 5-tuple identification methods, the baseline TSN standards assume that every Ethernet frame belonging to a TSN stream (i.e.  DetNet flow) carries a multicast destination MAC address that is unique to that flow within the bridged network over which it is carried.  Furthermore, IEEE8021CB describes three methods by which a packet sequence number can be encoded in an Ethernet frame. Ensuring that the proper Ethernet VLAN tag priority and destination MAC address are used on a DetNet/TSN packet may require further clarification of the customary L2/L3 transformations carried out by routers and edge label switches.  Edge nodes may also have to move sequence number fields among Layer 2, PW, and IP encapsulations. </del>  <del> 7. </del>  <del> [Editor's note: This section is TBD Covers Creation, mapping, removal of TSN Stream IDs, related parameters and,when needed, configuration of FRER.  Supported by management/control plane.  SEE sections in removed text file.] 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 below. 8. </del>  The security considerations of DetNet in general are discussed in I- <del> D.ietf-detnet-architecture and I-D.sdt-detnet-security.  Other security considerations will be added in a future version of this draft. </del>  <del> 9. </del>  This document makes no IANA requests.

Reviewer comments:
Similar structure and changes as in IP over TSN. Service protection interworking is out-of-scope.

Revised text:
Abstract This document specifies the Deterministic Networking MPLS data plane  <ins> when operating over a TSN sub-network. </ins> 1.  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. provides congestion protection (low loss, assured latency, and limited reordering) leveraging MPLS Traffic Engineering mechanisms.  <ins> 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. </ins> 2. 2.1. This document uses the terminology established in the DetNet  <ins> architecture I-D.ietf-detnet-architecture and I-D.ietf-detnet-mpls, and the reader is assumed to be familiar with that document and its terminology. </ins> 2.2. The following abbreviations are used in this document:  Control Word. Deterministic Networking. DetNet Flow.  <ins> Frame Replication and Elimination for Redundancy (TSN function). </ins> Layer 2.  Layer 3. Label Switching Router. Multiprotocol Label Switching.  Provider Edge.  Packet Replication, Elimination and Ordering Functions.  Packet Switched Network. PseudoWire.  Switching Provider Edge. Terminating Provider Edge. Time-Sensitive Network.  <ins> 2.3. </ins> The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 14 RFC2119 RFC8174 when, and only when, they appear in all capitals, as shown here.  <ins> 3. </ins>  <ins> 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. </ins> A node operating on a DetNet flow in the Detnet service sub-layer,  <ins> i.e.  a node processing a DetNet packet which has the S-Label as top </ins> 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  <ins> interface or LSP the packet arrives on.  The service sub-layer functions (i.e., PREOF) use a DetNet control word (d-CW). </ins> The DetNet MPLS data plane builds on MPLS Traffic Engineering encapsulations and mechanisms to provide a forwarding sub-layer that The forwarding sub-layer is supported by one or more forwarding labels (F-Labels).  <ins> fig_mpls_detnet_part 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. </ins>  <ins> DetNet edge/relay nodes are DetNet service sub-layer aware, </ins> understand the particular needs of DetNet flows and provide both DetNet service and forwarding sub-layer functions.  They add, remove  <ins> 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. </ins> 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  <ins> processing. 4. 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: </ins>  <ins> Service protection. </ins>  <ins> Resource allocation. </ins>  <ins> Explicit routes. </ins>  <ins> As described in the DetNet architecture I-D.ietf-detnet-architecture and also illustrated here in fig_mpls_detnet_part 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. </ins>  <ins> 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. </ins>  <ins> fig_mpls_detnet_to_tsn 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. </ins> The Time-Sensitive Networking (TSN) Task Group of the IEEE 802.1 Working Group have defined (and are defining) a number of amendments compatible with and useful to, DetNet networks.  All these functions have to identify flows those require TSN treatment.  <ins> TSN capabilities of the TSN sub-network are made available for MPLS (DetNet) flows via the protocol interworking function defined in 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 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. </ins>  <ins> 4.1. </ins>  <ins> 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. </ins>  <ins> IEEEP8021CBdb defines a Mask-and-Match Stream identification function that can be used as a passive function for MPLS DetNet flows. </ins>  <ins> 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. </ins>  <ins> 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. </ins>  <ins> 4.2. </ins>  <ins> This section covers required behavior of a TSN-aware MPLS (DetNet) node using a TSN sub-network. </ins>  <ins> 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. </ins>  <ins> 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. </ins>  <ins> 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 fig_mpls_with_tsn.  In such cases the MPLS (DetNet) node must provide the TSN sub-network specific Ethernet encapsulation over the link(s) towards the sub-network. </ins>  <ins> A TSN-aware MPLS (DetNet) node impementations MUST support the Stream Identification TSN component for recognizing flows. </ins>  <ins> 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 IEEE8021CB and IEEEP8021CBdb. </ins>  <ins> A TSN-aware MPLS (DetNet) node implementations MUST support the Sequencing function and the Sequence encode/decode function as defined in IEEE8021CB if FRER is used inside the TSN sub-network. </ins> The Sequence encode/decode function MUST support the Redundancy tag (R-TAG) format as per Clause 7.8 of IEEE8021CB.  <ins> A TSN-aware MPLS (DetNet) node implementations MUST support the Stream splitting function and the Individual recovery function as defined in IEEE8021CB when the node is a replication or elimination point for FRER. 4.3. </ins> TSN Streams supporting DetNet flows may use Frame Replication and  <ins> Elimination for Redundancy (FRER) as defined in 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. </ins> FRER function and the provided service recovery is available only  <ins> 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. 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. </ins>  <ins> 5. </ins>  <ins> [Editor's note: This section covers management/control plane related implications of creation, mapping, removal of TSN Stream IDs, their related parameters and, when needed, the configuration of FRER.] 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). 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 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.  Service protection interworking scenarios are left for further study. </ins>  <ins> 6. </ins> The security considerations of DetNet in general are discussed in I-  <ins> D.ietf-detnet-architecture and I-D.ietf-detnet-security.  DetNet IP data plane specific considerations are summarized in I-D.ietf-detnet- ip.  Encryption may provided by an underlying sub-net using MACSec IEEE802.1AE-2018 for DetNet IP over TSN flows. </ins>  <ins> 7. </ins> This document makes no IANA requests.