Change:
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> <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> <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> <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 <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> <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 <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> <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> <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> <ins> Service protection. </ins> <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> <ins> Resource allocation. </ins> <del> 6. </del> <ins> Explicit routes. </ins> <del> [Editor's note: this is a place holder section.  A standalone section on MPLS over IEEE 802.1 TSN.  Includes RFC2119 Language.] </del> <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> <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> <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> <del> Note: in case of MPLS Transit node there is no DetNet Service sub- layer processing. </del> <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

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