Draft: draft-ietf-detnet-mpls-over-tsn

Commentary: Similar structure and changes as in IP over TSN . Service protection interworking is out - of - scope .
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This document specifies the Deterministic Networking MPLS data plane
when operating over a TSN network.
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This document specifies the Deterministic Networking MPLS data plane
when operating over a TSN sub-network.
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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.
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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.
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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.
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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.
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This document uses the terminology established in the DetNet
architecture I-D.ietf-detnet-architecture, and the reader is assumed
to be familiar with that document and its terminology.
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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).
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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.
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A DetNet Control Word (d-CW) is used for sequencing and
identifying duplicate packets of a DetNet flow at the DetNet
service sub-layer.
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Attachment Circuit.
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Customer Edge equipment.
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Class of Service.
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DetNet Inter-Working Function.
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Layer 2 Virtual Private Network.
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Multiprotocol Label Switching - Traffic Engineering.
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Multiprotocol Label Switching - Transport Profile.
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Multi-Segment PseudoWire (MS-PW).
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Native Service Processing.
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Operations, Administration, and Maintenance.
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Packet Elimination Function.
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Packet Replication Function.
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Packet Ordering Function.
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Quality of Service.
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This document uses the terminology established in the DetNet
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.
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Frame Replication and Elimination for Redundancy (TSN function).
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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.
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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.
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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.
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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.
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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).
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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.
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DetNet end system and 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 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.
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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
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.
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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).
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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.
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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].
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An example DetNet MPLS network fragment and packet flow is
illustrated in fig_mpls_example.
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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.
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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.
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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.
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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).
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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.
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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.
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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.
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Use of allocated resources (queuing, policing, shaping) to ensure
that the congestion-related loss and latency/jitter requirements
of a DetNet flow are met.
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Use of a specific path for a flow.  This limits misordering and
bounds latency.
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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.
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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.
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For example, to support identification of misbehaving flows.
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For example, increase counters.
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For example, unexpected loss.
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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.
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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.
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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.
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Note: in case of MPLS Transit node there is no DetNet Service sub-
layer processing.
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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.
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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.
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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
processing.
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Service protection.
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Resource allocation.
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Explicit routes.
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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.
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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.
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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.
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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.
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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.
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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.
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The Stream Identification and The Sequencing functions are slightly
modified for frames passed down the protocol stack from the upper
layers.
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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.
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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.
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TSN Streams supporting DetNet flows may use Frame Replication and
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.
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FRER function and the provided service recovery is available only
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.
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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.
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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.
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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.
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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.
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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.
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The security considerations of DetNet in general are discussed in I-
D.ietf-detnet-architecture and I-D.sdt-detnet-security.  Other
security considerations will be added in a future version of this
draft.
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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.
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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.
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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.
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IEEEP8021CBdb defines a Mask-and-Match Stream identification function
that can be used as a passive function for MPLS DetNet flows.
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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.
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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.
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This section covers required behavior of a TSN-aware MPLS (DetNet)
node using a TSN sub-network.
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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.
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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.
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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.
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A TSN-aware MPLS (DetNet) node impementations MUST support the Stream
Identification TSN component for recognizing flows.
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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.
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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.
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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.
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TSN Streams supporting DetNet flows may use Frame Replication and
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.
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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.
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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.
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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.
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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).
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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.
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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.
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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.
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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).
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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.
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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.
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The security considerations of DetNet in general are discussed in I-
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.