This section covers how DetNet IP flows operate over an IEEE 802.1 TSN sub-network. Figure 1
illustrates such a scenario where two IP (DetNet) nodes are interconnected by a TSN sub-network. Dotted lines around the Service components of the IP (DetNet) nodes indicate that they are DetNet service aware but do not perform any DetNet service sub-layer function. Node-1 is single homed and Node-2 is dual homed to the TSN sub-network, and they are treated as Talker or Listener inside the TSN sub-network. Note that from the TSN perspective, dual-homed characteristics of Talker or Listener nodes are transparent to the IP Layer.
IP (DetNet) IP (DetNet)
<--: Service :-- DetNet flow ---: Service :-->
+--------.-+ <-TSN Str-> +-.-----.--+
\ ,-------. / /
+----[ TSN Sub-]---+ /
[ Network ]--------+
<----------------- DetNet IP ----------------->
At the time of this writing, the Time-Sensitive Networking (TSN) Task Group of the IEEE 802.1 Working Group have defined (and are defining) a number of amendments to [IEEE8021Q
] that provide zero congestion loss and bounded latency in bridged networks. Furthermore, [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 that require TSN treatment.
TSN capabilities of the TSN sub-network are made available for IP (DetNet) flows via the protocol interworking function described in Annex C.5 of [IEEE8021CB
]. For example, applied on the TSN edge port it can convert an ingress unicast IP (DetNet) flow to use a specific L2 multicast destination Media Access Control (MAC) address and a VLAN in order to forward 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 L2 destination MAC address and VLAN.
Placement of TSN functions depends on the TSN capabilities of nodes. IP (DetNet) nodes may or may not support TSN functions. For a given TSN Stream (i.e., a mapped DetNet flow), an IP (DetNet) node is treated as a Talker or a Listener inside the TSN sub-network.
Mapping of a DetNet IP 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 (Layer 2). The passive Stream identification function is used to catch the 6-tuple of a DetNet IP flow, and the active Stream identification function is used to modify the Ethernet header according to the ID of the mapped TSN Stream.
Clause 6.7 of [IEEE8021CB
] defines an IP Stream identification function that can be used as a passive function for IP DetNet flows using UDP or TCP. Clause 6.8 of [IEEEP8021CBdb
] defines a Mask-and-Match Stream identification function that can be used as a passive function for any IP DetNet flows.
Clause 6.6 of [IEEE8021CB
] defines an Active Destination MAC and VLAN Stream identification function that can replace some Ethernet header fields: (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 within 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.
This section covers the required behavior of a TSN-aware DetNet node using a TSN sub-network. The implementation of TSN packet-processing functions must be compliant with the relevant IEEE 802.1 standards.
From the TSN sub-network perspective, DetNet IP nodes are treated as a Talker or Listener that may be (1) TSN unaware or (2) TSN aware.
In cases of TSN-unaware IP DetNet nodes, the TSN relay nodes within the TSN sub-network must modify the Ethernet encapsulation of the DetNet IP 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 IP DetNet nodes in this document.
IP (DetNet) nodes being TSN aware can be treated as a combination of a TSN-unaware Talker/Listener and a TSN relay, as shown in Figure 2
. In such cases, the IP (DetNet) node must provide the TSN sub-network-specific Ethernet encapsulation over the link(s) towards the sub-network.
<--: Service :-- DetNet flow ------------------
| L2 | | L2 Relay with |<--- TSN ---
| | | TSN function | Stream
\__________/ \ \______
Talker / TSN Bridge
<----- TSN Sub-network -----
<------- TSN-aware Tlk/Lstn ------->
A TSN-aware IP (DetNet) node implementation must support the Stream identification TSN component for recognizing flows.
A Stream identification component must be able to instantiate the following: (1) Active Destination MAC and VLAN Stream identification, (2) IP Stream identification, (3) Mask-and-Match Stream identification, and (4) the related managed objects in Clause 9 of [IEEE8021CB
] and [IEEEP8021CBdb
A TSN-aware IP (DetNet) node implementation must support the Sequencing function and the Sequence encode/decode function as defined in Clauses 7.4 and 7.6 of [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 [IEEE8021CB
A TSN-aware IP (DetNet) node implementation must support the Stream splitting function and the Individual recovery function as defined in Clauses 7.7 and 7.5 of [IEEE8021CB
] when the node is a replication or elimination point for FRER.
TSN Streams supporting DetNet flows may use FRER as defined in Clause 8 of [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
The FRER function and the provided service recovery are 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 IP (DetNet) node represents an L3 border and as such, it terminates all related information elements encoded in the L2 frames.
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.