DetNet Data Plane: IP over IEEE 802.1 Time Sensitive Networking (TSN)EricssonMagyar Tudosok krt. 11.BudapestHungary1117balazs.a.varga@ericsson.comEricssonMagyar Tudosok krt. 11.BudapestHungary1117janos.farkas@ericsson.comIndependentagmalis@gmail.comFuturewei Technologiesstewart.bryant@gmail.comDetNet
This document specifies the Deterministic Networking IP data plane
when operating over a TSN sub-network.
Deterministic Networking (DetNet) is a service that can be offered by a network to DetNet flows.
DetNet provides these flows extremely low packet loss rates and assured maximum end-to-end
delivery latency. General background and concepts of DetNet can
be found in the DetNet Architecture .
specifies the DetNet data plane operation for IP
hosts and routers that provide DetNet service to IP encapsulated
data. This document focuses on the scenario where DetNet IP nodes
are interconnected by a TSN sub-network.
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). As described in
no DetNet specific headers are added to
support DetNet IP flows, only the forwarding sub-layer functions are
supported inside the DetNet domain. Service
protection can be provided on a per sub-network
basis as shown here for the IEEE802.1 TSN sub-network scenario.
This document uses the terminology and concepts established in
the DetNet architecture , and the reader is assumed
to be familiar with that document and its terminology.
The following abbreviations used in this document:
Deterministic Networking.DetNet Flow.Frame Replication and Elimination for Redundancy
(TSN function).Layer-2.Layer-3.Packet Replication, Ordering and Elimination Function.Time-Sensitive Networking, TSN is a Task Group of the IEEE
802.1 Working Group.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as
described in BCP 14 when, and only when, they appear in all
capitals, as shown here.
describes how IP is used by DetNet
nodes, i.e., hosts and routers, to identify DetNet flows and provide a
DetNet service. From a data plane perspective, an end-to-end IP model
is followed. DetNet uses "6-tuple" based flow identification, where
"6-tuple" refers to information carried in IP and higher layer protocol
headers.
DetNet flow aggregation may be enabled via the use of
wildcards, masks, prefixes and ranges. IP tunnels may also be
used to support flow aggregation. In these cases, it is
expected that DetNet aware intermediate nodes will provide
DetNet service assurance on the aggregate through resource
allocation and congestion control mechanisms.
Congestion protection, latency control and the resource allocation
(queuing, policing, shaping) are supported using the underlying link
/ sub-net specific mechanisms. Service protections (packet
replication and packet elimination functions) are not provided at
the DetNet layer end to end due the lack of a unified end to end
sequencing information that would be available for intermediate nodes.
However, such service protection can be provided on a per underlying
L2 link and sub-network basis.
illustrates an extract of a DetNet
enabled IP network, that uses a TSN sub-network as interconnection between
two DetNet Nodes. In this figure, an Edge Node sits at the boundary of
the DetNet domain and provide DetNet service proxies for the end
applications by initiating and terminating DetNet service for the
application's IP flows. Node and interface resources are allocated to
ensure DetNet service requirements.
Dotted lines around the Service components of the Edge and Relay Nodes
indicate that they are DetNet service aware but do not perform any
DetNet service sub-layer function, e.g., PREOF (Packet Replication,
Elimination, and Ordering Functions). In this example the
Edge Node and the Transit Node are interconnected by a TSN sub-network,
being the primary focus of this document.
DetNet routers ensure that detnet service requirements are met per hop
by allocating local resources, both receive and transmit, and by mapping
the service requirements of each flow to appropriate sub-network
mechanisms. Such mappings are sub-network technology specific.
The mapping of DetNet IP flows to TSN streams and TSN protection
mechanisms are covered in .
This section covers how DetNet IP flows operate over an IEEE 802.1 TSN
sub-network. illustrates such a
scenario, where two IP (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.
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 that
provide zero congestion loss and bounded latency in bridged
networks. Furthermore IEEE
802.1CB 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 defined in
IEEE 802.1CB. For example,
applied on the TSN edge port it can convert an ingress unicast
IP (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. IP (DetNet) Nodes may or may not support TSN functions. For
a given TSN Stream (i.e., 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. 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 ID of the mapped TSN
Stream.
IEEE 802.1CB defines an IP Stream
identification function that can be used as a passive function
for IP DetNet flows using UDP or TCP.
IEEE P802.1CBdb defines a
Mask-and-Match Stream identification function that can be used
as a passive function for any IP DetNet flows.
IEEE 802.1CB 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.
This section covers required behavior of a TSN-aware DetNet node
using a TSN sub-network.
From the TSN sub-network perspective DetNet IP nodes are treated
as 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 . In such cases the IP
(DetNet) node must provide the TSN sub-network specific Ethernet
encapsulation over the link(s) towards the sub-network.
A TSN-aware IP (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) IP Stream identification
function, (3) Mask-and-Match Stream identification function and
(4) the related managed objects in Clause 9 of
IEEE 802.1CB and
IEEE P802.1CBdb.
A TSN-aware IP (DetNet) node implementations MUST support the
Sequencing function and the Sequence encode/decode function as
defined in IEEE 802.1CB 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.
A TSN-aware IP (DetNet) node implementations MUST support the
Stream splitting
function and the Individual recovery function as defined in
IEEE 802.1CB when the node is
a replication or elimination point for FRER.
TSN Streams supporting DetNet flows may use Frame Replication
and Elimination for Redundancy (FRER) as defined in
IEEE 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 IEEE
802.1CB.
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 IP
(DetNet) node represents a 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.
DetNet flow and TSN Stream mapping related information are
required only for TSN-aware IP (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 IP DetNet nodes are member of both the DetNet
domain and the TSN sub-network. Within the TSN
sub-network the TSN-aware IP (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 IP 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 IP
(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 IP 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 IP (DetNet) node locally based on information
provided for configuration of the TSN Stream
identification functions (IP Stream identification,
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 IP (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.
The security considerations of DetNet in general are discussed in
and . DetNet IP data plane
specific considerations are summarized in
. Encryption may provided by an
underlying sub-net using MACSec
for DetNet IP over TSN flows.
None.
The authors wish to thank Norman Finn, Lou Berger, Craig Gunther,
Christophe Mangin and Jouni Korhonen for their various contributions
to this work.
IEEE Std 802.1AE-2018 MAC Security (MACsec)IEEE Standards AssociationStandard for Local and metropolitan area networks--Bridges
and Bridged Networks (IEEE Std 802.1Q-2014)IEEE 802.1Draft Standard for Local and metropolitan area networks -
Seamless RedundancyIEEE 802.1Extended Stream identification functionsIEEE 802.1