Deterministic Networking (DetNet) Data Plane: MPLS over IEEE 802.1 Time-Sensitive Networking (TSN)EricssonMagyar Tudosok krt. 11.BudapestHungary1117balazs.a.varga@ericsson.comEricssonMagyar Tudosok krt. 11.BudapestHungary1117janos.farkas@ericsson.comMalis Consultingagmalis@gmail.comFuturewei Technologiessb@stewartbryant.comDetNet
This document specifies the Deterministic Networking (DetNet) MPLS data plane
when operating over an IEEE 802.1 Time-Sensitive Networking (TSN)
sub-network. This document does not define
new procedures or processes. Whenever this document makes
statements or recommendations, they are taken from normative text in the
referenced RFCs.
Introduction
Deterministic Networking (DetNet) is a service that can be offered by a
network to DetNet flows. DetNet provides these flows with low packet loss
rate and assured maximum end-to-end delivery latency. General background
and concepts of DetNet can be found in .
The DetNet architecture decomposes 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 provide congestion
protection (low loss, assured latency, and limited reordering)
leveraging MPLS Traffic Engineering mechanisms.
specifies the DetNet data plane
operation for an MPLS-based 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 an IEEE 802.1 TSN sub-network.
There is close cooperation between the IETF DetNet Working Group and the IEEE 802.1 Time-Sensitive Networking Task Group (TSN TG).
TerminologyTerms Used in This Document
This document uses the terminology established in the DetNet architecture
. TSN-specific terms are defined in the TSN TG
of the IEEE 802.1 Working Group. The reader is assumed
to be familiar with these documents and their terminology.
Abbreviations
The following abbreviations are used in this document:
A-Label
Aggregation label; a special case of an S-Label.
d-CW
DetNet Control Word
DetNet
Deterministic Networking
F-Label
Forwarding label that identifies the LSP used by a
DetNet flow.
FRER
Frame Replication and Elimination for Redundancy
(TSN function)
L2
Layer 2
L3
Layer 3
LSP
Label Switched Path
MPLS
Multiprotocol Label Switching
PREOF
Packet Replication, Elimination, and Ordering Functions
DetNet MPLS Data Plane Overview
The basic approach defined in
supports the DetNet service sub-layer based on existing PW
encapsulations and mechanisms and supports the DetNet forwarding
sub-layer based on existing MPLS Traffic Engineering encapsulations
and mechanisms.
A node operates on a DetNet flow in the DetNet service sub-layer, i.e.,
a node processing a DetNet packet that has the service label (S-Label) as the top of stack uses
the local context associated with that S-Label, for example, a received
forwarding label (F-Label), to determine what local DetNet operation(s) is applied to that
packet. An S-Label may be unique when taken from the platform
label space , 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 d-CW.
The DetNet MPLS data plane builds on MPLS Traffic Engineering
encapsulations and mechanisms to provide a forwarding sub-layer that
is responsible for providing resource allocation and explicit
routes. The forwarding sub-layer is supported by one or more
F-Labels.
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 DetNet nodes and transit nodes include
DetNet forwarding sub-layer functions, notable support for
explicit routes, and resource allocation to eliminate (or
reduce) congestion loss and jitter. Unlike other DetNet node types,
transit nodes provide no service sub-layer processing.
MPLS (DetNet) nodes and transit nodes interconnected by a TSN
sub-network are the primary focus of this document.
The mapping of DetNet MPLS flows to TSN Streams and TSN protection
mechanisms are covered in .
DetNet MPLS Operation over IEEE 802.1 TSN Sub-networks
The DetNet WG collaborates with IEEE 802.1 TSN in order to define a
common architecture for both Layer 2 and Layer 3 that maintains
consistency across diverse networks. Both DetNet MPLS and TSN use
the same techniques to provide their deterministic service:
Service protection
Resource allocation
Explicit routes
As described in the DetNet architecture
, from the MPLS perspective, a sub-network provides
a single-hop connection between MPLS (DetNet) nodes.
Functions used for resource allocation and explicit routes
are treated as domain internal functions and do not require function
interworking across the DetNet MPLS network and the TSN sub-network.
In the 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 of this document
and left for further study.
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.
At the time of this writing,
the TSN TG of the IEEE 802.1
Working Group have defined (and are defining) a number of amendments
to that provide zero
congestion loss and bounded latency in bridged networks. Furthermore,
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 (i.e., applying TSN
functions during forwarding).
TSN capabilities of the TSN sub-network are made available for MPLS
(DetNet) flows via the protocol interworking function defined in Annex C.5 of
. For example,
when applied on the TSN edge port, it can convert an ingress unicast
MPLS (DetNet) flow to use a specific Layer 2 multicast destination
Media Access Control (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.
The placement of TSN functions depends on the TSN capabilities of the
nodes along the path. 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.
Functions for DetNet Flow to TSN Stream Mapping
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.
Clause 6.8 of defines a
Mask-and-Match Stream identification function that can be used
as a passive function for MPLS DetNet flows.
Clause 6.6 of defines an
Active Destination MAC and a VLAN Stream identification function
that 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 that is passed either 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 also be used
in a TSN bridge that is providing translation as a proxy service
for an end system.
TSN Requirements of MPLS DetNet Nodes
This section covers required behavior of a TSN-aware MPLS (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, MPLS (DetNet) nodes are treated
as a Talker or Listener, which may be (1) TSN-unaware or
(2) TSN-aware.
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.
MPLS (DetNet) nodes that are 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
MPLS (DetNet) node must provide the TSN sub-network-specific
Ethernet encapsulation over the link(s) towards the sub-network.
A TSN-aware MPLS (DetNet) node implementation 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) Mask-and-Match Stream identification function, and
(3) the related managed objects in Clause 9 of
and
.
A TSN-aware MPLS (DetNet) node implementation must support the
Sequencing function and the Sequence encode/decode function as
defined in Clauses 7.4 and 7.6 of
in order for FRER to be 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 .
A TSN-aware MPLS (DetNet) node implementation must support the
Stream splitting
function and the Individual recovery function as defined in
Clauses 7.5 and 7.7 of
in order for that node to be a replication or elimination
point for FRER.
Service Protection within the TSN Sub-network
TSN Streams supporting DetNet flows may use FRER as defined in Clause 8 of
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 .
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 an 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
similar MPLS flow parameters, FRER can be combined with PREOF
functions. Such service protection interworking scenarios may
require moving sequence number fields among TSN (L2) and PW
(MPLS) encapsulations, and they are left for further study.
Aggregation during DetNet Flow to TSN Stream Mapping
Implementation 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.
Management and Control Implications
Information related to DetNet flow and TSN Stream mapping is
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).
The following summarizes the set of information that is needed to
configure DetNet MPLS over TSN:
DetNet MPLS-related configuration information according to the
DetNet role of the DetNet MPLS node, as per
.
TSN-related configuration information according to the
TSN role of the DetNet MPLS node, as per
, , and
.
Mapping between a DetNet MPLS flow(s) (label information:
A-Labels, S-Labels, and F-Labels as defined in
) and a TSN
Stream(s) (as Stream identification information defined in
).
Note that managed objects for TSN Stream identification can be
found in .
This information must be provisioned per DetNet flow.
Mappings between DetNet and TSN management and control planes are
out of scope of this document. Some of the challenges are
highlighted below.
TSN-aware MPLS DetNet nodes are members 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 the
Multiple Stream Registration Protocol (MSRP)
behave differently. Therefore, management and control plane
design are important aspects 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 information specific to the TSN
sub-network. 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 end-to-end
DetNet path (i.e., a single hop from the 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 cases, 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).
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.
Security Considerations
Security considerations for DetNet are described in detail in
. General security considerations
are described in .
Considerations specific to the DetNet MPLS data plane are summarized in
.
This section considers exclusively security considerations that are
specific to the DetNet MPLS over TSN sub-network scenario.
The sub-network between DetNet nodes needs to be subject to appropriate
confidentiality. Additionally, knowledge of what DetNet/TSN services are
provided by a sub-network may supply information that can be used in a
variety of security attacks. The ability to modify information exchanges
between connected DetNet nodes may result in bogus operations. Therefore,
it is important that the interface between DetNet nodes and the TSN
sub-network are subject to authorization, authentication, and encryption.
The TSN sub-network operates at Layer 2, so various security mechanisms
defined by IEEE can be used to secure the connection between the DetNet
nodes (e.g., encryption may be provided using MACsec
).
IANA Considerations
This document has no IANA actions.
ReferencesNormative ReferencesIEEE Standard for Local and metropolitan area networks -- Frame Replication and Elimination for ReliabilityIEEEIEEE Std 802.1CB-2017Draft Standard for Local and metropolitan area networks --
Frame Replication and Elimination for Reliability -- Amendment:
Extended Stream Identification FunctionsIEEEIEEE P802.1CBdb / D1.3Informative ReferencesDeterministic Networking (DetNet) Security ConsiderationsDolby Laboratories, Inc.Huawei Network.IO Innovation LabMistIQ Technologies, IncIEEE Standard for Local and metropolitan area networks-Media Access Control (MAC) SecurityIEEEIEEE Std 802.1AE-2018IEEE Standard for Local and metropolitan area networks -- Bridges
and Bridged NetworksIEEEIEEE Std 802.1Q-2018Draft Standard for Local and metropolitan area networks -- Frame Replication and Elimination for Reliability -- Amendment: Information Model, YANG Data Model and Management Information Base ModuleIEEE 802.1IEEE P802.1CBcv, Draft 1.1Acknowledgements
The authors wish to thank , , ,
, and for their various contributions
to this work.