Internet Engineering Task Force (IETF) B. Varga, Ed.
Request for Comments: 9037 J. Farkas
Category: Informational Ericsson
ISSN: 2070-1721 A. Malis
Malis Consulting
S. Bryant
Futurewei Technologies
June 2021
Deterministic Networking (DetNet) Data Plane: MPLS over IEEE 802.1 Time-
Sensitive Networking (TSN)
Abstract
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.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9037.
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Table of Contents
1. Introduction
2. Terminology
2.1. Terms Used in This Document
2.2. Abbreviations
3. DetNet MPLS Data Plane Overview
4. DetNet MPLS Operation over IEEE 802.1 TSN Sub-networks
4.1. Functions for DetNet Flow to TSN Stream Mapping
4.2. TSN Requirements of MPLS DetNet Nodes
4.3. Service Protection within the TSN Sub-network
4.4. Aggregation during DetNet Flow to TSN Stream Mapping
5. Management and Control Implications
6. Security Considerations
7. IANA Considerations
8. References
8.1. Normative References
8.2. Informative References
Acknowledgements
Authors' Addresses
1. 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 [RFC8655].
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.
[RFC8964] 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).
2. Terminology
2.1. Terms Used in This Document
This document uses the terminology established in the DetNet
architecture [RFC8655] [RFC8964]. 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.
2.2. 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
PSN Packet Switched Network
PW Pseudowire
RSVP-TE Resource Reservation Protocol - Traffic Engineering
S-Label Service label
TSN Time-Sensitive Networking
3. DetNet MPLS Data Plane Overview
The basic approach defined in [RFC8964] 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
[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 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 Section 4.
4. 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 [RFC8655], 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.
Figure 1 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.
MPLS (DetNet) MPLS (DetNet)
Node-1 Node-2
+----------+ +----------+
<--| Service* |-- DetNet flow ---| Service* |-->
+----------+ +----------+
|Forwarding| |Forwarding|
+--------.-+ <-TSN Str-> +-.-----.--+
\ ,-------. / /
+----[ TSN Sub-]---+ /
[ network ]--------+
`-------'
<---------------- DetNet MPLS --------------->
Note: * no service sub-layer required for transit nodes
Figure 1: DetNet-Enabled MPLS Network over a 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
[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 (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 [IEEE8021CB]. 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.
4.1. 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 [IEEEP8021CBdb] defines a Mask-and-Match Stream
identification function that can be used as a passive function for
MPLS DetNet flows.
Clause 6.6 of [IEEE8021CB] 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.
4.2. 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 Figure 2. In such cases, the MPLS (DetNet) node must
provide the TSN sub-network-specific Ethernet encapsulation over the
link(s) towards the sub-network.
MPLS (DetNet)
Node
<---------------------------------->
+----------+
<--| Service* |-- DetNet flow ------------------
+----------+
|Forwarding|
+----------+ +---------------+
| L2 | | L2 Relay with |<--- TSN ---
| | | TSN function | Stream
+-----.----+ +--.------.---.-+
\__________/ \ \______
\_________
TSN-unaware
Talker / TSN-Bridge
Listener Relay
<----- TSN Sub-network -----
<------- TSN-aware Tlk/Lstn ------->
Note: * no service sub-layer required for transit nodes
Figure 2: MPLS (DetNet) Node with TSN Functions
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
[IEEE8021CB] and [IEEEP8021CBdb].
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 [IEEE8021CB] 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 [IEEE8021CB].
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 [IEEE8021CB] in order for that node to be a
replication or elimination point for FRER.
4.3. Service Protection within the TSN Sub-network
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].
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.
4.4. 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.
5. 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 [RFC8964].
* TSN-related configuration information according to the TSN role of
the DetNet MPLS node, as per [IEEE8021Q], [IEEE8021CB], and
[IEEEP8021CBdb].
* Mapping between a DetNet MPLS flow(s) (label information:
A-Labels, S-Labels, and F-Labels as defined in [RFC8964]) and a
TSN Stream(s) (as Stream identification information defined in
[IEEEP8021CBdb]). Note that managed objects for TSN Stream
identification can be found in [IEEEP8021CBcv].
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.
6. Security Considerations
Security considerations for DetNet are described in detail in
[DETNET-SECURITY]. General security considerations are described in
[RFC8655]. Considerations specific to the DetNet MPLS data plane are
summarized in [RFC8964]. 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 [IEEE802.1AE-2018]).
7. IANA Considerations
This document has no IANA actions.
8. References
8.1. Normative References
[IEEE8021CB]
IEEE, "IEEE Standard for Local and metropolitan area
networks -- Frame Replication and Elimination for
Reliability", IEEE Std 802.1CB-2017,
DOI 10.1109/IEEESTD.2017.8091139, October 2017,
<https://ieeexplore.ieee.org/document/8091139>.
[IEEEP8021CBdb]
IEEE, "Draft Standard for Local and metropolitan area
networks -- Frame Replication and Elimination for
Reliability -- Amendment: Extended Stream Identification
Functions", IEEE P802.1CBdb / D1.3, April 2021,
<https://1.ieee802.org/tsn/802-1cbdb/>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
[RFC8964] Varga, B., Ed., Farkas, J., Berger, L., Malis, A., Bryant,
S., and J. Korhonen, "Deterministic Networking (DetNet)
Data Plane: MPLS", RFC 8964, DOI 10.17487/RFC8964, January
2021, <https://www.rfc-editor.org/info/rfc8964>.
8.2. Informative References
[DETNET-SECURITY]
Grossman, E., Ed., Mizrahi, T., and A. Hacker,
"Deterministic Networking (DetNet) Security
Considerations", Work in Progress, Internet-Draft, draft-
ietf-detnet-security-16, 2 March 2021,
<https://tools.ietf.org/html/draft-ietf-detnet-security-
16>.
[IEEE802.1AE-2018]
IEEE, "IEEE Standard for Local and metropolitan area
networks-Media Access Control (MAC) Security", IEEE Std
802.1AE-2018, DOI 10.1109/IEEESTD.2018.8585421, December
2018, <https://ieeexplore.ieee.org/document/8585421>.
[IEEE8021Q]
IEEE, "IEEE Standard for Local and metropolitan area
networks -- Bridges and Bridged Networks", IEEE Std
802.1Q-2018, DOI 10.1109/IEEESTD.2018.8403927, July 2018,
<https://ieeexplore.ieee.org/document/8403927/>.
[IEEEP8021CBcv]
IEEE 802.1, "Draft Standard for Local and metropolitan
area networks -- Frame Replication and Elimination for
Reliability -- Amendment: Information Model, YANG Data
Model and Management Information Base Module", IEEE
P802.1CBcv, Draft 1.1, February 2021,
<https://1.ieee802.org/tsn/802-1cbcv/>.
Acknowledgements
The authors wish to thank Norman Finn, Lou Berger, Craig Gunther,
Christophe Mangin, and Jouni Korhonen for their various contributions
to this work.
Authors' Addresses
Balázs Varga (editor)
Ericsson
Budapest
Magyar Tudosok krt. 11.
1117
Hungary
Email: balazs.a.varga@ericsson.com
János Farkas
Ericsson
Budapest
Magyar Tudosok krt. 11.
1117
Hungary
Email: janos.farkas@ericsson.com
Andrew G. Malis
Malis Consulting
Email: agmalis@gmail.com
Stewart Bryant
Futurewei Technologies
Email: sb@stewartbryant.com