Internet Engineering Task Force (IETF) B. Varga, Ed.

Internet Engineering Task Force (IETF) B. Varga, Ed.
Request for Comments: 9023 J. Farkas
Category: Informational Ericsson
ISSN: 2070-1721 A. Malis
Malis Consulting
S. Bryant
Futurewei Technologies
June 2021

Deterministic Networking (DetNet) Data Plane: IP over IEEE 802.1
Time-Sensitive Networking (TSN)

Abstract

This document specifies the Deterministic Networking IP data plane
when operating over a Time-Sensitive Networking (TSN) sub-network.
This document does not define new procedures or processes. Whenever
this document makes statements or recommendations, these 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/rfc9023.

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Table of Contents

1. Introduction
2. Terminology
2.1. Terms Used in This Document
2.2. Abbreviations
3. DetNet IP Data Plane Overview
4. DetNet IP Flows over an IEEE 802.1 TSN Sub-network
4.1. Functions for DetNet Flow to TSN Stream Mapping
4.2. TSN Requirements of IP 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 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 [RFC8655].

[RFC8939] 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 Time-Sensitive Networking (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
provide congestion protection (low loss, assured latency, and limited
reordering). As described in [RFC8939], no DetNet-specific headers
are added to support DetNet IP flows. So, only the forwarding sub-
layer functions can be supported inside the DetNet IP domain.
Service protection can be provided on a per-sub-network basis as
shown here for the IEEE 802.1 TSN sub-network scenario.

2. Terminology

2.1. Terms Used in This Document

This document uses the terminology and concepts established in the
DetNet Architecture [RFC8655]. TSN-specific terms are defined by the
TSN Task Group 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:

DetNet Deterministic Networking

FRER Frame Replication and Elimination for Redundancy (TSN
function)

L2 Layer 2

L3 Layer 3

TSN Time-Sensitive Networking; TSN is a Task Group of the
IEEE 802.1 Working Group.

3. DetNet IP Data Plane Overview

[RFC8939] 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 flow identification based on a "6-tuple", where "6-tuple" refers
to information carried in IP- and higher-layer protocol headers as
defined in [RFC8939].

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, and shaping) are supported using the underlying
link / sub-net-specific mechanisms. Service protections (packet-
replication and packet-elimination functions) are not provided at the
IP DetNet layer end to end due to the lack of unified end-to-end
sequencing information that would be available for intermediate
nodes. However, such service protection can be provided per
underlying L2 link and per sub-network.

DetNet routers ensure that DetNet service requirements are met per
hop by allocating local resources, by both receiving and
transmitting, and by mapping the service requirements of each flow to
appropriate sub-network mechanisms. Such mappings are sub-network
technology specific. DetNet nodes interconnected by a TSN sub-
network are the primary focus of this document. The mapping of
DetNet IP flows to TSN Streams and TSN protection mechanisms are
covered in Section 4.

4. DetNet IP Flows over an IEEE 802.1 TSN Sub-network

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)
Node-1 Node-2

............ ............
<--: Service :-- DetNet flow ---: Service :-->
+----------+ +----------+
|Forwarding| |Forwarding|
+--------.-+ <-TSN Str-> +-.-----.--+
\ ,-------. / /
+----[ TSN Sub-]---+ /
[ Network ]--------+
`-------'
<----------------- DetNet IP ----------------->

Figure 1: DetNet-Enabled IP Network over a TSN Sub-network

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.

4.1. Functions for DetNet Flow to TSN Stream Mapping

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.

4.2. TSN Requirements of IP DetNet Nodes

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.

IP (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 ------->

Figure 2: IP (DetNet) Node with TSN Functions

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.

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].

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.

4.4. Aggregation during DetNet Flow to TSN Stream Mapping

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.

5. Management and Control Implications

DetNet flows 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).

The following summarizes the set of information that is needed to
configure DetNet IP over TSN:

* DetNet-IP-related configuration information according to the
DetNet role of the DetNet IP node, as per [RFC8939].

* TSN-related configuration information according to the TSN role of
the DetNet IP node, as per [IEEE8021Q], [IEEE8021CB], and
[IEEEP8021CBdb].

* Mapping between DetNet IP flow(s) and TSN Stream(s). DetNet IP
flow identification is summarized in Section 5.1 of [RFC8939] and
includes all wildcards, port ranges, and the ability to ignore
specific IP fields. Information on TSN Stream identification
information is defined in [IEEE8021CB] and [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 IP DetNet nodes are members 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 the Multiple Stream Registration
Protocol (MSRP) of IEEE 802.1 behave 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
information. 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., single hop from an 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 cases, 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 not be 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 the 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.

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 IP data plane are
summarized in [RFC8939]. This section discusses security
considerations that are specific to the DetNet IP-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 802.1CB-2017,
DOI 10.1109/IEEESTD.2017.8091139, October 2017,
<https://standards.ieee.org/standard/802_1CB-2017.html>.

[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/>.

[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>.

[RFC8939] Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S.
Bryant, "Deterministic Networking (DetNet) Data Plane:
IP", RFC 8939, DOI 10.17487/RFC8939, November 2020,
<https://www.rfc-editor.org/info/rfc8939>.

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, 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
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
Network--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: [email protected]

János Farkas
Ericsson
Budapest
Magyar Tudosok krt. 11.
1117
Hungary

Email: [email protected]

Andrew G. Malis
Malis Consulting

Email: [email protected]

Stewart Bryant
Futurewei Technologies

Email: [email protected]