Internet DRAFT - draft-ietf-detnet-problem-statement
draft-ietf-detnet-problem-statement
DetNet N. Finn
Internet-Draft Huawei Technologies Co. Ltd
Intended status: Informational P. Thubert
Expires: June 21, 2019 Cisco
December 18, 2018
Deterministic Networking Problem Statement
draft-ietf-detnet-problem-statement-09
Abstract
This paper documents the needs in various industries to establish
multi-hop paths for characterized flows with deterministic
properties.
Status of This Memo
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This Internet-Draft will expire on June 21, 2019.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. On Deterministic Networking . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Supported topologies . . . . . . . . . . . . . . . . . . 6
3.2. Flow Characterization . . . . . . . . . . . . . . . . . . 6
3.3. Centralized Path Computation and Installation . . . . . . 6
3.4. Distributed Path Setup . . . . . . . . . . . . . . . . . 7
3.5. Duplicated data format . . . . . . . . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
7. Informative References . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The Deterministic Networking Use Cases [I-D.ietf-detnet-use-cases]
document illustrates that beyond the classical case of industrial
automation and control systems (IACS), there are in fact multiple
industries with strong and yet relatively similar needs for
deterministic network services with latency guarantees and ultra-low
packet loss.
The generalization of the needs for more deterministic networks have
led to the IEEE 802.1 AVB Task Group becoming the Time-Sensitive
Networking (TSN) [IEEE802.1TSNTG] Task Group (TG), with a much-
expanded constituency from the industrial and vehicular markets.
Along with this expansion, the networks in consideration are becoming
larger and structured, requiring deterministic forwarding beyond the
LAN boundaries. For instance, IACS segregates the network along the
broad lines of the Purdue Enterprise Reference Architecture (PERA)
[ISA95], typically using deterministic local area networks for level
2 control systems, whereas public infrastructures such as Electricity
Automation require deterministic properties over the Wide Area. The
realization is now coming that the convergence of IT and Operational
Technology (OT) networks requires Layer-3, as well as Layer-2,
capabilities.
While the initial user base has focused almost entirely on Ethernet
physical media and Ethernet-based bridging protocol from several
Standards Development Organizations, the need for Layer-3 expressed
above, must not be confined to Ethernet and Ethernet-like media.
While such media must be encompassed by any useful Deterministic
Networking (DetNet) Architecture, cooperation between IETF and other
SDOs must not be limited to IEEE or IEEE 802. Furthermore, while the
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work completed and ongoing in other SDOs, and in IEEE 802 in
particular, provide an obvious starting point for a DetNet
architecture, we must not assume that these other SDOs' work confines
the space in which the DetNet architecture progresses.
The properties of deterministic networks will have specific
requirements for the use of routed networks to support these
applications and a new model must be proposed to integrate
determinism in IT technology. The proposed model should enable a
fully scheduled operation orchestrated by a central controller, and
may support a more distributed operation with probably lesser
capabilities. In any fashion, the model should not compromise the
ability of a network to keep carrying the sorts of traffic that is
already carried today in conjunction with new, more deterministic
flows. Forward note: The DetNet Architecture
[I-D.ietf-detnet-architecture] is the document produced by the DetNet
WG to describe that model.
At the time of this writing, the expectation is that once the
abstract model is agreed upon, the IETF will specify the signaling
elements to be used to establish a path and the tagging elements to
be used identify the flows that are to be forwarded along that path.
The expectation is also that IETF will specify the necessary
protocols, or protocol additions, based on relevant IETF
technologies, to implement the selected model.
A desirable outcome of the work is the capability to establish a
multi-hop path over the IP or MPLS network, for a particular flow
with given timing and precise throughput requirements, and carry this
particular flow along the multi-hop path with such characteristics as
low latency and ultra-low jitter, reordering and/or replication and
elimination of packets over non-congruent paths for a higher delivery
ratio, and/or zero congestion loss, regardless of the amount of other
flows in the network.
Depending on the network capabilities and on the current state,
requests to establish a path by an end-node or a network management
entity may be granted or rejected, an existing path may be moved or
removed, and DetNet flows exceeding their contract may face packet
declassification and drop.
2. On Deterministic Networking
The Internet is not the only digital network that has grown
dramatically over the last 30-40 years. Video and audio
entertainment, and control systems for machinery, manufacturing
processes, and vehicles are also ubiquitous, and are now based almost
entirely on digital technologies. Over the past 10 years, engineers
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in these fields have come to realize that significant advantages in
both cost and in the ability to accelerate growth can be obtained by
basing all of these disparate digital technologies on packet
networks.
The goals of Deterministic Networking are to enable the migration of
applications with critical timing and reliability issues that
currently use special-purpose fieldbus technologies (HDMI, CANbus,
ProfiBus, etc... even RS-232!) to packet technologies in general, and
the Internet Protocol in particular, and to support both these new
applications, and existing packet network applications, over the same
physical network. In other words, a Deterministic Network is
backwards compatible with (capable of transporting) statistically
multiplexed traffic while preserving the properties of the accepted
deterministic flows.
The Deterministic Networking Use Cases [I-D.ietf-detnet-use-cases]
document indicates that applications in multiple fields need some or
all of a suite of features that includes:
1. Time synchronization of all host and network nodes (routers and/
or bridges), accurate to something between 10 nanoseconds and 10
microseconds, depending on the application.
2. Support for Deterministic packet flows that:
* Can be unicast or multicast;
* Need absolute guarantees of minimum and maximum latency end-
to-end across the network; sometimes a tight jitter is
required as well;
* Need a packet loss ratio beyond the classical range for a
particular medium, in the range of 10^-9 to 10^-12, or better,
on Ethernet, and in the order of 10^-5 in Wireless Sensor Mesh
Networks;
* Can, in total, absorb more than half of the network's
available bandwidth (that is, massive over-provisioning is
ruled out as a solution);
* Cannot suffer throttling, congestion feedback, or any other
network-imposed transmission delay, although the flows can be
meaningfully characterized either by a fixed, repeating
transmission schedule, or by a maximum bandwidth and packet
size;
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3. Multiple methods to schedule, shape, limit, and otherwise control
the transmission of critical packets at each hop through the
network data plane;
4. Robust defenses against misbehaving hosts, routers, or bridges,
both in the data and control planes, with guarantees that a
critical flow within its guaranteed resources cannot be affected
by other flows whatever the pressures on the network - more on
the specific threats against DetNet in the DetNet Security
Considerations [I-D.ietf-detnet-security] document;
5. One or more methods to reserve resources in bridges and routers
to carry these flows.
Time synchronization techniques need not be addressed by an IETF
Working Group; there are a number of standards available for this
purpose, including IEEE 1588, IEEE 802.1AS, and more.
The multicast, latency, loss ratio, and non-throttling needs are made
necessary by the algorithms employed by the applications. They are
not simply the transliteration of fieldbus needs to a packet-based
fieldbus simulation, but reflect fundamental mathematics of the
control of a physical system.
With classical forwarding latency- and loss-sensitive packets across
a network, interactions among different critical flows introduce
fundamental uncertainties in delivery schedules. The details of the
queuing, shaping, and scheduling algorithms employed by each bridge
or router to control the output sequence on a given port affect the
detailed makeup of the output stream, e.g. how finely a given flow's
packets are mixed among those of other flows.
This, in turn, has a strong effect on the buffer requirements, and
hence the latency guarantees deliverable, by the next bridge or
router along the path. For this reason, the IEEE 802.1 Time-
Sensitive Networking Task Group has defined a new set of queuing,
shaping, and scheduling algorithms that enable each bridge or router
to compute the exact number of buffers to be allocated for each flow
or class of flows.
Robustness is a common need for networking protocols, but plays a
more important part in real-time control networks, where expensive
equipment, and even lives, can be lost due to misbehaving equipment.
Reserving resources before packet transmission is the one fundamental
shift in the behavior of network applications that is impossible to
avoid. In the first place, a network cannot deliver finite latency
and practically zero packet loss to an arbitrarily high offered load.
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Secondly, achieving practically zero packet loss for un-throttled
(though bandwidth limited) flows means that bridges and routers have
to dedicate buffer resources to specific flows or to classes of
flows. The requirements of each reservation have to be translated
into the parameters that control each host's, bridge's, and router's
queuing, shaping, and scheduling functions and delivered to the
hosts, bridges, and routers.
3. Problem Statement
3.1. Supported topologies
In some use cases, the end point which run the application is
involved in the deterministic networking operation, for instance by
controlling certain aspects of its throughput such as rate or precise
time of emission. In that case, the deterministic path is end-to-end
from application host to application host.
On the other end, the deterministic portion of a path may be a tunnel
between an ingress and an egress router. In any case, routers and
switches in between should not need to be aware whether the path is
end-to-end or a tunnel.
While it is clear that DetNet does not aim at setting up
deterministic paths over the global Internet, there is still a lack
of clarity on the limits of a domain where a deterministic path can
be set up. These limits may depend in the technology that is used to
set the path up, whether it is centralized or distributed.
3.2. Flow Characterization
Deterministic forwarding can only apply on flows with well-defined
characteristics such as periodicity and burstiness. Before a path
can be established to serve them, the expression of those
characteristics, and how the network can serve them, for instance in
shaping and forwarding operations, must be specified.
3.3. Centralized Path Computation and Installation
A centralized routing model, such as provided with a Path Computation
Element (PCE) (see [RFC4655]), enables global and per-flow
optimizations. The model is attractive but a number of issues are
left to be solved. In particular:
o whether and how the path computation can be installed by 1) an end
device or 2) a Network Management entity,
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o and how the path is set up, either by installing state at each hop
with a direct interaction between the forwarding device and the
PCE, or along a path by injecting a source-routed request at one
end of the path following classical Traffic Engineering (TE)
models.
To enable a centralized model, DetNet should produce a description of
the high level interaction and data models to:
o report the topology and device capabilities to the central
controller;
o establish a direct interface between the centralized PCE to each
device under its control in order to enable a vertical signaling
o request a path setup for a new flow with particular
characteristics over the service interface and control it through
its life cycle;
o support for life cycle management for a path
(instantiate/modify/update/delete)
o support for adaptability to cope with various events such as loss
of a link, etc...
o expose the status of the path to the end devices (UNI interface)
o provide additional reliability through redundancy, in particular
with packet Packet Replication, Elimination and Ordering Functions
(PREOF) where the former may generate an out-of-order delivery
that may need to be corrected corrected by the latter;
o indicate the flows and packet sequences in-band with the flows,
this is needed for flows that require PREOF in order to isolate
duplicates and reorder in the end;
3.4. Distributed Path Setup
Whether a distributed alternative without a PCE can be valuable could
be studied as well. Such an alternative could for instance inherit
from the Resource ReSerVation Protocol [RFC3209] (RSVP-TE) flows.
But the focus of the work should be to deliver the centralized
approach first.
To enable a RSVP-TE like functionality, the following steps would
take place:
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1. Neighbors and their capabilities are discovered and exposed to
compute a path that fits the DetNet constraints, typically of
latency, time precision and resource availability.
2. A constrained path is calculated with an improved version of
Constrained Shortest Path First (CSPF) that is aware of DetNet.
3. The path may be installed using a control protocol such as RSVP-
TE, associated with flow identification, per-hop behavior such as
Packet Replication and Elimination, and blocked resources. In
that case, traffic flows can be transported through an MPLS-TE
tunnel, using the reserved resources for this flow at each hop.
3.5. Duplicated data format
In some cases the duplication and elimination of packets over non-
congruent paths is required to achieve a sufficiently high delivery
ratio to meet application needs. In these cases, a small number of
packet formats and supporting protocols are required (preferably,
just one) to serialize the packets of a DetNet stream at one point in
the network, replicate them at one or more points in the network, and
discard duplicates at one or more other points in the network,
including perhaps the destination host. Using an existing solution
would be preferable to inventing a new one.
4. Security Considerations
Security in the context of Deterministic Networking has an added
dimension; the time of delivery of a packet can be just as important
as the contents of the packet, itself. A man-in-the-middle attack,
for example, can impose, and then systematically adjust, additional
delays into a link, and thus disrupt or subvert a real-time
application without having to crack any encryption methods employed.
See [RFC7384] for an exploration of this issue in a related context.
Typical control networks today rely on complete physical isolation to
prevent rogue access to network resources. DetNet enables the
virtualization of those networks over a converged IT/OT
infrastructure. Doing so, DetNet introduces an additional risk that
flows interact and interfere with one another as they share physical
resources such as Ethernet trunks and radio spectrum. The
requirement is that there is no possible data leak from and into a
deterministic flow, and in a more general fashion there is no
possible influence whatsoever from the outside on a deterministic
flow. The expectation is that physical resources are effectively
associated with a given flow at a given point of time. In that
model, Time Sharing of physical resources becomes transparent to the
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individual flows which have no clue whether the resources are used by
other flows at other times.
The overall security of a deterministic system must cover:
o the protection of the signaling protocol
o the authentication and authorization of the controlling nodes
including plug-and-play participating end systems.
o the identification and shaping of the flows
o the isolation of flows from leakage and other influences from any
activity sharing physical resources.
The specific threats against DetNet are further discussed in the
DetNet Security Considerations [I-D.ietf-detnet-security] document.
5. IANA Considerations
This document does not require an action from IANA.
6. Acknowledgments
The authors wish to thank Lou Berger, Pat Thaler, Jouni Korhonen,
Janos Farkas, Stewart Bryant, Andrew Malis, Ethan Grossman, Patrick
Wetterwald, Subha Dhesikan, Matthew Miller, Erik Nordmark, George
Swallow, Rodney Cummings, Ines Robles, Shwetha Bhandari, Rudy Klecka,
Anca Zamfir, David Black, Thomas Watteyne, Shitanshu Shah, Kiran
Makhijani, Craig Gunther, Warren Kumari, Wilfried Steiner, Marcel
Kiessling, Karl Weber, Alissa Cooper, and Benjamin Kaduk for their
various contributions to this work.
7. Informative References
[I-D.ietf-detnet-architecture]
Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", draft-ietf-
detnet-architecture-09 (work in progress), October 2018.
[I-D.ietf-detnet-security]
Mizrahi, T., Grossman, E., Hacker, A., Das, S., Dowdell,
J., Austad, H., Stanton, K., and N. Finn, "Deterministic
Networking (DetNet) Security Considerations", draft-ietf-
detnet-security-03 (work in progress), October 2018.
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[I-D.ietf-detnet-use-cases]
Grossman, E., "Deterministic Networking Use Cases", draft-
ietf-detnet-use-cases-19 (work in progress), October 2018.
[IEEE802.1TSNTG]
IEEE Standards Association, "IEEE 802.1 Time-Sensitive
Networks Task Group", 2013,
<http://www.ieee802.org/1/pages/avbridges.html>.
[ISA95] ANSI/ISA, "Enterprise-Control System Integration Part 1:
Models and Terminology", 2000,
<https://www.isa.org/isa95/>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in
Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384,
October 2014, <https://www.rfc-editor.org/info/rfc7384>.
Authors' Addresses
Norman Finn
Huawei Technologies Co. Ltd
3755 Avocado Blvd.
PMB 436
La Mesa, California 91941
US
Phone: +1 925 980 6430
Email: norman.finn@mail01.huawei.com
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Pascal Thubert
Cisco Systems
Village d'Entreprises Green Side
400, Avenue de Roumanille
Batiment T3
Biot - Sophia Antipolis 06410
FRANCE
Phone: +33 497 232 634
Email: pthubert@cisco.com
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