Networking Working Group K. Pister
Internet-Draft Dust Networks
Intended status: Informational P. Thubert
Expires: October 30, 2008 Cisco Systems, Inc
April 28, 2008
Industrial Routing Requirements in Low Power and Lossy Networks
draft-ietf-roll-indus-routing-reqs-00
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Abstract
Wireless, low power field devices enable industrial users to
significantly increase the amount of information collected and the
number of control points that can be remotely managed. The
deployment of these wireless devices will significantly improve the
productivity and safety of the plants while increasing the efficiency
of the plant workers. For wireless devices to have a significant
advantage over wired devices in an industrial environment the
wireless network needs to have three qualities: low power, high
reliability, and easy installation and maintenance. The aim of this
document is to analyze the requirements for the routing protocol used
for low power and lossy networks (L2N) in industrial environments.
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Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Applications and Traffic Patterns . . . . . . . . . . . . 5
2.2. Network Topology of Industrial Applications . . . . . . . 6
2.2.1. The Physical Topology . . . . . . . . . . . . . . . . 7
3. Service Requirements . . . . . . . . . . . . . . . . . . . . . 9
3.1. Configurable Application Requirement . . . . . . . . . . . 10
3.2. Different Routes for Different Flows . . . . . . . . . . . 11
4. Reliability Requirements . . . . . . . . . . . . . . . . . . . 11
5. Device-Aware Routing Requirements . . . . . . . . . . . . . . 12
6. Broadcast/Multicast . . . . . . . . . . . . . . . . . . . . . 13
7. Route Establishment Time . . . . . . . . . . . . . . . . . . . 13
8. Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9. Manageability . . . . . . . . . . . . . . . . . . . . . . . . 14
10. Security . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
13.1. Normative References . . . . . . . . . . . . . . . . . . . 15
13.2. Informative References . . . . . . . . . . . . . . . . . . 16
13.3. External Informative References . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . . . 17
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1. Terminology
Actuator: a field device that moves or controls plant equipment.
Closed Loop Control: A process whereby a device controller controls
an actuator based on information sensed by one or more field devices.
Downstream: Data direction traveling from the plant application to
the field device.
Field Device: physical devices placed in the plant's operating
environment (both RF and environmental). Field devices include
sensors and actuators as well as network routing devices and L2N
access points in the plant.
HART: "Highway Addressable Remote Transducer", a group of
specifications for industrial process and control devices
administered by the HART Foundation (see [HART]). The latest version
for the specifications is HART7 which includes the additions for
WirelessHART.
ISA: "International Society of Automation". ISA is an ANSI
accredited standards-making society. ISA100 is an ISA working group
whose charter includes defining a family of standards for industrial
automation. ISA100.11a is a work group within ISA100 that is working
on a standard for non-critical process and control applications.
L2N Access Point: The L2N access point is an infrastructure device
that connects the low power and lossy network system to a plant's
backbone network.
Open Loop Control: A process whereby a plant technician controls an
actuator over the network where the decision is influenced by
information sensed by field devices.
Plant Application: The plant application is a process running in the
plant that communicates with field devices to perform tasks on that
may include control, monitoring and data gathering.
Upstream: Data direction traveling from the field device to the plant
application.
RL2N: Routing in Low power and Lossy Networks.
2. Introduction
Wireless, low-power field devices enable industrial users to
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significantly increase the amount of information collected and the
number of control points that can be remotely managed. The
deployment of these wireless devices will significantly improve the
productivity and safety of the plants while increasing the efficiency
of the plant workers.
Wireless field devices enable expansion of networked points by
appreciably reducing cost of installing a device. The cost
reductions come from eliminating cabling costs and simplified
planning. Cabling for a field device can run from $100s/ft to
$1,000s/ft depending on the safety regulations of the plant. Cabling
also carries an overhead cost associated with planning the
installation, determining where the cable has to run, and interfacing
with the various organizations required to coordinate its deployment.
Doing away with the network and power cables reduces the planning and
administrative overhead of installing a device.
For wireless devices to have a significant advantage over wired
devices in an industrial environment, the wireless network needs to
have three qualities: low power, high reliability, and easy
installation and maintenance. The routing protocol used for low
power and lossy networks (L2N) is important to fulfilling these
goals.
Industrial automation is segmented into two distinct application
spaces, known as "process" or "process control" and "discrete
manufacturing" or "factory automation". In industrial process
control, the product is typically a fluid (oil, gas, chemicals ...).
In factory automation or discrete manufacturing, the products are
individual elements (screws, cars, dolls). While there is some
overlap of products and systems between these two segments, they are
surprisingly separate communities. The specifications targeting
industrial process control tend to have more tolerance for network
latency than what is needed for factory automation.
Both application spaces desire battery operated networks of hundreds
of sensors and actuators communicating with L2N access points. In an
oil refinery, the total number of devices is likely to exceed one
million, but the devices will be clustered into smaller networks that
report to an existing plant network infrastructure.
Existing wired sensor networks in this space typically use
communication protocols with low data rates, from 1,200 baud (e.g.
wired HART) to the one to two hundred Kbps range for most of the
others. The existing protocols are often master/slave with command/
response.
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2.1. Applications and Traffic Patterns
The industrial market classifies process applications into three
broad categories and six classes.
o Safety
* Class 0: Emergency action - Always a critical function
o Control
* Class 1: Closed loop regulatory control - Often a critical
function
* Class 2: Closed loop supervisory control - Usually non-critical
function
* Class 3: Open loop control - Operator takes action and controls
the actuator (human in the loop)
o Monitoring
* Class 4: Alerting - Short-term operational effect (for example
event-based maintenance)
* Class 5: Logging and downloading / uploading - No immediate
operational consequence (e.g., history collection, sequence-of-
events, preventive maintenance)
Critical functions effect the basic safety or integrity of the plant.
Timely deliveries of messages becomes more important as the class
number decreases.
Industrial users are interested in deploying wireless networks for
the monitoring classes 4 and 5, and in the non-critical portions of
classes 3 through 1.
Classes 4 and 5 also include asset monitoring and tracking which
include equipment monitoring and are essentially separate from
process monitoring. An example of equipment monitoring is the
recording of motor vibrations to detect bearing wear.
In the near future, most low power and lossy network systems will be
for low frequency data collection. Packets containing samples will
be generated continuously, and 90% of the market is covered by packet
rates of between 1/s and 1/hour, with the average under 1/min. In
industrial process, these sensors include temperature, pressure,
fluid flow, tank level, and corrosion. Some sensors are bursty, such
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as vibration monitors that may generate and transmit tens of kilo-
bytes (hundreds to thousands of packets) of time-series data at
reporting rates of minutes to days.
Almost all of these sensors will have built-in microprocessors that
may detect alarm conditions. Time-critical alarm packets are
expected to have lower latency than sensor data.
Some devices will transmit a log file every day, again with typically
tens of Kbytes of data. For these applications there is very little
"downstream" traffic coming from the L2N access point and traveling
to particular sensors. During diagnostics, however, a technician may
be investigating a fault from a control room and expect to have "low"
latency (human tolerable) in a command/response mode.
Low-rate control, often with a "human in the loop" (also referred to
as "open loop"), is implemented today via communication to a
centralized controller. The sensor data makes its way through the
L2N access point to the centralized controller where it is processed,
the operator sees the information and takes action, and the control
information is then sent out to the actuator node in the network.
In the future, it is envisioned that some open loop processes will be
automated (closed loop) and packets will flow over local loops and
not involve the L2N access point. These closed loop controls for
non-critical applications will be implemented on L2Ns. Non-critical
closed loop applications have a latency requirement that can be as
low as 100 ms but many control loops are tolerant of latencies above
1 s.
In critical control, tens of milliseconds of latency is typical. In
many of these systems, if a packet does not arrive within the
specified interval, the system enters an emergency shutdown state,
often with substantial financial repercussions. For a one-second
control loop in a system with a mean-time between shutdowns target of
30 years, the latency requirement implies nine 9s of reliability.
2.2. Network Topology of Industrial Applications
Although network topology is difficult to generalize, the majority of
existing applications can be met by networks of 10 to 200 field
devices and maximum number of hops from two to twenty. It is assumed
that the field devices themselves will provide routing capability for
the network, and additional repeaters/routers will not be required in
most cases.
For most industrial applications, a manager, gateway or backbone
router acts as a sink for the wireless sensor network. The vast
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majority of the traffic is real time publish/subscribe sensor data
from the field devices over a L2N towards one or more sinks.
Increasingly over time, these sinks will be a part of a backbone but
today they are often fragmented and isolated.
The wireless sensor network is a Low Power and Lossy Network of field
devices for which two logical roles are defined, the field routers
and the non routing devices. It is acceptable and even probable that
the repartition of the roles across the field devices change over
time to balance the cost of the forwarding operation amongst the
nodes.
The backbone is a high speed network that interconnects multiple WSNs
through backbone routers. Infrastructure devices can be connected to
the backbone. A gateway / manager that interconnects the backbone to
the plant network of the corporate network can be viewed as
collapsing the backbone and the infrastructure devices into a single
device that operates all the required logical roles. The backbone is
likely to always become an important function of the industrial
network. The Internet at large is not considered as a viable option
to perform the backbone function.
A plant or corporate network is also present on the factory site.
This is the typical IT nework for the factory operations beyond
process control. That network is out of scope for this document.
2.2.1. The Physical Topology
There is no specific physical topology for an industrial process
control network. One extreme example is a multi-square-kilometer
refinery where isolated tanks, some of them with power but most with
no backbone connectivity, compose a farm that spans over of the
surface of the plant. A few hundred field devices are deployed to
ensure the global coverage using a wireless self-forming self-healing
mesh network that might be 5 to 10 hops across. Local feedback loops
and mobile workers tend to be only one or two hops. The backbone is
in the refinery proper, many hops away. Even there, powered
infrastructure is also typically several hops away. So hopping to/
from the powered infrastructure will in general be more costly than
the direct route.
In the opposite extreme case, the backbone network spans all the
nodes and most nodes are in direct sight of one or more backbone
router. Most communication between field devices and infrastructure
devices as well as field device to field device occurs across the
backbone. Form afar, this model resembles the WIFI ESS (Extended
Service Set). But from a layer 3 perspective, the issues are the
default (backbone) router selection and the routing inside the
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backbone whereas the radio hop towards the field device is in fact a
simple local delivery.
---+------------------------
| Plant Network
|
+-----+
| | Gateway
| |
+-----+
|
| Backbone
+--------------------+------------------+
| | |
+-----+ +-----+ +-----+
| | Backbone | | Backbone | | Backbone
| | router | | router | | router
+-----+ +-----+ +-----+
o o o o o o o o o o o o o
o o o o o o o o o o o o o o o o o o
o o o o o o o o o o o M o o o o o
o o M o o o o o o o o o o o o o
o o o o o o o o o
o o o o o
L2N
Considering that though each field device to field device route
computation has specific constraints in terms of latency and
availability it can be expected that the shortest path possible will
often be selected and that this path will be routed inside the LLN as
opposed to via the backbone. It can also be noted that the lifetimes
of the routes might range from minutes for a mobile workers to tens
of years for a command and control closed loop. Finally, time-
varying user requirements for latency and bandwidth will change the
constraints on the routes, which might either trigger a constrained
route recomputation, a reprovisioning of the underlying L2 protocols,
or both in that order. For instance, a wireless worker may initiate
a bulk transfer to configure or diagnose a field device. A level
sensor device may need to perform a calibration and send a bulk file
to a plant.
For these reasons, the ROLL routing infrastructure MUST be able to
compute and update constrained routes on demand (that is reactively),
and it can be expected that this model will become more prevalent for
field device to field device connectivity as well as for some field
device to Infrastructure devices over time.
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3. Service Requirements
The industrial applications fall into four large service categories
[ISA100.11a]:
1. Periodic data (aka buffered). Data that is generated
periodically and has a well understood data bandwidth
requirement, both deterministic and predictable. Timely delivery
of such data is often the core function of a wireless sensor
network and permanent resources are assigned to ensure that the
required bandwidth stays available. Buffered data usually
exhibits a short time to live, and the newer reading obsoletes
the previous. In some cases, alarms are low priority information
that gets repeated over and over. The end-to-end latency of this
data is not as important as the regularity with which the data is
presented to the plant application.
2. Event data. This category includes alarms and aperiodic data
reports with bursty data bandwidth requirements. In certain
cases, alarms are critical and require a priority service from
the network.
3. Client/Server. Many industrial applications are based on a
client/server model and implement a command response protocol.
The data bandwidth required is often bursty. The acceptable
round-trip latency for some legacy systems was based on the time
to send tens of bytes over a 1200 baud link. Hundreds of
milliseconds is typical. This type of request is statistically
multiplexed over the L2N and cost-based fair-share best-effort
service is usually expected.
4. Bulk transfer. Bulk transfers involve the transmission of blocks
of data in multiple packets where temporary resources are
assigned to meet a transaction time constraint. Transient
resources are assigned for a limited period of time (related to
file size and data rate) to meet the bulk transfers service
requirements.
For industrial applications Service parameters include but might not
be limited to:
o Data bandwidth - the bandwidth might be allocated permanently or
for a period of time to a specific flow that usually exhibits well
defined properties of burstiness and throughput. Some bandwidth
will also be statistically shared between flows in a best effort
fashion.
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o Latency - the time taken for the data to transit the network from
the source to the destination. This may be expressed in terms of
a deadline for delivery. Most monitoring latencies will be in
seconds to minutes.
o Transmission phase - process applications can be synchronized to
wall clock time and require coordinated transmissions. A common
coordination frequency is 4 Hz (250 ms).
o Service contract type - revocation priority. L2Ns have limited
network resources that can vary with time. This means the system
can become fully subscribed or even over subscribed. System
policies determine how resources are allocated when resources are
over subscribed. The choices are blocking and graceful
degradation.
o Transmission priority - the means by which limited resources
within field devices are allocated across multiple services. For
transmissions, a device has to select which packet in its queue
will be sent at the next transmission opportunity. Packet
priority is used as one criterion for selecting the next packet.
For reception, a device has to decide how to store a received
packet. The field devices are memory constrained and receive
buffers may become full. Packet priority is used to select which
packets are stored or discarded.
The routing protocol MUST also support different metric types for
each link used to compute the path according to some objective
function (e.g. minimize latency).
Industrial application data flows between field devices are not
necessarily symmetric. In particular, asymmetrical cost and
unidirectional routes are common for published data and alerts, which
represent the most part of the sensor traffic. The routing protocol
MUST be able to set up unidirectional or asymmetrical cost routes
that are composed of one or more non congruent paths.
3.1. Configurable Application Requirement
Time-varying user requirements for latency and bandwidth will require
changes in the provisioning of the underlying L2 protocols. A
technician may initiate a query/response session or bulk transfer to
diagnose or configure a field device. A level sensor device may need
to perform a calibration and send a bulk file to a plant. The
routing protocol MUST route on paths that are changed to
appropriately provision the application requirements. The routing
protocol MUST support the ability to recompute paths based on
underlying link characteristics that may change dynamically.
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3.2. Different Routes for Different Flows
Because different services categories have different service
requirements, it is often desirable to have different routes for
different data flows between the same two endpoints. For example,
alarm or periodic data from A to Z may require path diversity with
specific latency and reliability. A file transfer between A and Z
may not need path diversity. The routing algorithm MUST be able to
generate different routes for different flows.
4. Reliability Requirements
Another critical aspect for the routing is the capability to ensure
maximum disruption time and route maintainance. The maximum
disruption time is the time it takes at most for a specific path to
be restored when broken. Route maintainance ensures that a path is
monitored to be restored when broken within the maximum disruption
time. Maintenance should also ensure that a path continues to
provide the service for which it was established for instance in
terms of bandwidth, jitter and latency.
In industrial applications, reliability is usually defined with
respect to end-to-end delivery of packets within a bounded latency.
Reliability requirements vary over many orders of magnitude. Some
non-critical monitoring applications may tolerate a reliability of
less than 90% with hours of latency. Most industrial standards, such
as HART7, have set user reliability expectations at 99.9%.
Regulatory requirements are a driver for some industrial
applications. Regulatory monitoring requires high data integrity
because lost data is assumed to be out of compliance and subject to
fines. This can drive reliability requirements to higher then 99.9%.
Hop-by-hop path diversity is used to improve latency-bounded
reliability. Additionally, bicasting or pluricasting may be used
over multiple non congruent / non overlapping paths to ensure that at
least one instance of a critical packet is actually delivered.
Because data from field devices are aggregated and funneled at the
L2N access point before they are routed to plant applications, L2N
access point redundancy is an important factor in overall
reliability. A route that connects a field device to a plant
application may have multiple paths that go through more than one L2N
access point. The routing protocol MUST support multiple L2N access
points and load distribution among L2N access points. The routing
protocol MUST support multiple L2N access points when L2N access
point redundancy is required. Because L2Ns are lossy in nature,
multiple paths in a L2N route MUST be supported. The reliability of
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each path in a route can change over time. Hence, it is important to
measure the reliability on a per-path basis and select a path (or
paths) according to the reliability requirements.
5. Device-Aware Routing Requirements
Wireless L2N nodes in industrial environments are powered by a
variety of sources. Battery operated devices with lifetime
requirements of at least five years are the most common. Battery
operated devices have a cap on their total energy, and typically can
report an estimate of remaining energy, and typically do not have
constraints on the short-term average power consumption. Energy
scavenging devices are more complex. These systems contain both a
power scavenging device (such as solar, vibration, or temperature
difference) and an energy storage device, such as a rechargeable
battery or a capacitor. These systems, therefore, have limits on
both long-term average power consumption (which cannot exceed the
average scavenged power over the same interval) as well as the short-
term limits imposed by the energy storage requirements. For solar-
powered systems, the energy storage system is generally designed to
provide days of power in the absence of sunlight. Many industrial
sensors run off of a 4-20 mA current loop, and can scavenge on the
order of milliwatts from that source. Vibration monitoring systems
are a natural choice for vibration scavenging, which typically only
provides tens or hundreds of microwatts. Due to industrial
temperature ranges and desired lifetimes, the choices of energy
storage devices can be limited, and the resulting stored energy is
often comparable to the energy cost of sending or receiving a packet
rather than the energy of operating the node for several days. And
of course, some nodes will be line-powered.
Example 1: solar panel, lead-acid battery sized for two weeks of
rain.
Example 2: vibration scavenger, 1mF tantalum capacitor.
Field devices have limited resources. Low-power, low-cost devices
have limited memory for storing route information. Typical field
devices will have a finite number of routes they can support for
their embedded sensor/actuator application and for forwarding other
devices packets in a mesh network slotted-link.
Users may strongly prefer that the same device have different
lifetime requirements in different locations. A sensor monitoring a
non-critical parameter in an easily accessed location may have a
lifetime requirement that is shorter and tolerate more statistical
variation than a mission-critical sensor in a hard-to-reach place
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that requires a plant shutdown in order to replace.
The routing algorithm MUST support node-constrained routing (e.g.
taking into account the existing energy state as a node constraint).
Node constraints include power and memory, as well as constraints
placed on the device by the user, such as battery life.
6. Broadcast/Multicast
Existing industrial plant applications do not use broadcast or
multicast addressing to communicate to field devices. Unicast
address support is sufficient. However wireless field devices with
communication controllers and protocol stacks will require control
and configuration, such as firmware downloading, that may benefit
from broadcast or multicast addressing.
The routing protocol SHOULD support broadcast or multicast
addressing.
7. Route Establishment Time
During network formation, installers with no networking skill must be
able to determine if their devices are "in the network" with
sufficient connectivity to perform their function. Installers will
have sufficient skill to provision the devices with a sample rate or
activity profile. The routing algorithm MUST find the appropriate
route(s) and report success or failure within several minutes, and
SHOULD report success or failure within tens of seconds.
Network connectivity in real deployments is always time varying, with
time constants from seconds to months. So long as the underlying
connectivity has not been compromised, this link churn should not
substantially affect network operation. The routing algorithm MUST
respond to normal link failure rates with routes that meet the
Service requirements (especially latency) throughout the routing
response. The routing algorithm SHOULD always be in the process of
optimizing the system in response to changing link statistics. The
routing algorithm MUST re-optimize the paths when field devices
change due to insertion, removal or failure, and this re-optimization
MUST not cause latencies greater than the specified constraints
(typically seconds to minutes).
8. Mobility
Various economic factors have contributed to a reduction of trained
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workers in the plant. The industry as a whole appears to be trying
to solve this problem with what is called the "wireless worker".
Carrying a PDA or something similar, this worker will be able to
accomplish more work in less time than the older, better-trained
workers that he or she replaces. Whether the premise is valid, the
use case is commonly presented: the worker will be wirelessly
connected to the plant IT system to download documentation,
instructions, etc., and will need to be able to connect "directly" to
the sensors and control points in or near the equipment on which he
or she is working. It is possible that this "direct" connection
could come via the normal L2Ns data collection network. This
connection is likely to require higher bandwidth and lower latency
than the normal data collection operation.
The routing protocol SHOULD support the wireless worker with fast
network connection times of a few of seconds, and low command and
response latencies to the plant behind the L2N access points, to
applications, and to field devices. The routing protocol SHOULD also
support the bandwidth allocation for bulk transfers between the field
device and the handheld device of the wireless worker. The routing
protocol SHOULD support walking speeds for maintaining network
connectivity as the handheld device changes position in the wireless
network.
Some field devices will be mobile. These devices may be located on
moving parts such as rotating components or they may be located on
vehicles such as cranes or fork lifts. The routing protocol SHOULD
support vehicular speeds of up to 35 kmph.
9. Manageability
The process and control industry is manpower constrained. The aging
demographics of plant personnel are causing a looming manpower
problem for industry across many markets. The goal for the
industrial networks is to have the installation process not require
any new skills for the plant personnel. The person would install the
wireless sensor or wireless actuator the same way the wired sensor or
wired actuator is installed, except the step to connect wire is
eliminated.
The routing protocol for L2Ns is expected to be easy to deploy and
manage. Because the number of field devices in a network is large,
provisioning the devices manually would not make sense. Therefore,
the routing protocol MUST support auto-provisioning of field devices.
The protocol also MUST support the distribution of configuration from
a centralized management controller if operator-initiated
configuration change is allowed.
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10. Security
Given that wireless sensor networks in industrial automation operate
in systems that have substantial financial and human safety
implications, security is of considerable concern. Levels of
security violation that are tolerated as a "cost of doing business"
in the banking industry are not acceptable when in some cases
literally thousands of lives may be at risk.
Industrial wireless device manufactures are specifying security at
the MAC layer and the transport layer. A shared key is used to
authenticate messages at the MAC layer. At the transport layer,
commands are encrypted with unique randomly-generated end-to-end
Session keys. HART7 and ISA100.11a are examples of security systems
for industrial wireless networks.
Industrial plants may not maintain the same level of physical
security for field devices that is associated with traditional
network sites such as locked IT centers. In industrial plants it
must be assumed that the field devices have marginal physical
security and the security system needs to have limited trust in them.
The routing protocol SHOULD place limited trust in the field devices
deployed in the plant network.
The routing protocol SHOULD compartmentalize the trust placed in
field devices so that a compromised field device does not destroy the
security of the whole network. The routing MUST be configured and
managed using secure messages and protocols that prevent outsider
attacks and limit insider attacks from field devices installed in
insecure locations in the plant.
11. IANA Considerations
This document includes no request to IANA.
12. Acknowledgements
Many thanks to Rick Enns and Chol Su Kang for their contributions.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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13.2. Informative References
[I-D.culler-rl2n-routing-reqs]
Vasseur, J. and D. Cullerot, "Routing Requirements for Low
Power And Lossy Networks",
draft-culler-rl2n-routing-reqs-01 (work in progress),
July 2007.
13.3. External Informative References
[HART] www.hartcomm.org, "Highway Addressable Remote Transducer",
a group of specifications for industrial process and
control devices administered by the HART Foundation".
[ISA100.11a]
ISA, "SP100.11 Working Group Draft Standard, Version 0.1",
December 2007.
Authors' Addresses
Kris Pister
Dust Networks
30695 Huntwood Ave.
Hayward, 94544
USA
Email: kpister@dustnetworks.com
Pascal Thubert
Cisco Systems, Inc
Village d'Entreprises Green Side - 400, Avenue de Roumanille
Sophia Antipolis, 06410
FRANCE
Email: pthubert@cisco.com
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