Networking Working Group J. Martocci, Ed.
Internet-Draft Johnson Controls Inc.
Intended status: Informational Pieter De Mil
Expires: June 2, 2010 Ghent University IBCN
W. Vermeylen
Arts Centre Vooruit
Nicolas Riou
Schneider Electric
December 2, 2009
Building Automation Routing Requirements in Low Power and Lossy
Networks
draft-ietf-roll-building-routing-reqs-08
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Abstract
The Routing Over Low power and Lossy network (ROLL) Working Group has
been chartered to work on routing solutions for Low Power and Lossy
networks (LLN) in various markets: Industrial, Commercial (Building),
Home and Urban networks. Pursuant to this effort, this document
defines the IPv6 routing requirements for building automation.
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 (RFC2119).
Table of Contents
1. Terminology....................................................4
2. Introduction...................................................4
3. Overview of Building Automation Networks.......................5
3.1. Introduction..............................................5
3.2. Building Systems Equipment................................7
3.2.1. Sensors/Actuators....................................7
3.2.2. Area Controllers.....................................7
3.2.3. Zone Controllers.....................................7
3.3. Equipment Installation Methods............................8
3.4. Device Density............................................8
3.4.1. HVAC Device Density..................................8
3.4.2. Fire Device Density..................................9
3.4.3. Lighting Device Density..............................9
3.4.4. Physical Security Device Density.....................9
4. Traffic Pattern...............................................10
5. Building Automation Routing Requirements......................11
5.1. Device and Network Commissioning.........................11
5.1.1. Zero-Configuration Installation.....................12
5.1.2. Local Testing.......................................12
5.1.3. Device Replacement..................................12
5.2. Scalability..............................................13
5.2.1. Network Domain......................................13
5.2.2. Peer-to-Peer Communication..........................13
5.3. Mobility.................................................13
5.3.1. Mobile Device Requirements..........................14
5.4. Resource Constrained Devices.............................14
5.4.1. Limited Memory Footprint on Host Devices............14
5.4.2. Limited Processing Power for Routers................15
5.4.3. Sleeping Devices....................................15
5.5. Addressing...............................................15
5.6. Manageability............................................16
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5.6.1. Diagnostics.........................................16
5.6.2. Route Tracking......................................17
5.7. Route Selection..........................................17
5.7.1. Route Cost..........................................17
5.7.2. Route Adaptation....................................17
5.7.3. Route Redundancy....................................17
5.7.4. Route Discovery Time................................18
5.7.5. Route Preference....................................18
5.7.6. Real-time Performance Measures......................18
5.7.7. Prioritized Routing.................................18
5.8. Security Requirements....................................18
5.8.1. Authentication......................................19
5.8.2. Encryption..........................................19
5.8.3. Disparate Security Policies.........................20
5.8.4. Routing Security Policies To Sleeping Devices.......20
6. Security Considerations.......................................20
7. IANA Considerations...........................................21
8. Acknowledgments...............................................21
9. References....................................................21
9.1. Normative References.....................................21
9.2. Informative References...................................21
10. Appendix A: Additional Building Requirements.................21
10.1. Additional Commercial Product Requirements..............22
10.1.1. Wired and Wireless Implementations.................22
10.1.2. World-wide Applicability...........................22
10.2. Additional Installation and Commissioning Requirements..22
10.2.1. Unavailability of an IP network....................22
10.3. Additional Network Requirements.........................22
10.3.1. TCP/UDP............................................22
10.3.2. Interference Mitigation............................22
10.3.3. Packet Reliability.................................22
10.3.4. Merging Commissioned Islands.......................23
10.3.5. Adjustable Routing Table Sizes.....................23
10.3.6. Automatic Gain Control.............................23
10.3.7. Device and Network Integrity.......................23
10.4. Additional Performance Requirements.....................23
10.4.1. Data Rate Performance..............................23
10.4.2. Firmware Upgrades..................................23
10.4.3. Route Persistence..................................24
11. Authors' Addresses...........................................25
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1. Terminology
For description of the terminology used in this specification, please
see [I-D.ietf-roll-terminology].
2. Introduction
The Routing Over Low power and Lossy network (ROLL) Working Group has
been chartered to work on routing solutions for Low Power and Lossy
networks (LLN) in various markets: Industrial, Commercial (Building),
Home and Urban networks. Pursuant to this effort, this document
defines the IPv6 routing requirements for building automation.
Commercial buildings have been fitted with pneumatic and subsequently
electronic communication routes connecting sensors to their
controllers for over one hundred years. Recent economic and
technical advances in wireless communication allow facilities to
increasingly utilize a wireless solution in lieu of a wired solution;
thereby reducing installation costs while maintaining highly reliant
communication.
The cost benefits and ease of installation of wireless sensors allow
customers to further instrument their facilities with additional
sensors; providing tighter control while yielding increased energy
savings.
Wireless solutions will be adapted from their existing wired
counterparts in many of the building applications including, but not
limited to Heating, Ventilation, and Air Conditioning (HVAC),
Lighting, Physical Security, Fire, and Elevator/Lift systems. These
devices will be developed to reduce installation costs; while
increasing installation and retrofit flexibility, as well as
increasing the sensing fidelity to improve efficiency and building
service quality.
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Sensing devices may be battery-less; battery or mains powered.
Actuators and area controllers will be mains powered. Due to
building code and/or device density (e.g., equipment room), it is
envisioned that a mix of wired and wireless sensors and actuators
will be deployed within a building.
Facility Management Systems (FMS) are deployed in a large set of
vertical markets including universities; hospitals; government
facilities; Kindergarten through High School (K-12); pharmaceutical
manufacturing facilities; and single-tenant or multi-tenant office
buildings. These buildings range in size from 100K sqft structures (5
story office buildings), to 1M sqft skyscrapers (100 story
skyscrapers) to complex government facilities such as the Pentagon.
The described topology is meant to be the model to be used in all
these types of environments, but clearly must be tailored to the
building class, building tenant and vertical market being served.
Section 3 describes the necessary background to understand the
context of building automation including the sensor, actuator, area
controller and zone controller layers of the topology; typical device
density; and installation practices.
Section 4 defines the traffic flow of the aforementioned sensors,
actuators and controllers in commercial buildings.
Section 5 defines the full set of IPv6 routing requirements for
commercial buildings.
Appendix A documents important commercial building requirements that
are out of scope for routing yet will be essential to the final
acceptance of the protocols used within the building.
Sections 3 and Appendix A are mainly included for educational
purposes.
The expressed aim of this document is to provide the set of IPv6
routing requirements for LLNs in buildings as described in Section 5.
3. Overview of Building Automation Networks
3.1. Introduction
To understand the network systems requirements of a facility
management system in a commercial building, this document uses a
framework to describe the basic functions and composition of the
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system. An FMS is a hierarchical system of sensors, actuators,
controllers and user interface devices that interoperate to provide a
safe and comfortable environment while constraining energy costs.
An FMS may is divided functionally across alike, but different
building subsystems such as heating, ventilation and air conditioning
(HVAC); Fire; Security; Lighting; Shutters and Elevator/Lift control
systems as denoted in Figure 1.
Much of the makeup of an FMS is optional and installed at the behest
of the customer. Sensors and actuators have no standalone
functionality. All other devices support partial or complete
standalone functionality. These devices can optionally be tethered
to form a more cohesive system. The customer requirements dictate
the level of integration within the facility. This architecture
provides excellent fault tolerance since each node is designed to
operate in an independent mode if the higher layers are unavailable.
+------+ +-----+ +------+ +------+ +------+ +------+
Bldg App'ns | | | | | | | | | | | |
| | | | | | | | | | | |
Building Cntl | | | | | S | | L | | S | | E |
| | | | | E | | I | | H | | L |
Area Control | H | | F | | C | | G | | U | | E |
| V | | I | | U | | H | | T | | V |
Zone Control | A | | R | | R | | T | | T | | A |
| C | | E | | I | | I | | E | | T |
Actuators | | | | | T | | N | | R | | O |
| | | | | Y | | G | | S | | R |
Sensors | | | | | | | | | | | |
+------+ +-----+ +------+ +------+ +------+ +------+
Figure 1: Building Systems and Devices
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3.2. Building Systems Equipment
3.2.1. Sensors/Actuators
As Figure 1 indicates an FMS may be composed of many functional
stacks or silos that are interoperably woven together via Building
Applications. Each silo has an array of sensors that monitor the
environment and actuators that effect the environment as determined
by the upper layers of the FMS topology. The sensors typically are
at the edge of the network structure providing environmental data
into the system. The actuators are the sensors' counterparts
modifying the characteristics of the system based on the sensor data
and the applications deployed.
3.2.2. Area Controllers
An area describes a small physical locale within a building,
typically a room. HVAC (temperature and humidity) and Lighting (room
lighting, shades, solar loads) vendors often times deploy area
controllers. Area controls are fed by sensor inputs that monitor the
environmental conditions within the room. Common sensors found in
many rooms that feed the area controllers include temperature,
occupancy, lighting load, solar load and relative humidity. Sensors
found in specialized rooms (such as chemistry labs) might include air
flow, pressure, CO2 and CO particle sensors. Room actuation includes
temperature setpoint, lights and blinds/curtains.
3.2.3. Zone Controllers
Zone Control supports a similar set of characteristics as the Area
Control albeit to an extended space. A zone is normally a logical
grouping or functional division of a commercial building. A zone may
also coincidentally map to a physical locale such as a floor.
Zone Control may have direct sensor inputs (smoke detectors for
fire), controller inputs (room controllers for air-handlers in HVAC)
or both (door controllers and tamper sensors for security). Like
area/room controllers, zone controllers are standalone devices that
operate independently or may be attached to the larger network for
more synergistic control.
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3.3. Equipment Installation Methods
Commercial controllers have been traditionally deployed in a facility
using serial media following the EIA-485 electrical standard
operating nominally at 76800 baud with distances upward to 15000
feet. EIA-485 is a multi-drop media allowing upwards to 255 devices
to be connected to a single trunk.
Wired FMS installation is a multifaceted procedure depending on the
extent of the system and the software interoperability requirement.
However, at the sensor/actuator and controller level, the procedure
is typically a two or three step process.
The installer arrives on-site during the construction of the building
prior to drywall and ceiling installation. The installer allocates
wall space installs the controller and sensor networks. The Building
Controllers and Enterprise network are not normally installed until
months later. The electrician completes the task by running a
verification procedure that verifies proper wired or wireless
continuity between the devices.
Months later, the higher order controllers are installed, programmed
and commissioned together with the previously installed sensors,
actuators and controllers. In most cases the IP network is still not
in place. The Building Controllers are completely commissioned using
a crossover cable or a temporary IP switch together with static IP
addresses.
After occupancy, when the IP network is operational, the FMS often
connects to the enterprise network. Dynamic IPs replace static IPs.
VLANs oft time segregate the facility and IT systems. For multi-
building multi-site facilities VPNs, NATs and firewalls are also
introduced.
3.4. Device Density
Device density differs depending on the application and as dictated
by the local building code requirements. The following sections
detail typical installation densities for different applications.
3.4.1. HVAC Device Density
HVAC room applications typically have sensors/actuators and
controllers spaced about 50ft apart. In most cases there is a 3:1
ratio of sensors/actuators to controllers. That is, for each room
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there is an installed temperature sensor, flow sensor and damper
actuator for the associated room controller.
HVAC equipment room applications are quite different. An air handler
system may have a single controller with upwards to 25 sensors and
actuators within 50 ft of the air handler. A chiller or boiler is
also controlled with a single equipment controller instrumented with
25 sensors and actuators. Each of these devices would be
individually addressed since the devices are mandated or optional as
defined by the specified HVAC application. Air handlers typically
serve one or two floors of the building. Chillers and boilers may be
installed per floor, but many times service a wing, building or the
entire complex via a central plant.
These numbers are typical. In special cases, such as clean rooms,
operating rooms, pharmaceuticals and labs, the ratio of sensors to
controllers can increase by a factor of three. Tenant installations
such as malls would opt for packaged units where much of the sensing
and actuation is integrated into the unit. Here a single device
address would serve the entire unit.
3.4.2. Fire Device Density
Fire systems are much more uniformly installed with smoke detectors
installed about every 50 feet. This is dictated by local building
codes. Fire pull boxes are installed uniformly about every 150 feet.
A fire controller will service a floor or wing. The fireman's fire
panel will service the entire building and typically is installed in
the atrium.
3.4.3. Lighting Device Density
Lighting is also very uniformly installed with ballasts installed
approximately every 10 feet. A lighting panel typically serves 48 to
64 zones. Wired systems tether many lights together into a single
zone. Wireless systems configure each fixture independently to
increase flexibility and reduce installation costs.
3.4.4. Physical Security Device Density
Security systems are non-uniformly oriented with heavy density near
doors and windows and lighter density in the building interior space.
The recent influx of interior and perimeter camera systems is
increasing the security footprint. These cameras are atypical
endpoints requiring upwards to 1 megabit/second (Mbit/s) data rates
per camera as contrasted by the few Kbits/s needed by most other FMS
sensing equipment. Previously, camera systems had been deployed on
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proprietary wired high speed network. More recent implementations
utilize wired or wireless IP cameras integrated to the enterprise
LAN.
4. Traffic Pattern
The independent nature of the automation subsystems within a building
plays heavy onto the network traffic patterns. Much of the real-time
sensor environmental data and actuator control stays within the local
LLN environment; while alarming and other event data will percolate
to higher layers.
Each sensor in the LLN unicasts P2P about 200 bytes of sensor data to
its associated controller each minute and expects an application
acknowledgment unicast returned from the destination. Each
controller unicasts messages at a nominal rate of 6kB/min to peer or
supervisory controllers. 30% of each node's packets are destined for
other nodes within the LLN. 70% of each node's packets are destined
for an aggregation device (MP2P)and routed off the LLN. These
messages also require a unicast acknowledgment from the destination.
The above values assume direct node-to-node communication; meshing
and error retransmissions are not considered.
Multicasts (P2MP) to all nodes in the LLN occur for node and object
discovery when the network is first commissioned. This data is
typically a one-time bind that is henceforth persisted. Lighting
systems will also readily use multicasting during normal operations
to turn banks of lights 'on' and 'off' simultaneously.
FMS systems may be either polled or event based. Polled data systems
will generate a uniform and constant packet load on the network.
Polled architectures, however have proven not scalable. Today, most
vendors have developed event based systems which pass data on event.
These systems are highly scalable and generate low data on the
network at quiescence. Unfortunately, the systems will generate a
heavy load on startup since all initial sensor data must migrate to
the controller level. They also will generate a temporary but heavy
load during firmware upgrades. This latter load can normally be
mitigated by performing these downloads during off-peak hours.
Devices will also need to reference peers periodically for sensor
data or to coordinate operation across systems. Normally, though,
data will migrate from the sensor level upwards through the local,
area then supervisory level. Traffic bottlenecks will typically form
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at the funnel point from the area controllers to the supervisory
controllers.
Initial system startup after a controlled outage or unexpected power
failure puts tremendous stress on the network and on the routing
algorithms. An FMS system is comprised of a myriad of control
algorithms at the room, area, zone, and enterprise layers. When
these control algorithms are at quiescence, the real-time data rate
is small and the network will not saturate. An overall network
traffic load of 6KBps is typical at quiescence. However, upon any
power loss, the control loops and real-time data quickly atrophy. A
short power disruption of only ten minutes may have a long-term
deleterious impact on the building control systems taking many hours
to regain proper control. Control application that cannot handle
this level of disruption (e.g., Hospital Operating Rooms) must be
fitted with a secondary power source.
Power disruptions are unexpected and in most cases will immediately
impact lines-powered devices. Power disruptions however, are
transparent to battery powered devices. These devices will continue
to attempt to access the LLN during the outage. Battery powered
devices designed to buffer data that has not been delivered will
further stress the network operation when power returns.
Upon restart, lines-powered devices will naturally dither due to
primary equipment delays or variance in the device self-tests.
However, most lines-powered devices will be ready to access the LLN
network within 10 seconds of power up. Empirical testing indicates
that routes acquired during startup will tend to be very oblique
since the available neighbor lists are incomplete. This demands an
adaptive routing protocol to allow for route optimization as the
network stabilizes.
5. Building Automation Routing Requirements
Following are the building automation routing requirements for
networks used to integrate building sensor, actuator and control
products. These requirements are written not presuming any
preordained network topology, physical media (wired) or radio
technology (wireless).
5.1. Device and Network Commissioning
Building control systems typically are installed and tested by
electricians having little computer knowledge and no network
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communication knowledge whatsoever. These systems are often
installed during the building construction phase before the drywall
and ceilings are in place. For new construction projects, the
building enterprise IP network is not in place during installation of
the building control system. For retrofit applications, the
installer will still operate independently from the IP network so as
not to affect network operations during the installation phase.
In traditional wired systems correct operation of a light
switch/ballast pair was as simple as flipping on the light switch.
In wireless applications, the tradesperson has to assure the same
operation, yet be sure the operation of the light switch is
associated to the proper ballast.
System level commissioning will later be deployed using a more
computer savvy person with access to a commissioning device (e.g., a
laptop computer). The completely installed and commissioned
enterprise IP network may or may not be in place at this time.
Following are the installation routing requirements.
5.1.1. Zero-Configuration Installation
It MUST be possible to fully commission network devices without
requiring any additional commissioning device (e.g., laptop). From
the ROLL perspective, zero-configuration means that a node can obtain
an address and join the network on its own, without human
intervention.
5.1.2. Local Testing
During installation, the room sensors, actuators and controllers
SHOULD be able to route packets amongst themselves and to any other
device within the LLN without requiring any additional routing
infrastructure or routing configuration.
5.1.3. Device Replacement
To eliminate the need to reconfigure the application upon replacing a
failed device in the LLN; the replaced device must be able to
advertise the old IP address of the failed device in addition to its
new IP address. The routing protocols MUST support hosts and routers
that advertise multiple IPv6 addresses.
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5.2. Scalability
Building control systems are designed for facilities from 50000 sq.
ft. to 1M+ sq. ft. The networks that support these systems must
cost-effectively scale accordingly. In larger facilities
installation may occur simultaneously on various wings or floors, yet
the end system must seamlessly merge. Following are the scalability
requirements.
5.2.1. Network Domain
The routing protocol MUST be able to support networks with at least
2000 nodes where 1000 nodes would act as routers and the other 1000
nodes would be hosts. Subnetworks (e.g., rooms, primary equipment)
within the network must support upwards to 255 sensors and/or
actuators.
5.2.2. Peer-to-Peer Communication
The data domain for commercial FMS systems may sprawl across a vast
portion of the physical domain. For example, a chiller may reside in
the facility's basement due to its size, yet the associated cooling
towers will reside on the roof. The cold-water supply and return
pipes serpentine through all the intervening floors. The feedback
control loops for these systems require data from across the
facility.
A network device MUST be able to communicate in a end-to-end manner
with any other device on the network. Thus, the routing protocol MUST
provide routes between arbitrary hosts within the appropriate
administrative domain.
5.3. Mobility
Most devices are affixed to walls or installed on ceilings within
buildings. Hence the mobility requirements for commercial buildings
are few. However, in wireless environments location tracking of
occupants and assets is gaining favor. Asset tracking applications,
such as tracking capital equipment (e.g., wheel chairs) in medical
facilities, require monitoring movement with granularity of a minute.
This soft real-time performance requirement is reflected in the
performance requirements below.
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5.3.1. Mobile Device Requirements
To minimize network dynamics, mobile devices should not be allowed to
act as forwarding devices (routers) for other devices in the LLN.
Network configuration should allow devices to be configured as
routers or hosts.
5.3.1.1. Device Mobility within the LLN
An LLN typically spans a single floor in a commercial building.
Mobile devices may move within this LLN. For example, a wheel chair
may be moved from one room on the floor to another room on the same
floor.
A mobile LLN device that moves within the confines of the same LLN
SHOULD reestablish end-to-end communication to a fixed device also in
the LLN within 5 seconds after it ceases movement. The LLN network
convergence time should be less than 10 seconds once the mobile
device stops moving.
5.3.1.2. Device Mobility across LLNs
A mobile device may move across LLNs, such as a wheel chair being
moved to a different floor.
A mobile device that moves outside its original LLN SHOULD
reestablish end-to-end communication to a fixed device also in the
new LLN within 10 seconds after the mobile device ceases movement.
The network convergence time should be less than 20 seconds once the
mobile device stops moving.
5.4. Resource Constrained Devices
Sensing and actuator device processing power and memory may be 4
orders of magnitude less (i.e., 10,000x) than many more traditional
client devices on an IP network. The routing mechanisms must
therefore be tailored to fit these resource constrained devices.
5.4.1. Limited Memory Footprint on Host Devices
The software size requirement for non-routing devices (e.g., sleeping
sensors and actuators) SHOULD be implementable in 8-bit devices with
no more than 128KB of memory.
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5.4.2. Limited Processing Power for Routers
The software size requirements for routing devices (e.g., room
controllers) SHOULD be implementable in 8-bit devices with no more
than 256KB of flash memory.
5.4.3. Sleeping Devices
Sensing devices will, in some cases, utilize battery power or energy
harvesting techniques for power and will operate mostly in a sleep
mode to maintain power consumption within a modest budget. The
routing protocol MUST take into account device characteristics such
as power budget.
Typically, sensor battery life (2000mAh) needs to extend for at least
5 years when the device is transmitting its data (200 octets) once
per minute over a low power transceiver (25ma) and expecting an
application acknowledgment. In this case the transmitting device
must leave its receiver in a high powered state awaiting the return
of the application ACK. To minimize this latency, a highly efficient
routing protocol that minimizes hops and hence end-to-end
communication is required. The routing protocol MUST take into
account node properties such as 'Low-powered node' which produce
efficient low latency routes that minimize radio 'on' time for these
devices.
Sleeping devices MUST be able to receive inbound data. Messages sent
to battery powered nodes MUST be buffered and retried by the last hop
router for a period of at least 20 seconds when the destination node
is currently in its sleep cycle.
5.5. Addressing
Facility Management systems require different communication schemes
to solicit or post network information. Multicasts or anycasts need
be used to resolve unresolved references within a device when the
device first joins the network.
As with any network communication, multicasting should be minimized.
This is especially a problem for small embedded devices with limited
network bandwidth. Multicasts are typically used for network joins
and application binding in embedded systems. Routing MUST support
anycast, unicast, and multicast.
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5.6. Manageability
As previously noted in Clause 3.3, installation of LLN devices
follows a bottoms-up work flow. Edge devices are installed first and
tested for communication and application integrity. These devices
are then aggregated into islands, then LLNs and later affixed onto
the enterprise network.
The need for diagnostics most often occurs during the installation
and commissioning phase; although at times diagnostic information may
be requested during normal operation. Battery powered wireless
devices typically will have a self diagnostic mode that can be
initiated via a button press on the device. The device will display
its link status and/or end-to-end connectivity when the button is
depressed. Lines-powered devices will continuously display
communication status via a bank of LEDs; possibly denoting signal
strength and end-to-end application connectivity.
The local diagnostics noted above often times are suitable for
defining room level networks. However, as these devices aggregate,
system level diagnostics may need to be executed to ameliorate route
vacillation, excessive hops, communication retries and/or network
bottlenecks.
On operational networks, due to the mission critical nature of the
application, the LLN devices will be temporally monitored by the
higher layers to assure communication integrity is maintained.
Failure to maintain this communication will result in an alarm being
forwarded to the enterprise network from the monitoring node for
analysis and remediation.
In addition to the initial installation and commissioning of the
system, it is equally important for the ongoing maintenance of the
system to be simple and inexpensive. This implies a straightforward
device swap when a failed device is replaced as noted in Clause
5.1.3.
5.6.1. Diagnostics
To improve diagnostics, the routing protocol SHOULD be able to be
placed in and out of 'verbose' mode. Verbose mode is a temporary
debugging mode that provides additional communication information
including at least total number of routed packets sent and received,
number of routing failures (no route available), neighbor table
members, and routing table entries. The data provided in verbose
mode should be sufficient that a network connection graph could be
constructed and maintained by the monitoring node.
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Diagnostic data should be kept by the routers continuously and be
available for solicitation at anytime by any other node on the
internetwork. Verbose mode will be activated/deactivated via either
a unicast, multicast or other means. Devices having available
resources may elect to support verbose mode continually.
5.6.2. Route Tracking
Route diagnostics SHOULD be supported providing information such as
route quality; number of hops; available alternate active routes with
associated costs. Route quality is the relative measure of
'goodness' of the selected source to destination route as compared to
alternate routes. This composite value may be measured as a function
of hop count, signal strength, available power, existing active
routes or any other criteria deemed by ROLL as the route cost
differentiator.
5.7. Route Selection
Route selection determines reliability and quality of the
communication among the devices by optimizing routes over time and
resolving any nuances developed at system startup when nodes are
asynchronously adding themselves to the network.
5.7.1. Route Cost
The routing protocol MUST support a metric of route quality and
optimize selection according to such metrics within constraints
established for links along the routes. These metrics SHOULD reflect
metrics such as signal strength, available bandwidth, hop count,
energy availability and communication error rates.
5.7.2. Route Adaptation
Communication routes MUST be adaptive and converge toward optimality
of the chosen metric (e.g., signal quality, hop count) in time.
5.7.3. Route Redundancy
The routing layer SHOULD be configurable to allow secondary and
tertiary routes to be established and used upon failure of the
primary route.
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5.7.4. Route Discovery Time
Mission critical commercial applications (e.g., Fire, Security)
require reliable communication and guaranteed end-to-end delivery of
all messages in a timely fashion. Application layer time-outs must
be selected judiciously to cover anomalous conditions such as lost
packets and/or route discoveries; yet not be set too large to over
damp the network response. If route discovery occurs during packet
transmission time (proactive routing), it SHOULD NOT add more than
120ms of latency to the packet delivery time.
5.7.5. Route Preference
The routing protocol SHOULD allow for the support of manually
configured static preferred routes.
5.7.6. Real-time Performance Measures
A node transmitting a 'request with expected reply' to another node
must send the message to the destination and receive the response in
not more than 120 ms. This response time should be achievable with 5
or less hops in each direction. This requirement assumes network
quiescence and a negligible turnaround time at the destination node.
5.7.7. Prioritized Routing
Network and application packet routing prioritization must be
supported to assure that mission critical applications (e.g., Fire
Detection) cannot be deferred while less critical applications access
the network. The routing protocol MUST be able to provide routes
with different characteristics, also referred to as "QoS" routing.
5.8. Security Requirements
Security policies, especially wireless encryption and device
authentication needs to be considered, especially with concern to the
impact on the processing capabilities and additional latency incurred
on the sensors, actuators and controllers.
FMS systems are typically highly configurable in the field and hence
the security policy is most often dictated by the type of building to
which the FMS is being installed. Single tenant owner occupied
office buildings installing lighting or HVAC control are candidates
for implementing a low level of security on the LLN. Antithetically,
military or pharmaceutical facilities require strong security
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policies. As noted in the installation procedures, security policies
must be facile to allow for no security policy during the
installation phase (prior to building occupancy), yet easily raise
the security level network wide during the commissioning phase of the
system.
5.8.1. Authentication
Authentication SHOULD be optional on the LLN. Authentication SHOULD
be fully configurable on-site. Authentication policy and updates MUST
be routable over-the-air. Authentication SHOULD occur upon joining
or rejoining a network. However, once authenticated devices SHOULD
NOT need to reauthenticate with any other devices in the LLN.
Packets may need authentication at the source and destination nodes,
however, packets routed through intermediate hops should not need
reauthentication at each hop.
These requirements mean that at least one LLN routing protocol
solution specification MUST include support for authentication.
5.8.2. Encryption
5.8.2.1. Encryption Types
Data encryption of packets MUST be supported by all protocol solution
specifications. Support can be provided by use of either a network
wide key and/or an application key. The network key would apply to
all devices in the LLN. The application key would apply to a subset
of devices on the LLN.
The network key and application keys would be mutually exclusive.
The routing protocol MUST allow routing a packet encrypted with an
application key through forwarding devices without requiring each
node in the route to have the application key.
5.8.2.2. Packet Encryption
The encryption policy MUST support both encryption of the payload
only or of the entire packet. Payload only encryption would
eliminate the decryption/re-encryption overhead at every hop
providing more real-time performance.
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5.8.3. Disparate Security Policies
Due to the limited resources of an LLN, the security policy defined
within the LLN MUST be able to differ from that of the rest of the IP
network within the facility yet packets MUST still be able to route
to or through the LLN from/to these networks.
5.8.4. Routing Security Policies To Sleeping Devices
The routing protocol MUST gracefully handle routing temporal security
updates (e.g., dynamic keys) to sleeping devices on their 'awake'
cycle to assure that sleeping devices can readily and efficiently
access the network.
6. Security Considerations
The requirements placed on the LLN routing protocol in order to
provide the correct level of security support are presented in
Section 5.8.
LLNs deployed in a building environment may be entirely isolated from
other networks, attached to normal IP networks within the building
yet physically disjoint from the wider Internet, or connected either
directly or through other IP networks to the Internet. Additionally,
even where no wired connectivity exists out of the building, the use
of wireless infrastructure within the building means that physical
connectivity to the LLN is possible for an attacker.
Therefore, it is important that any routing protocol solution
designed to meet the requirements included in this document addresses
the security features requirements described in Section 5.8.
Implementations of these protocols will be required in the protocol
specifications to provide the level of support indicated in Section
5.8, and will be encouraged to make the support flexibly configurable
to enable an operator to make a judgment of the level of security
that they want to deploy at any time.
As noted in Section 5.8, use/deployment of the different security
features is intended to be optional. This means that, although the
protocols developed must conform to the requirements specified, the
operator is free to determine the level of risk and the trade-offs
against performance. An implementation must not make those choices on
behalf of the operator by avoiding implementing any mandatory-to-
implement security features.
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This informational requirements specification introduces no new
security concerns.
7. IANA Considerations
This document includes no request to IANA.
8. Acknowledgments
In addition to the authors; JP. Vasseur, David Culler, Ted Humpal and
Zach Shelby are gratefully acknowledged for their contributions to
this document.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[I-D.ietf-roll-terminology]Vasseur, JP., "Terminology in Low power
And Lossy Networks", draft-ietf-roll-terminology-00 (work in
progress), October 2008.
10. Appendix A: Additional Building Requirements
Appendix A contains additional building requirements that were deemed
out of scope for ROLL, yet provided ancillary substance for the
reader.
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10.1. Additional Commercial Product Requirements
10.1.1. Wired and Wireless Implementations
Vendors will likely not develop a separate product line for both
wired and wireless networks. Hence, the solutions set forth must
support both wired and wireless implementations.
10.1.2. World-wide Applicability
Wireless devices must be supportable unlicensed bands.
10.2. Additional Installation and Commissioning Requirements
10.2.1. Unavailability of an IP network
Product commissioning must be performed by an application engineer
prior to the installation of the IP network (e.g., switches, routers,
DHCP, DNS).
10.3. Additional Network Requirements
10.3.1. TCP/UDP
Connection based and connectionless services must be supported
10.3.2. Interference Mitigation
The network must automatically detect interference and seamlessly
migrate the network hosts channel to improve communication. Channel
changes and nodes response to the channel change must occur within 60
seconds.
10.3.3. Packet Reliability
In building automation, it is required for the network to meet the
following minimum criteria:
< 1% MAC layer errors on all messages; After no more than three
retries
< .1% Network layer errors on all messages;
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After no more than three additional retries;
< 0.01% Application layer errors on all messages.
Therefore application layer messages will fail no more than once
every 100,000 messages.
10.3.4. Merging Commissioned Islands
Subsystems are commissioned by various vendors at various times
during building construction. These subnetworks must seamlessly
merge into networks and networks must seamlessly merge into
internetworks since the end user wants a holistic view of the system.
10.3.5. Adjustable Routing Table Sizes
The routing protocol must allow constrained nodes to hold an
abbreviated set of routes. That is, the protocol should not mandate
that the node routing tables be exhaustive.
10.3.6. Automatic Gain Control
For wireless implementations, the device radios should incorporate
automatic transmit power regulation to maximize packet transfer and
minimize network interference regardless of network size or density.
10.3.7. Device and Network Integrity
Commercial Building devices must all be periodically scanned to
assure that the device is viable and can communicate data and alarm
information as needed. Router should maintain previous packet flow
information temporally to minimize overall network overhead.
10.4. Additional Performance Requirements
10.4.1. Data Rate Performance
An effective data rate of 20kbits/s is the lowest acceptable
operational data rate acceptable on the network.
10.4.2. Firmware Upgrades
To support high speed code downloads, routing should support
transports that provide parallel downloads to targeted devices yet
guarantee packet delivery. In cases where the spatial position of
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the devices requires multiple hops, the algorithm should recurse
through the network until all targeted devices have been serviced.
Devices receiving a download may cease normal operation, but upon
completion of the download must automatically resume normal
operation.
10.4.3. Route Persistence
To eliminate high network traffic in power-fail or brown-out
conditions previously established routes should be remembered and
invoked prior to establishing new routes for those devices reentering
the network.
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11. Authors' Addresses
Jerry Martocci
Johnson Control
507 E. Michigan Street
Milwaukee, Wisconsin, 53202
USA
Phone: +1 414 524 4010
Email: jerald.p.martocci@jci.com
Nicolas Riou
Schneider Electric
Technopole 38TEC T3
37 quai Paul Louis Merlin
38050 Grenoble Cedex 9
France
Phone: +33 4 76 57 66 15
Email: nicolas.riou@fr.schneider-electric.com
Pieter De Mil
Ghent University - IBCN
G. Crommenlaan 8 bus 201
Ghent 9050
Belgium
Phone: +32 9331 4981
Fax: +32 9331 4899
Email: pieter.demil@intec.ugent.be
Wouter Vermeylen
Arts Centre Vooruit
Ghent 9000
Belgium
Email: wouter@vooruit.be
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