RFC 5867

Internet Engineering Task Force (IETF)                  J. Martocci, Ed.
Request for Comments: 5867                         Johnson Controls Inc.
Category: Informational                                        P. De Mil
ISSN: 2070-1721                                  Ghent University - IBCN
                                                                 N. Riou
                                                      Schneider Electric
                                                            W. Vermeylen
                                                     Arts Centre Vooruit
                                                               June 2010

                Building Automation Routing Requirements
                    in Low-Power and Lossy Networks


   The Routing Over Low-Power and Lossy (ROLL) networks Working Group
   has been chartered to work on routing solutions for Low-Power and
   Lossy Networks (LLNs) in various markets: industrial, commercial
   (building), home, and urban networks.  Pursuant to this effort, this
   document defines the IPv6 routing requirements for building

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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RFC 5867    Building Automation Routing Requirements in LLNs   June 2010

Copyright Notice

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RFC 5867    Building Automation Routing Requirements in LLNs   June 2010

Table of Contents

   1. Introduction ....................................................4
   2. Terminology .....................................................6
      2.1. Requirements Language ......................................6
   3. Overview of Building Automation Networks ........................6
      3.1. Introduction ...............................................6
      3.2. Building Systems Equipment .................................7
           3.2.1. Sensors/Actuators ...................................7
           3.2.2. Area Controllers ....................................7
           3.2.3. Zone Controllers ....................................8
      3.3. Equipment Installation Methods .............................8
      3.4. Device Density .............................................9
           3.4.1. HVAC Device Density .................................9
           3.4.2. Fire Device Density .................................9
           3.4.3. Lighting Device Density ............................10
           3.4.4. Physical Security Device Density ...................10
   4. Traffic Pattern ................................................10
   5. Building Automation Routing Requirements .......................12
      5.1. Device and Network Commissioning ..........................12
           5.1.1. Zero-Configuration Installation ....................12
           5.1.2. Local Testing ......................................12
           5.1.3. Device Replacement .................................13
      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 ..............................15
           5.4.1. Limited Memory Footprint on Host Devices ...........15
           5.4.2. Limited Processing Power for Routers ...............15
           5.4.3. Sleeping Devices ...................................15
      5.5. Addressing ................................................16
      5.6. Manageability .............................................16
           5.6.1. Diagnostics ........................................17
           5.6.2. Route Tracking .....................................17
      5.7. Route Selection ...........................................17
           5.7.1. Route Cost .........................................17
           5.7.2. Route Adaptation ...................................18
           5.7.3. Route Redundancy ...................................18
           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

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      5.8. Security Requirements .....................................19
           5.8.1. Building Security Use Case .........................19
           5.8.2. Authentication .....................................20
           5.8.3. Encryption .........................................20
           5.8.4. Disparate Security Policies ........................21
           5.8.5. Routing Security Policies to Sleeping Devices ......21
   6. Security Considerations ........................................21
   7. Acknowledgments ................................................22
   8. References .....................................................22
      8.1. Normative References ......................................22
      8.2. Informative References ....................................22
   Appendix A. Additional Building Requirements ......................23
      A.1. Additional Commercial Product Requirements ................23
           A.1.1. Wired and Wireless Implementations .................23
           A.1.2. World-Wide Applicability ...........................23
      A.2. Additional Installation and Commissioning Requirements ....23
           A.2.1. Unavailability of an IP Network ....................23
      A.3. Additional Network Requirements ...........................23
           A.3.1. TCP/UDP ............................................23
           A.3.2. Interference Mitigation ............................23
           A.3.3. Packet Reliability .................................24
           A.3.4. Merging Commissioned Islands .......................24
           A.3.5. Adjustable Routing Table Sizes .....................24
           A.3.6. Automatic Gain Control .............................24
           A.3.7. Device and Network Integrity .......................24
      A.4. Additional Performance Requirements .......................24
           A.4.1. Data Rate Performance ..............................24
           A.4.2. Firmware Upgrades ..................................25
           A.4.3. Route Persistence ..................................25

1.  Introduction

   The Routing Over Low-Power and Lossy (ROLL) networks Working Group
   has been chartered to work on routing solutions for Low-Power and
   Lossy Networks (LLNs) in various markets: industrial, commercial
   (building), home, and urban networks.  Pursuant to this effort, this
   document defines the IPv6 routing requirements for building

   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

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   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

   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.

   Sensing devices may be battery-less, battery-powered, 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.

   Building management systems (BMSs) 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-sq.-ft.
   structures (5-story office buildings), to 1M-sq.-ft. 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 of these types of environments but clearly must be tailored to
   the building class, building tenant, and vertical market being

   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.

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RFC 5867    Building Automation Routing Requirements in LLNs   June 2010

   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.

   Section 3 and Appendix A are mainly included for educational

   The expressed aim of this document is to provide the set of IPv6
   routing requirements for LLNs in buildings, as described in
   Section 5.

2.  Terminology

   For a description of the terminology used in this specification,
   please see [ROLL-TERM].

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Overview of Building Automation Networks

3.1.  Introduction

   To understand the network systems requirements of a building
   management system in a commercial building, this document uses a
   framework to describe the basic functions and composition of the
   system.  A BMS 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.

   A BMS is divided functionally across different but interrelated
   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 a BMS 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.

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RFC 5867    Building Automation Routing Requirements in LLNs   June 2010

                 +------+ +-----+ +------+ +------+ +------+ +------+

   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

3.2.  Building Systems Equipment

3.2.1.  Sensors/Actuators

   As Figure 1 indicates, a BMS 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 modify the environment, as determined
   by the upper layers of the BMS topology.  The sensors typically are
   at the edge of the network structure, providing environmental data
   for 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 oftentimes deploy area
   controllers.  Area controllers are fed by sensor inputs that monitor

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   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, and CO2 and CO particle sensors.  Room actuation
   includes temperature setpoint, lights, and blinds/curtains.

3.2.3.  Zone Controllers

   Zone controllers support a similar set of characteristics to area
   controllers, albeit for 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

   Zone controllers 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.

3.3.  Equipment Installation Methods

   A BMS is installed very differently from most other IT networks.  IT
   networks are typically installed as an overlay onto the existing
   environment and are installed from the inside out.  That is, the
   network wiring infrastructure is installed; the switches, routers,
   and servers are connected and made operational; and finally, the
   endpoints (e.g., PCs, VoIP phones) are added.

   BMSs, on the other hand, are installed from the outside in.  That is,
   the endpoints (thermostats, lights, smoke detectors) are installed in
   the spaces first; local control is established in each room and
   tested for proper operation.  The individual rooms are later lashed
   together into a subsystem (e.g., lighting).  The individual
   subsystems (e.g., lighting, HVAC) then coalesce.  Later, the entire
   system may be merged onto the enterprise network.

   The rationale for this is partly due to the different construction
   trades having access to a building under construction at different
   times.  The sheer size of a building often dictates that even a
   single trade may have multiple independent teams working
   simultaneously.  Furthermore, the HVAC, lighting, and fire systems
   must be fully operational before the building can obtain its
   occupancy permit.  Hence, the BMS must be in place and configured
   well before any of the IT servers (DHCP; Authentication,
   Authorization, and Accounting (AAA); DNS; etc.) are operational.

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   This implies that the BMS cannot rely on the availability of the IT
   network infrastructure or application servers.  Rather, the BMS
   installation should be planned to dovetail into the IT system once
   the IT system is available for easy migration onto the IT network.
   Front-end planning of available switch ports, cable runs, access
   point (AP) placement, firewalls, and security policies will
   facilitate this adoption.

3.4.  Device Density

   Device density differs, depending on the application and as dictated
   by the local building code requirements.  The following subsections
   detail typical installation densities for different applications.

3.4.1.  HVAC Device Density

   HVAC room applications typically have sensors/actuators and
   controllers spaced about 50 ft. apart.  In most cases, there is a 3:1
   ratio of sensors/actuators to controllers.  That is, for each room
   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 up 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 they 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, pharmaceutical facilities, 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 ft.  This is dictated by local building
   codes.  Fire pull boxes are installed uniformly about every 150 ft.
   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.

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3.4.3.  Lighting Device Density

   Lighting is also very uniformly installed, with ballasts installed
   approximately every 10 ft.  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's interior

   The recent influx of interior and perimeter camera systems is
   increasing the security footprint.  These cameras are atypical
   endpoints requiring up to 1 megabit/second (Mbit/s) data rates per
   camera, as contrasted by the few kbit/s needed by most other BMS
   sensing equipment.  Previously, camera systems had been deployed on
   proprietary wired high-speed networks.  More recent implementations
   utilize wired or wireless IP cameras integrated into the enterprise

4.  Traffic Pattern

   The independent nature of the automation subsystems within a building
   can significantly affect network traffic patterns.  Much of the real-
   time sensor environmental data and actuator control stays within the
   local LLN environment, while alarms and other event data will
   percolate to higher layers.

   Each sensor in the LLN unicasts point to point (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 6 kbit/minute
   to peer or supervisory controllers.  Thirty percent of each node's
   packets are destined for other nodes within the LLN.  Seventy percent
   of each node's packets are destined for an aggregation device
   (multipoint to point (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 (point to multipoint (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.

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   BMSs 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 to be scalable.  Today, most
   vendors have developed event-based systems that 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 and
   area levels, and then to the supervisory level.  Traffic bottlenecks
   will typically form 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.  A BMS 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 6
   kbit/s is typical at quiescence.  However, upon any power loss, the
   control loops and real-time data quickly atrophy.  A short power
   disruption of only 10 minutes may have a long-term deleterious impact
   on the building control systems, taking many hours to regain proper
   control.  Control applications 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 network operations 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.

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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
   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 with 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., a laptop).  From
   the ROLL perspective, "zero configuration" means that a node can
   obtain an address and join the network on its own, without human

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.

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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.

5.2.  Scalability

   Building control systems are designed for facilities from 50,000 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

5.2.1.  Network Domain

   The routing protocol MUST be able to support networks with at least
   2,000 nodes, where 1,000 nodes would act as routers and the other
   1,000 nodes would be hosts.  Subnetworks (e.g., rooms, primary
   equipment) within the network must support up to 255 sensors and/or

5.2.2.  Peer-to-Peer Communication

   The data domain for commercial BMSs 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 snake through all of the intervening floors.  The feedback
   control loops for these systems require data from across the

   A network device MUST be able to communicate in an 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., wheelchairs) in medical

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   facilities, require monitoring movement with granularity of a minute;
   however, tracking babies in a pediatric ward would require latencies
   less than a few seconds.

   The following subsections document the mobility requirements in the
   routing layer for mobile devices.  Note, however, that mobility can
   be implemented at various layers of the system, and the specific
   requirements depend on the chosen layer.  For instance, some devices
   may not depend on a static IP address and are capable of re-
   establishing application-level communications when given a new IP
   address.  Alternatively, mobile IP may be used, or the set of routers
   in a building may give an impression of a building-wide network and
   allow devices to retain their addresses regardless of where they are,
   handling routing between the devices in the background.

5.3.1.  Mobile Device Requirements

   To minimize network dynamics, mobile devices while in motion 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.  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 wheelchair
   may be moved from one room on the floor to another room on the same

   A mobile LLN device that moves within the confines of the same LLN
   SHOULD re-establish end-to-end communication with 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.  Device Mobility across LLNs

   A mobile device may move across LLNs, such as a wheelchair being
   moved to a different floor.

   A mobile device that moves outside of its original LLN SHOULD re-
   establish end-to-end communication with 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.

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RFC 5867    Building Automation Routing Requirements in LLNs   June 2010

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 128 KB of memory.

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 256 KB 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 (2,000 mAh) 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 (25 mA) 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", that produce
   efficient low-latency routes that minimize radio "on" time for these

   Sleeping devices MUST be able to receive inbound data.  Messages sent
   to battery-powered nodes MUST be buffered by the last-hop router for
   a period of at least 20 seconds when the destination node is
   currently in its sleep cycle.

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RFC 5867    Building Automation Routing Requirements in LLNs   June 2010

5.5.  Addressing

   Building management systems require different communication schemes
   to solicit or post network information.  Multicasts or anycasts need
   to be used to decipher 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.

5.6.  Manageability

   As previously noted in Section 3.3, installation of LLN devices
   within a BMS follows an "outside-in" 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
   pressed.  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 oftentimes 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

   In operational networks, due to the mission-critical nature of the
   application, the LLN devices will be temporally monitored by the
   higher layers to assure that 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.

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   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 Section

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, the total number of routed packets sent and
   received, the 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.

   Diagnostic data should be kept by the routers continuously and be
   available for solicitation at any time by any other node on the
   internetwork.  Verbose mode will be activated/deactivated via
   unicast, multicast, or other means.  Devices having available
   resources may elect to support verbose mode continuously.

5.6.2.  Route Tracking

   Route diagnostics SHOULD be supported, providing information such as
   route quality, number of hops, and 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

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.

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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.

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 (reactive routing), it SHOULD NOT add more than 120
   ms 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 Quality of
   Service (QoS) routing.

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RFC 5867    Building Automation Routing Requirements in LLNs   June 2010

5.8.  Security Requirements

   This section sets forth specific requirements that are placed on any
   protocols developed or used in the ROLL building environment, in
   order to ensure adequate security and retain suitable flexibility of
   use and function of the protocol.

   Due to the variety of buildings and tenants, the BMSs must be
   completely configurable on-site.

   Due to the quantity of the BMS devices (thousands) and their
   inaccessibility (oftentimes above ceilings), security configuration
   over the network is preferred over local configuration.

   Wireless encryption and device authentication security policies need
   to be considered in commercial buildings, while keeping in mind the
   impact on the limited processing capabilities and additional latency
   incurred on the sensors, actuators, and controllers.

   BMSs are typically highly configurable in the field, and hence the
   security policy is most often dictated by the type of building to
   which the BMS 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, especially when
   the LLN is not connected to an external network.  Antithetically,
   military or pharmaceutical facilities require strong security
   policies.  As noted in the installation procedures described in
   Sections 3.3 and 5.2, security policies MUST support dynamic
   configuration to allow for a low level of security during the
   installation phase (prior to building occupancy, when it may be
   appropriate to use only diagnostic levels of security), yet to make
   it possible to easily raise the security level network-wide during
   the commissioning phase of the system.

5.8.1.  Building Security Use Case

   LLNs for commercial building applications should always implement and
   use encrypted packets.  However, depending on the state of the LLN,
   the security keys may either be:

   1) a key obtained from a trust center already operable on the LLN;

   2) a pre-shared static key as defined by the general contractor or
      its designee; or

   3) a well-known default static key.

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   Unless a node entering the network had previously received its
   credentials from the trust center, the entering node will try to
   solicit the trust center for the network key.  If the trust center is
   accessible, the trust center will MAC-authenticate the entering node
   and return the security keys.  If the trust center is not available,
   the entering node will check to determine if it has been given a
   network key by an off-band means and use it to access the network.
   If no network key has been configured in the device, it will revert
   to the default network key and enter the network.  If neither of
   these keys were valid, the device would signal via a fault LED.

   This approach would allow for independent simplified commissioning,
   yet centralized authentication.  The building owner or building type
   would then dictate when the trust center would be deployed.  In many
   cases, the trust center need not be deployed until all of the local
   room commissioning is complete.  Yet, at the province of the owner,
   the trust center may be deployed from the onset, thereby trading
   installation and commissioning flexibility for tighter security.

5.8.2.  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.

5.8.3.  Encryption  Encryption Types

   Data encryption of packets MUST be supported by all protocol solution
   specifications.  Support can be provided by use of 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 in the LLN.

   The network key and application key 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.

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RFC 5867    Building Automation Routing Requirements in LLNs   June 2010  Packet Encryption

   The encryption policy MUST support either 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.

5.8.4.  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.

5.8.5.  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 outside 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

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RFC 5867    Building Automation Routing Requirements in LLNs   June 2010

   against performance.  An implementation must not make those choices
   on behalf of the operator by avoiding implementing any mandatory-to-
   implement security features.

   This informational requirements specification introduces no new
   security concerns.

7.  Acknowledgments

   In addition to the authors, JP. Vasseur, David Culler, Ted Humpal,
   and Zach Shelby are gratefully acknowledged for their contributions
   to this document.

8.  References

8.1.  Normative References

   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

8.2.  Informative References

   [ROLL-TERM] Vasseur, JP., "Terminology in Low power And Lossy
               Networks", Work in Progress, March 2010.

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RFC 5867    Building Automation Routing Requirements in LLNs   June 2010

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

A.1.  Additional Commercial Product Requirements

A.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.

A.1.2.  World-Wide Applicability

   Wireless devices must be supportable unlicensed bands.

A.2.  Additional Installation and Commissioning Requirements

A.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).

A.3.  Additional Network Requirements

A.3.1.  TCP/UDP

   Connection-based and connectionless services must be supported.

A.3.2.  Interference Mitigation

   The network must automatically detect interference and seamlessly
   switch the channel to improve communication.  Channel changes, and
   the nodes' responses to a given channel change, must occur within 60

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A.3.3.  Packet Reliability

   In building automation, it is required that the network meet the
   following minimum criteria:

   <1% MAC-layer errors on all messages, after no more than three

   <0.1% network-layer errors on all messages, 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.

A.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.

A.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.

A.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.

A.3.7.  Device and Network Integrity

   Commercial-building devices must all be periodically scanned to
   assure that each device is viable and can communicate data and alarm
   information as needed.  Routers should maintain previous packet flow
   information temporally to minimize overall network overhead.

A.4.  Additional Performance Requirements

A.4.1.  Data Rate Performance

   An effective data rate of 20 kbit/s is the lowest acceptable
   operational data rate on the network.

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A.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
   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

A.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 re-
   entering the network.

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RFC 5867    Building Automation Routing Requirements in LLNs   June 2010

Authors' Addresses

   Jerry Martocci
   Johnson Controls Inc.
   507 E. Michigan Street
   Milwaukee, WI  53202
   Phone: +1 414 524 4010
   EMail: jerald.p.martocci@jci.com

   Pieter De Mil
   Ghent University - IBCN
   G. Crommenlaan 8 bus 201
   Ghent  9050
   Phone: +32 9331 4981
   Fax:   +32 9331 4899
   EMail: pieter.demil@intec.ugent.be

   Nicolas Riou
   Schneider Electric
   Technopole 38TEC T3
   37 quai Paul Louis Merlin
   38050 Grenoble Cedex 9
   Phone: +33 4 76 57 66 15
   EMail: nicolas.riou@fr.schneider-electric.com

   Wouter Vermeylen
   Arts Centre Vooruit
   Ghent  9000
   EMail: wouter@vooruit.be

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