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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

Martocci, et al. Informational [Page 1] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 ( in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Martocci, et al. Informational [Page 2] 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

Martocci, et al. Informational [Page 3] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

    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

Martocci, et al. Informational [Page 4] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

 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.

Martocci, et al. Informational [Page 5] 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.

Martocci, et al. Informational [Page 6] 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

Martocci, et al. Informational [Page 7] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

 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.

Martocci, et al. Informational [Page 8] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

 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.

Martocci, et al. Informational [Page 9] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

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.

Martocci, et al. Informational [Page 10] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

 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.

Martocci, et al. Informational [Page 11] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

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.

Martocci, et al. Informational [Page 12] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

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

Martocci, et al. Informational [Page 13] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

 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.

Martocci, et al. Informational [Page 14] 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.

Martocci, et al. Informational [Page 15] 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.

Martocci, et al. Informational [Page 16] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

 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.

Martocci, et al. Informational [Page 17] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

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.

Martocci, et al. Informational [Page 18] 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.

Martocci, et al. Informational [Page 19] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

 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.

Martocci, et al. Informational [Page 20] 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

Martocci, et al. Informational [Page 21] 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.

Martocci, et al. Informational [Page 22] 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,

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

Martocci, et al. Informational [Page 23] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

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.

Martocci, et al. Informational [Page 24] RFC 5867 Building Automation Routing Requirements in LLNs June 2010

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.

Martocci, et al. Informational [Page 25] 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
 Pieter De Mil
 Ghent University - IBCN
 G. Crommenlaan 8 bus 201
 Ghent  9050
 Phone: +32 9331 4981
 Fax:   +32 9331 4899
 Nicolas Riou
 Schneider Electric
 Technopole 38TEC T3
 37 quai Paul Louis Merlin
 38050 Grenoble Cedex 9
 Phone: +33 4 76 57 66 15
 Wouter Vermeylen
 Arts Centre Vooruit
 Ghent  9000

Martocci, et al. Informational [Page 26]

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