Networking Working Group                                      A. Brandt
Internet Draft                                             Zensys, Inc.
Intended status: Informational                                 G. Porcu
Expires: January 2009                                    Telecom Italia
                                                          July 14, 2008

    Home Automation Routing Requirement in Low Power and Lossy Networks

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Copyright Notice

   Copyright (C) The IETF Trust (2008).


   This document presents home control and automation application
   specific requirements for ROuting in Low power and Lossy networks
   (ROLL). In a modern home, a high number of wireless devices are used
   for a wide set of purposes. Examples include lighting control,
   heating control, sensors, leak detectors, healthcare systems and
   advanced remote controls. Because such devices only cover a limited

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   radio range, multi-hop routing is often required. The aim of this
   document is to specify the routing requirements for networks
   comprising such constrained devices in a home network environment.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [RFC2119].

Table of Contents

   1. Terminology....................................................3
   2. Introduction...................................................3
   3. Home automation applications...................................4
      3.1. Turning off the house when leaving........................4
      3.2. Energy conservation and optimizing energy consumption.....5
      3.3. Moving a remote control around............................5
      3.4. Adding a new lamp module to the system....................6
      3.5. Controlling battery operated window shades................6
      3.6. Remote video surveillance.................................6
      3.7. Healthcare................................................7
         3.7.1. At-home health reporting.............................7
         3.7.2. At-home health monitoring............................8
         3.7.3. Healthcare routing considerations....................8
      3.8. Alarm systems.............................................8
      3.9. Battery-powered devices...................................9
   4. Unique requirements of home automation applications............9
      4.1. Support of groupcast......................................9
      4.2. Constraint-based Routing.................................10
      4.3. Support of Mobility......................................10
      4.4. Support of Periodical Scanning...........................11
      4.5. Scalability..............................................11
      4.6. Convergence Time.........................................11
      4.7. Manageability............................................12
   5. Traffic Pattern...............................................12
   6. Open issues...................................................13
   7. Security Considerations.......................................13
   8. IANA Considerations...........................................13
   9. Acknowledgments...............................................13
   10. References...................................................14
      10.1. Normative References....................................14
      10.2. Informative References..................................14
   Disclaimer of Validity...........................................15

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1. Terminology

   ROLL:        ROuting in Low-power and Lossy networks

   ROLL device:  A ROLL network node with constrained CPU and memory
                 resources; potentially constrained power resources.

   Access Point: The access point is an infrastructure device that
                 connects the low power and lossy network system to the
                 Internet, possibly via a customer premises local area
                 network (LAN).

   LAN:         Local Area Network.

   PAN:         Personal Area Network.
                 A geographically limited wireless network based on
                 e.g. 802.15.4 or Z-Wave radio.

   Channel:      Radio frequency band used to transmit a modulated
                 signal carrying packets.

   Downstream:   Data direction traveling from a Local Area Network
                 (LAN) to a Personal Area Network (PAN) device.

   Upstream:     Data direction traveling from a PAN to a LAN device.

   Sensor:      A PAN device that measures data and/or detects an

2. Introduction

   This document presents the home control and automation application
   specific requirements for Routing in Low power and Lossy Networks
   (ROLL). In a modern home, a high number of wireless devices are used
   for a wide set of purposes. Examples include lighting control
   modules, heating control panels, light sensors, temperature sensors,
   gas/water leak detectors, motion detectors, video surveillance,
   healthcare systems and advanced remote controls. Basic home control
   modules such as wall switches and plug-in modules may be turned into
   an advanced home automation solution via the use of an IP-enabled
   application responding to events generated by wall switches, motion
   sensors, light sensors, rain sensors, and so on.

   Because such devices only cover a limited radio range, multi-hop
   routing is often required. These devices are usually highly

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   constrained in term of resources such as battery and memory and
   operate in unstable environments. Persons moving around in a house,
   opening or closing a door or starting a microwave oven affect the
   reception of weak radio signals. Reflection and absorption may cause
   a reliable radio link to turn unreliable for a period of time and
   then being reusable again, thus the term "lossy".

   Unlike other categories of PANs, the connected home area is very much
   consumer-oriented. The implications on network nodes in this aspect,
   is that devices are very cost sensitive, which leads to resource-
   constrained environments having slow CPUs and small memory
   footprints. At the same time, nodes have to be physically small which
   puts a limit to the physical size of the battery; and thus, the
   battery capacity. As a result, it is common for low-power sensor-
   style nodes to shut down radio and CPU resources for most of the
   time. Often, the radio uses the same power for listening as for

   Section 3 describes a few typical use cases for home automation
   applications. Section 4 discusses the routing requirements for
   networks comprising such constrained devices in a home network
   environment. These requirements may be overlapping requirements
   derived from other application-specific requirements.

3. Home automation applications

   Home automation applications represent a special segment of networked
   wireless devices with its unique set of requirements. To facilitate
   the requirements discussion in Section 4, this section lists a few
   typical use cases of home automation applications. New applications
   are being developed at a high pace and this section does not mean to
   be exhaustive. Most home automation applications tend to be running
   some kind of command/response protocol. The command may come from
   several places. For instance a lamp may be turned on, not only be a
   wall switch but also from a movement sensor.

3.1. Turning off the house when leaving

   Using the direct analogy to an electronic car key, a house owner may
   activate the "leaving home" function from an electronic house key,
   mobile phone, etc. For the sake of visual impression, all lights
   should turn off at the same time. At least, it should appear to
   happen at the same time. A well-known problem in wireless home
   automation is the "popcorn effect": Lamps are turned on one at a
   time, at a rate so slow that it is clearly visible. Some existing
   home automation solutions use a clever mix of a "subnet groupcast"

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   message with no acknowledgement and no forwarding before sending
   acknowledged singlecast messages to each lighting device.

   The controller forms the groups and decides which nodes should
   receive "turn-off" or "turn-on" requests.

3.2. Energy conservation and optimizing energy consumption

   Parts of the world using air conditioning may let shades go down and
   turn off the AC device when leaving home. Air conditioning may start
   by timer or via motion sensor when the owner returns home. The owner
   may even activate the air conditioning via cell phone before getting

   Geographical areas using central heating may turn off heating when
   not at home and use a reduced temperature during night time.

   The power grid may experience periods where more wind-generated power
   is produced than is needed. Typically this may happen during night
   hours. The washing machine and dish washer may just as well work
   while power is cheap. The electric car should also charge its
   batteries on cheap power.

   In periods where electricity demands exceed available supply,
   appliances such as air conditioning, climate control systems, washing
   machines etc. can be turned off to avoid overloading the power grid.
   Wireless remote control of the household appliances is well-suited
   for this application. The start/stop decision for the appliances can
   be regulated by dynamic power pricing information obtained from the
   electricity utility companies. Moreover, in order to achieve
   effective electricity savings, the energy monitoring application
   running on the Wireless Sensor Network (WSN) must guarantee that the
   power consumption of the ROLL devices is much lower than that of the
   appliance itself.

   Most of these applications are mains powered and are thus ideal for
   providing reliable, always-on routing resources. Battery-powered
   nodes, by comparison, are constrained routing resources and may only
   provide reliable routing under some circumstances.

3.3. Moving a remote control around

   A remote control is a typical example of a mobile device in a home
   automation network. An advanced remote control may be used for
   dimming the light in the dining room while eating and later on,
   turning up the music while doing the dishes in the kitchen. Reaction
   must appear to be instant (within a few hundred milliseconds) even

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   when the remote control has moved to a new location. The remote
   control may be communicating to either a central home automation
   controller or directly to the lamps and the media center.

3.4. Adding a new lamp module to the system

   Small-size, low-cost modules may have no user interface except for a
   single button. Thus, an automated inclusion process is needed for
   controllers to find new modules. Inclusion covers the detection of
   neighbors and assignment of a unique node ID. Inclusion should be
   completed within a few seconds.

   Distribution of unique addresses is usually performed by a central
   controller. In this case, it must be possible to route the inclusion
   request from the joining node to the central controller even before
   the joining node is assigned a unique address.

3.5. Controlling battery operated window shades

   In consumer premises, window shades are often battery-powered as
   there is no access to mains power over the windows. For battery
   conservation purposes, the receiver is sleeping most of the time. A
   home automation controller sending commands to window shades via ROLL
   devices will have no problems delivering the packet to the router,
   but the router may have to wait for some time before the command can
   be delivered to the window shades if the receiver is sleeping; e.g.
   up to 250ms.

3.6. Remote video surveillance

   Remote video surveillance is a fairly classic application for Home
   networking providing the ability for the end user to get a video
   stream from a Web Cam reached via the Internet, which can be
   triggered by the end-user that has received an alarm from a movement
   sensor or smoke detector - or the user simply wants to check the home
   status via video.
   Note that in the former case, more than likely, there will be a form
   of inter-device communication: indeed, upon detecting some movement
   in the home, the movement sensor may send a request to the light
   controller to turn-on the lights, to the Web Cam to start a video
   stream that would then be directed to the end user (cell phone, PDA)
   via the Internet.
   By contrast with other applications, e.g. industrial sensors where
   data would mainly be originated by sensor to a sink and vice versa,
   this scenario implicates a direct inter-device communication between
   ROLL devices.

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3.7. Healthcare

   By adding communication capability to devices, patients and elderly
   citizens may be able to do simple measurements at home. Thanks to
   online devices, a doctor can keep an eye on the patient's health and
   receive warnings if a new trend is discovered by automated filters.

   Fine-grained daily measurements presented in proper ways may allow
   the doctor to establish a more precise diagnosis.

   Such applications may be realized as wearable products which
   frequently do a measurement and automatically deliver the result to a
   data sink locally or over the Internet.

   Applications falling in this category are referred to as at-home
   health reporting. Whether measurements are done in a fixed interval
   or if they are manually activated, they leave all processing to the
   receiving data sink.

   A more active category of applications may send an alarm if some
   alarm condition is triggered. This category of applications is
   referred to as at-home health monitoring. Measurements are
   interpreted in the device and may cause reporting of an event if an
   alarm is triggered.

   Many implementations may overlap both categories.

3.7.1. At-home health reporting

   Applications might include:

   o  Temperature

   o  Weight

   o  Blood pressure

   o  Insulin level

   Measurements may be stored for long term statistics. At the same
   time, a critically high blood pressure may cause the generation of an
   alarm report. Refer to 3.7.2.

   To avoid a high number of request messages, nodes may be configured
   to autonomously do a measurement and send a report in intervals.

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3.7.2. At-home health monitoring

   An alarm event may become active e.g. if the measured blood pressure
   exceeds a threshold or if a person falls to the ground.

   Applications might include:

   o  Temperature

   o  Weight

   o  Blood pressure

   o  Insulin level

   o  Electrocardiogram (ECG)

   o  Position tracker

3.7.3. Healthcare routing considerations

   From a ROLL perspective, all the above-mentioned applications may run
   on battery. They may also be portable and therefore need to locate a
   new neighbor router on a frequent basis.
   Not being powered most of the time, the nodes should not be used as
   routing nodes. However, sleeping, battery-powered nodes may be
   involved in routing. Examples include cases where a person falls
   during a power blackout. In that case it may be that no mains-powered
   routers are available for forwarding the alarm message to a (battery-
   backed) internet gateway located out of direct range.

   Delivery of measurement data has a more relaxed requirement for route
   discovery time compared to a remote control. On the other hand, it is
   critical that a "person fell" alarm is actually delivered in the end.

3.8. Alarm systems

   A home security alarm system is comprised of various devices like
   vibration detectors, fire or carbon monoxide detection system, door
   or window contacts, glass-break detector, presence sensor, panic
   button, home security key.

   Some smoke alarms are battery powered and at the same time mounted in
   a high place. Battery-powered safety devices should only be used for
   routing if no other alternatives exist to avoid draining the battery.
   A smoke alarm with a drained battery does not provide a lot of

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   safety. Also, it may be inconvenient to exchange battery in a smoke

   Alarm system applications may have both a synchronous and an
   asynchronous behavior; i.e. they may be periodically queried by a
   central control application (e.g. for a periodical refreshment of the
   network state), or send a message to the control application on their
   own initiative basing upon the status of the environment they

   When a node (or a group of nodes) identifies a risk situation (e.g.
   intrusion, smoke, fire), it sends an alarm message to the control
   centre that could autonomously forward it via Internet or interact
   with the WSN (e.g. trying to obtain more detailed information or
   asking to other nodes close to the alarm event).  Alarm messages
   have, obviously, strict low-latency requirements.

   Finally, routing via battery-powered nodes may be very slowly
   reacting if the nodes are sleeping most of the time (they could
   appear unresponsive to the alarm detection). To ensure fast message
   delivery and avoid battery drain, routing should be avoided via this
   category of devices.

3.9. Battery-powered devices

   For convenience and low operational costs, power consumption of
   consumer products must be kept at a very low level to achieve a long
   battery lifetime. One implication of this fact is that RAM memory is
   limited and it may even be powered down; leaving only a few 100 bytes
   of RAM alive during the sleep phase.

   The use of battery powered devices reduces installation costs and
   does enable installation of devices even where main power lines are
   not available. On the other hand, in order to be cost effective and
   efficient, the devices have to maximize the sleep phase with a duty
   cycle lower than 10%.

4. Unique requirements of home automation applications

   Home automation applications have a number of specific requirements
   related to the set of home networking applications and the perceived
   operation of the system.

4.1. Support of groupcast

   Groupcast, in the context of home automation, is defined as the
   ability to simultaneously transmit a message to a group of recipients

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   without prior interaction with the group members (i.e. group setup).
   A use-case for groupcast is given in Section 3.1.

   Broadcast and groupcast in home automation MAY be used to deliver the
   illusion that all recipients respond simultaneously. Distant
   recipients out of direct range may not react to the (unacknowledged)
   groupcast.  Acknowledged unicast delivery MUST be used subsequently.

   The support of unicast, groupcast and broadcast also has an
   implication on the addressing scheme and are outside the scope of
   this document that focuses on the routing requirements aspects.

   It MUST be to possible to address a group of receivers known by the
   sender even if the receivers do not know that they have been grouped
   by the sender.

4.2. Constraint-based Routing

   Simple battery-powered nodes such as movement sensors on garage doors
   and rain meters may not be able to assist in routing. Depending on
   the node type, the node never listens at all, listens rarely or makes
   contact on demand to a pre-configured target node. Attempting to
   communicate to such nodes may require long time before getting a

   Other battery-powered nodes may have the capability to participate in
   routing. The routing protocol should either share the load between
   nodes to preserve battery or only route via mains-powered nodes if
   possible. The most reliable routing resource may be a battery-backed,
   mains-powered smoke alarm.

   The routing protocol MUST support constraint-based routing taking
   into account node properties (CPU, memory, level of energy, sleep
   intervals, safety/convenience of changing battery).

4.3. Support of Mobility

   In a home environment, although the majority of devices are fixed
   devices, there is still a variety of mobile devices: for example a
   multi-purpose remote control is likely to move. Another example of
   mobile devices is wearable healthcare devices.

   While healthcare devices delivering measurement results can tolerate
   route discovery times measured in seconds, a remote control appears
   unresponsive if using more than 0.5 seconds to e.g. pause the music.

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   While, in theory, all battery-powered devices and mains-powered plug-
   in modules may be moved, the predominant case is that the sending
   node has moved while the rest of the network has not changed.

   The routing protocol MUST provide mobility with convergence time
   below 0.5 second if only the sender has moved.

   A non-responsive node can either be caused by 1) a failure in the
   node, 2) a failed link on the path to the node or 3) a moved node. In
   the first two cases, the node can be expected to reappear at roughly
   the same location in the network, whereas it can return anywhere in
   the network in the latter case. The search strategy in the routing
   protocol will behave differently depending on this expectation. The
   routing protocol SHOULD make use of the fact that if not being able
   to deliver a packet, it is most likely that the sending node moved;
   rather than a failure occurred in that node or in a link on the path
   towards it.

4.4. Support of Periodical Scanning

   The routing protocol MUST support the recognition of neighbors and
   periodical scanning. This process SHOULD preserve energy capacity as
   much as possible.

   (Derived from use case 3.8. Alarm Systems)

4.5. Scalability

   Looking at the number of wall switches, power outlets, sensors of
   various nature, video equipment and so on in a modern house, it seems
   quite realistic that hundreds of low power devices may form a home
   automation network in a fully populated "smart" home. Moving towards
   professional building automation, the number of such devices may be
   in the order of several thousands.

   Thus, the routing protocol MUST support 250 devices in a subnet.
   The routing protocol SHOULD support 2500 devices in a subnet.

4.6. Convergence Time

   A home automation Personal Area Network (PAN) is subject to various
   instability due to signal strength variation, moving persons and the
   like. Furthermore, as the number of devices increases, the
   probability of a node failure also increases.

   Measured from the transmission of a packet, the following convergence
   time requirements apply.

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   The routing protocol MUST converge within 0.5 second if no nodes have

   The routing protocol MUST converge within 2 seconds if the
   destination node of the packet has moved.

4.7. Manageability

   The ability of the home network to support auto-configuration is of
   the utmost importance. Indeed, most end users will not have the
   expertise and the skills to perform advanced configuration and
   troubleshooting. Thus the routing protocol designed for home PAN MUST
   provide a set of features including zero-configuration of the routing
   protocol for a new node to be added to the network. From ROLL
   perspective, zero-configuration means that a node can obtain an
   address and join the network on its own, without human intervention.

   The routing protocol MUST support the ability to isolate a
   misbehaving node thus preserving the correct operation of overall

5. Traffic Pattern

   Depending on the philosophy of the home network, wall switches may be
   configured to directly control individual lamps or alternatively, all
   wall switches send control commands to a central lighting control
   computer which again sends out control commands to relevant devices.

   In a distributed system, the traffic tends to be any-to-many. In a
   centralized system, it is a mix of any-to-one and one-to-many.

   Wall switches only generate traffic when activated, which typically
   happens from a one to tens of times per hour.

   Remote controls have a similar transmit pattern to wall switches, but
   are activated more frequently.

   Temperature/air pressure/rain sensors send frames when queried by the
   user or can be preconfigured to send measurements at fixed intervals
   (typically minutes). Motion sensors typically send a frame when
   motion is first detected and another frame when an idle period with
   no movement has elapsed. The highest transmission frequency depends
   on the idle period used in the sensor. Sometimes, a timer will
   trigger a frame transmission when an extended period without status
   change has elapsed.

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   All frames sent in the above examples are quite short, typically less
   than 5 bytes of payload. Lost frames and interference from other
   transmitters may lead to retransmissions. In all cases,
   acknowledgment frames with a size of a few bytes are used.

6. Open issues

   Other items to be addressed in further revisions of this document

   o  Load Balancing (Symmetrical and Asymmetrical)

   o  Security

7. Security Considerations

   Encryption can be employed to provide confidentiality, integrity and
   authentication of the messages carried on the wireless links. Adding
   these capabilities to the ROLL devices will degrade energy efficiency
   and increase cost, so a trade-off must be made for each specific

   Door locks, alarm sensors and medication dosage equipment are
   examples where strong encryption and authentication are needed. The
   command to unlock a door must be authenticated, as must the
   communication between an alarm sensor and the central alarm
   controller. Furthermore, traffic analysis of the alarm system
   communication must not reveal if the alarm is activated.

   Light dimmers, window shades, motion sensors, weight sensors etc. may
   not need encryption.

   Protection against unintentional inclusion in neighboring networks
   must be provided. Providing confidentiality, integrity and
   authentication against malicious opponents is optional.

8. IANA Considerations

   This document includes no request to IANA.

9. Acknowledgments

   J. P. Vasseur, Jonathan Hui, Eunsook "Eunah" Kim, Mischa Dohler and
   Massimo Maggiorotti are gratefully acknowledged for their
   contributions to this document.

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   This document was prepared using

10. References

10.1. Normative References

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

10.2. Informative References

Author's Addresses

   Anders Brandt
   Zensys, Inc.
   Emdrupvej 26
   Copenhagen, DK-2100


   Giorgio Porcu
   Telecom Italia
   Piazza degli Affari, 2
   20123 Milan


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