Home Automation Routing Requirements in Low-Power and Lossy Networks

Abstract

This document presents requirements specific to home control and automation applications for Routing Over Low power and Lossy (ROLL) networks. In the near future, many homes will contain high numbers of wireless devices for a wide set of purposes. Examples include actuators (relay, light dimmer, heating valve), sensors (wall switch, water leak, blood pressure), and advanced controllers (radio- frequency-based AV remote control, central server for light and heat control). Because such devices only cover a limited radio range, routing is often required. The aim of this document is to specify the routing requirements for networks comprising such constrained devices in a home-control and automation environment.

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 http://www.rfc-editor.org/info/rfc5286.

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Table of Contents

   1. Introduction ....................................................3
      1.1. Terminology ................................................4
      1.2. Requirements Language ......................................6
   2. Home Automation Applications ....................................6
      2.1. Lighting Application in Action .............................6
      2.2. Energy Conservation and Optimizing Energy Consumption ......6
      2.3. Moving a Remote Control Around .............................7
      2.4. Adding a New Module to the System ..........................7
      2.5. Controlling Battery-Operated Window Shades .................8
      2.6. Remote Video Surveillance ..................................8
      2.7. Healthcare .................................................9
           2.7.1. At-Home Health Reporting ...........................10
           2.7.2. At-Home Health Monitoring ..........................10
      2.8. Alarm Systems .............................................10
   3. Unique Routing Requirements of Home Automation Applications ....11
      3.1. Constraint-Based Routing ..................................12
      3.2. Support of Mobility .......................................12
      3.3. Scalability ...............................................13
      3.4. Convergence Time ..........................................13
      3.5. Manageability .............................................14
      3.6. Stability .................................................14
   4. Traffic Pattern ................................................14
   5. Security Considerations ........................................15
   6. Acknowledgments ................................................16
   7. References .....................................................16
      7.1. Normative References ......................................16
      7.2. Informative References ....................................17

1. Introduction

This document presents requirements specific to home control and automation applications for Routing Over Low power and Lossy (ROLL) networks. In the near future, many homes will contain high numbers of wireless devices for a wide set of purposes. Examples include actuators (relay, light dimmer, heating valve), sensors (wall switch, water leak, blood pressure), and advanced controllers. 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.

Network nodes may be sensors and actuators at the same time. An example is a wall switch for replacement in existing homes. The push buttons may generate events for a controller node or for activating other actuator nodes. At the same time, a built-in relay may act as actuator for a controller or other remote sensors.

Because ROLL nodes only cover a limited radio range, routing is often required. These devices are usually highly constrained in terms 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 become reusable again, thus the term "lossy". All traffic in a ROLL network is carried as IPv6 packets.

The connected home area is very much consumer oriented. The implication on network nodes 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 battery-operated, sensor-style nodes to shut down radio and CPU resources for most of the time. The radio tends to use the same power for listening as for transmitting.

Although this document focuses its text on radio-based wireless networks, home-automation networks may also operate using a variety of links, such as IEEE 802.15.4, Bluetooth, Low-Power WiFi, wired or other low-power PLC (Power-Line Communication) links. Many such low- power link technologies share similar characteristics with low-power wireless and this document should be regarded as applying equally to all such links.

Section 2 describes a few typical use cases for home automation applications. Section 3 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 routing requirements presented in [BUILDING-REQS], [RFC5673], and [RFC5548].

A full list of requirements documents may be found in Section 7.

1.1. Terminology

   ROLL:          Routing Over Low-power and Lossy networks.  A ROLL
   
                  node may be classified as a sensor, actuator, or
                  controller.
   
   Actuator:      Network node that performs some physical action.
                  Dimmers and relays are examples of actuators.  If
                  sufficiently powered, actuator nodes may participate
                  in routing network messages.

Border router:

Infrastructure device that connects a ROLL network to the Internet or some backbone network.

   Channel:       Radio frequency band used to carry network packets.
   
   Controller:    Network node that controls actuators.  Control
                  decisions may be based on sensor readings, sensor
                  events, scheduled actions, or incoming commands from
                  the Internet or other backbone networks.  If
                  sufficiently powered, controller nodes may participate
                  in routing network messages.
   
   Downstream:    Data direction traveling from a Local Area Network
                  (LAN) to a Personal Area Network (PAN) device.
   
   DR:            Demand-Response.  The mechanism of users adjusting
                  their power consumption in response to the actual
                  pricing of power.
   
   DSM:           Demand-Side Management.  Process allowing power
                  utilities to enable and disable loads in consumer
                  premises.  Where DR relies on voluntary action from
                  users, DSM may be based on enrollment in a formal
                  program.
   
   LLNs:          Low-Power and Lossy Networks.
   
   LAN:           Local Area Network.
   
   PAN:           Personal Area Network.  A geographically limited
                  wireless network based on, e.g., 802.15.4 or Z-Wave
                  radio.
   
   PDA            Personal Digital Assistant.  A small, handheld
                  computer.
   
   PLC            Power-Line Communication.
   
   RAM            Random Access Memory.
   
   Sensor:        Network node that measures some physical parameter
                  and/or detects an event.  The sensor may generate a
                  trap message to notify a controller or directly
                  activate an actuator.  If sufficiently powered, sensor
                  nodes may participate in routing network messages.
   
   Upstream:      Data direction traveling from a PAN to a LAN device.

Refer to the ROLL terminology reference document [ROLL-TERM] for a full list of terms used in the IETF ROLL WG.

1.2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

2. Home Automation Applications

Home automation applications represent a special segment of networked devices with its unique set of requirements. Historically, such applications used wired networks or power-line communication (PLC) but wireless solutions have emerged, allowing existing homes to be upgraded more easily.

To facilitate the requirements discussion in Section 3, 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.

2.1. Lighting Application in Action

A lamp may be turned on, not only by a wall switch but also by a movement sensor. The wall-switch module may itself be a push-button sensor and an actuator at the same time. This will often be the case when upgrading existing homes as existing wiring is not prepared for automation.

One event may cause many actuators to be activated at the same time.

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.

2.2. Energy Conservation and Optimizing Energy Consumption

In order to save energy, air conditioning, central heating, window shades, etc., may be controlled by timers, motion sensors, or remotely via Internet or cell. Central heating may also be set to a reduced temperature during nighttime.

The power grid may experience periods where more wind-generated power is produced than is needed. Typically this may happen during night hours.

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.

This is known as Demand-Side Management (DSM). Remote control of household appliances is well-suited for this application.

The start/stop decision for the appliances can also be regulated by dynamic power pricing information obtained from the electricity utility companies. This method, called Demand-Response (DR), works by motivation of users via pricing, bonus points, etc. For example, 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 order to achieve effective electricity savings, the energy monitoring application must guarantee that the power consumption of the ROLL devices is much lower than that of the appliance itself.

Most of these appliances 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.

2.3. 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 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.

2.4. Adding a New 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 the assignment of a unique node ID. Inclusion should be completed within a few seconds.

For ease of use in a consumer application space such as home control, nodes may be included without having to type in special codes before inclusion. One way to achieve an acceptable balance between security and convenience is to block inclusion during normal operation, explicitly enable inclusion support just before adding a new module, and disable it again just after adding a new module.

For security considerations, refer to Section 5.

If assignment of unique addresses is performed by a central controller, it must be possible to route the inclusion request from the joining node to the central controller before the joining node has been included in the network.

2.5. 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, such an actuator node is sleeping most of the time. A controller sending commands to a sleeping actuator node via ROLL devices will have no problems delivering the packet to the nearest powered router, but that router may experience a delay until the next wake-up time before the command can be delivered.

2.6. Remote Video Surveillance

Remote video surveillance is a fairly classic application for home networking. It provides the ability for the end-user to get a video stream from a web cam reached via the Internet. The video stream may be triggered by the end-user after receiving an alarm from a sensor (movement 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: 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's cell phone or Personal Digital Assistant (PDA) via the Internet.

In contrast to other applications, e.g., industrial sensors, where data would mainly be originated by a sensor to a sink and vice versa, this scenario implicates a direct inter-device communication between ROLL devices.

2.7. 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 that 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 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.

Since wireless and battery operated systems may never reach 100% guaranteed operational time, healthcare and security systems will need a management layer implementing alarm mechanisms for low battery, report activity, etc.

For instance, if a blood pressure sensor did not report a new measurement, say five minutes after the scheduled time, some responsible person must be notified.

The structure and performance of such a management layer is outside the scope of the routing requirements listed in this document.

2.7.1. 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 Section 2.7.2.

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

2.7.2. 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. Alarm conditions must be reported with the highest priority and timeliness.

Applications might include:

o Temperature
o Weight
o Blood pressure
o Insulin level
o Electrocardiogram (ECG)
o Position tracker

2.8. Alarm Systems

   A home security alarm system is comprised of various sensors
   (vibration, fire, carbon monoxide, door/window, glass-break,
   presence, panic button, etc.).

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 safety. Also, it may be inconvenient to change the batteries in a smoke alarm.

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.

When a node (or a group of nodes) identifies a risk situation (e.g., intrusion, smoke, fire), it sends an alarm message to a central controller that could autonomously forward it via the Internet or interact with other network nodes (e.g., try to obtain more detailed information or ask other nodes close to the alarm event).

Finally, routing via battery-powered nodes may be very slow 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 sleeping devices.

3. Unique Routing Requirements of Home Automation Applications

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

The relations of use cases to requirements are outlined in the table below:

   +------------------------------+-----------------------------+
   | Use case                     | Requirement                 |
   +------------------------------+-----------------------------+
   |2.1. Lighting Application in  |3.2. Support of Mobility     |
   |Action                        |3.3. Scalability             |
   +------------------------------+-----------------------------+
   |2.2. Energy Conservation and  |3.1. Constraint-Based Routing|
   |Optimizing Energy Consumption |                             |
   +------------------------------+-----------------------------+
   |2.3. Moving a Remote Control  |3.2. Support of Mobility     |
   |Around                        |3.4. Convergence Time        |
   +------------------------------+-----------------------------+
   |2.4. Adding a New Module to   |3.4. Convergence Time        |
   |the System                    |3.5. Manageability           |
   +------------------------------+-----------------------------+
   |2.7. Healthcare               |3.1. Constraint-Based Routing|
   |                              |3.2. Support of Mobility     |
   |                              |3.4. Convergence Time        |
   +------------------------------+-----------------------------+
   |2.8. Alarm Systems            |3.3. Scalability             |
   |                              |3.4. Convergence Time        |
   +------------------------------+-----------------------------+

3.1. Constraint-Based Routing

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 Random Access Memory (RAM) 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 1%.

Some devices only wake up in response to an event, e.g., a push button.

Simple battery-powered nodes such as movement sensors on garage doors and rain sensors 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 with such nodes may at best require a long time before getting a response.

Other battery-powered nodes may have the capability to participate in routing. The routing protocol SHOULD route via mains-powered nodes if possible.

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).

3.2. 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 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.

On more rare occasions, receiving nodes may also have moved. Examples include a safety-off switch in a clothes iron, a vacuum cleaner robot, or the wireless chime of doorbell set.

Refer to Section 3.4 for routing protocol convergence times.

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.

3.3. Scalability

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

The routing protocol needs to be able to support a basic home deployment and so MUST be able to support at least 250 devices in the network. Furthermore, the protocol SHOULD be extensible to support more sophisticated and future deployments with a larger number of devices.

3.4. Convergence Time

A wireless home automation network is subject to various instabilities due to signal strength variation, moving persons, and the like.

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

The routing protocol MUST converge within 0.5 seconds if no nodes have moved (see Section 3.2 for motivation).

The routing protocol MUST converge within four seconds if nodes have moved to re-establish connectivity within a time that a human operator would find tolerable as, for example, when moving a remote control unit.

In both cases, "converge" means "the originator node has received a response from the destination node". The above-mentioned convergence time requirements apply to a home control network environment of up to 250 nodes with up to four repeating nodes between source and destination.

3.5. 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- automation networks MUST provide a set of features including zero- configuration of the routing protocol for a new node to be added to the network. From a routing perspective, zero-configuration means that a node can obtain an address and join the network on its own, almost without human intervention.

3.6. Stability

If a node is found to fail often compared to the rest of the network, this node SHOULD NOT be the first choice for routing of traffic.

4. Traffic Pattern

Depending on the design 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 multipoint-to- multipoint. In a centralized system, it is a mix of multipoint-to- point and point-to-multipoint.

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

Remote controls have a similar transmit pattern to wall switches but may be activated more frequently in some deployments.

Temperature/air and 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.

All frames sent in the above examples are quite short, typically less than five 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.

5. Security Considerations

As is the case with every network, LLNs are exposed to routing security threats that need to be addressed. The wireless and distributed nature of these networks increases the spectrum of potential routing security threats. This is further amplified by the resource constraints of the nodes, thereby preventing resource- intensive routing security approaches from being deployed. A viable routing security approach SHOULD be sufficiently lightweight that it may be implemented across all nodes in a LLN. These issues require special attention during the design process, so as to facilitate a commercially attractive deployment.

An attacker can snoop, replay, or originate arbitrary messages to a node in an attempt to manipulate or disable the routing function.

To mitigate this, the LLN MUST be able to authenticate a new node prior to allowing it to participate in the routing decision process. The routing protocol MUST support message integrity.

A further example of routing security issues that may arise is the abnormal behavior of nodes that exhibit an egoistic conduct, such as not obeying network rules or forwarding no or false packets.

Other important issues may arise in the context of denial-of-service (DoS) attacks, malicious address space allocations, advertisement of variable addresses, a wrong neighborhood, etc. The routing protocol(s) SHOULD support defense against DoS attacks and other attempts to maliciously or inadvertently cause the mechanisms of the routing protocol(s) to over-consume the limited resources of LLN nodes, e.g., by constructing forwarding loops or causing excessive routing protocol overhead traffic, etc.

The properties of self-configuration and self-organization that are desirable in a LLN introduce additional routing security considerations. Mechanisms MUST be in place to deny any node that attempts to take malicious advantage of self-configuration and self- organization procedures. Such attacks may attempt, for example, to cause DoS, drain the energy of power-constrained devices, or to hijack the routing mechanism. A node MUST authenticate itself to a trusted node that is already associated with the LLN before the former can take part in self-configuration or self-organization. A node that has already authenticated and associated with the LLN MUST deny, to the maximum extent possible, the allocation of resources to any unauthenticated peer. The routing protocol(s) MUST deny service to any node that has not clearly established trust with the HC-LLN.

In a home-control environment, it is considered unlikely that a network is constantly being snooped and at the same time, ease of use is important. As a consequence, the network key MAY be exposed for short periods during inclusion of new nodes.

Electronic door locks and other critical applications SHOULD apply end-to-end application security on top of the network transport security.

If connected to a backbone network, the LLN SHOULD be capable of limiting the resources utilized by nodes in said backbone network so as not to be vulnerable to DoS. This should typically be handled by border routers providing access from a backbone network to resources in the LLN.

With low-computation power and scarce energy resources, LLNs' nodes may not be able to resist any attack from high-power malicious nodes (e.g., laptops and strong radios). However, the amount of damage generated to the whole network SHOULD be commensurate with the number of nodes physically compromised. For example, an intruder taking control over a single node SHOULD NOT be able to completely deny service to the whole network.

In general, the routing protocol(s) SHOULD support the implementation of routing security best practices across the LLN. Such an implementation ought to include defense against, for example, eavesdropping, replay, message insertion, modification, and man-in- the-middle attacks.

The choice of the routing security solutions will have an impact on the routing protocol(s). To this end, routing protocol(s) proposed in the context of LLNs MUST support authentication and integrity measures and SHOULD support confidentiality (routing security) measures.

6. Acknowledgments

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

7. References

7.1. Normative References

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

7.2. Informative References

[BUILDING-REQS] Martocci, J., Ed., De Mil, P., Vermeylen, W., and N.

Riou, "Building Automation Routing Requirements in Low Power and Lossy Networks", Work in Progress, January 2010.

   [RFC5548]       Dohler, M., Ed., Watteyne, T., Ed., Winter, T., Ed.,
                   and D. Barthel, Ed., "Routing Requirements for Urban
                   Low-Power and Lossy Networks", RFC 5548, May 2009.
   
   [RFC5673]       Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T.
                   Phinney, "Industrial Routing Requirements in Low-
                   Power and Lossy Networks", RFC 5673, October 2009.
   
   [ROLL-TERM]     Vasseur, JP. "Terminology in Low power And Lossy
                   Networks", Work in Progress, October 2009.

Authors' Addresses

Anders Brandt
Sigma Designs, Inc.
Emdrupvej 26
Copenhagen, DK-2100
Denmark

EMail:

          abr@sdesigns.dk

Jakob Buron
Sigma Designs, Inc.
Emdrupvej 26
Copenhagen, DK-2100
Denmark

EMail:

          jbu@sdesigns.dk

Giorgio Porcu
Telecom Italia
Piazza degli Affari, 2
20123 Milan
Italy

EMail:

          gporcu@gmail.com