Networking Working Group A. Brandt
Internet Draft Zensys, Inc.
Intended status: Informational G. Porcu
Expires: May 2009 Telecom Italia
November 19, 2008
Home Automation Routing Requirements in Low Power and Lossy
Networks
draft-ietf-roll-home-routing-reqs-05
draft-ietf-roll-home-routing-reqs-06
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Copyright (C) The IETF Trust (2008).
Abstract
This document presents home control and automation application
specific requirements for Routing Over 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
actuators (relay, light dimmer, heating valve), sensors (wall
switch, water leak, blood pressure) and advanced controllers.
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.
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].
Table of Contents
Terminology......................................................3
1. Introduction..................................................5
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...............................................8
2.7.1. At-home Health Reporting............................9
2.7.2. At-home Health Monitoring...........................9
2.8. Alarm Systems............................................9
3. Unique Routing Requirements of Home Automation Applications..10
3.1. Constraint-based Routing................................11
3.2. Support of Mobility.....................................12
3.3. Sleeping Nodes..........................................12
3.4. Healthcare Routing......................................12
3.5. Scalability.............................................13
3.6. Convergence Time........................................13
3.7. Manageability...........................................13
3.8. Stability...............................................14
4. Traffic Pattern..............................................14
5. Open Issues..................................................14
6. Security Considerations......................................15
7. IANA Considerations..........................................15
8. Acknowledgments..............................................15
9. References...................................................15
9.1. Normative References....................................15
9.2. Informative References..................................16
Disclaimer of Validity..........................................17
Terminology
ROLL: Routing Over Low-power and Lossy networks
A ROLL node may be classified as sensor, actuator
or controller.
Actuator: Network node which 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 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.
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 data 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 for a full list
of terms used in the IETF ROLL WG. WG (I-D.draft-ietf-roll-terminology).
1. Introduction
This document presents home control and automation application
specific requirements for Routing Over 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
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 buildings.
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
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 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 low-power
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
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. A
full list of requirements documents may be found in the end of the
document.
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 buildings 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 buildings 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. 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" message in direct range with no acknowledgement
before sending acknowledged singlecast messages to each device.
Subnet groupcast, being an application-level feature, is not
further discussed in this specification.
The controller forms the group and decides which nodes should
receive a message.
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 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.
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 assignment of a unique node ID.
Inclusion should be completed within a few seconds.
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 providing 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 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 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.
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 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 or 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 exchange battery
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 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 |3.5. 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 |3.6. Convergence Time |
+-------------------------------+-----------------------------+
|2.4. Adding A New Module To The |3.6. Convergence Time |
|System |3.7. Manageability |
+-------------------------------+-----------------------------+
|2.5. Controlling Battery |3.3. Sleeping Nodes |
|Operated Window Shades | |
+-------------------------------+-----------------------------+
|2.7. Healthcare |3.1. Constraint-based Routing|
| |3.2. Support of Mobility |
| |3.4. Healthcare Routing |
| |3.6. Convergence Time |
+-------------------------------+-----------------------------+
|2.8. Alarm Systems |3.5. Scalability |
| |3.6. 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 to such nodes may at best require 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
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.
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.
3.3. Sleeping Nodes
Sleeping nodes may appear to be non-responsive. The routing
protocol MUST take into account the delivery time to a sleeping
target node.
The wake-up interval of a sleeping node MUST be less than one
second.
3.4. Healthcare Routing
Because most health care applications may run on battery, this
leads to specific requirements for the routing protocol. Most
health care applications 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, 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.
3.5. 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.
The routing protocol MUST support 250 devices in the network.
3.6. Convergence Time
A wireless home automation network is subject to various
instabilities 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.
The routing protocol MUST converge within 0.5 second if no nodes
have moved.
The routing protocol MUST converge within 2 seconds if the
destination node of the packet has moved.
In both cases, "converge" means "the originator node has received
a response from the destination node".
3.7. 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
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, without human intervention.
3.8. Stability
The routing protocol MUST support the ability to isolate a
misbehaving node thus preserving the correct operation of the
overall network.
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 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.
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. Security Considerations
Implementing security mechanisms in ROLL network devices may
degrade energy efficiency and increase cost.
The routing protocol chosen for ROLL MUST allow for low-power,
low-cost network devices with limited security needs.
Protection against unintentional inclusion in neighboring networks
MUST be provided.
7. IANA Considerations
This document includes no request to IANA.
8. Acknowledgments
J. P. Vasseur, Jonathan Hui, Eunsook "Eunah" Kim, Mischa Dohler
and Massimo Maggiorotti are gratefully acknowledged for their
contributions to this document.
This document was prepared using 2-Word-v2.0.template.dot.
9. References
As an exception, this internet draft contains references to other
internet drafts. The reason is that the referenced internet drafts
are developed in parallel to this document.
When promoted to an RFC, the references MUST be updated to RFCs as
well or removed from the references section.
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[I-D.draft-ietf-roll-indus-routing-reqs]
"Industrial Routing Requirements in Low Power and Lossy
Networks", Kris Pister, Pascal Thubert, Sicco Dwars,
Tom Phinney, draft-ietf-roll-indus-routing-reqs-02
(work in progress), October 2008
[I-D.draft-ietf-roll-urban-routing-reqs]
"Urban WSNs Routing Requirements in Low Power and Lossy
Networks", Mischa Dohler, Thomas Watteyne, Tim Winter,
Dominique Barthel, Christian Jacquenet,
Giyyarpuram Madhusudan, Gabriel Chegaray,
draft-ietf-roll-urban-routing-reqs-02 (work in progress)
October 2008
[I-D.draft-martocci-roll-building-routing-reqs]
"Building Automation Routing Requirements in Low Power
and Lossy Networks", Jerry Martocci, Nicolas Riou,
Pieter Mil, Wouter Vermeylen,
draft-martocci-roll-building-routing-reqs-01
(work in progress), October 2008
[I-D.draft-martocci-roll-commercial-routing-reqs]
"Commercial Routing Requirements in Low Power and
Lossy Networks", Jerry Martocci, Ted Humpal, Nicolas Riou,
Jon Williamsson,
draft-martocci-roll-commercial-routing-reqs-00.txt
(work in progress), July 2008
[I-D.draft-vasseur-roll-terminology]
[I-D.draft-ietf-roll-terminology]
"Terminology in Low power And Lossy Networks",
JP Vasseur, draft-ietf-roll-terminology-00
(work in progress), October 2008
Author's Addresses
Anders Brandt
Zensys, Inc.
Emdrupvej 26
Copenhagen, DK-2100
Denmark
Email: abr@zen-sys.com
Jakob Buron
Zensys, Inc.
Emdrupvej 26
Copenhagen, DK-2100
Denmark
Email: jbu@zen-sys.com
Giorgio Porcu
Telecom Italia
Piazza degli Affari, 2
20123 Milan
Italy
Email: giorgio.porcu@guest.telecomitalia.it
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