Internet DRAFT - draft-brandt-roll-rpl-applicability-home-building
draft-brandt-roll-rpl-applicability-home-building
Roll A. Brandt
Internet-Draft Sigma Designs
Intended status: Informational E. Baccelli
Expires: November 14, 2013 INRIA
R. Cragie
Gridmerge
P. van der Stok
Consultant
May 13, 2013
Applicability Statement: The use of the RPL protocol set in Home
Automation and Building Control
draft-brandt-roll-rpl-applicability-home-building-04
Abstract
The purpose of this document is to provide guidance in the selection
and use of RPL protocols to implement the features required in
building and home environments.
Status of This Memo
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Overview of requirements . . . . . . . . . . . . . . . . 3
1.3. Out of scope requirements . . . . . . . . . . . . . . . . 3
2. Deployment Scenario . . . . . . . . . . . . . . . . . . . . . 3
2.1. Network Topologies . . . . . . . . . . . . . . . . . . . 4
2.2. Traffic Characteristics . . . . . . . . . . . . . . . . . 5
2.2.1. Human user responsiveness . . . . . . . . . . . . . . 5
2.2.2. Source-sink (SS) communication paradigm . . . . . . . 6
2.2.3. Peer-to-peer (P2P) communication paradigm . . . . . . 6
2.2.4. Peer-to-multipeer (P2MP) communication paradigm . . . 6
2.2.5. RPL applicability per communication paradigm . . . . 7
2.3. Link layer applicability . . . . . . . . . . . . . . . . 7
3. Using RPL-P2P to meet requirements . . . . . . . . . . . . . 7
4. RPL Profile for RPL-P2P . . . . . . . . . . . . . . . . . . . 7
4.1. RPL Features . . . . . . . . . . . . . . . . . . . . . . 7
4.1.1. RPL Instances . . . . . . . . . . . . . . . . . . . . 8
4.1.2. Non-Storing Mode . . . . . . . . . . . . . . . . . . 8
4.1.3. DAO Policy . . . . . . . . . . . . . . . . . . . . . 8
4.1.4. Path Metrics . . . . . . . . . . . . . . . . . . . . 8
4.1.5. Objective Function . . . . . . . . . . . . . . . . . 9
4.1.6. DODAG Repair . . . . . . . . . . . . . . . . . . . . 9
4.1.7. Multicast . . . . . . . . . . . . . . . . . . . . . . 9
4.1.8. Security . . . . . . . . . . . . . . . . . . . . . . 9
4.1.9. P2P communications . . . . . . . . . . . . . . . . . 9
4.2. Layer 2 features . . . . . . . . . . . . . . . . . . . . 9
4.2.1. Security functions provided by layer-2 . . . . . . . 10
4.2.2. 6LowPAN options assumed . . . . . . . . . . . . . . . 10
4.2.3. MLE and other things . . . . . . . . . . . . . . . . 10
4.3. Recommended Configuration Defaults and Ranges . . . . . . 10
5. Manageability Considerations . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6.1. Security Considerations during initial deployment . . . . 10
6.2. Security Considerations during incremental deployment . . 10
7. Other related protocols . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . 12
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Appendix A. RPL shortcomings in home and building deployments . 12
A.1. Risk of undesired long P2P routes . . . . . . . . . . . . 13
A.1.1. Traffic concentration at the root . . . . . . . . . . 13
A.1.2. Excessive battery consumption in source nodes . . . . 13
A.2. Risk of delayed route repair . . . . . . . . . . . . . . 13
A.2.1. Broken service . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
TODO: Adapt to new template
Home automation and building control application spaces share a
substantial number of properties. The purpose of this document is to
give guidance in the use of RPL-P2P to provide the features required
by the requirements documents "Home Automation Routing Requirements
in Low-Power and Lossy Networks" [RFC5826] and "Building Automation
Routing Requirements in Low-Power and Lossy Networks" [RFC5867].
1.1. 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.
1.2. Overview of requirements
Applicable requirements are described in [RFC5826] and [RFC5867].
1.3. Out of scope requirements
The considered network diameter is limited to a max diameter of 10
hops and a typical diameter of 5 hops, which captures the most common
cases in home automation and building control networks.
This document does not consider the applicability of RPL-related
specifications for urban and industrial applications [RFC5548],
[RFC5673], which may exhibit significantly larger network diameters.
2. Deployment Scenario
Networking in buildings is essential to satisfy the energy saving
regulations. Comfort of buildings is adapted to the presence of
individuals. When no one is present, energy consumption can be
reduced. Cost is the main driving factor behind wireless networking
in buildings. Especially for retrofit, wireless connectivity saves
cabling costs.
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A typical home automation network is less than 100 nodes. Large
building deployments may span 10,000 nodes but to ensure
uninterrupted service of light and air conditioning systems in
individual zones of the building, nodes are organized in subnetworks.
Each subnetwork in a building automation deployment typically
contains contains tens to hundreds of nodes.
The main purpose of the network is to provide control over light and
heating/cooling resources. User intervention may be enabled via wall
controllers combined with movement, light and temperature sensors to
enable automatic adjustment of window blinds, reduction of room
temperature, etc.
People expect immediate and reliable responses to their presence or
actions. A light not switching on after entry into a room leads to
confusion and a profound dissatisfaction with the light product.
The surveillance of the correct functioning is at least as important.
Devices communicate regularly their status and send alarm messages
announcing a dysfunction of equipment or network.
In building control the infrastructure of the building management
network can be shared with the security/access, the IP telephony, and
the fire/alarm networks. This approach has a strong impact on the
operation and cost of the network.
2.1. Network Topologies
The typical home automation network or building control subnetwork
can consist of a wired and one or more wireless subnetworks.
Especially in large buildings the wireless network is connected to an
IP backbone network where all infrastructure services are located,
such as DNS, automation servers, etc. The wireless subnetwork is a
mesh network with a border router located at a convenient place in
the home (building).
In a building control network there may be several redundant border
routers to each subnetwork. Subnetworks often overlap geographically
(and from a wireless perspective). Due to the two purposes of the
network, (i) direct control and (ii) surveillance, there may exist
two types of routing topologies in a given subnetwork (i) a tree-
shaped collection of routes spanning from a central building
controller via the border router, on to destination nodes in the
subnetwork, and/or (ii) a flat, un-directed collection of intra-
network routes between functionally related nodes in the subnetwork.
Nodes in Home and Building automation networks are typically
inexpensive devices with very low memory capacity, such as individual
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wall switches. Only a few nodes (such as multi-purpose remote
controls) are more expensive devices, which can afford more memory
capacity.
2.2. Traffic Characteristics
Traffic may enter the network from a central controller or it may
originate from an intra-network node. The majority of traffic is
light-weight point-to-point control style; e.g. Put-Ack or Get-
Response. There are however exceptions. Bulk data transfer is used
for firmware update and logging. Multicast is used for service
discovery or to control groups of nodes, such as light fixtures.
Firmware updates enter the network while logs leave the network.
Often, there is a direct relation between a controlling sensor and
the controlled equipment. The bulk of senders and receivers are
separated by a distance that allows one-hop direct path
communication. A graph of the communication will show several fully
connected subsets of nodes. However, due to interference, multipath
fading, reflection and other transmission mechanisms, the one-hop
direct path may be temporally disconnected. For reliability
purposes, it is therefore essential that alternative n-hop
communication routes exist for quick error recovery. Looking over
time periods of a day, the networks are very lightly loaded.
However, bursts of traffic can be generated by the entry of several
persons simultaneously, the occurrence of a defect, and other
unforeseen events. Under those conditions, the timeliness must
nevertheless be maintained. Therefore, measures are necessary to
remove any unnecessary traffic. Short routes are preferred. Long
multi-hop routes via the edge router, should be avoided whenever
possible. Group communication is essential for lighting control.
For example, once the presence of a person is detected in a given
room, all involved lights in the room and no other lights should be
dimmed, or switched on/off. Several rooms may be covered by the same
wireless subnetwork. To reduce network load, it is advisable that
messages to the lights in a room are not distributed further in the
mesh than necessary on the basis of intended receivers.
2.2.1. Human user responsiveness
While air conditioning and other environmental-control applications
may accept certain response delays, alarm and light control
applications may be regarded as soft real-time systems. A slight
delay is acceptable, but the perceived quality of service degrades
significantly if response times exceed 250 msec. If the light does
not turn on at short notice, a user will activate the controls again,
causing a sequence of commands such as Light{on,off,on,off,..} or
Volume{up,up,up,up,up,...}.
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The reactive discovery features of RPL-P2P ensures that commands are
normally delivered within the 250msec time window and when
connectivity needs to be restored, it is typically completed within
seconds. In most cases an alternative route will work. Thus, route
rediscovery is not even necessary.
2.2.2. Source-sink (SS) communication paradigm
Source-sink (SS) traffic is a common traffic type in home and
building networks. The traffic is generated by environmental sensors
which push periodic readings to a central server. The readings may
be used for pure logging, or more often, to adjust light, heating and
ventilation. Alarm sensors also generate SS style traffic.
With regards to message latency, most SS transmissions can tolerate
worst-case delays measured in tens of seconds. Alarm sensors,
however, represent an exception.
2.2.3. Peer-to-peer (P2P) communication paradigm
Peer-to-peer (P2P) traffic is a common traffic type in home networks.
Some building networks also rely on P2P traffic while others send all
control traffic to a local controller box for advanced scene and
group control; thus generating more SS and P2MP traffic.
P2P traffic is typically generated by remote controls and wall
controllers which push control messages directly to light or heat
sources. P2P traffic has a strong requirement for low latency since
P2P traffic often carries application messages that are invoked by
humans. As mentioned in Section 2.2.1 application messages should be
delivered within less than a second - even when a route repair is
needed before the message can be delivered. .
2.2.4. Peer-to-multipeer (P2MP) communication paradigm
Peer-to-multipeer (P2MP) traffic is common in home and building
networks. Often, a wall switch in a living room responds to user
activation by sending commands to a number of light sources
simultaneously.
Individual wall switches are typically inexpensive devices with
extremely low memory capacities. Multi-purpose remote controls for
use in a home environment typically have more memory but such devices
are asleep when there is no user activity. RPL-P2P reactive
discovery allows a node to wake up and find new routes within a few
seconds while memory constrained nodes only have to keep routes to
relevant targets.
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2.2.5. RPL applicability per communication paradigm
TODO: align with new template
Describe here when we use RPL, RPL-P2P and MPL based on sections on
SS P2P, PMP, and N-cast.
2.3. Link layer applicability
This document applies to [IEEE802.15.4] and [G.9959] which are
adapted to IPv6 by the adaption layers [RFC4944] and [I-D.lowpanz].
Due to the limited memory of a majority of devices (such as
individual light dimmers) RPL-P2P MUST be used with source routing in
non-storing mode. The abovementioned adaptation layers leverage on
the compression capabilities of [RFC6554] and [RFC6282]. Header
compression allows small IP packets to fit into a single layer 2
frame even when source routing is used. A network diameter limited
to 5 hops helps achieving this.
Packet drops are often experienced in the targeted environments.
ICMP, UDP and even TCP flows may benefit from link layer unicast
acknowledgments and retransmissions. Link layer unicast
acknowledgments MUST be enabled when [IEEE802.15.4] or [G.9959] is
used with RPL-P2P.
3. Using RPL-P2P to meet requirements
RPL-P2P SHOULD be used in home and building networks, as point-to-
point style traffic is substantial and route repair needs to be
completed within seconds. RPL- P2P provides a reactive mechanism for
quick, efficient and root- independent route discovery/repair. The
use of RPL-P2P furthermore allows data traffic to avoid having to go
through a central region around the root of the tree, and drastically
reduces path length [SOFT11] [INTEROP12]. These characteristics are
desirable in home and building automation networks because they
substantially decrease unnecessary network congestion around the
tree's root.
4. RPL Profile for RPL-P2P
RPL-P2P MUST be used in home and building networks. Non-storing mode
allows for constrained memory in repeaters when source routing is
used. Reactive discovery allows for low application response times
even when on-the-fly route repair is needed.
4.1. RPL Features
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TODO: New subsection for prefix and address assignment
In one constrained deployment, the link layer master node handing out
the logical network identifier and unique node identifiers may be a
remote control which returns to sleep once new nodes have been added.
There may be no global routable prefixes at all. Likewise, there may
be no authoritative always-on root node since there is no border
router to host this function.
In another constrained deployment, there may be battery powered
sensors and wall controllers configured to contact other nodes in
response to events and then return to sleep. Such nodes may never
detect the announcement of new prefixes via multicast.
In each of the abovementioned constrained deployments, the link layer
master node SHOULD assume the role as authoritative root node,
transmitting singlecast RAs with a ULA prefix information option to
nodes during the inclusion process to prepare the nodes for a later
operational phase, where a border router is added.
A border router SHOULD be designed to be aware of sleeping nodes in
order to support the distribution of updated global prefixes to such
sleeping nodes.
One COULD implement gateway-centric tree-based routing and global
prefix distribution as defined by [RFC6550]. This would however only
work for always-on nodes.
4.1.1. RPL Instances
When operating P2P-RPL on a stand-alone basis, there is no
authoritative root node maintaining a permanent RPL DODAG. A node
MUST be able to join one RPL instance as an instance is created
during each P2P-RPL route discovery operation. A node MAY be
designed to join multiple RPL instances.
4.1.2. Non-Storing Mode
Non-storing mode MUST be used to cope with the extremely constrained
memory of a majority of nodes in the network (such as individual
light switches).
4.1.3. DAO Policy
TBD.
4.1.4. Path Metrics
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TBD.
4.1.5. Objective Function
OF0 MUST be supported and is the RECOMMENDED OF to use. Other
Objective Functions MAY be used as well.
4.1.6. DODAG Repair
Since RPL-P2P only creates DODAGs on a temporary basis during route
repair, there is no need to repair DODAGs.
4.1.7. Multicast
Commercial light deployments may have a need for multicast beyond the
link-local scope. RPL and P2P-RPL do not provide any means for this
transmission mode natively.
Several mechanisms exist for achieving such functionality; [MPL] is
RECOMMENDED for home and building deployments.
[TODO/TBD: text on MPL repeater density]
4.1.8. Security
In order to support low-cost devices and devices running on battery,
the following RPL security parameter values SHOULD be used:
o T = '0': Do not use timestamp in the Counter Field.
o Algorithm = '0': Use CCM with AES-128
o KIM = '10': Use group key, Key Source present, Key Index present
o LVL = 0: Use MAC-32
4.1.9. P2P communications
RPL-P2P [RPL-P2P] MUST be used to accommodate P2P traffic, which is
typically substantial in home and building automation networks.
4.2. Layer 2 features
For deployments based on
[IEEE802.15.4] and [G.9959], security MUST be applied at layer 2
using the mechanisms provided by the relevant standards. Residential
light control can accept a lower security level than other contexts
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(e.g. a nuclear research lab). Safety critical devices like
electronic door locks SHOULD employ additional higher-layer security
while light and heating devices may be sufficiently protected by a
single network key. The border router MAY enforce access policies to
limit access to the trusted LLN domain from the LAN.
4.2.1. Security functions provided by layer-2
TBD.
4.2.2. 6LowPAN options assumed
TBD.
4.2.3. MLE and other things
TBD.
4.3. Recommended Configuration Defaults and Ranges
TODO
5. Manageability Considerations
TODO
6. Security Considerations
TODO
6.1. Security Considerations during initial deployment
TODO: (This section explains how nodes get their initial trust
anchors, initial network keys. It explains if this happens at the
factory, in a deployment truck, if it is done in the field, perhaps
like http://www.lix.polytechnique.fr/hipercom/SmartObjectSecurity/
papers/CullenJennings.pdf)
6.2. Security Considerations during incremental deployment
Replacing a failed node means re-assigning the short address of the
failed node to the new node added to the network. This again allows
a new node replacing a failed node to obtain the same IPv6 addresses
as per the lines of [IPHC].
As it is recommended to base security on a shared group key, it is
possible to replace failed nodes. For specific details on how to
replace failed nodes; refer to the actual link layer documentation.
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TODO / TBD: Special concerns for adding a new node?
7. Other related protocols
Application transport protocols may be CoAP over UDP or equivalents.
Typically, UDP is used for IP transport to keep down the application
response time and bandwidth overhead.
Several features required by [RFC5826], [RFC5867] challenge the P2P
paths provided by RPL. Appendix A reviews these challenges. In some
cases, a node may need to spontaneously initiate the discovery of a
path towards a desired destination that is neither the root of a DAG,
nor a destination originating DAO signaling. Furthermore, P2P paths
provided by RPL are not satisfactory in all cases because they
involve too many intermediate nodes before reaching the destination.
RPL-P2P [RPL-P2P] provides the features requested by [RFC5826] and
[RFC5867]. RPL-P2P uses a subset of the frame formats and features
defined for RPL [RFC6550] but may be combined with RPL frame flows in
advanced deployments.
8. IANA Considerations
9. Acknowledgements
This document reflects discussions and remarks from several
individuals including (in alphabetical order): Michael Richardson,
Mukul Goyal, Jerry Martocci, Charles Perkins, and Zach Shelby
10. References
11. References
11.1. Normative References
[RFC5826] , "Home Automation Routing Requirements in Low-Power and
Lossy Networks", .
[RFC5867] , "Building Automation Routing Requirements in Low-Power
and Lossy Networks", .
[RFC5673] , "Industrial Routing Requirements in Low-Power and Lossy
Networks", .
[RFC5548] , "Routing Requirements for Urban Low-Power and Lossy
Networks", .
[IEEE802.15.4]
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, "IEEE 802.15.4 - Standard for Local and metropolitan
area networks -- Part 15.4: Low-Rate Wireless Personal
Area Networks", , <IEEE Standard 802.15.4>.
[RFC4944] , "Transmission of IPv6 Packets over IEEE 802.15.4
Networks", .
[G.9959] , "ITU-T G.9959 Short range narrow-band digital
radiocommunication transceivers - PHY and MAC layer
specifications", , <ITU-T G.9959>.
[I-D.lowpanz]
Brandt, A., "Transmission of IPv6 Packets over ITU-T
G.9959 Networks", , <draft-brandt-6man-lowpanz>.
[RFC6282] Hui, J., Thubert, P., , , , "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC6282 ,
September 2011.
[RFC6554] Hui, J., Vasseur, JP., Culler, D., Manral, V., , "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC6554 , March
2012.
[RFC6550] , "RPL: IPv6 Routing Protocol for Low-Power and Lossy
Networks", .
[RPL-P2P] Goyal, M., Baccelli, E., Phillip, M., Brandt, A., and J.
Martocci, "Reactive Discovery of Point-to-Point Routes in
Low Power and Lossy Networks", draft-ietf-roll-p2p-rpl ,
May 2012.
11.2. Informative References
[SOFT11] Baccelli, E., Phillip, M., and M. Goyal, "The P2P-RPL
Routing Protocol for IPv6 Sensor Networks: Testbed
Experiments", Proceedings of the Conference on Software
Telecommunications and Computer Networks, Split, Croatia,
September 2011., September 2011.
[INTEROP12]
Baccelli, E., Phillip, M., Brandt, A., Valev , H., and J.
Buron , "Report on P2P-RPL Interoperability Testing",
RR-7864 INRIA Research Report RR-7864, Janurary 2012.
Appendix A. RPL shortcomings in home and building deployments
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This document reflects discussions and remarks from several
individuals including (in alphabetical order): Charles Perkins, Jerry
Martocci, Michael Richardson, Mukul Goyal and Zach Shelby.
A.1. Risk of undesired long P2P routes
The DAG, being a tree structure is formed from a root. If nodes
residing in different branches have a need for communicating
internally, DAG mechanisms provided in RPL [RFC6550] will propagate
traffic towards the root, potentially all the way to the root, and
down along another branch. In a typical example two nodes could
reach each other via just two router nodes but in unfortunate cases,
RPL may send traffic three hops up and three hops down again. This
leads to several undesired phenomena described in the following
sections
A.1.1. Traffic concentration at the root
If many P2P data flows have to move up towards the root to get down
again in another branch there is an increased risk of congestion the
nearer to the root of the DAG the data flows. Due to the broadcast
nature of RF systems any child node of the root is not just directing
RF power downwards its sub-tree but just as much upwards towards the
root; potentially jamming other MP2P traffic leaving the tree or
preventing the root of the DAG from sending P2MP traffic into the DAG
because the listen-before-talk link-layer protection kicks in.
A.1.2. Excessive battery consumption in source nodes
Battery-powered nodes originating P2P traffic depend on the route
length. Long routes cause source nodes to stay awake for longer
periods before returning to sleep. Thus, a longer route translates
proportionally (more or less) into higher battery consumption.
A.2. Risk of delayed route repair
The RPL DAG mechanism uses DIO and DAO messages to monitor the health
of the DAG. In rare occasions, changed radio conditions may render
routes unusable just after a destination node has returned a DAO
indicating that the destination is reachable. Given enough time, the
next Trickle timer-controlled DIODAO update will eventually repair
the broken routes. In a worst-case event this is however too late.
In an apparently stable DAG, Trickle-timer dynamics may reduce the
update rate to a few times every hour. If a user issues an actuator
command, e.g. light on in the time interval between the last DAO
message was issued the destination module and the time one of the
parents sends the next DIO, the destination cannot be reached.
Nothing in RPL kicks in to restore connectivity in a reactive
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fashion. The consequence is a broken service in home and building
applications.
A.2.1. Broken service
Experience from the telecom industry shows that if the voice delay
exceeds 250ms users start getting confused, frustrated and/or
annoyed. In the same way, if the light does not turn on within the
same period of time, a home control user will activate the controls
again, causing a sequence of commands such as
Light{on,off,off,on,off,..} or Volume{up,up,up,up,up,...} Whether the
outcome is nothing or some unintended response this is unacceptable.
A controlling system must be able to restore connectivity to recover
from the error situation. Waiting for an unknown period of time is
not an option. While this issue was identified during the P2P
analysis it applies just as well to application scenarios where an IP
application outside the LLN controls actuators, lights, etc.
Authors' Addresses
Anders Brandt
Sigma Designs
Email: abr@sdesigns.dk
Emmanuel Baccelli
INRIA
Email: Emmanuel.Baccelli@inria.fr
Robert Cragie
Gridmerge
Email: robert.cragie@gridmerge.com
Peter van der Stok
Consultant
Email: consultancy@vanderstok.org
Brandt, et al. Expires November 14, 2013 [Page 14]
