One document matched: draft-ietf-roll-applicability-home-building-01.xml
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<rfc category="info" docName="draft-ietf-roll-applicability-home-building-01"
ipr="trust200902">
<front>
<title abbrev="RPL in home and building">Applicability Statement:
The use of the RPL protocol set in Home Automation and Building
Control</title>
<author fullname="Anders Brandt" initials="A." surname="Brandt">
<organization>Sigma Designs</organization>
<address>
<email>abr@sdesigns.dk</email>
</address>
</author>
<author fullname="Emmanuel Baccelli" initials="E." surname="Baccelli">
<organization>INRIA</organization>
<address>
<email>Emmanuel.Baccelli@inria.fr</email>
</address>
</author>
<author fullname="Robert Cragie" initials="R." surname="Cragie">
<organization>Gridmerge</organization>
<address>
<email>robert.cragie@gridmerge.com</email>
</address>
</author>
<author fullname="Peter van der Stok" initials="P." surname="van der Stok">
<organization>Consultant</organization>
<address>
<email>consultancy@vanderstok.org</email>
</address>
</author>
<date day="17" month="August" year="2013"/>
<area>Routing Area</area>
<workgroup>Roll</workgroup>
<keyword>sensor network</keyword>
<keyword>ad hoc network</keyword>
<keyword>routing</keyword>
<keyword>RPL</keyword>
<keyword>applicability</keyword>
<keyword>routing</keyword>
<keyword>IP networks</keyword>
<abstract>
<t>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.</t>
</abstract>
</front>
<middle>
<section anchor="cid1" title="Introduction">
<t>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 the RPL protocol suite to provide the features required by
the requirements documents "Home Automation Routing Requirements in
Low-Power and Lossy Networks" <xref target="RFC5826"/> and "Building
Automation Routing Requirements in Low-Power and Lossy Networks" <xref
target="RFC5867"/>.</t>
<section title="Terminology">
<t>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 <xref target="RFC2119"/>.</t>
<t>Additionally, this document uses terminology from <xref target="RFC6997"/>,
<xref target="I-D.ietf-roll-trickle-mcast"/>, and <xref target="RFC6550"/>.
</t>
</section>
<section title="Required Reading">
<t>Applicable requirements are described in <xref target="RFC5826"/>
and <xref target="RFC5867"/>.</t>
</section>
<section title="Out of scope requirements">
<t>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.</t>
<t>This document does not consider the applicability of RPL-related
specifications for urban and industrial applications <xref
target="RFC5548"/>, <xref target="RFC5673"/>, which may exhibit
significantly larger network diameters.</t>
</section>
</section>
<section title="Deployment Scenario">
<t>The use of communications networks in buildings is essential to satisfy the energy saving
regulations. Environmental conditions of buildings can be adapted to suit the comfort of the individuals present. Consequently when no one is present, energy consumption can be reduced.
Cost is the main driving factor behind utilizing wireless networking in buildings.
Especially for retrofit, wireless connectivity saves cabling costs.</t>
<t>A typical home automation network is comprised of 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 typically organized in sub-networks. Each sub-network in a
building automation deployment typically contains tens to
hundreds of nodes.</t>
<t>The main purpose of the home or building automation 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. In general, the sensors and actuators in a home or building
typically have fixed physical locations and will remain in the
same home- or building automation network.</t>
<t>People expect an immediate and reliable response to their presence or
actions. A light not switching on after entry into a room may lead to
confusion and a profound dissatisfaction with the lighting product.</t>
<t>Monitoring of functional correctness is at least as important.
Devices typically communicate their status regularly and send alarm messages
notifying a malfunction of equipment or network.</t>
<t>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 positive impact on the
operation and cost of the network.</t>
<section title="Network Topologies">
<t>In general, The home automation network or building control network
consists of wired and wireless sub-networks.
In large buildings especially, the wireless sub-networks can be connected to an
IP backbone network where all infrastructure services are located,
such as DNS, automation servers, etc. The wireless sub-network is typically a
multi-node network with a border router located at a convenient place in the
home (building).</t>
<t>In a building control network, there may be several redundant border
routers to each sub-network. Sub-networks often overlap geographically
and from a wireless coverage perspective. Due to two purposes of the
network, (i) direct control and (ii) monitoring, there may exist two
types of routing topologies in a given sub-network: (i) a tree-shaped
collection of routes spanning from a central building controller via
the border router, on to destination nodes in the sub-network; and/or
(ii) a flat, un-directed collection of intra-network routes between
functionally related nodes in the sub-network.</t>
<t>The majority of nodes in home and building automation networks are typically
devices with very low memory capacity, such as individual
wall switches. Only a few nodes (such as multi-purpose remote
controls) are more expensive devices, which can afford more memory
capacity.</t>
</section>
<section title="Traffic Characteristics">
<t>Traffic may enter the network originating 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, where firmware updates enter the network
and logs leave the network. Group communication is used for service
discovery or to control groups of nodes, such as light fixtures.
</t><t>
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 border router, should be
avoided whenever possible.
</t><t>
Group communication is essential for
lighting control. For example, once the presence of a person is
detected in a given room, lighting control is focused in that room and no other
lights should be dimmed, or switched on/off. In many cases,
this means that a multicast message with a 1-hop and 2-hop radius would
suffice to control the required lights. To reduce network load, it is
advisable that messages to the lights in a room are not distributed
any further in the mesh than necessary based on intended receivers.</t>
<section anchor="SEC_General"
title="General">
<t>Whilst air conditioning and other environmental-control
applications may accept response delays of tens of seconds or longer, 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 may activate the
controls again, thus causing a sequence of commands such as
Light{on,off,on,off,..} or Volume{up,up,up,up,up,...}.</t>
</section>
<section title="Source-sink (SS) communication paradigm">
<t>This paradigm translates to many sources sending messages to the
same sink, sometimes reachable via the border router.
As such, source-sink (SS) traffic can be present in home and
building networks. The traffic is generated by environmental sensors
(often present in a wireless sub-network)
which push periodic readings to a central server. The readings may
be used for pure logging, or more often, processed to adjust light, heating
and ventilation. Alarm sensors also generate SS style traffic.
The central server in a home automation network will be connected mostly to a wired sub-network.
The central server in a building automation network may be connected to a backbone or
be placed outside the building.</t>
<t>With regards to message latency, most SS transmissions can
tolerate worst-case delays measured in tens of seconds. Alarm
sensors, however, represent an exception. Special provisions with
respect to the location of the Alarm server(s) need to be put in place to respect the specified delays.</t>
</section>
<section title="Publish-subscribe (PS, or pub/sub)) communication paradigm">
<t>This paradigm translates to a number of devices expressing their interest
for a service provided by a server device. For example, a server device can be a sensor
delivering temperature readings on the basis of delivery criteria, like changes in acquisition value
or age of the latest acquisition. In building automation networks, this paradigm may be closely related
to the SS paradigm as servers, which are connected to the backbone or outside the building,
can subscribe to data collectors that are present at
strategic places in the building automation network. The use of PS will probably
differ significantly from installation to installation.</t>
</section>
<section anchor="SEC_PeerToPeerCommunication"
title="Peer-to-peer (P2P) communication paradigm">
<t> This paradigm translates to a device transferring data to another device
often connected to the same sub-network.
Peer-to-peer (P2P) traffic is a common traffic type in home
automation networks. Some building automation networks also rely on P2P traffic while
others send all control traffic to a local controller box for
advanced scene and group control. The latter controller boxes can be connected
to service control boxes thus generating more SS or PS traffic.</t>
<t>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 <xref target="SEC_General"/>
application messages should be delivered within a few hundred milliseconds -
even when connections fail momentarily.</t>
</section>
<section title="Peer-to-multipeer (P2MP) communication paradigm">
<t> This paradigm translates to a device sending a message as many times
as there are destination devices.
Peer-to-multipeer (P2MP) traffic is common in home and building automation
networks. Often, a thermostat in a living room responds to temperature changes
by sending temperature acquisitions to several fans and valves
consecutively.</t>
</section>
<section title="N-cast communication paradigm">
<t>This paradigm translates to a device sending a message to many destinations in one network transfer invocation.
Multicast is well suited for lighting where a presence sensor sends
a presence message to a set of lighting devices. Multicast increases the probability that
the message is delivered within the strict time constraints. The chosen multicast algorithm
(e.g. xref target="I-D.ietf-roll-trickle-mcast"/>) assures that messages are delivered to ALL destinations.</t>
</section>
<section title="RPL applicability per communication paradigm">
<t> In the case of SS over a wireless sub-network to a server reachable via a border router,
the use of RPL <xref target="RFC6550"/> is recommended. Given the low resources of
the devices, source routing will be used for messages from outside the wireless
sub-network to the destination in the wireless sub-network. No specific timing constraints
are associated with the SS type messages so network repair does not violate the operational constraints.
When no SS traffic takes place, it is recommended to load only RPL-P2P code into the network stack to satisfy memory
requirements by reducing code. </t>
<t>All P2P and P2MP traffic, taking place within a wireless sub-network, requires P2P-RPL <xref target="RFC6997"/>
to assure responsiveness. Source and destination are typically close together
to satisfy the living conditions of one room. Consequently, most P2P and P2MP traffic is 1-hop
or 2-hop traffic. <xref target="RPL_shortcomings"/> explains why RPL-P2P is preferable to RPL for this
type of communication.</t>
<t>Additional advantages of RPL-P2P for home and building automation networks are, for example:
<list style="symbols">
<t>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.</t>
<t>The reactive discovery features of RPL-P2P ensure 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 (earlier discovered) route will work.
Thus, route rediscovery is not even necessary.</t>
</list>
Due to the limited memory of the majority of devices, RPL-P2P MUST be used with source routing in
non-storing mode as explained in <xref target="sec-storing"/>.</t>
<t>N-cast over the wireless network will be done using multicast with MPL <xref target="I-D.ietf-roll-trickle-mcast"/>. Configuration constraints
that are necessary to meet reliability and timeliness with MPL are discussed in <xref target="sec-multicast"/>.
</t>
</section>
</section>
<section title="Layer-2 applicability">
<t>This document applies to <xref target="IEEE802.15.4"/> and <xref
target="G.9959"/> which are adapted to IPv6 by the adaption layers
<xref target="RFC4944"/> and <xref target="I-D.brandt-6man-lowpanz"/>.</t>
<t>The above mentioned adaptation layers leverage on the
compression capabilities of <xref target="RFC6554"/> and <xref
target="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 to achieve this.</t>
<t>Dropped packets 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 <xref target="IEEE802.15.4"/> or
<xref target="G.9959"/> is used with RPL and RPL-P2P.</t>
</section>
</section>
<section title="Using RPL to meet Functional Requirements">
<t>RPL-P2P MUST be present in home and building automation 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 <xref target="SOFT11"/> <xref target="INTEROP12"/>. These
characteristics are desirable in home and building automation networks
because they substantially decrease unnecessary network congestion
around the root of the tree.</t>
<t> When reliability is required, multiple independent paths are used with
RPL-P2P. For 1-hop destinations this means that one 1-hop communication and
a second 2-hop communication take place via a neigboring node. The same
reliability can be achieved by using MPL where the seed is a repeater and
a second repeater is 1 hop removed from the seed and the destination node.
</t>
</section>
<section title="RPL Profile">
<t>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.</t>
<section title="RPL Features">
<t>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.</t>
<t>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.</t>
<t>In each of the above mentioned 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.</t>
<t>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.</t>
<t>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.</t>
<section title="RPL Instances">
<t>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.</t>
</section>
<section anchor="sec-storing" title="Storing vs. Non-Storing Mode">
<t>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).</t>
</section>
<section title="DAO Policy">
<t>A node MAY be
designed to join multiple RPL instances; in that case DAO policies may be needed.</t>
<t> DAO policy is out of scope for this applicability statement. </t>
</section>
<section title="Path Metrics">
<t>OF0 is RECOMMENDED. <xref target="RFC6551"/> provides other options. Using other objective functions
than OF0 may affect inter-operability.</t>
</section>
<section title="Objective Function">
<t>OF0 MUST be supported and is the RECOMMENDED Objective Function to use. Other
Objective Functions MAY be used as well.</t>
</section>
<section title="DODAG Repair">
<t>Since RPL-P2P only creates DODAGs on a temporary basis during
route repair, there is no need to repair DODAGs.</t>
</section>
<section anchor="sec-multicast" title="Multicast">
<t>Commercial light deployments may have a need for multicast.
Several mechanisms exist for achieving such functionality; <xref target="I-D.ietf-roll-trickle-mcast"/>
is RECOMMENDED for home and building deployments.</t>
<t>Guaranteeing timeliness is intimately related to the density of the MPL routers.
In ideal circumstances the message is propagated as a single wave through the network, such
that the maximum delay is related to the number of hops times the smallest repetition interval of MPL.
Each repeater that receives the message, passes the message on to the next hop by repeating the
message. Repetition of the message can be inhibited by a small value of k. Therefore the value of k
should be chosen high enough to make sure that messages are repeated immediately.
However, a network that is too dense leads to a saturation of the medium that can only be prevented by selecting a
low value of k. Consequently, timeliness is assured by choosing a relatively high value of k
but assuring at the same time a low enough density of repeaters to reduce the risk of medium saturation.
Depending on the reliability of the network channels, it is advisable to choose the network such
that at least 2 repeaters (one repeater located on the seed) can repeat messages to the same set of destinations.</t>
<t>There are no rules about selecting repeaters for MPL. In buildings with central managment tools, the repeaters can be selected,
but in the home is not possible to automatically configure the repeater topology at this moment.
</t>
</section>
<section title="Security">
<t>In order to support low-cost devices and devices running on
battery, RPL MAY use either unsecured messages or secured messages. If RPL is used with unsecured messages, link layer security SHOULD be used. If RPL is used with secured messages, the following RPL security parameter values SHOULD be used:</t>
<t><list style="symbols">
<t>T = ‘0’: Do not use timestamp in the Counter
Field.</t>
<t>Algorithm = ‘0’: Use CCM with AES-128</t>
<t>KIM = ‘10’: Use group key, Key Source present,
Key Index present</t>
<t>LVL = 0: Use MAC-32</t>
</list></t>
</section>
<section title="P2P communications">
<t><xref target="RFC6997"/> MUST be used to accommodate
P2P traffic, which is typically substantial in home and building
automation networks.</t>
</section>
<section title="IPv6 adddress configuration">
<t>Assigned IP addresses MUST be routable and unique within the routing domain.</t>
</section>
</section>
<section title="Layer 2 features">
<t>No particular requirements exist for layer 2 but for the ones cited in the IP over Foo RFCs.</t>
<!--
<section title="Specifics about layer-2">
<t>Not applicable</t>
</section>
<section title="Services provided at layer-2">
<t>Not applicable</t>
</section>
<section title="6LowPAN options assumed">
<t>Not applicable</t>
</section>
-->
</section>
<section title="Recommended Configuration Defaults and Ranges ">
<t>The following sections describe the recommended parameter values for RPL-P2P, Trickle, and MPL. </t>
<section title="RPL-P2P parameters">
<t>RPL-P2P <xref target="RFC6997"/> provides the features requested by
<xref target="RFC5826"/> and <xref target="RFC5867"/>. RPL-P2P uses a
subset of the frame formats and features defined for RPL <xref
target="RFC6550"/> but may be combined with RPL frame flows in advanced
deployments.</t>
<t>Parameter values for RPL-P2P are:
<list style="symbols">
<t>MinHopRankIncrease 1</t>
<t>MaxRankIncrease 0</t>
<t>MaxRank 6</t>
<t>Objective function: OF0</t>
</list> </t>
</section>
<section title="Trickle parameters">
<t>Trickle is used to distribute network parameter values to all nodes without stringent
time restrictions. Trickle parameter values are:
<list style="symbols">
<t>DIOIntervalMin 4 = 16 ms</t>
<t>DIOIntervalDoublings 14</t>
<t>DIORedundancyConstant 1</t>
</list>
</t>
</section>
<section title="MPL parameters">
<t>MPL is used to distribute values to groups of devices. In MPL, based on Trickle algorithm, also timeliness should be guaranteed.
Under the condition that the density of MPL repeaters can be limited, it is possible to choose low
MPL repeat intervals (Imin) connected to k values such that k>2. The minimum value of k is related to:
<list style="symbols">
<t>Value of Imin. The length of Imin determines the number of packets that can be received within the listening period of Imin.</t>
<t>Number of repeaters repeating the same 1-hop broadcast message.
These repeaters repeat within the same Imin interval, thus increasing the c counter.</t>
</list>
Suggested MPL parameter values are:
<list style="symbols">
<t> I_min = 10 - 50.</t>
<t> I_max = 200 - 400. </t>
<t> k > 2 (see above). </t>
<t> max_expiration = 2 - 4. </t>
</list>
</t>
</section>
</section>
</section>
<section title="Manageability Considerations">
<t>Manageability is out of scope for home network scenarios. In building automation scenarios, central control should be applied based on MIBs.</t>
</section>
<section title="Security Considerations">
<t>Refer to the security considerations of <xref target="RFC6997"/>, <xref target="RFC6550"/>,
and <xref target="I-D.ietf-roll-trickle-mcast"/>.</t>
<section title="Security Considerations for distribution of credentials required for RPL">
<t>Communications network security is based on providing integrity protection and
encryption to messages. This can be applied at various layers in the network protocol
stack based on using various credentials and a network identity.</t>
<t>The credentials which are relevant in the case of RPL are: (i) the credential used
at the link layer in the case where link layer security is applied or (ii) the credential
used for securing RPL messages. In both cases, the assumption is that the credential is a
shared key. Therefore, there MUST be a mechanism in place which allows secure distribution
of a shared key and configuration of network identity. Both MAY be done using (i) pre-installation using an out-of-band method,
(ii) delivered securely when a device is introduced into the network or (iii) delivered
securely by a trusted neighboring device. The shared key MUST be stored in a secure fashion which makes
it difficult to be read by an unauthorized party. An example of a method whereby this can be achieved
is detailed in <xref target="SmartObj"/> </t>
</section>
<section title="Security Considerations for P2P uses">
<t>Refer to the security considerations of <xref target="RFC6997"/>.</t>
</section>
</section>
<section title="Other related protocols">
<t>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.</t>
<t>Several features required by <xref target="RFC5826"/>, <xref
target="RFC5867"/> challenge the P2P paths provided by RPL. <xref
target="RPL_shortcomings"/> 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.</t>
</section>
<section title="IANA Considerations">
<t> No considerations for IANA pertain to this document. </t>
</section>
<section title="Acknowledgements">
<t>This document reflects discussions and remarks from several
individuals including (in alphabetical order): Mukul
Goyal, Jerry Martocci, Charles Perkins, Michael Richardson, and Zach Shelby</t>
</section>
<section title="Changelog">
<t>
Changes from version 0 to version 1.
<list style="symbols">
<t>Adapted section structure to template. </t>
<t>Standardized the reference syntax.</t>
<t>Section 2.2, moved everything concerning algorithms to section 2.2.7, and adpted text in 2.2.1-2.2.6.</t>
<t>Added MPL parameter text to section 4.1.7 and section 4.3.1.</t>
<t> Replaced all TODO sections with text. </t>
<t> Consistent use of border router, mintoring, home- and building network. </t>
<t> Reformulated security aspects with references to other publications. </t>
<t> MPL and RPL parameter values introduced.</t>
</list>
</t>
</section>
</middle>
<back>
<references title="Normative References">
&RFC2119;
&RFC4944;
&RFC5548;
&RFC5673;
&RFC5826;
&RFC5867;
&RFC6282;
&RFC6550;
&RFC6551;
&RFC6554;
&RFC6997;
&I-D.brandt-6man-lowpanz;
&I-D.ietf-roll-trickle-mcast;
<reference anchor="IEEE802.15.4" target="IEEE Standard 802.15.4">
<front>
<title>IEEE 802.15.4 - Standard for Local and metropolitan area
networks -- Part 15.4: Low-Rate Wireless Personal Area
Networks</title>
<author fullname="IEEE Computer Society" initials="" surname="">
<organization/>
</author>
<date/>
</front>
</reference>
<reference anchor="G.9959" target="ITU-T G.9959">
<front>
<title>ITU-T G.9959 Short range narrow-band digital
radiocommunication transceivers - PHY and MAC layer
specifications</title>
<author fullname="ITU-T SG 15" initials="" surname="">
<organization/>
</author>
<date/>
</front>
</reference>
</references>
<references title="Informative References">
<reference anchor="SOFT11">
<front>
<title>The P2P-RPL Routing Protocol for IPv6 Sensor Networks:
Testbed Experiments</title>
<author fullname="E. Baccelli" initials="E." surname="Baccelli"/>
<author fullname="M. Philipp" initials="M." surname="Phillip"/>
<author fullname="M.Goyal" initials="M." surname="Goyal"/>
<date day="8" month="September" year="2011"/>
</front>
<seriesInfo name=""
value="Proceedings of the Conference on Software Telecommunications and Computer Networks, Split, Croatia, September 2011."/>
</reference>
<reference anchor="INTEROP12">
<front>
<title>Report on P2P-RPL Interoperability Testing</title>
<author fullname="E. Baccelli" initials="E." surname="Baccelli"/>
<author fullname="M. Philipp" initials="M." surname="Phillip"/>
<author fullname="A. Brandt" initials="A." surname="Brandt"/>
<author fullname="H. Valev " initials="H." surname="Valev "/>
<author fullname="J. Buron " initials="J." surname="Buron "/>
<date day="20" month="Janurary" year="2012"/>
</front>
<seriesInfo name="RR-7864" value="INRIA Research Report RR-7864"/>
</reference>
<reference anchor="SmartObj">
<front>
<title>Transitive Trust Enrollment for Constrained Devices</title>
<author fullname="Cullen Jennings" initials="C." surname="Jennings"/>
<date day="14" month="February" year="2012"/>
</front>
<seriesInfo name="Web" value="http://www.lix.polytechnique.fr/hipercom/SmartObjectSecurity/papers/CullenJennings.pdf"/>
</reference>
</references>
<section anchor="RPL_shortcomings"
title="RPL shortcomings in home and building deployments">
<t>This document reflects discussions and remarks from several
individuals including (in alphabetical order): Charles Perkins, Jerry
Martocci, Michael Richardson, Mukul Goyal and Zach Shelby.</t>
<section title="Risk of undesired long P2P routes ">
<t>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 <xref target="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</t>
<section title="Traffic concentration at the root ">
<t>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.</t>
</section>
<section title="Excessive battery consumption in source nodes ">
<t>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.</t>
</section>
</section>
<section title="Risk of delayed route repair ">
<t>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 DIO/DAO update will eventually repair
the broken routes, however this may not occur in a timely manner appropriate to the application. 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. There is no mechanism in RPL to
initiate restoration of connectivity in a reactive fashion. The consequence is a
broken service in home and building applications.</t>
<section title="Broken service">
<t>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.</t>
</section>
</section>
</section>
</back>
</rfc>
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