Internet DRAFT - draft-ietf-roll-applicability-home-building
draft-ietf-roll-applicability-home-building
Roll A. Brandt
Internet-Draft Sigma Designs
Intended status: Standards Track E. Baccelli
Expires: January 22, 2016 INRIA
R. Cragie
ARM Ltd.
P. van der Stok
Consultant
July 21, 2015
Applicability Statement: The use of the RPL protocol suite in Home
Automation and Building Control
draft-ietf-roll-applicability-home-building-12
Abstract
The purpose of this document is to provide guidance in the selection
and use of protocols from the RPL protocol suite to implement the
features required for control in building and home environments.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 22, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Relationship to other documents . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Required Reading . . . . . . . . . . . . . . . . . . . . 5
1.4. Out of scope requirements . . . . . . . . . . . . . . . . 5
2. Deployment Scenario . . . . . . . . . . . . . . . . . . . . . 5
2.1. Network Topologies . . . . . . . . . . . . . . . . . . . 6
2.2. Traffic Characteristics . . . . . . . . . . . . . . . . . 7
2.2.1. General . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.2. Source-sink (SS) communication paradigm . . . . . . . 8
2.2.3. Publish-subscribe (PS, or pub/sub)) communication
paradigm . . . . . . . . . . . . . . . . . . . . . . 9
2.2.4. Peer-to-peer (P2P) communication paradigm . . . . . . 9
2.2.5. Peer-to-multipeer (P2MP) communication paradigm . . . 10
2.2.6. Additional considerations: Duocast and N-cast . . . . 10
2.2.7. RPL applicability per communication paradigm . . . . 10
2.3. Layer-2 applicability . . . . . . . . . . . . . . . . . . 11
3. Using RPL to meet Functional Requirements . . . . . . . . . . 12
4. RPL Profile . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.1. RPL Features . . . . . . . . . . . . . . . . . . . . . . 13
4.1.1. RPL Instances . . . . . . . . . . . . . . . . . . . . 13
4.1.2. Storing vs. Non-Storing Mode . . . . . . . . . . . . 14
4.1.3. DAO Policy . . . . . . . . . . . . . . . . . . . . . 14
4.1.4. Path Metrics . . . . . . . . . . . . . . . . . . . . 14
4.1.5. Objective Function . . . . . . . . . . . . . . . . . 14
4.1.6. DODAG Repair . . . . . . . . . . . . . . . . . . . . 14
4.1.7. Multicast . . . . . . . . . . . . . . . . . . . . . . 15
4.1.8. Security . . . . . . . . . . . . . . . . . . . . . . 16
4.1.9. P2P communications . . . . . . . . . . . . . . . . . 19
4.1.10. IPv6 address configuration . . . . . . . . . . . . . 19
4.2. Layer 2 features . . . . . . . . . . . . . . . . . . . . 19
4.2.1. Specifics about layer-2 . . . . . . . . . . . . . . . 19
4.2.2. Services provided at layer-2 . . . . . . . . . . . . 19
4.2.3. 6LowPAN options assumed . . . . . . . . . . . . . . . 20
4.2.4. Mesh Link Establishment (MLE) and other things . . . 20
4.3. Recommended Configuration Defaults and Ranges . . . . . . 20
4.3.1. Trickle parameters . . . . . . . . . . . . . . . . . 20
4.3.2. Other Parameters . . . . . . . . . . . . . . . . . . 20
5. MPL Profile . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.1. Recommended configuration Defaults and Ranges . . . . . . 21
5.1.1. Real-Time optimizations . . . . . . . . . . . . . . . 21
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5.1.2. Trickle parameters . . . . . . . . . . . . . . . . . 21
5.1.3. Other parameters . . . . . . . . . . . . . . . . . . 22
6. Manageability Considerations . . . . . . . . . . . . . . . . 23
7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
7.1. Security considerations during initial deployment . . . . 23
7.2. Security Considerations during incremental deployment . . 24
7.3. Security Considerations for P2P uses . . . . . . . . . . 25
7.4. MPL routing . . . . . . . . . . . . . . . . . . . . . . . 25
7.5. RPL Security features . . . . . . . . . . . . . . . . . . 25
8. Other related protocols . . . . . . . . . . . . . . . . . . . 25
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 26
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
12.1. Normative References . . . . . . . . . . . . . . . . . . 28
12.2. Informative References . . . . . . . . . . . . . . . . . 32
Appendix A. RPL shortcomings in home and building deployments . 33
A.1. Risk of undesired long P2P routes . . . . . . . . . . . . 33
A.1.1. Traffic concentration at the root . . . . . . . . . . 34
A.1.2. Excessive battery consumption in source nodes . . . . 34
A.2. Risk of delayed route repair . . . . . . . . . . . . . . 34
A.2.1. Broken service . . . . . . . . . . . . . . . . . . . 34
Appendix B. Communication failures . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction
The primary purpose of this document is to give guidance in the use
of the Routing Protocol for Low power and lossy networks (RPL)
protocol suite in two application domains:
o Home automation
o Building automation
The guidance is based on 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] respectively.
The Advanced Metering Infrastructure is also considered where
appropriate. The applicability domains distinguish themselves in the
way they are operated, their performance requirements, and the most
likely network structures. An abstract set of distinct communication
paradigms is then used to frame the applicability domains.
Home automation and building automation application domains share a
substantial number of properties:
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o In both domains, the network can be disconnected from the ISP and
must still continue to provide control to the occupants of the
home/building. Routing needs to be possible independent of the
existence of a border router
o Both domains are subject to unreliable links but require instant
and very reliable reactions. This has impact on routing because
of timeliness and multipath routing.
The differences between the two application domains mostly appear in
commissioning, maintenance and the user interface, which do not
typically affect routing. Therefore, the focus of this applicability
document is on reliability, timeliness, and local routing.
It should be noted that adherence to the guidance does not
necessarily guarantee fully interoperable solutions in home
automation networks and building control networks and that additional
rigorous and managed programs will be needed to ensure
interoperability.
1.1. Relationship to other documents
The Routing Over Low power and Lossy networks (ROLL) working group
has specified a set of routing protocols for Low-Power and Lossy
Networks (LLN) [RFC6550]. This applicability text describes a subset
of those protocols and the conditions under which the subset is
appropriate and provides recommendations and requirements for the
accompanying parameter value ranges.
In addition, an extension document has been produced specifically to
provide a solution for reactive discovery of point-to-point routes in
LLNs [RFC6997]. The present applicability document provides
recommendations and requirements for the accompanying parameter value
ranges.
A common set of security threats are described in [RFC7416]. The
applicability statements complement the security threats document by
describing preferred security settings and solutions within the
applicability statement conditions. This applicability statement
recommends lighter weight security solutions appropriate for home and
building environments and indicates why these solutions are
appropriate.
1.2. Terminology
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 [RFC2119].
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Additionally, this document uses terminology from [RFC6997],
[I-D.ietf-roll-trickle-mcast], [RFC7102], [IEEE802.15.4], and
[RFC6550].
1.3. Required Reading
Applicable requirements are described in [RFC5826] and [RFC5867]. A
survey of the application field is described in [BCsurvey].
1.4. Out of scope requirements
The considered network diameter is limited to a maximum 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 Routing Protocol
for Low-Power and Lossy Networks (RPL)-related specifications for
urban and industrial applications [RFC5548], [RFC5673], which may
exhibit significantly larger network diameters.
2. Deployment Scenario
The use of communications networks in buildings is essential to
satisfy energy saving regulations. Environmental conditions of
buildings can be adapted to suit the comfort of the individuals
present inside. Consequently when no one is present, energy
consumption can be reduced. Cost is the main driving factor behind
deployment of wireless networking in buildings, especially in the
case of retrofitting, where wireless connectivity saves costs
incurred due to cabling and building modifications.
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, and for critical
operations may operate independently from the other sub-networks.
The main purpose of the home or building automation network is to
provide control over light and heating/cooling resources. User
intervention via wall controllers is 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.
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People expect an immediate and reliable response to their presence or
actions. For example, a light not switching on after entry into a
room may lead to confusion and a profound dissatisfaction with the
lighting product.
Monitoring of functional correctness is at least as important as
timely responses. Devices typically communicate their status
regularly and send alarm messages notifying a malfunction of
controlled equipment or network.
In building control, the infrastructure of the building management
network can be shared with the security/access, the Internet Protocol
(IP) telephony, and the fire/alarm networks. This approach has a
positive impact on the operation and cost of the network; however,
care should be taken to ensure that the availability of the building
management network does not become compromised beyond the ability for
critical functions to perform adequately.
In homes, the entertainment network for audio/video streaming and
gaming has different requirements, where the most important
requirement is the need for high bandwidth not typically needed for
home or building control. It is therefore expected that the
entertainment network in the home will mostly be separate from the
control network, which also lessens the impact on availability of the
control network
2.1. Network Topologies
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 Domain Name System (DNS), automation servers, etc.
The wireless sub-network can be configured according to any of the
following topologies:
o A stand-alone network of 10-100 nodes without border router. This
typically occurs in the home with a stand-alone control network,
in low cost buildings, and during installation of high end control
systems in buildings.
o A connected network with one border router. This configuration
will happen in homes where home appliances are controlled from
outside the home, possibly via a smart phone, and in many building
control scenarios.
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o A connected network with multiple border routers. This will
typically happen in installations of large buildings.
Many of the nodes are battery-powered and may be sleeping nodes which
wake up according to clock signals or external events.
In a building control network, for a large installation with multiple
border routers, sub-networks often overlap both 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.
The majority of nodes in home and building automation networks are
typically class 0 devices [RFC7228], such as individual wall
switches. Only a few nodes (such as multi-purpose remote controls)
are more expensive Class 1 devices, which can afford more memory
capacity.
2.2. Traffic Characteristics
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.
Often, there is a direct physical relation between a controlling
sensor and the controlled equipment. For example the temperature
sensor and room controller are located in the same room sharing the
same climate conditions. Consequently, 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. (See Appendix B
for motivation.)
Looking over time periods of a day, the networks are very lightly
loaded. However, bursts of traffic can be generated by e.g.
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incessant pushing of the button of a remote control, 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.
Group communication is essential for lighting control. For example,
once the presence of a person is detected in a given room, lighting
control applies to that room only 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. The same argument holds for Heating,
Ventilating, and Air Conditioning (HVAC) and other climate control
devices. 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.
An example of an office surface is shown in [office-light], and the
current use of wireless lighting control products is shown in
[occuswitch].
2.2.1. General
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 ms. 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,...}. In addition
the repetitive sending of commands creates an unnecessary loading of
the network, which in turn increases the bad responsiveness of the
network.
2.2.2. Source-sink (SS) communication paradigm
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 may be 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
may also generate SS style traffic. The central server in a home
automation network will be connected mostly to a wired network
segment of the home network, although it is likely that cloud
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services will also be used. The central server in a building
automation network may be connected to a backbone or be placed
outside the building.
With regards to message latency, most SS transmissions can tolerate
worst-case delays measured in tens of seconds. Fire detectors,
however, represent an exception; For example, special provisions with
respect to the location of the Fire detectors and the smoke dampers
need to be put in place to meet the stringent delay requirements
measured in seconds.
2.2.3. Publish-subscribe (PS, or pub/sub)) communication paradigm
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 given that
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.
2.2.4. Peer-to-peer (P2P) communication paradigm
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. Most
building automation networks rely on P2P traffic, described in the
next paragraph. Other building automation networks rely on P2P
control traffic between controls and a local controller box for
advanced group control. A local controller box can be further
connected to service control boxes, thus generating more SS or PS
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 stringent 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 a few hundred milliseconds - even when
connections fail momentarily.
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2.2.5. Peer-to-multipeer (P2MP) communication paradigm
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. This paradigm is also closely related to the PS
paradigm in the case where a single server device has multiple
subscribers.
2.2.6. Additional considerations: Duocast and N-cast
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 recommended multicast algorithm (e.g.
[I-D.ietf-roll-trickle-mcast]) provides a mechanism for delivering
messages to all intended destinations.
2.2.7. RPL applicability per communication paradigm
In the case of the SS paradigm applied to a wireless sub-network to a
server reachable via a border router, the use of RPL [RFC6550] in
non-storing mode is appropriate. Given the low resources of the
devices, source routing will be used from the border router to the
destination in the wireless sub-network for messages generated
outside the mesh 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 good practice to load only RPL code enabling P2P mode of
operation [RFC6997] to reduce the code size and satisfy memory
requirements.
P2P-RPL [RFC6997] is required for all P2P and P2MP traffic taking
place between nodes within a wireless sub-network (excluding the
border router) to assure responsiveness. Source and destination
devices are typically physically close based on room layout.
Consequently, most P2P and P2MP traffic is 1-hop or 2-hop traffic.
Appendix A explains why P2P-RPL is preferable to RPL for this type of
communication. Appendix B explains why reliability measures such as
multi-path routing are necessary even when 1-hop communication
dominates.
Additional advantages of P2P-RPL for home and building automation
networks are, for example:
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o Individual wall switches are typically inexpensive class 0 devices
[RFC7228] 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.
P2P-RPL 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.
o The reactive discovery features of P2P-RPL ensure that commands
are normally delivered within the 250 ms time window. When
connectivity needs to be restored, discovery is typically
completed within seconds. In most cases, an alternative (earlier
discovered) route will work and route rediscovery is not
necessary.
o Broadcast storms typically associated with route discovery for Ad
hoc On-Demand Distance Vector (AODV) [RFC3561] are less disruptive
for P2P-RPL. P2P-RPL has a "STOP" bit which is set by the target
of a route discovery to notify all other nodes that no more
Directed Acyclic Graph (DAG) Information Option (DIO) messages
should be forwarded for this temporary DAG. Something looking
like a broadcast storm may happen when no target is responding
however, in this case, the Trickle suppression mechanism kicks in,
limiting the number of DIO forwards in dense networks.
Due to the limited memory of the majority of devices, P2P-RPL SHOULD
be deployed with source routing in non-storing mode as explained in
Section 4.1.2.
Multicast with Multicast Protocol for Low power and Lossy Networks
(MPL) [I-D.ietf-roll-trickle-mcast] is preferably deployed for N-cast
over the wireless network. Configuration constraints that are
necessary to meet reliability and timeliness with MPL are discussed
in Section 4.1.7.
2.3. Layer-2 applicability
This document applies to [IEEE802.15.4] and [G.9959] which are
adapted to IPv6 by the adaption layers [RFC4944] and [RFC7428].
Other layer-2 technologies, accompanied by an "IP over Foo"
specification, are also relevant provided there is no frame size
issue, and there are link layer acknowledgements.
The above mentioned 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 to
achieve this even while using source routing.
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Dropped packets are often experienced in the targeted environments.
Internet Control Message Protocol (ICMP), User Datagram Protocol
(UDP) and even Transmission Control Protocol (TCP) flows may benefit
from link layer unicast acknowledgments and retransmissions. Link
layer unicast acknowledgments SHOULD be enabled when [IEEE802.15.4]
or [G.9959] is used with RPL and P2P-RPL.
3. Using RPL to meet Functional Requirements
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 Destination Advertisement Object (DAO)
signalling. Furthermore, P2P paths provided by RPL are not
satisfactory in all cases because they involve too many intermediate
nodes before reaching the destination.
P2P-RPL [RFC6997] SHOULD be used in home automation and building
control networks, as point-to-point style traffic is substantial and
route repair needs to be completed within seconds. P2P-RPL provides
a reactive mechanism for quick, efficient and root-independent route
discovery/repair. The use of P2P-RPL 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 root of the tree.
When more reliability is required, P2P-RPL enables the establishment
of multiple independent paths. For 1-hop destinations this means
that one 1-hop communication and a second 2-hop communication take
place via a neighbouring node. Such a pair of redundant
communication paths can be achieved by using MPL where the source is
a MPL forwarder, while a second MPL forwarder is 1 hop away from both
the source and the destination node. When the source multicasts the
message, it may be received by both the destination and the 2nd
forwarder. The 2nd forwarder forwards the message to the
destination, thus providing two routes from sender to destination.
To provide more reliability with multiple paths, P2P-RPL can maintain
two independent P2P source routes per destination, at the source.
Good practice is to use the paths alternately to assess their
existence. When one P2P path has failed (possibly only temporarily),
as described in Appendix B, the alternative P2P path can be used
without discarding the failed path. The failed P2P path, unless
proven to work again, can be safely discarded after a timeout
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(typically 15 minutes). A new route discovery is done when the
number of P2P paths is exhausted due to persistent link failures.
4. RPL Profile
P2P-RPL SHOULD be used in home automation and building control
networks. Its reactive discovery allows for low application response
times even when on-the-fly route repair is needed. Non-storing mode
SHOULD be used to reduce memory consumption in repeaters with
constrained memory when source routing is used.
4.1. RPL Features
An important constraint on the application of RPL is the presence of
sleeping nodes.
For example, in a stand-alone network, the master node (or
coordinator) providing the logical layer-2 identifier and unique node
identifiers to connected nodes may be a remote control which returns
to sleep once new nodes have been added. Due to the absence of the
border router, 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 a network with a border router and many sleeping nodes, 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 above mentioned constrained deployments, a link layer
node (e.g. coordinator or master) SHOULD assume the role of
authoritative root node, transmitting unicast Router Advertisement
(RA) messages with a Unique Local Address (ULA) prefix information
option to nodes during the joining 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.
4.1.1. RPL Instances
When operating P2P-RPL on a stand-alone basis, there is no
authoritative root node maintaining a permanent RPL Direction-
Oriented Directed Acyclic Graph (DODAG). A node MUST be able to join
at least one RPL instance, as a new, temporary instance is created
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during each P2P-RPL route discovery operation. A node MAY be
designed to join multiple RPL instances.
4.1.2. Storing vs. 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
Nodes send DAO messages to establish downward paths from the root to
themselves. DAO messages are not acknowledged in networks composed
of battery operated field devices in order to minimize the power
consumption overhead associated with path discovery. The DAO
messages build up a source route because the nodes MUST be in non-
storing mode.
If devices in LLNs participate in multiple RPL instances and DODAGs,
both the RPLInstance ID and the DODAGID SHOULD be included in the
DAO.
4.1.4. Path Metrics
Expected Transmission Count (ETX) is the RECOMMENDED metric.
[RFC6551] provides other options.
Packets from asymmetric and/or unstable links SHOULD be deleted at
layer 2.
4.1.5. Objective Function
Objective Function 0 (OF0) MUST be the Objective Function. Other
Objective Functions MAY be used when dictated by circumstances.
4.1.6. DODAG Repair
Since P2P-RPL only creates DODAGs on a temporary basis during route
repair or route discovery, there is no need to repair DODAGs.
For SS traffic, local repair is sufficient. The accompanying process
is known as poisoning and is described in Section 8.2.2.5 of
[RFC6550]. Given that the majority of nodes in the building do not
physically move around, creating new DODAGs should not happen
frequently.
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4.1.7. Multicast
Commercial lighting deployments may have a need for multicast to
distribute commands to a group of lights in a timely fashion.
Several mechanisms exist for achieving such functionality;
[I-D.ietf-roll-trickle-mcast] is the RECOMMENDED protocol for home
and building deployments. This section relies heavily on the
conclusions of [RT-MPL].
At reception of a packet, the MPL forwarder starts a series of
consecutive trickle timer intervals, where the first interval has a
minimum size of Imin. Each consecutive interval is twice as long as
the former with a maximum value of Imax. There is a maximum number
of intervals given by max_expiration. For each interval of length I,
a time t is randomly chosen in the period [I/2, I]. For a given
packet, p, MPL counts the number of times it receives p during the
period [0, t] in a counter c. At time t, MPL re-broadcasts p when c
< k, where k is a predefined constant with a value k > 0.
The density of forwarders and the frequency of message generation are
important aspects to obtain timeliness during control operations. A
high frequency of message generation can be expected when a remote
control button is incessantly pressed, or when alarm situations
arise.
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 forwarder that receives the message passes the message
on to the next hop by repeating the message. When several copies of
a message reach the forwarder, it is specified that the copy need not
be repeated. Repetition of the message can be inhibited by a small
value of k. To assure timeliness, the value of k should be chosen
high enough to make sure that messages are repeated at the first
arrival of the message in the forwarder. 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 forwarders to reduce the risk of
medium saturation. Depending on the reliability of the network
links, it is advisable to choose the network such that at least 2
forwarders per hop repeat messages to the same set of destinations.
There are no rules about selecting forwarders for MPL. In buildings
with central management tools, the forwarders can be selected, but in
the home is not possible to automatically configure the forwarder
topology at the time of writing this document.
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4.1.8. Security
RPL MAY use unsecured RPL messages to reduce message size. If there
is a single node that uses unsecured RPL messages, link-layer
security MUST be used on all nodes. Therefore all RPL messages MUST
be secured using either:
o RPL message security, or
o Link-layer security, or
o Both RPL message security and link-layer security
A symmetric key is used to secure a RPL message using either RPL
message security or link-layer security. The symmetric key MUST be
distributed or established in a secure fashion. There may be more
than one symmetric key in use by any node at any one time. The same
symmetric key MUST NOT be used for both RPL message security and
link-layer security between two peer nodes.
4.1.8.1. Symmetric key distribution
The scope of symmetric key distribution MUST be no greater than the
network itself, i.e. a group key. This document describes what needs
to be implemented to meet this requirement. The scope of symmetric
key distribution MAY be smaller than the network, for example:
o A pairwise symmetric key between two peers.
o A group key shared between a subset of nodes in the network.
4.1.8.2. Symmetric key distribution mechanism
The authentication mechanism as described in Section 6.9 of
[ZigBeeIP] SHALL be used to securely distribute a network-wide
symmetric key.
The purpose of the authentication procedure is to provide mutual
authentication resulting in:
o Preventing untrusted nodes without appropriate credentials from
joining the trusted network.
o Preventing trusted nodes with appropriate credentials from joining
an untrusted network.
There is an Authentication Server, which is responsible for
authenticating the nodes on the network. If the authentication is
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successful, the Authentication Server sends the network security
material to the joining node through the PANA protocol ([RFC5191],
[RFC6345]). The joining node becomes a full participating node in
the network and is able to apply layer 2 security to RPL messages
using the distributed network key.
The joining node does not initially have access to the network
security material. Therefore, it is not able to apply layer 2
security for the packets exchanged during the authentication process.
The enforcement point rules at the edge of the network ensure that
the packets involved in the PANA authentication are processed even
though they are unsecured at MAC layer. The rules also ensure that
any other incoming traffic that is not secured at the MAC layer is
discarded and is not forwarded.
4.1.8.2.1. Authentication Stack
Authentication can be viewed as a protocol stack as a layer
encapsulates the layers above it.
o TLS [RFC5246] MUST be used at the highest layer of the
authentication stack and carries the authentication exchange.
There is one cipher suite based on pre-shared key [RFC6655] and
one cipher suite based on ECC [RFC7251].
o EAP-TLS [RFC5216] MUST be used at the next layer to carry the TLS
records for the authentication protocol.
o The Extensible Authentication Protocol [RFC3748] MUST be used to
provide the mechanisms for mutual authentication. EAP requires a
way to transport EAP packets between the joining node and the node
on which the Authentication Server resides. These nodes are not
necessarily in radio range of each other, so it is necessary to
have multi-hop support in the EAP transport method. The PANA
protocol [RFC5191], [RFC6345], which operates over UDP, MUST be
used for this purpose. [RFC3748] specifies the derivation of a
session key using the EAP key hierarchy; only the EAP Master
Session Key shall be derived, as [RFC5191] specifies that it is
used to set up keys for PANA authentication and encryption.
o PANA [RFC5191] and PANA relay [RFC6345] MUST be used at the next
layer:
* The joining node MUST act as the PANA Client (PaC)
* The parent edge router node MUST act as a PANA relay (PRE)
according to [RFC6345], unless it is also the Authentication
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Server. All routers at the edge of the network MUST be capable
of functioning in the PRE role.
* The Authentication Server node MUST act as the PANA
Authentication Agent (PAA). The Authentication Server MUST be
able to handle packets relayed according to [RFC6345].
This network authentication process uses link-local IPv6 addresses
for transport between the new node and its parent. If the parent is
not the Authentication Server, it MUST then relay packets from the
joining node to the Authentication Server and vice-versa using PANA
relay mechanism [RFC6345]. The joining node MUST use a link-local
address based on its EUI-64 as the source address for initial PANA
authentication message exchanges.
4.1.8.2.2. Applicability Statements
The applicability statements describe the relationship between the
various specifications.
4.1.8.2.2.1. Applicability Statement for PSK TLS
[RFC6655] contains AEAD TLS cipher suites that are very similar to
[RFC5487] whose AEAD part is detailed in [RFC5116]. [RFC5487]
references both [RFC5288] and the original PSK cipher suite document
[RFC4279], which references [RFC5246], which defines the TLS 1.2
messages.
4.1.8.2.2.2. Applicability Statement for ECC TLS
[RFC7251] contains AEAD TLS cipher suites that are very similar to
[RFC5289] whose AEAD part is detailed in [RFC5116]. [RFC5289]
references the original ECC cipher suite document [RFC4492], which
references [RFC5246], which defines the TLS 1.2 messages.
4.1.8.2.2.3. Applicability Statement for EAP-TLS and PANA
[RFC5216] specifies how [RFC3748] is used to package [RFC5246] TLS
records into EAP packets. [RFC5191] provides transportation for the
EAP packets and the network-wide key carried in an encrypted AVP
specified in [RFC6786]. The proposed PRF and AUTH hashes based on
SHA-256 are represented as in [RFC5996] and detailed in [RFC4868].
4.1.8.2.3. Security using RPL message security
If RPL is used with secured messages [RFC6550], the following RPL
security parameter values SHOULD be used:
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o Counter Time Flag (T) = 0: Do not use timestamp in the Counter
Field. Counters based on timestamps are typically more applicable
to industrial networks where strict timing synchronization between
nodes is often implemented. Home and building networks typically
do not implement such strict timing synchronization therefore a
monotonically increasing counter is more appropriate.
o Algorithm = 0: Use Counter with Cipher Block Chaining Message
Authentication Code (CBC-MAC Mode) (CCM) with Advanced Encryption
Standard (AES)-128. This is the only assigned mode at present.
o Key Identifier Mode (KIM) = 10: Use group key, Key Source present,
Key Index present. Given the relatively confined perimeter of a
home or building network, a group key is usually sufficient to
protect RPL messages sent between nodes. The use of the Key
Source field allows multiple group keys to be used within the
network.
o Security Level (LVL) = 0: Use MAC-32. This is recommended as
integrity protection for RPL messages is the basic requirement.
Encryption is unlikely to be necessary given the relatively non-
confidential nature of RPL message payloads.
4.1.9. P2P communications
[RFC6997] MUST be used to accommodate P2P traffic, which is typically
substantial in home and building automation networks.
4.1.10. IPv6 address configuration
Assigned IP addresses MUST be routable and unique within the routing
domain [RFC5889].
4.2. Layer 2 features
No particular requirements exist for layer 2 but for the ones cited
in the IP over Foo RFCs (see Section 2.3).
4.2.1. Specifics about layer-2
Not applicable
4.2.2. Services provided at layer-2
Not applicable
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4.2.3. 6LowPAN options assumed
Not applicable
4.2.4. Mesh Link Establishment (MLE) and other things
Not applicable
4.3. Recommended Configuration Defaults and Ranges
The following sections describe the recommended parameter values for
P2P-RPL and Trickle.
4.3.1. Trickle parameters
Trickle is used to distribute network parameter values to all nodes
without stringent time restrictions. The recommended Trickle
parameter values are:
o DIOIntervalMin 4 = 16 ms
o DIOIntervalDoublings 14
o DIORedundancyConstant 1
When a node sends a changed DIO, this is an inconsistency and forces
the receiving node to respond within Imin. So when something happens
which affects the DIO, the change is ideally communicated to a node,
n hops away, within n times Imin. Often, dependent on the node
density, packets are lost, or not sent, leading to larger delays.
In general we can expect DIO changes to propagate within 1 to 3
seconds within the envisaged networks.
When nothing happens, the DIO sending interval increases to 4.37
minutes, thus drastically reducing the network load. When a node
does not receive DIO messages during more than 10 minutes it can
safely conclude the connection with other nodes has been lost.
4.3.2. Other Parameters
This section discusses the P2P-RPL parameters.
P2P-RPL [RFC6997] provides the features requested by [RFC5826] and
[RFC5867]. P2P-RPL uses a subset of the frame formats and features
defined for RPL [RFC6550] but may be combined with RPL frame flows in
advanced deployments.
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The recommended parameter values for P2P-RPL are:
o MinHopRankIncrease 1
o MaxRankIncrease 0
o MaxRank 6
o Objective function: OF0
5. MPL Profile
MPL is used to distribute values to groups of devices. Using MPL,
based on the Trickle algorithm, timeliness should also be guaranteed.
A deadline of 200 ms needs to be met when human action is followed by
an immediately observable action such as switching on lights. The
deadline needs to be met in a building where the number of hops from
seed to destination varies between 1 and 10.
5.1. Recommended configuration Defaults and Ranges
5.1.1. Real-Time optimizations
When the network is heavily loaded, MAC delays contribute
significantly to the end to end delays when MPL intervals between 10
to 100 ms are used to meet the 200 ms deadline. It is possible to
set the number of buffers in the MAC to 1 and set the number of Back-
off repetitions to 1. The number of MPL repetitions compensates for
the reduced probability of transmission per MAC invocation [RT-MPL].
In addition, end to end delays and message losses are reduced, by
adding a real-time layer between MPL and MAC to throw away the
earliest messages (exploiting the MPL message numbering) and favour
the most recent ones.
5.1.2. Trickle parameters
This section proposes values for the Trickle parameters used by MPL
for the distribution of packets that need to meet a 200 ms deadline.
The probability of meeting the deadline is increased by (1) choosing
a small Imin value,(2) reducing the number of MPL intervals thus
reducing the load, and (3) reducing the number of MPL forwarders to
also reduce the load.
The consequence of this approach is that the value of k can be larger
than 1 because network load reduction is already guaranteed by the
network configuration.
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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>1. The minimum value of k is related to:
o Value of Imin. The length of Imin determines the number of
packets that can be received within the listening period of Imin.
o Number of repeaters receiving the broadcast message from the same
forwarder or seed. These repeaters repeat within the same Imin
interval, thus increasing the c counter.
Within the first MPL interval a limited number, q, of messages can be
transmitted. Assuming a 3 ms transmission interval, q is given by q
= Imin/3. Assuming that at most q message copies can reach a given
forwarder within the first repeat interval of length Imin, the
related MPL parameter values are suggested in the following sections.
5.1.2.1. Imin
The recommended value is Imin = 10 to 50 ms.
When Imin is chosen much smaller, the interference between the copies
leads to significant losses given that q is much smaller than the
number of repeated packets. With much larger intervals the
probability that the deadline will be met decreases with increasing
hop count.
5.1.2.2. Imax
The recommended value is Imax = 100 to 400 ms.
The value of Imax is less important than the value of max_expiration.
Given an Imin value of 10 ms, the 3rd MPL interval has a value of
10*2*2 = 40 ms. When Imin has a value of 40 ms, the 3rd interval has
a value of 160 ms. Given that more than 3 intervals are unnecessary,
the Imax does not contribute much to the performance.
5.1.3. Other parameters
Other parameters are the k parameter and the max_expiration
parameter.
k > q (see condition above). Under this condition and for small
Imin, a value of k=2 or k=3 is usually sufficient to minimize the
losses of packets in the first repeat interval.
max_expiration = 2 - 4. Higher values lead to more network load
while generating copies which will probably not meet their deadline.
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6. Manageability Considerations
At this moment it is not clear how homenets will be managed.
Consequently it is not clear which tools will be used and which
parameters must be exposed for management.
In building control, management is mandatory. It is expected that
installations will be managed using the set of currently available
tools(including IETF tools like Management Information Base (MIB)
modules, NETCONF modules, Dynamic Host Configuration Protocol (DHCP)
and others) with large differences between the ways an installation
is managed.
7. Security Considerations
This section refers to the security considerations of [RFC6997],
[RFC6550], [I-D.ietf-roll-trickle-mcast], and the counter measures
discussed in sections 6 and 7 of [RFC7416].
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.
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 (see Section 7.1) 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 neighbouring device as described in
Section 4.1.8.1. The shared key MUST be stored in a secure fashion
which makes it difficult to be read by an unauthorized party.
This document mandates that a layer-2 mechanism be used during
initial and incremental deployment. Please see the following
sections.
7.1. Security considerations during initial deployment
Wireless mesh networks are typically secured at the link layer in
order to prevent unauthorized parties from accessing the information
exchanged over the links. It is a basic practice to create a network
of nodes which share the same keys for link layer security and
exclude nodes sending unsecured messages. With per-message data
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origin authentication, it is possible to prevent unauthorized nodes
joining the mesh.
At initial deployment the network is secured by consecutively
securing nodes at the link layer, thus building a network of secured
nodes. Section 4.1.8.2 describes a mechanism for building a network
of secured nodes.
This document does not specify a multicast security solution.
Networks deployed with this specification will depend upon layer-2
security to prevent outsiders from sending multicast traffic. It is
recognized that this does not protect this control traffic from
impersonation by already trusted devices. This is an area for a
future specification.
For building control an installer will use an installation tool that
establishes a secure communication path with the joining node. It is
recognized that the recommendations for initial deployment of
Section 7 and Section 7.1 do not cover all building requirements such
as selecting the node-to-secure independent of network topology.
It is expected that a set of protocol combinations will evolve within
currently existing alliances of building control manufacturers. Each
set satisfies the installation requirements of installers, operators,
and manufacturers of building control networks in a given
installation context, e.g lighting deployment in offices, HVAC
installation, incremental addition of equipment in homes, and others.
In the home, nodes can be visually inspected by the home owner and a
simple procedure, e.g. pushing buttons simultaneously on an already
secured device and an unsecured joining device is usually sufficient
to ensure that the unsecured joining device is authenticated and
configured securely, and paired appropriately.
This recommendation is in line with the countermeasures described in
section 6.1.1 of [RFC7416].
7.2. Security Considerations during incremental deployment
Once a network is operational, new nodes need to be added, or nodes
fail and need to be replaced. When a new node needs to be added to
the network, the new node is joined to the network via an assisting
node in the manner described in Section 7.1.
On detection of a compromised node, all trusted nodes need to have
their symmetric keys known to be shared with the compromised node re-
keyed, and the trusted network is built up as described in
Section 7.1.
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7.3. Security Considerations for P2P uses
Refer to the security considerations of [RFC6997].
7.4. MPL routing
The routing of MPL is determined by the enabling of the interfaces
for specified Multicast addresses. The specification of these
addresses can be done via a Constrained Application Protocol (CoAP)
application as specified in [RFC7390]. An alternative is the
creation of a MPL MIB and use of Simple Network Management Protocol
(SNMP)v3 [RFC3411] or equivalent techniques to specify the Multicast
addresses in the MIB. For secure dissemination of MPL packets, layer
2 security SHOULD be used and the configuration of multicast
addresses as described in this section MUST be secure.
7.5. RPL Security features
This section follows the structure of section 8, "RPL security
features" of [RFC7416]. [RFC7416] provides a thorough analysis of
security threats and proposed counter measures relevant to RPL and
MPL.
In accordance with section 8.1 of [RFC7416], "Confidentiality
features", RPL message security implements payload protection, as
explained in Section 7 of this document. The attributes key-length
and life-time of the keys depend on operational conditions,
maintenance and installation procedures.
Section 7.1 and Section 7.2 of this document recommend link-layer
security to assure integrity in accordance with section 8.2 of
[RFC7416], "Integrity features".
The provision of multiple paths recommended in section 8.3
"Availability features" of [RFC7416] is also recommended from a
reliability point of view. Randomly choosing paths MAY be supported.
A mechanism for key management, discussed in section 8.4, "Key
Management" of [RFC7416], is provided in Section 4.1.8.2.
Section 7.5, "Considerations on Matching Application Domain Needs" of
[RFC7416] applies as such.
8. Other related protocols
Application and transport protocols used in home and building
automation domains are expected to mostly consist in CoAP over UDP,
or equivalents. Typically, UDP is used for IP transport to keep down
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the application response time and bandwidth overhead. CoAP is used
at the application layer to reduce memory footprint and bandwidth
requirements.
9. IANA Considerations
No considerations for IANA pertain to this document.
10. Acknowledgements
This document reflects discussions and remarks from several
individuals including (in alphabetical order): Stephen Farrell, Mukul
Goyal, Sandeep Kumar, Jerry Martocci, Catherine Meadows, Yoshihira
Ohba, Charles Perkins, Yvonne-Anne Pignolet, Michael Richardson, Ines
Robles, Zach Shelby, and Meral Sherazipour.
11. Changelog
RFC editor, please delete this section before publication.
Changes from version 0 to version 1.
o Adapted section structure to template.
o Standardized the reference syntax.
o Section 2.2, moved everything concerning algorithms to section
2.2.7, and adapted text in 2.2.1-2.2.6.
o Added MPL parameter text to section 4.1.7 and section 4.3.1.
o Replaced all TODO sections with text.
o Consistent use of border router, monitoring, home- and building
network.
o Reformulated security aspects with references to other
publications.
o MPL and RPL parameter values introduced.
Changes from version 1 to version 2.
o Clarified common characteristics of control in home and building.
o Clarified failure behaviour of point to point communication in
appendix.
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o Changed examples, more hvac and less lighting.
o Clarified network topologies.
o replaced reference to smart_object paper by reference to I-D.roll-
security-threats
o Added a concise definition of secure delivery and secure storage
o Text about securing network with PANA
Changes from version 2 to version 3.
o Changed security section to follow the structure of security
threats draft.
o Added text to DODAG repair sub-section
Changes from version 3 to version 4.
o Renumbered sections and moved text to conform to applicability
template
o Extended MPL parameter value text
o Added references to building control products
Changes from version 4 to version 5.
o Large editing effort to streamline text
o Rearranged Normative and Informative references
o Replaced RFC2119 terminology by non-normative terminology
o Rearranged text of section 7, 7.1, and 7.2 to agree with the
intention of section 7.2
Changes from version 5 to version 6.
o Issues #162 - #166 addressed
Changes from version 6 to version 7.
o Text of section 7.1 edited for better security coverage.
Changes from version 7 to version 8.
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o Requirements language paragraph removed
o Acronyms clarified
o MPL parameters clarified
Changes from version 8 to version 9.
o More acronyms clarified
o References updated
Changes from version 9 to version 10.
o Changes due to IESG and security review
o Requirements language reinstated
o RPL security parameter selection clarified
o Removed multicast security reference
Changes from version 10 to 11.
o Further changes due to IESG and security review
o ZigBee IP authentication and key establishment specified
Changes from version 11 to 12.
o Further clarifications added
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, Ed., "Extensible Authentication Protocol
(EAP)", RFC 3748, DOI 10.17487/RFC3748, June 2004,
<http://www.rfc-editor.org/info/rfc3748>.
[RFC4279] Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
Ciphersuites for Transport Layer Security (TLS)",
RFC 4279, DOI 10.17487/RFC4279, December 2005,
<http://www.rfc-editor.org/info/rfc4279>.
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[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492,
DOI 10.17487/RFC4492, May 2006,
<http://www.rfc-editor.org/info/rfc4492>.
[RFC4868] Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
384, and HMAC-SHA-512 with IPsec", RFC 4868,
DOI 10.17487/RFC4868, May 2007,
<http://www.rfc-editor.org/info/rfc4868>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<http://www.rfc-editor.org/info/rfc4944>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<http://www.rfc-editor.org/info/rfc5116>.
[RFC5191] Forsberg, D., Ohba, Y., Ed., Patil, B., Tschofenig, H.,
and A. Yegin, "Protocol for Carrying Authentication for
Network Access (PANA)", RFC 5191, DOI 10.17487/RFC5191,
May 2008, <http://www.rfc-editor.org/info/rfc5191>.
[RFC5216] Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS
Authentication Protocol", RFC 5216, DOI 10.17487/RFC5216,
March 2008, <http://www.rfc-editor.org/info/rfc5216>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
DOI 10.17487/RFC5288, August 2008,
<http://www.rfc-editor.org/info/rfc5288>.
[RFC5289] Rescorla, E., "TLS Elliptic Curve Cipher Suites with SHA-
256/384 and AES Galois Counter Mode (GCM)", RFC 5289,
DOI 10.17487/RFC5289, August 2008,
<http://www.rfc-editor.org/info/rfc5289>.
[RFC5487] Badra, M., "Pre-Shared Key Cipher Suites for TLS with SHA-
256/384 and AES Galois Counter Mode", RFC 5487,
DOI 10.17487/RFC5487, March 2009,
<http://www.rfc-editor.org/info/rfc5487>.
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[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, DOI 10.17487/RFC5548, May
2009, <http://www.rfc-editor.org/info/rfc5548>.
[RFC5673] Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T.
Phinney, "Industrial Routing Requirements in Low-Power and
Lossy Networks", RFC 5673, DOI 10.17487/RFC5673, October
2009, <http://www.rfc-editor.org/info/rfc5673>.
[RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation
Routing Requirements in Low-Power and Lossy Networks",
RFC 5826, DOI 10.17487/RFC5826, April 2010,
<http://www.rfc-editor.org/info/rfc5826>.
[RFC5867] Martocci, J., Ed., De Mil, P., Riou, N., and W. Vermeylen,
"Building Automation Routing Requirements in Low-Power and
Lossy Networks", RFC 5867, DOI 10.17487/RFC5867, June
2010, <http://www.rfc-editor.org/info/rfc5867>.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, DOI 10.17487/RFC5996, September 2010,
<http://www.rfc-editor.org/info/rfc5996>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<http://www.rfc-editor.org/info/rfc6282>.
[RFC6345] Duffy, P., Chakrabarti, S., Cragie, R., Ohba, Y., Ed., and
A. Yegin, "Protocol for Carrying Authentication for
Network Access (PANA) Relay Element", RFC 6345,
DOI 10.17487/RFC6345, August 2011,
<http://www.rfc-editor.org/info/rfc6345>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<http://www.rfc-editor.org/info/rfc6550>.
[RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
and D. Barthel, "Routing Metrics Used for Path Calculation
in Low-Power and Lossy Networks", RFC 6551,
DOI 10.17487/RFC6551, March 2012,
<http://www.rfc-editor.org/info/rfc6551>.
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[RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC 6554,
DOI 10.17487/RFC6554, March 2012,
<http://www.rfc-editor.org/info/rfc6554>.
[RFC6655] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
Transport Layer Security (TLS)", RFC 6655,
DOI 10.17487/RFC6655, July 2012,
<http://www.rfc-editor.org/info/rfc6655>.
[RFC6786] Yegin, A. and R. Cragie, "Encrypting the Protocol for
Carrying Authentication for Network Access (PANA)
Attribute-Value Pairs", RFC 6786, DOI 10.17487/RFC6786,
November 2012, <http://www.rfc-editor.org/info/rfc6786>.
[RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and
J. Martocci, "Reactive Discovery of Point-to-Point Routes
in Low-Power and Lossy Networks", RFC 6997,
DOI 10.17487/RFC6997, August 2013,
<http://www.rfc-editor.org/info/rfc6997>.
[RFC6998] Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci,
"A Mechanism to Measure the Routing Metrics along a Point-
to-Point Route in a Low-Power and Lossy Network",
RFC 6998, DOI 10.17487/RFC6998, August 2013,
<http://www.rfc-editor.org/info/rfc6998>.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <http://www.rfc-editor.org/info/rfc7102>.
[RFC7251] McGrew, D., Bailey, D., Campagna, M., and R. Dugal, "AES-
CCM Elliptic Curve Cryptography (ECC) Cipher Suites for
TLS", RFC 7251, DOI 10.17487/RFC7251, June 2014,
<http://www.rfc-editor.org/info/rfc7251>.
[RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A.,
and M. Richardson, Ed., "A Security Threat Analysis for
the Routing Protocol for Low-Power and Lossy Networks
(RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015,
<http://www.rfc-editor.org/info/rfc7416>.
[I-D.ietf-roll-trickle-mcast]
Hui, J. and R. Kelsey, "Multicast Protocol for Low power
and Lossy Networks (MPL)", draft-ietf-roll-trickle-
mcast-12 (work in progress), June 2015.
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[IEEE802.15.4]
"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>.
[G.9959] "ITU-T G.9959 Short range narrow-band digital
radiocommunication transceivers - PHY and MAC layer
specifications", <ITU-T G.9959>.
12.2. Informative References
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
DOI 10.17487/RFC3411, December 2002,
<http://www.rfc-editor.org/info/rfc3411>.
[RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-
Demand Distance Vector (AODV) Routing", RFC 3561,
DOI 10.17487/RFC3561, July 2003,
<http://www.rfc-editor.org/info/rfc3561>.
[RFC5889] Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing
Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889,
September 2010, <http://www.rfc-editor.org/info/rfc5889>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<http://www.rfc-editor.org/info/rfc7228>.
[RFC7390] Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for
the Constrained Application Protocol (CoAP)", RFC 7390,
DOI 10.17487/RFC7390, October 2014,
<http://www.rfc-editor.org/info/rfc7390>.
[RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets
over ITU-T G.9959 Networks", RFC 7428,
DOI 10.17487/RFC7428, February 2015,
<http://www.rfc-editor.org/info/rfc7428>.
[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.
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[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, January 2012.
[RT-MPL] van der Stok, P., "Real-Time multicast for wireless mesh
networks using MPL", White paper,
http://www.vanderstok.org/papers/Real-time-MPL.pdf, April
2014.
[occuswitch]
Lighting, Philips., "OccuSwitch wireless", Brochure, http
://www.philipslightingcontrols.com/assets/cms/uploads/file
s/osw/MK_OSWNETBROC_5.pdf, May 2012.
[office-light]
Clanton and Associates, ., "A Life Cycle Cost Evaluation
of Multiple Lighting Control Strategies", Wireless
Lighting Control, http://www.daintree.net/wp-
content/uploads/2014/02/
clanton_lighting_control_report_0411.pdf, February 2014.
[RTN2011] Holtman, K. and P. van der Stok, "Real-time routing for
low-latency 802.15.4 control networks", International
Workshop on Real-Time Networks; Euromicro Conference on
Real-Time Systems, July 2011.
[MEAS] Holtman, K., "Connectivity loss in large scale IEEE
802.15.4 network", Private Communication, November 2013.
[BCsurvey]
Kastner, W., Neugschwandtner, G., Soucek, S., and H.
Newman, "Communication Systems for Building Automation and
Control", Proceedings of the IEEE Vol 93, No 6, June
2005.
[ZigBeeIP]
ZigBee Alliance, ., "ZigBee IP specification", ZigBee
document 095023r34, March 2014.
Appendix A. RPL shortcomings in home and building deployments
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
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down along another branch [RFC6998]. 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 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.
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
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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.
Appendix B. Communication failures
Measurements on the connectivity between neighbouring nodes are
discussed in [RTN2011] and [MEAS].
The work is motivated by the measurements in literature which affirm
that the range of an antenna is not circle symmetric but that the
signal strength of a given level follows an intricate pattern around
the antenna, and there may be holes within the area delineated by an
iso-strength line. It is reported that communication is not
symmetric: reception of messages from node A by node B does not imply
reception of messages from node B by node A. The quality of the
signal fluctuates over time, and also the height of the antenna
within a room can have consequences for the range. As function of
the distance from the source, three regions are generally recognized:
(1) a clear region with excellent signal quality, (2) a region with
fluctuating signal quality, (3) a region without reception. In the
text below it is shown that installation of meshes with neighbours in
the clear region is not sufficient.
[RTN2011] extends existing work by:
o Observations over periods of at least a week,
o Testing links that are in the clear region,
o Observation in an office building during working hours,
o Concentrating on one-hop and two-hop routes.
Eight nodes were distributed over a surface of 30m2. All nodes are
at one hop distance from each other and are situated in the clear
region of each other. Each node sends messages to each of its
neighbours, and repeats the message until it arrives. The latency of
the message was measured over periods of at least a week. It is
noticed that latencies longer than a second occurred without apparent
reasons, but only during working days and never in the weekends. Bad
periods could last for minutes. By sending messages via two paths:
(1) one hop path directly, and (2) two hop path via a randomly chosen
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neighbour, the probability of delays larger than 100 ms decreased
significantly.
The conclusion is that even for 1-hop communication between not too
distant "Line of Sight" nodes, there are periods of low reception in
which communication deadlines of 200 ms are exceeded. It pays to
send a second message over a 2-hop path to increase the reliability
of timely message transfer.
[MEAS] confirms that temporary bad reception by close neighbours can
occur within other types of areas. Nodes were installed on the
ceiling in a grid with a distance of 30-50 cm between nodes. 200
nodes were distributed over an area of 10m x 5m. It clearly
transpired that with increasing distance the probability of reception
decreases. At the same time a few nodes furthest away from the
sender had a high probability of message reception, while some close
neighbours of the sender did not receive messages. The patterns of
clear reception nodes evolved over time.
The conclusion is that even for direct neighbours reception can
temporarily be bad during periods of several minutes. For a reliable
and timely communication it is imperative to have at least two
communication paths available (e.g. two hop paths next to the 1-hop
path for direct neighbours).
Authors' Addresses
Anders Brandt
Sigma Designs
Email: anders_Brandt@sigmadesigns.com
Emmanuel Baccelli
INRIA
Email: Emmanuel.Baccelli@inria.fr
Robert Cragie
ARM Ltd.
110 Fulbourn Road
Cambridge CB1 9NJ
UK
Email: robert.cragie@gridmerge.com
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Peter van der Stok
Consultant
Email: consultancy@vanderstok.org
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