Roll                                                           A. Brandt
Internet-Draft                                             Sigma Designs
Intended status: Informational                               E. Baccelli
Expires: August 9, 2013                                            INRIA
                                                               R. Cragie
                                                               Gridmerge
                                                        February 5, 2013


Applicability Statement: The use of RPL-P2P in Home and Building Control
          draft-brandt-roll-rpl-applicability-home-building-03

Abstract

   The purpose of this document is to provide guidance in the use of
   RPL-P2P to implement the features required 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.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 9, 2013.

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   document authors.  All rights reserved.

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   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
     1.2.  Overview of requirements . . . . . . . . . . . . . . . . .  4
     1.3.  Out of scope requirements  . . . . . . . . . . . . . . . .  4
   2.  Deployment Scenario  . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Network Topologies . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Traffic Characteristics  . . . . . . . . . . . . . . . . .  5
       2.2.1.  Human user responsiveness  . . . . . . . . . . . . . .  5
       2.2.2.  Source-sink (SS) communication paradigm  . . . . . . .  6
       2.2.3.  Peer-to-peer (P2P) communication paradigm  . . . . . .  6
       2.2.4.  Peer-to-multipeer (P2MP) communication paradigm  . . .  6
     2.3.  Link layer applicability . . . . . . . . . . . . . . . . .  6
   3.  Using RPL-P2P to meet requirements . . . . . . . . . . . . . .  7
   4.  RPL Profile for RPL-P2P  . . . . . . . . . . . . . . . . . . .  7
     4.1.  RPL Features . . . . . . . . . . . . . . . . . . . . . . .  7
       4.1.1.  RPL Instances  . . . . . . . . . . . . . . . . . . . .  7
       4.1.2.  Non-Storing Mode . . . . . . . . . . . . . . . . . . .  7
       4.1.3.  DAO Policy . . . . . . . . . . . . . . . . . . . . . .  8
       4.1.4.  Path Metrics . . . . . . . . . . . . . . . . . . . . .  8
       4.1.5.  Objective Function . . . . . . . . . . . . . . . . . .  8
       4.1.6.  DODAG Repair . . . . . . . . . . . . . . . . . . . . .  8
       4.1.7.  Multicast  . . . . . . . . . . . . . . . . . . . . . .  8
       4.1.8.  Security . . . . . . . . . . . . . . . . . . . . . . .  8
       4.1.9.  P2P communications . . . . . . . . . . . . . . . . . .  8
     4.2.  Layer 2 features . . . . . . . . . . . . . . . . . . . . .  8
       4.2.1.  Security functions provided by layer-2 . . . . . . . .  8
       4.2.2.  6LowPAN options assumed  . . . . . . . . . . . . . . .  9
       4.2.3.  MLE and other things . . . . . . . . . . . . . . . . .  9
     4.3.  Recommended Configuration Defaults and Ranges  . . . . . .  9
   5.  Manageability Considerations . . . . . . . . . . . . . . . . .  9
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
     6.1.  Security Considerations during initial deployment  . . . .  9
     6.2.  Security Considerations during incremental deployment  . .  9
   7.  Other related protocols  . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     11.2. Informative References . . . . . . . . . . . . . . . . . . 11
   Appendix A.  RPL shortcomings in home and building deployments . . 11
     A.1.  Risk of undesired long P2P routes  . . . . . . . . . . . . 11
       A.1.1.  Traffic concentration at the root  . . . . . . . . . . 12



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       A.1.2.  Excessive battery consumption in source nodes  . . . . 12
     A.2.  Risk of delayed route repair . . . . . . . . . . . . . . . 12
       A.2.1.  Broken service . . . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13















































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1.  Introduction

   Home automation and building control application spaces share a
   substantial number of properties.  The purpose of this document is to
   give guidance in the use of RPL-P2P to provide the features required
   by the requirements documents "Home Automation Routing Requirements
   in Low-Power and Lossy Networks" [RFC5826] and "Building Automation
   Routing Requirements in Low-Power and Lossy Networks" [RFC5867].

1.1.  Requirements Language

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

1.2.  Overview of requirements

   Applicable requirements are described in [RFC5826] and [RFC5867].

1.3.  Out of scope requirements

   The considered network diameter is limited to a max diameter of 10
   hops and a typical diameter of 5 hops, which captures the most common
   cases in home automation and building control networks.

   This document does not consider the applicability of RPL-related
   specifications for urban and industrial applications [RFC5548],
   [RFC5673], which may exhibit significantly larger network diameters.


2.  Deployment Scenario

   A typical home automation network is less than 100 nodes.  Large
   building deployments may span 10,000 nodes but to ensure
   uninterrupted service of light and air conditioning systems in
   individual zones of the building, nodes are organized in subnetworks.
   Each subnetwork in a building automation deployment is typically less
   than 200 nodes and rarely more than 500 nodes.

   The main purpose of the network is to provide control over light and
   heating/cooling resources.  User intervention may be enabled via wall
   controllers combined with movement, light and temperature sensors to
   enable automatic adjustment of window blinds, reduction of room
   temperature, etc.

   Alarm systems are also important applications in home and building
   networks.




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2.1.  Network Topologies

   The typical home automation network or building control subnetwork is
   a mesh network with a border router located at a convenient place in
   the home.  In a building control network there may be several
   redundant border routers.  The network often consists in a number of
   overlapping wireless subnetworks.  Two types of routing topologies
   may exist in each subnetwork (i) a tree-shaped collection of routes
   spanning from a central building controller via the border router, on
   to destination nodes in the subnetwork, and/or (ii) a flat, un-
   directed collection of intra-network routes between arbitrary nodes
   in the subnetwork.

   Nodes in Home and Building automation networks are typically
   inexpensive devices with extremely low memory capacities, such as
   individual wall switches.  Only a few nodes (such as multi-purpose
   remote controls for instance) are more expensive devices, which can
   afford more memory capacity.

2.2.  Traffic Characteristics

   Traffic may enter the network from a central controller or it may
   originate from an intra-network node, such as a wall switch.  The
   majority of traffic is light-weight point-to-point control style;
   e.g.  Put-Ack or Get-Response.  There are however exceptions.  Bulk
   data transfer is used for firmware update and logging.  Multicast is
   used for service discovery or to control groups of nodes, such as
   light fixtures.  Firmware updates enter the network while logs leave
   the network.

2.2.1.  Human user responsiveness

   While airconditioning and other environmental-control applications
   may accept certain response delays, alarm and light control
   applications may be regarded as soft real-time systems.  A slight
   delay is acceptable, but the perceived quality of service degrades
   significantly if response times exceed 250 msec.  If the light does
   not turn on at short notice, a user will activate the controls again,
   causing a sequence of commands such as Light{on,off,on,off,..} or
   Volume{up,up,up,up,up,...}.

   The reactive discovery features of RPL-P2P ensures that commands are
   normally delivered within the 250msec time window and when
   connectivity needs to be restored, it is typically completed within
   seconds.






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2.2.2.  Source-sink (SS) communication paradigm

   Source-sink (SS) traffic is a common traffic type in home and
   building networks.  The traffic is generated by environmental sensors
   which push periodic readings to a central server.  The readings may
   be used for pure logging, or more often, to adjust light, heating and
   ventilation.  Alarm sensors also generate SS style traffic.

   With regards to message latency, most SS transmissions can tolerate
   worst-case delays measured in tens of seconds.  Alarm sensors,
   however, represent one exception.

2.2.3.  Peer-to-peer (P2P) communication paradigm

   Peer-to-peer (P2P) traffic is a common traffic type in home networks.
   Some building networks also rely on P2P traffic while others send all
   control traffic to a local controller box for advanced scene and
   group control; thus generating more SS and P2MP traffic.

   P2P traffic is typically generated by remote controls and wall
   controllers which push control messages directly to light or heat
   sources.  P2P traffic has a strong requirement for low latency since
   P2P traffic often carries application messages that are invoked by
   humans.  As mentioned in Section 2.2.1 application messages need to
   be delivered within less than a second - even when a route repair is
   needed before the message can be delivered.

2.2.4.  Peer-to-multipeer (P2MP) communication paradigm

   Peer-to-multipeer (P2MP) traffic is common in home and building
   networks.  Often, a wall switch in a living room responds to user
   activation by sending commands to a number of light sources
   simultaneously.

   Individual wall switches are typically inexpensive devices with
   extremely low memory capacities.  Multi-purpose remote controls for
   use in a home environment typically have more memory but such devices
   are asleep when there is no user activity.  RPL-P2P reactive
   discovery allows a node to wake up and find new routes within a few
   seconds while memory constrained nodes only have to keep routes to
   relevant targets.

2.3.  Link layer applicability

   This document applies to [IEEE802.15.4] and [G.9959] which are
   adapted to IPv6 by the adaption layers [RFC4944] and [I-D.lowpanz].

   Due to the limited memory of a majority of devices (such as



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   individual light-switches) RPL-P2P MUST be used with source routing
   in non-storing mode.  The abovementioned adaptation layers leverage
   on the compression capabilities of [RFC6554] and [RFC6282].  Header
   compression allows small IP packets to fit into a single layer 2
   frame even when source routing is used.  A network diameter limited
   to 5 hops helps achieving this.

   Packet drops are often experienced in the targeted environments.
   ICMP, UDP and even TCP flows may benefit from link layer unicast
   acknowledgments and retransmissions.  Link layer unicast
   acknowledgments MUST be enabled when [IEEE802.15.4] or [G.9959] is
   used with RPL-P2P.


3.  Using RPL-P2P to meet requirements

   RPL-P2P MUST be used in home and building networks, as P2P traffic is
   substantial and route repair must be completed within seconds.  RPL-
   P2P provides a reactive mechanism for quick, efficient and root-
   independent route discovery/repair.  The use of RPL-P2P furthermore
   allows data traffic to avoid having to go through a central region
   around the root of the tree, and drastically reduces path length
   [SOFT11] [INTEROP12].  These characteristics are desirable in home
   and building automation networks because they substantially decrease
   unnecessary network congestion around the tree's root.


4.  RPL Profile for RPL-P2P

   RPL-P2P MUST be used in home and building networks.  Non-storing mode
   allows for constrained memory in repeaters when source routing is
   used.  Reactive discovery allows for low application response times
   even when on-the-fly route repair is needed.

4.1.  RPL Features

4.1.1.  RPL Instances

   TBD.

4.1.2.  Non-Storing Mode

   Non-storing mode MUST be used to cope with the extremely constrained
   memory of a majority of nodes in the network (such as individual
   light switches).






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4.1.3.  DAO Policy

   TBD.

4.1.4.  Path Metrics

   TBD.

4.1.5.  Objective Function

   OF0 MUST be supported and is the RECOMMENDED OF to use.  Other
   Objective Functions MAY be used as well.

4.1.6.  DODAG Repair

   Since RPL-P2P only creates DODAGs on a temporary basis during route
   repair, there is no need to repair DODAGs.

4.1.7.  Multicast

   TBD.

4.1.8.  Security

   TBD.

4.1.9.  P2P communications

   RPL-P2P [RPL-P2P] MUST be used to accomodate P2P traffic, which is
   typically substantial in home and building automation networks.

4.2.  Layer 2 features

   Security MUST be applied at layer 2 for [IEEE802.15.4] and [G.9959].
   Residential light control can accept a lower security level than
   other contexts (e.g. a nuclear research lab).  Safety critical
   devices like electronic door locks SHOULD employ additional higher-
   layer security while light and heating devices may be sufficiently
   protected by a single network key.  The border router MAY enforce
   access policies to limit access to the trusted LLN domain from the
   LAN.

4.2.1.  Security functions provided by layer-2

   TBD.






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4.2.2.  6LowPAN options assumed

   TBD.

4.2.3.  MLE and other things

   TBD.

4.3.  Recommended Configuration Defaults and Ranges

   TODO


5.  Manageability Considerations

   TODO


6.  Security Considerations

   TODO

6.1.  Security Considerations during initial deployment

   TODO: (This section explains how nodes get their initial trust
   anchors, initial network keys.  It explains if this happens at the
   factory, in a deployment truck, if it is done in the field, perhaps
   like http://www.lix.polytechnique.fr/hipercom/SmartObjectSecurity/
   papers/CullenJennings.pdf)

6.2.  Security Considerations during incremental deployment

   TODO: (This section explains how that replaces a failed node takes on
   the dead nodes' identity, or not.  How are nodes retired.  How are
   nodes removed if they are compromised)


7.  Other related protocols

   Application transport protocols may be CoAP over UDP or equivalents.
   Typically, UDP is used for IP transport to keep down the application
   response time and bandwidth overhead.

   Several features required by [RFC5826], [RFC5867] challenge the P2P
   paths provided by RPL.  Appendix A reviews these challenges.  In some
   cases, a node may need to spontaneously initiate the discovery of a
   path towards a desired destination that is neither the root of a DAG,
   nor a destination originating DAO signaling.  Furthermore, P2P paths



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   provided by RPL are not satisfactory in all cases because they
   involve too many intermediate nodes before reaching the destination.

   RPL-P2P [RPL-P2P] provides the features requested by [RFC5826] and
   [RFC5867].  RPL-P2P uses a subset of the frame formats and features
   defined for RPL [RFC6550] but may be combined with RPL frame flows in
   advanced deployments.


8.  IANA Considerations


9.  Acknowledgements

   This document reflects discussions and remarks from several
   individuals including (in alphabetical order): Michael Richardson,
   Mukul Goyal, Jerry Martocci, Charles Perkins, and Zach Shelby


10.  References


11.  References

11.1.  Normative References

   [RFC5826]  "Home Automation Routing Requirements in Low-Power and
              Lossy Networks".

   [RFC5867]  "Building Automation Routing Requirements in Low-Power and
              Lossy Networks".

   [RFC5673]  "Industrial Routing Requirements in Low-Power and Lossy
              Networks".

   [RFC5548]  "Routing Requirements for Urban Low-Power and Lossy
              Networks".

   [IEEE802.15.4]
              "IEEE 802.15.4 - Standard for Local and metropolitan area
              networks -- Part 15.4: Low-Rate Wireless Personal Area
              Networks", <IEEE Standard 802.15.4>.

   [RFC4944]  "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks".

   [G.9959]   "ITU-T G.9959 Short range narrow-band digital
              radiocommunication transceivers - PHY and MAC layer



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              specifications", <ITU-T G.9959>.

   [I-D.lowpanz]
              Brandt, A., "Transmission of IPv6 Packets over ITU-T
              G.9959 Networks", <draft-brandt-6man-lowpanz>.

   [RFC6282]  Hui, J. and Thubert, P., "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC6282 ,
              September 2011.

   [RFC6554]  Hui, J., Vasseur, JP., Culler, D., and Manral, V., "An
              IPv6 Routing Header for Source Routes with the Routing
              Protocol for Low-Power and Lossy Networks (RPL)",
              RFC6554 , March 2012.

   [RFC6550]  "RPL: IPv6 Routing Protocol for Low-Power and Lossy
              Networks".

   [RPL-P2P]  Goyal, M., Baccelli, E., Phillip, M., Brandt, A., and J.
              Martocci, "Reactive Discovery of Point-to-Point Routes in
              Low Power and Lossy Networks", draft-ietf-roll-p2p-rpl ,
              May 2012.

11.2.  Informative References

   [SOFT11]   Baccelli, E., Phillip, M., and M. Goyal, "The P2P-RPL
              Routing Protocol for IPv6 Sensor Networks: Testbed
              Experiments",  Proceedings of the Conference on Software
              Telecommunications and Computer Networks, Split, Croatia,
              September 2011., September 2011.

   [INTEROP12]
              Baccelli, E., Phillip, M., Brandt, A., Valev , H., and J.
              Buron , "Report on P2P-RPL Interoperability Testing", RR-
              7864 INRIA Research Report RR-7864, Janurary 2012.


Appendix A.  RPL shortcomings in home and building deployments

   This document reflects discussions and remarks from several
   individuals including (in alphabetical order): Charles Perkins, Jerry
   Martocci, Michael Richardson, Mukul Goyal and Zach Shelby.

A.1.  Risk of undesired long P2P routes

   The DAG, being a tree structure is formed from a root.  If nodes
   residing in different branches have a need for communicating
   internally, DAG mechanisms provided in RPL [RFC6550] will propagate



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   traffic towards the root, potentially all the way to the root, and
   down along another branch.  In a typical example two nodes could
   reach each other via just two router nodes but in unfortunate cases,
   RPL may send traffic three hops up and three hops down again.  This
   leads to several undesired phenomena described in the following
   sections

A.1.1.  Traffic concentration at the root

   If many P2P data flows have to move up towards the root to get down
   again in another branch there is an increased risk of congestion the
   nearer to the root of the DAG the data flows.  Due to the broadcast
   nature of RF systems any child node of the root is not just directing
   RF power downwards its subtree but just as much upwards towards the
   root; potentially jamming other MP2P traffic leaving the tree or
   preventing the root of the DAG from sending P2MP traffic into the DAG
   because the listen-before-talk link-layer protection kicks in.

A.1.2.  Excessive battery consumption in source nodes

   Battery-powered nodes originating P2P traffic depend on the route
   length.  Long routes cause source nodes to stay awake for longer
   periods before returning to sleep.  Thus, a longer route translates
   proportionally (more or less) into higher battery consumption.

A.2.  Risk of delayed route repair

   The RPL DAG mechanism uses DIO and DAO messages to monitor the health
   of the DAG.  In rare occasions, changed radio conditions may render
   routes unusable just after a destination node has returned a DAO
   indicating that the destination is reachable.  Given enough time, the
   next Trickle timer-controlled DIODAO update will eventually repair
   the broken routes.  In a worst-case event this is however too late.
   In an apparently stable DAG, Trickle-timer dynamics may reduce the
   update rate to a few times every hour.  If a user issues an actuator
   command, e.g. light on in the time interval between the last DAO
   message was issued the destination module and the time one of the
   parents sends the next DIO, the destination cannot be reached.
   Nothing in RPL kicks in to restore connectivity in a reactive
   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 andor 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,



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   causing a sequence of commands such as Light{on,off,off,on,off,..} or
   Volume{up,up,up,up,up,...} Whether the outcome is nothing or some
   unintended response this is unacceptable.  A controlling system must
   be able to restore connectivity to recover from the error situation.
   Waiting for an unknown period of time is not an option.  While this
   issue was identified during the P2P analysis it applies just as well
   to application scenarios where an IP application outside the LLN
   controls actuators, lights, etc.


Authors' Addresses

   Anders Brandt
   Sigma Designs

   Email: abr@sdesigns.dk


   Emmanuel Baccelli
   INRIA

   Email: Emmanuel.Baccelli@inria.fr


   Robert Cragie
   Gridmerge

   Email: robert.cragie@gridmerge.com























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