[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits] [IPR]

Versions: (draft-brandt-roll-rpl-applicability-home-building) 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 7733

Roll                                                           A. Brandt
Internet-Draft                                             Sigma Designs
Intended status: Informational                               E. Baccelli
Expires: November 14, 2013                                         INRIA
                                                               R. Cragie
                                                               Gridmerge
                                                         P. van der Stok
                                                              Consultant
                                                            May 13, 2013


    Applicability Statement: The use of the RPL protocol set in Home
                    Automation and Building Control
             draft-ietf-roll-applicability-home-building-00

Abstract

   The purpose of this document is to provide guidance in the selection
   and use of RPL protocols to implement the features required in
   building and home environments.

Status of This Memo

   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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 14, 2013.

Copyright Notice

   Copyright (c) 2013 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



Brandt, et al.         Expires November 14, 2013                [Page 1]


Internet-Draft     RPL protocols in building control            May 2013


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



Brandt, et al.         Expires November 14, 2013                [Page 2]


Internet-Draft     RPL protocols in building control            May 2013


   Appendix A.  RPL shortcomings in home and building deployments  .  12
     A.1.  Risk of undesired long P2P routes . . . . . . . . . . . .  13
       A.1.1.  Traffic concentration at the root . . . . . . . . . .  13
       A.1.2.  Excessive battery consumption in source nodes . . . .  13
     A.2.  Risk of delayed route repair  . . . . . . . . . . . . . .  13
       A.2.1.  Broken service  . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   TODO: Adapt to new template

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

1.1.  Requirements Language

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

1.2.  Overview of requirements

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

1.3.  Out of scope requirements

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

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

2.  Deployment Scenario

   Networking in buildings is essential to satisfy the energy saving
   regulations.  Comfort of buildings is adapted to the presence of
   individuals.  When no one is present, energy consumption can be
   reduced.  Cost is the main driving factor behind wireless networking
   in buildings.  Especially for retrofit, wireless connectivity saves
   cabling costs.




Brandt, et al.         Expires November 14, 2013                [Page 3]


Internet-Draft     RPL protocols in building control            May 2013


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

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

   People expect immediate and reliable responses to their presence or
   actions.  A light not switching on after entry into a room leads to
   confusion and a profound dissatisfaction with the light product.

   The surveillance of the correct functioning is at least as important.
   Devices communicate regularly their status and send alarm messages
   announcing a dysfunction of equipment or network.

   In building control the infrastructure of the building management
   network can be shared with the security/access, the IP telephony, and
   the fire/alarm networks.  This approach has a strong impact on the
   operation and cost of the network.

2.1.  Network Topologies

   The typical home automation network or building control subnetwork
   can consist of a wired and one or more wireless subnetworks.
   Especially in large buildings the wireless network is connected to an
   IP backbone network where all infrastructure services are located,
   such as DNS, automation servers, etc.  The wireless subnetwork is a
   mesh network with a border router located at a convenient place in
   the home (building).

   In a building control network there may be several redundant border
   routers to each subnetwork.  Subnetworks often overlap geographically
   (and from a wireless perspective).  Due to the two purposes of the
   network, (i) direct control and (ii) surveillance, there may exist
   two types of routing topologies in a given subnetwork (i) a tree-
   shaped collection of routes spanning from a central building
   controller via the border router, on to destination nodes in the
   subnetwork, and/or (ii) a flat, un-directed collection of intra-
   network routes between functionally related nodes in the subnetwork.

   Nodes in Home and Building automation networks are typically
   inexpensive devices with very low memory capacity, such as individual



Brandt, et al.         Expires November 14, 2013                [Page 4]


Internet-Draft     RPL protocols in building control            May 2013


   wall switches.  Only a few nodes (such as multi-purpose remote
   controls) are more expensive devices, which can afford more memory
   capacity.

2.2.  Traffic Characteristics

   Traffic may enter the network from a central controller or it may
   originate from an intra-network node.  The majority of traffic is
   light-weight point-to-point control style; e.g.  Put-Ack or Get-
   Response.  There are however exceptions.  Bulk data transfer is used
   for firmware update and logging.  Multicast is used for service
   discovery or to control groups of nodes, such as light fixtures.
   Firmware updates enter the network while logs leave the network.
   Often, there is a direct relation between a controlling sensor and
   the controlled equipment.  The bulk of senders and receivers are
   separated by a distance that allows one-hop direct path
   communication.  A graph of the communication will show several fully
   connected subsets of nodes.  However, due to interference, multipath
   fading, reflection and other transmission mechanisms, the one-hop
   direct path may be temporally disconnected.  For reliability
   purposes, it is therefore essential that alternative n-hop
   communication routes exist for quick error recovery.  Looking over
   time periods of a day, the networks are very lightly loaded.
   However, bursts of traffic can be generated by the entry of several
   persons simultaneously, the occurrence of a defect, and other
   unforeseen events.  Under those conditions, the timeliness must
   nevertheless be maintained.  Therefore, measures are necessary to
   remove any unnecessary traffic.  Short routes are preferred.  Long
   multi-hop routes via the edge router, should be avoided whenever
   possible.  Group communication is essential for lighting control.
   For example, once the presence of a person is detected in a given
   room, all involved lights in the room and no other lights should be
   dimmed, or switched on/off.  Several rooms may be covered by the same
   wireless subnetwork.  To reduce network load, it is advisable that
   messages to the lights in a room are not distributed further in the
   mesh than necessary on the basis of intended receivers.

2.2.1.  Human user responsiveness

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




Brandt, et al.         Expires November 14, 2013                [Page 5]


Internet-Draft     RPL protocols in building control            May 2013


   The reactive discovery features of RPL-P2P ensures that commands are
   normally delivered within the 250msec time window and when
   connectivity needs to be restored, it is typically completed within
   seconds.  In most cases an alternative route will work.  Thus, route
   rediscovery is not even necessary.

2.2.2.  Source-sink (SS) communication paradigm

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

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

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

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

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

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

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

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




Brandt, et al.         Expires November 14, 2013                [Page 6]


Internet-Draft     RPL protocols in building control            May 2013


2.2.5.  RPL applicability per communication paradigm

   TODO: align with new template

   Describe here when we use RPL, RPL-P2P and MPL based on sections on
   SS P2P, PMP, and N-cast.

2.3.  Link layer applicability

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

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

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

3.  Using RPL-P2P to meet requirements

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

4.  RPL Profile for RPL-P2P

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

4.1.  RPL Features




Brandt, et al.         Expires November 14, 2013                [Page 7]


Internet-Draft     RPL protocols in building control            May 2013


   TODO: New subsection for prefix and address assignment

   In one constrained deployment, the link layer master node handing out
   the logical network identifier and unique node identifiers may be a
   remote control which returns to sleep once new nodes have been added.
   There may be no global routable prefixes at all.  Likewise, there may
   be no authoritative always-on root node since there is no border
   router to host this function.

   In another constrained deployment, there may be battery powered
   sensors and wall controllers configured to contact other nodes in
   response to events and then return to sleep.  Such nodes may never
   detect the announcement of new prefixes via multicast.

   In each of the abovementioned constrained deployments, the link layer
   master node SHOULD assume the role as authoritative root node,
   transmitting singlecast RAs with a ULA prefix information option to
   nodes during the inclusion process to prepare the nodes for a later
   operational phase, where a border router is added.

   A border router SHOULD be designed to be aware of sleeping nodes in
   order to support the distribution of updated global prefixes to such
   sleeping nodes.

   One COULD implement gateway-centric tree-based routing and global
   prefix distribution as defined by [RFC6550].  This would however only
   work for always-on nodes.

4.1.1.  RPL Instances

   When operating P2P-RPL on a stand-alone basis, there is no
   authoritative root node maintaining a permanent RPL DODAG.  A node
   MUST be able to join one RPL instance as an instance is created
   during each P2P-RPL route discovery operation.  A node MAY be
   designed to join multiple RPL instances.

4.1.2.  Non-Storing Mode

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

4.1.3.  DAO Policy

   TBD.

4.1.4.  Path Metrics




Brandt, et al.         Expires November 14, 2013                [Page 8]


Internet-Draft     RPL protocols in building control            May 2013


   TBD.

4.1.5.  Objective Function

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

4.1.6.  DODAG Repair

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

4.1.7.  Multicast

   Commercial light deployments may have a need for multicast beyond the
   link-local scope.  RPL and P2P-RPL do not provide any means for this
   transmission mode natively.

   Several mechanisms exist for achieving such functionality; [MPL] is
   RECOMMENDED for home and building deployments.

   [TODO/TBD: text on MPL repeater density]

4.1.8.  Security

   In order to support low-cost devices and devices running on battery,
   the following RPL security parameter values SHOULD be used:

   o  T = '0': Do not use timestamp in the Counter Field.

   o  Algorithm = '0': Use CCM with AES-128

   o  KIM = '10': Use group key, Key Source present, Key Index present

   o  LVL = 0: Use MAC-32

4.1.9.  P2P communications

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

4.2.  Layer 2 features

   For deployments based on

   [IEEE802.15.4] and [G.9959], security MUST be applied at layer 2
   using the mechanisms provided by the relevant standards.  Residential
   light control can accept a lower security level than other contexts



Brandt, et al.         Expires November 14, 2013                [Page 9]


Internet-Draft     RPL protocols in building control            May 2013


   (e.g.  a nuclear research lab).  Safety critical devices like
   electronic door locks SHOULD employ additional higher-layer security
   while light and heating devices may be sufficiently protected by a
   single network key.  The border router MAY enforce access policies to
   limit access to the trusted LLN domain from the LAN.

4.2.1.  Security functions provided by layer-2

   TBD.

4.2.2.  6LowPAN options assumed

   TBD.

4.2.3.  MLE and other things

   TBD.

4.3.  Recommended Configuration Defaults and Ranges

   TODO

5.  Manageability Considerations

   TODO

6.  Security Considerations

   TODO

6.1.  Security Considerations during initial deployment

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

6.2.  Security Considerations during incremental deployment

   Replacing a failed node means re-assigning the short address of the
   failed node to the new node added to the network.  This again allows
   a new node replacing a failed node to obtain the same IPv6 addresses
   as per the lines of [IPHC].

   As it is recommended to base security on a shared group key, it is
   possible to replace failed nodes.  For specific details on how to
   replace failed nodes; refer to the actual link layer documentation.



Brandt, et al.         Expires November 14, 2013               [Page 10]


Internet-Draft     RPL protocols in building control            May 2013


   TODO / TBD: Special concerns for adding a new node?

7.  Other related protocols

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

   Several features required by [RFC5826], [RFC5867] challenge the P2P
   paths provided by RPL.  Appendix A reviews these challenges.  In some
   cases, a node may need to spontaneously initiate the discovery of a
   path towards a desired destination that is neither the root of a DAG,
   nor a destination originating DAO signaling.  Furthermore, P2P paths
   provided by RPL are not satisfactory in all cases because they
   involve too many intermediate nodes before reaching the destination.

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

8.  IANA Considerations

9.  Acknowledgements

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

10.  References

11.  References

11.1.  Normative References

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

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

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

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

   [IEEE802.15.4]



Brandt, et al.         Expires November 14, 2013               [Page 11]


Internet-Draft     RPL protocols in building control            May 2013


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

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

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

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

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

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

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

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

11.2.  Informative References

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

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

Appendix A.  RPL shortcomings in home and building deployments





Brandt, et al.         Expires November 14, 2013               [Page 12]


Internet-Draft     RPL protocols in building control            May 2013


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

A.1.  Risk of undesired long P2P routes

   The DAG, being a tree structure is formed from a root.  If nodes
   residing in different branches have a need for communicating
   internally, DAG mechanisms provided in RPL [RFC6550] will propagate
   traffic towards the root, potentially all the way to the root, and
   down along another branch.  In a typical example two nodes could
   reach each other via just two router nodes but in unfortunate cases,
   RPL may send traffic three hops up and three hops down again.  This
   leads to several undesired phenomena described in the following
   sections

A.1.1.  Traffic concentration at the root

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

A.1.2.  Excessive battery consumption in source nodes

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

A.2.  Risk of delayed route repair

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



Brandt, et al.         Expires November 14, 2013               [Page 13]


Internet-Draft     RPL protocols in building control            May 2013


   fashion.  The consequence is a broken service in home and building
   applications.

A.2.1.  Broken service

   Experience from the telecom industry shows that if the voice delay
   exceeds 250ms users start getting confused, frustrated and/or
   annoyed.  In the same way, if the light does not turn on within the
   same period of time, a home control user will activate the controls
   again, causing a sequence of commands such as
   Light{on,off,off,on,off,..} or Volume{up,up,up,up,up,...} Whether the
   outcome is nothing or some unintended response this is unacceptable.
   A controlling system must be able to restore connectivity to recover
   from the error situation.  Waiting for an unknown period of time is
   not an option.  While this issue was identified during the P2P
   analysis it applies just as well to application scenarios where an IP
   application outside the LLN controls actuators, lights, etc.

Authors' Addresses

   Anders Brandt
   Sigma Designs

   Email: abr@sdesigns.dk


   Emmanuel Baccelli
   INRIA

   Email: Emmanuel.Baccelli@inria.fr


   Robert Cragie
   Gridmerge

   Email: robert.cragie@gridmerge.com


   Peter van der Stok
   Consultant

   Email: consultancy@vanderstok.org








Brandt, et al.         Expires November 14, 2013               [Page 14]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/