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rfc:rfc5548

Network Working Group M. Dohler, Ed. Request for Comments: 5548 CTTC Category: Informational T. Watteyne, Ed.

                                                     BSAC, UC Berkeley
                                                        T. Winter, Ed.
                                                           Eka Systems
                                                       D. Barthel, Ed.
                                                    France Telecom R&D
                                                              May 2009
    Routing Requirements for Urban Low-Power and Lossy Networks

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (c) 2009 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 in effect on the date of
 publication of this document (http://trustee.ietf.org/license-info).
 Please review these documents carefully, as they describe your rights
 and restrictions with respect to this document.

Abstract

 The application-specific routing requirements for Urban Low-Power and
 Lossy Networks (U-LLNs) are presented in this document.  In the near
 future, sensing and actuating nodes will be placed outdoors in urban
 environments so as to improve people's living conditions as well as
 to monitor compliance with increasingly strict environmental laws.
 These field nodes are expected to measure and report a wide gamut of
 data (for example, the data required by applications that perform
 smart-metering or that monitor meteorological, pollution, and allergy
 conditions).  The majority of these nodes are expected to communicate
 wirelessly over a variety of links such as IEEE 802.15.4, low-power
 IEEE 802.11, or IEEE 802.15.1 (Bluetooth), which given the limited
 radio range and the large number of nodes requires the use of
 suitable routing protocols.  The design of such protocols will be
 mainly impacted by the limited resources of the nodes (memory,
 processing power, battery, etc.) and the particularities of the
 outdoor urban application scenarios.  As such, for a wireless

Dohler, et al. Informational [Page 1] RFC 5548 Routing Requirements for U-LLNs May 2009

 solution for Routing Over Low-Power and Lossy (ROLL) networks to be
 useful, the protocol(s) ought to be energy-efficient, scalable, and
 autonomous.  This documents aims to specify a set of IPv6 routing
 requirements reflecting these and further U-LLNs' tailored
 characteristics.

Table of Contents

 1. Introduction ....................................................3
 2. Terminology .....................................................3
    2.1. Requirements Language ......................................4
 3. Overview of Urban Low-Power and Lossy Networks ..................4
    3.1. Canonical Network Elements .................................4
         3.1.1. Sensors .............................................4
         3.1.2. Actuators ...........................................5
         3.1.3. Routers .............................................6
    3.2. Topology ...................................................6
    3.3. Resource Constraints .......................................7
    3.4. Link Reliability ...........................................7
 4. Urban LLN Application Scenarios .................................8
    4.1. Deployment of Nodes ........................................8
    4.2. Association and Disassociation/Disappearance of Nodes ......9
    4.3. Regular Measurement Reporting ..............................9
    4.4. Queried Measurement Reporting .............................10
    4.5. Alert Reporting ...........................................11
 5. Traffic Pattern ................................................11
 6. Requirements of Urban-LLN Applications .........................13
    6.1. Scalability ...............................................13
    6.2. Parameter-Constrained Routing .............................13
    6.3. Support of Autonomous and Alien Configuration .............14
    6.4. Support of Highly Directed Information Flows ..............15
    6.5. Support of Multicast and Anycast ..........................15
    6.6. Network Dynamicity ........................................16
    6.7. Latency ...................................................16
 7. Security Considerations ........................................16
 8. References .....................................................18
    8.1. Normative References ......................................18
    8.2. Informative References ....................................18
 Appendix A.  Acknowledgements .....................................20
 Appendix B.  Contributors .........................................20

Dohler, et al. Informational [Page 2] RFC 5548 Routing Requirements for U-LLNs May 2009

1. Introduction

 This document details application-specific IPv6 routing requirements
 for Urban Low-Power and Lossy Networks (U-LLNs).  Note that this
 document details the set of IPv6 routing requirements for U-LLNs in
 strict compliance with the layered IP architecture.  U-LLN use cases
 and associated routing protocol requirements will be described.
 Section 2 defines terminology useful in describing U-LLNs.
 Section 3 provides an overview of U-LLN applications.
 Section 4 describes a few typical use cases for U-LLN applications
 exemplifying deployment problems and related routing issues.
 Section 5 describes traffic flows that will be typical for U-LLN
 applications.
 Section 6 discusses the routing requirements for networks comprising
 such constrained devices in a U-LLN environment.  These requirements
 may overlap with or be derived from other application-specific
 requirements documents [ROLL-HOME] [ROLL-INDUS] [ROLL-BUILD].
 Section 7 provides an overview of routing security considerations of
 U-LLN implementations.

2. Terminology

 The terminology used in this document is consistent with and
 incorporates that described in "Terminology in Low power And Lossy
 Networks" [ROLL-TERM].  This terminology is extended in this document
 as follows:
 Anycast:  Addressing and Routing scheme for forwarding packets to at
           least one of the "nearest" interfaces from a group, as
           described in RFC4291 [RFC4291] and RFC1546 [RFC1546].
 Autonomous:  Refers to the ability of a routing protocol to
              independently function without requiring any external
              influence or guidance.  Includes self-configuration and
              self-organization capabilities.
 DoS:  Denial of Service, a class of attack that attempts to cause
       resource exhaustion to the detriment of a node or network.

Dohler, et al. Informational [Page 3] RFC 5548 Routing Requirements for U-LLNs May 2009

 ISM band:  Industrial, Scientific, and Medical band.  This is a
            region of radio spectrum where low-power, unlicensed
            devices may generally be used, with specific guidance from
            an applicable local radio spectrum authority.
 U-LLN:  Urban Low-Power and Lossy Network.
 WLAN: Wireless Local Area Network.

2.1. 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 [RFC2119].

3. Overview of Urban Low-Power and Lossy Networks

3.1. Canonical Network Elements

 A U-LLN is understood to be a network composed of three key elements,
 i.e.,
 1.  sensors,
 2.  actuators, and
 3.  routers
 that communicate wirelessly.  The aim of the following sections
 (3.1.1, 3.1.2, and 3.1.3) is to illustrate the functional nature of a
 sensor, actuator, and router in this context.  That said, it must be
 understood that these functionalities are not exclusive.  A
 particular device may act as a simple router or may alternatively be
 a router equipped with a sensing functionality, in which case it will
 be seen as a "regular" router as far as routing is concerned.

3.1.1. Sensors

 Sensing nodes measure a wide gamut of physical data, including but
 not limited to:
 1.  municipal consumption data, such as smart-metering of gas, water,
     electricity, waste, etc.;
 2.  meteorological data, such as temperature, pressure, humidity, UV
     index, strength and direction of wind, etc.;

Dohler, et al. Informational [Page 4] RFC 5548 Routing Requirements for U-LLNs May 2009

 3.  pollution data, such as gases (sulfur dioxide, nitrogen oxide,
     carbon monoxide, ozone), heavy metals (e.g., mercury), pH,
     radioactivity, etc.;
 4.  ambient data, such as levels of allergens (pollen, dust),
     electromagnetic pollution, noise, etc.
 Sensor nodes run applications that typically gather the measurement
 data and send it to data collection and processing application(s) on
 other node(s) (often outside the U-LLN).
 Sensor nodes are capable of forwarding data.  Sensor nodes are
 generally not mobile in the majority of near-future roll-outs.  In
 many anticipated roll-outs, sensor nodes may suffer from long-term
 resource constraints.
 A prominent example is a "smart grid" application that consists of a
 city-wide network of smart meters and distribution monitoring
 sensors.  Smart meters in an urban "smart grid" application will
 include electric, gas, and/or water meters typically administered by
 one or multiple utility companies.  These meters will be capable of
 advanced sensing functionalities such as measuring the quality of
 electrical service provided to a customer, providing granular
 interval data, or automating the detection of alarm conditions.  In
 addition, they may be capable of advanced interactive
 functionalities, which may invoke an actuator component, such as
 remote service disconnect or remote demand reset.  More advanced
 scenarios include demand response systems for managing peak load, and
 distribution automation systems to monitor the infrastructure that
 delivers energy throughout the urban environment.  Sensor nodes
 capable of providing this type of functionality may sometimes be
 referred to as Advanced Metering Infrastructure (AMI).

3.1.2. Actuators

 Actuator nodes are capable of controlling urban devices; examples are
 street or traffic lights.  They run applications that receive
 instructions from control applications on other nodes (possibly
 outside the U-LLN).  The amount of actuator points is well below the
 number of sensing nodes.  Some sensing nodes may include an actuator
 component, e.g., an electric meter node with integrated support for
 remote service disconnect.  Actuators are capable of forwarding data.
 Actuators are not likely to be mobile in the majority of near-future
 roll-outs.  Actuator nodes may also suffer from long-term resource
 constraints, e.g., in the case where they are battery powered.

Dohler, et al. Informational [Page 5] RFC 5548 Routing Requirements for U-LLNs May 2009

3.1.3. Routers

 Routers generally act to close coverage and routing gaps within the
 interior of the U-LLN; examples of their use are:
 1.  prolong the U-LLN's lifetime,
 2.  balance nodes' energy depletion, and
 3.  build advanced sensing infrastructures.
 There can be several routers supporting the same U-LLN; however, the
 number of routers is well below the amount of sensing nodes.  The
 routers are generally not mobile, i.e., fixed to a random or pre-
 planned location.  Routers may, but generally do not, suffer from any
 form of (long-term) resource constraint, except that they need to be
 small and sufficiently cheap.  Routers differ from actuator and
 sensing nodes in that they neither control nor sense.  That being
 said, a sensing node or actuator may also be a router within the
 U-LLN.
 Some routers provide access to wider infrastructures, such as the
 Internet, and are named Low-Power and Lossy Network Border Routers
 (LBRs) in that context.
 LBR nodes in particular may also run applications that communicate
 with sensor and actuator nodes (e.g., collecting and processing data
 from sensor applications, or sending instructions to actuator
 applications).

3.2. Topology

 Whilst millions of sensing nodes may very well be deployed in an
 urban area, they are likely to be associated with more than one
 network.  These networks may or may not communicate between one
 another.  The number of sensing nodes deployed in the urban
 environment in support of some applications is expected to be in the
 order of 10^2 to 10^7; this is still very large and unprecedented in
 current roll-outs.
 Deployment of nodes is likely to happen in batches, e.g., boxes of
 hundreds to thousands of nodes arrive and are deployed.  The location
 of the nodes is random within given topological constraints, e.g.,
 placement along a road, river, or at individual residences.

Dohler, et al. Informational [Page 6] RFC 5548 Routing Requirements for U-LLNs May 2009

3.3. Resource Constraints

 The nodes are highly resource constrained, i.e., cheap hardware, low
 memory, and no infinite energy source.  Different node powering
 mechanisms are available, such as:
 1.  non-rechargeable battery;
 2.  rechargeable battery with regular recharging (e.g., sunlight);
 3.  rechargeable battery with irregular recharging (e.g.,
     opportunistic energy scavenging);
 4.  capacitive/inductive energy provision (e.g., passive Radio
     Frequency IDentification (RFID));
 5.  always on (e.g., powered electricity meter).
 In the case of a battery-powered sensing node, the battery shelf life
 is usually in the order of 10 to 15 years, rendering network lifetime
 maximization with battery-powered nodes beyond this lifespan useless.
 The physical and electromagnetic distances between the three key
 elements, i.e., sensors, actuators, and routers, can generally be
 very large, i.e., from several hundreds of meters to one kilometer.
 Not every field node is likely to reach the LBR in a single hop,
 thereby requiring suitable routing protocols that manage the
 information flow in an energy-efficient manner.

3.4. Link Reliability

 The links between the network elements are volatile due to the
 following set of non-exclusive effects:
 1.  packet errors due to wireless channel effects;
 2.  packet errors due to MAC (Medium Access Control) (e.g.,
     collision);
 3.  packet errors due to interference from other systems;
 4.  link unavailability due to network dynamicity; etc.
 The wireless channel causes the received power to drop below a given
 threshold in a random fashion, thereby causing detection errors in
 the receiving node.  The underlying effects are path loss, shadowing
 and fading.

Dohler, et al. Informational [Page 7] RFC 5548 Routing Requirements for U-LLNs May 2009

 Since the wireless medium is broadcast in nature, nodes in their
 communication radios require suitable medium access control protocols
 that are capable of resolving any arising contention.  Some available
 protocols may not be able to prevent packets of neighboring nodes
 from colliding, possibly leading to a high Packet Error Rate (PER)
 and causing a link outage.
 Furthermore, the outdoor deployment of U-LLNs also has implications
 for the interference temperature and hence link reliability and range
 if Industrial, Scientific, and Medical (ISM) bands are to be used.
 For instance, if the 2.4 GHz ISM band is used to facilitate
 communication between U-LLN nodes, then heavily loaded Wireless Local
 Area Network (WLAN) hot-spots may become a detrimental performance
 factor, leading to high PER and jeopardizing the functioning of the
 U-LLN.
 Finally, nodes appearing and disappearing causes dynamics in the
 network that can yield link outages and changes of topologies.

4. Urban LLN Application Scenarios

 Urban applications represent a special segment of LLNs with its
 unique set of requirements.  To facilitate the requirements
 discussion in Section 6, this section lists a few typical but not
 exhaustive deployment problems and usage cases of U-LLN.

4.1. Deployment of Nodes

 Contrary to other LLN applications, deployment of nodes is likely to
 happen in batches out of a box.  Typically, hundreds to thousands of
 nodes are being shipped by the manufacturer with pre-programmed
 functionalities which are then rolled-out by a service provider or
 subcontracted entities.  Prior to or after roll-out, the network
 needs to be ramped-up.  This initialization phase may include, among
 others, allocation of addresses, (possibly hierarchical) roles in the
 network, synchronization, determination of schedules, etc.
 If initialization is performed prior to roll-out, all nodes are
 likely to be in one another's one-hop radio neighborhood.  Pre-
 programmed Media Access Control (MAC) and routing protocols may hence
 fail to function properly, thereby wasting a large amount of energy.
 Whilst the major burden will be on resolving MAC conflicts, any
 proposed U-LLN routing protocol needs to cater for such a case.  For
 instance, zero-configuration and network address allocation needs to
 be properly supported, etc.

Dohler, et al. Informational [Page 8] RFC 5548 Routing Requirements for U-LLNs May 2009

 After roll-out, nodes will have a finite set of one-hop neighbors,
 likely of low cardinality (in the order of 5 to 10).  However, some
 nodes may be deployed in areas where there are hundreds of
 neighboring devices.  In the resulting topology, there may be regions
 where many (redundant) paths are possible through the network.  Other
 regions may be dependent on critical links to achieve connectivity
 with the rest of the network.  Any proposed LLN routing protocol
 ought to support the autonomous self-organization and self-
 configuration of the network at lowest possible energy cost [Lu2007],
 where autonomy is understood to be the ability of the network to
 operate without external influence.  The result of such organization
 should be that each node or set of nodes is uniquely addressable so
 as to facilitate the set up of schedules, etc.
 Unless exceptionally needed, broadcast forwarding schemes are not
 advised in urban sensor networking environments.

4.2. Association and Disassociation/Disappearance of Nodes

 After the initialization phase and possibly some operational time,
 new nodes may be injected into the network as well as existing nodes
 removed from the network.  The former might be because a removed node
 is replaced as part of maintenance, or new nodes are added because
 more sensors for denser readings/actuations are needed, or because
 routing protocols report connectivity problems.  The latter might be
 because a node's battery is depleted, the node is removed for
 maintenance, the node is stolen or accidentally destroyed, etc.
 The protocol(s) hence should be able to convey information about
 malfunctioning nodes that may affect or jeopardize the overall
 routing efficiency, so that self-organization and self-configuration
 capabilities of the sensor network might be solicited to facilitate
 the appropriate reconfiguration.  This information may include, e.g.,
 exact or relative geographical position, etc.  The reconfiguration
 may include the change of hierarchies, routing paths, packet
 forwarding schedules, etc.  Furthermore, to inform the LBR(s) of the
 node's arrival and association with the network as well as freshly
 associated nodes about packet forwarding schedules, roles, etc.,
 appropriate updating mechanisms should be supported.

4.3. Regular Measurement Reporting

 The majority of sensing nodes will be configured to report their
 readings on a regular basis.  The frequency of data sensing and
 reporting may be different but is generally expected to be fairly
 low, i.e., in the range of once per hour, per day, etc.  The ratio
 between data sensing and reporting frequencies will determine the
 memory and data aggregation capabilities of the nodes.  Latency of an

Dohler, et al. Informational [Page 9] RFC 5548 Routing Requirements for U-LLNs May 2009

 end-to-end delivery and acknowledgements of a successful data
 delivery may not be vital as sensing outages can be observed at data
 collection applications -- when, for instance, there is no reading
 arriving from a given sensor or cluster of sensors within a day.  In
 this case, a query can be launched to check upon the state and
 availability of a sensing node or sensing cluster.
 It is not uncommon to gather data on a few servers located outside of
 the U-LLN.  In such cases, a large number of highly directional
 unicast flows from the sensing nodes or sensing clusters are likely
 to transit through a LBR.  Thus, the protocol(s) should be optimized
 to support a large number of unicast flows from the sensing nodes or
 sensing clusters towards a LBR, or highly directed multicast or
 anycast flows from the nodes towards multiple LBRs.
 Route computation and selection may depend on the transmitted
 information, the frequency of reporting, the amount of energy
 remaining in the nodes, the recharging pattern of energy-scavenged
 nodes, etc.  For instance, temperature readings could be reported
 every hour via one set of battery-powered nodes, whereas air quality
 indicators are reported only during the daytime via nodes powered by
 solar energy.  More generally, entire routing areas may be avoided
 (e.g., at night) but heavily used during the day when nodes are
 scavenging energy from sunlight.

4.4. Queried Measurement Reporting

 Occasionally, network-external data queries can be launched by one or
 several applications.  For instance, it is desirable to know the
 level of pollution at a specific point or along a given road in the
 urban environment.  The queries' rates of occurrence are not regular
 but rather random, where heavy-tail distributions seem appropriate to
 model their behavior.  Queries do not necessarily need to be reported
 back to the same node from where the query was launched.  Round-trip
 times, i.e., from the launch of a query from a node until the
 delivery of the measured data to a node, are of importance.  However,
 they are not very stringent where latencies should simply be
 sufficiently smaller than typical reporting intervals; for instance,
 in the order of seconds or minutes.  The routing protocol(s) should
 consider the selection of paths with appropriate (e.g., latency)
 metrics to support queried measurement reporting.  To facilitate the
 query process, U-LLN devices should support unicast and multicast
 routing capabilities.
 The same approach is also applicable for schedule update,
 provisioning of patches and upgrades, etc.  In this case, however,
 the provision of acknowledgements and the support of unicast,
 multicast, and anycast are of importance.

Dohler, et al. Informational [Page 10] RFC 5548 Routing Requirements for U-LLNs May 2009

4.5. Alert Reporting

 Rarely, the sensing nodes will measure an event that classifies as an
 alarm where such a classification is typically done locally within
 each node by means of a pre-programmed or prior-diffused threshold.
 Note that on approaching the alert threshold level, nodes may wish to
 change their sensing and reporting cycles.  An alarm is likely being
 registered by a plurality of sensing nodes where the delivery of a
 single alert message with its location of origin suffices in most,
 but not all, cases.  One example of alert reporting is if the level
 of toxic gases rises above a threshold; thereupon, the sensing nodes
 in the vicinity of this event report the danger.  Another example of
 alert reporting is when a recycling glass container -- equipped with
 a sensor measuring its level of occupancy -- reports that the
 container is full and hence needs to be emptied.
 Routes clearly need to be unicast (towards one LBR) or multicast
 (towards multiple LBRs).  Delays and latencies are important;
 however, for a U-LLN deployed in support of a typical application,
 deliveries within seconds should suffice in most of the cases.

5. Traffic Pattern

 Unlike traditional ad hoc networks, the information flow in U-LLNs is
 highly directional.  There are three main flows to be distinguished:
 1.  sensed information from the sensing nodes to applications outside
     the U-LLN, going through one or a subset of the LBR(s);
 2.  query requests from applications outside the U-LLN, going through
     the LBR(s) towards the sensing nodes;
 3.  control information from applications outside the U-LLN, going
     through the LBR(s) towards the actuators.
 Some of the flows may need the reverse route for delivering
 acknowledgements.  Finally, in the future, some direct information
 flows between field devices without LBRs may also occur.
 Sensed data is likely to be highly correlated in space, time, and
 observed events; an example of the latter is when temperature
 increase and humidity decrease as the day commences.  Data may be
 sensed and delivered at different rates with both rates being
 typically fairly low, i.e., in the range of minutes, hours, days,
 etc.  Data may be delivered regularly according to a schedule or a
 regular query; it may also be delivered irregularly after an
 externally triggered query; it may also be triggered after a sudden
 network-internal event or alert.  Schedules may be driven by, for

Dohler, et al. Informational [Page 11] RFC 5548 Routing Requirements for U-LLNs May 2009

 example, a smart-metering application where data is expected to be
 delivered every hour, or an environmental monitoring application
 where a battery-powered node is expected to report its status at a
 specific time once a day.  Data delivery may trigger acknowledgements
 or maintenance traffic in the reverse direction.  The network hence
 needs to be able to adjust to the varying activity duty cycles, as
 well as to periodic and sporadic traffic.  Also, sensed data ought to
 be secured and locatable.
 Some data delivery may have tight latency requirements, for example,
 in a case such as a live meter reading for customer service in a
 smart-metering application, or in a case where a sensor reading
 response must arrive within a certain time in order to be useful.
 The network should take into consideration that different application
 traffic may require different priorities in the selection of a route
 when traversing the network, and that some traffic may be more
 sensitive to latency.
 A U-LLN should support occasional large-scale traffic flows from
 sensing nodes through LBRs (to nodes outside the U-LLN), such as
 system-wide alerts.  In the example of an AMI U-LLN, this could be in
 response to events such as a city-wide power outage.  In this
 scenario, all powered devices in a large segment of the network may
 have lost power and be running off of a temporary "last gasp" source
 such as a capacitor or small battery.  A node must be able to send
 its own alerts toward an LBR while continuing to forward traffic on
 behalf of other devices that are also experiencing an alert
 condition.  The network needs to be able to manage this sudden large
 traffic flow.
 A U-LLN may also need to support efficient large-scale messaging to
 groups of actuators.  For example, an AMI U-LLN supporting a city-
 wide demand response system will need to efficiently broadcast
 demand-response control information to a large subset of actuators in
 the system.
 Some scenarios will require internetworking between the U-LLN and
 another network, such as a home network.  For example, an AMI
 application that implements a demand-response system may need to
 forward traffic from a utility, across the U-LLN, into a home
 automation network.  A typical use case would be to inform a customer
 of incentives to reduce demand during peaks, or to automatically
 adjust the thermostat of customers who have enrolled in such a demand
 management program.  Subsequent traffic may be triggered to flow back
 through the U-LLN to the utility.

Dohler, et al. Informational [Page 12] RFC 5548 Routing Requirements for U-LLNs May 2009

6. Requirements of Urban-LLN Applications

 Urban Low-Power and Lossy Network applications have a number of
 specific requirements related to the set of operating conditions, as
 exemplified in the previous sections.

6.1. Scalability

 The large and diverse measurement space of U-LLN nodes -- coupled
 with the typically large urban areas -- will yield extremely large
 network sizes.  Current urban roll-outs are composed of sometimes
 more than one hundred nodes; future roll-outs, however, may easily
 reach numbers in the tens of thousands to millions.  One of the
 utmost important LLN routing protocol design criteria is hence
 scalability.
 The routing protocol(s) MUST be capable of supporting the
 organization of a large number of sensing nodes into regions
 containing on the order of 10^2 to 10^4 sensing nodes each.
 The routing protocol(s) MUST be scalable so as to accommodate a very
 large and increasing number of nodes without deteriorating selected
 performance parameters below configurable thresholds.  The routing
 protocols(s) SHOULD support the organization of a large number of
 nodes into regions of configurable size.

6.2. Parameter-Constrained Routing

 Batteries in some nodes may deplete quicker than in others; the
 existence of one node for the maintenance of a routing path may not
 be as important as of another node; the energy-scavenging methods may
 recharge the battery at regular or irregular intervals; some nodes
 may have a constant power source; some nodes may have a larger memory
 and are hence be able to store more neighborhood information; some
 nodes may have a stronger CPU and are hence able to perform more
 sophisticated data aggregation methods, etc.
 To this end, the routing protocol(s) MUST support parameter-
 constrained routing, where examples of such parameters (CPU, memory
 size, battery level, etc.) have been given in the previous paragraph.
 In other words, the routing protocol MUST be able to advertise node
 capabilities that will be exclusively used by the routing protocol
 engine for routing decision.  For the sake of example, such a
 capability could be related to the node capability itself (e.g.,
 remaining power) or some application that could influence routing
 (e.g., capability to aggregate data).

Dohler, et al. Informational [Page 13] RFC 5548 Routing Requirements for U-LLNs May 2009

 Routing within urban sensor networks SHOULD require the U-LLN nodes
 to dynamically compute, select, and install different paths towards
 the same destination, depending on the nature of the traffic.  Such
 functionality in support of, for example, data aggregation, may imply
 use of some mechanisms to mark/tag the traffic for appropriate
 routing decision using the IPv6 packet format (e.g., use of Diffserv
 Code Point (DSCP), Flow Label) based on an upper-layer marking
 decision.  From this perspective, such nodes MAY use node
 capabilities (e.g., to act as an aggregator) in conjunction with the
 anycast endpoints and packet marking to route the traffic.

6.3. Support of Autonomous and Alien Configuration

 With the large number of nodes, manually configuring and
 troubleshooting each node is not efficient.  The scale and the large
 number of possible topologies that may be encountered in the U-LLN
 encourages the development of automated management capabilities that
 may (partly) rely upon self-organizing techniques.  The network is
 expected to self-organize and self-configure according to some prior
 defined rules and protocols, as well as to support externally
 triggered configurations (for instance, through a commissioning tool
 that may facilitate the organization of the network at a minimum
 energy cost).
 To this end, the routing protocol(s) MUST provide a set of features
 including zero-configuration at network ramp-up, (network-internal)
 self-organization and configuration due to topological changes, and
 the ability to support (network-external) patches and configuration
 updates.  For the latter, the protocol(s) MUST support multicast and
 anycast addressing.  The protocol(s) SHOULD also support the
 formation and identification of groups of field devices in the
 network.
 The routing protocol(s) SHOULD be able to dynamically adapt, e.g.,
 through the application of appropriate routing metrics, to ever-
 changing conditions of communication (possible degradation of quality
 of service (QoS), variable nature of the traffic (real-time versus
 non-real-time, sensed data versus alerts), node mobility, a
 combination thereof, etc.).
 The routing protocol(s) SHOULD be able to dynamically compute,
 select, and possibly optimize the (multiple) path(s) that will be
 used by the participating devices to forward the traffic towards the
 actuators and/or a LBR according to the service-specific and traffic-
 specific QoS, traffic engineering, and routing security policies that

Dohler, et al. Informational [Page 14] RFC 5548 Routing Requirements for U-LLNs May 2009

 will have to be enforced at the scale of a routing domain (that is, a
 set of networking devices administered by a globally unique entity),
 or a region of such domain (e.g., a metropolitan area composed of
 clusters of sensors).

6.4. Support of Highly Directed Information Flows

 As pointed out in Section 4.3, it is not uncommon to gather data on a
 few servers located outside of the U-LLN.  In this case, the
 reporting of the data readings by a large amount of spatially
 dispersed nodes towards a few LBRs will lead to highly directed
 information flows.  For instance, a suitable addressing scheme can be
 devised that facilitates the data flow.  Also, as one gets closer to
 the LBR, the traffic concentration increases, which may lead to high
 load imbalances in node usage.
 To this end, the routing protocol(s) SHOULD support and utilize the
 large number of highly directed traffic flows to facilitate
 scalability and parameter-constrained routing.
 The routing protocol MUST be able to accommodate traffic bursts by
 dynamically computing and selecting multiple paths towards the same
 destination.

6.5. Support of Multicast and Anycast

 Routing protocols activated in urban sensor networks MUST support
 unicast (traffic is sent to a single field device), multicast
 (traffic is sent to a set of devices that are subscribed to the same
 multicast group), and anycast (where multiple field devices are
 configured to accept traffic sent on a single IP anycast address)
 transmission schemes.
 The support of unicast, multicast, and anycast also has an
 implication on the addressing scheme, but it is beyond the scope of
 this document that focuses on the routing requirements.
 Some urban sensing systems may require low-level addressing of a
 group of nodes in the same subnet, or for a node representative of a
 group of nodes, without any prior creation of multicast groups.  Such
 addressing schemes, where a sender can form an addressable group of
 receivers, are not currently supported by IPv6, and not further
 discussed in this specification [ROLL-HOME].
 The network SHOULD support internetworking when identical protocols
 are used, while giving attention to routing security implications of
 interfacing, for example, a home network with a utility U-LLN.  The

Dohler, et al. Informational [Page 15] RFC 5548 Routing Requirements for U-LLNs May 2009

 network may support the ability to interact with another network
 using a different protocol, for example, by supporting route
 redistribution.

6.6. Network Dynamicity

 Although mobility is assumed to be low in urban LLNs, network
 dynamicity due to node association, disassociation, and
 disappearance, as well as long-term link perturbations is not
 negligible.  This in turn impacts reorganization and reconfiguration
 convergence as well as routing protocol convergence.
 To this end, local network dynamics SHOULD NOT impact the entire
 network to be reorganized or re-reconfigured; however, the network
 SHOULD be locally optimized to cater for the encountered changes.
 The routing protocol(s) SHOULD support appropriate mechanisms in
 order to be informed of the association, disassociation, and
 disappearance of nodes.  The routing protocol(s) SHOULD support
 appropriate updating mechanisms in order to be informed of changes in
 connectivity.  The routing protocol(s) SHOULD use this information to
 initiate protocol-specific mechanisms for reorganization and
 reconfiguration as necessary to maintain overall routing efficiency.
 Convergence and route establishment times SHOULD be significantly
 lower than the smallest reporting interval.
 Differentiation SHOULD be made between node disappearance, where the
 node disappears without prior notification, and user- or node-
 initiated disassociation ("phased-out"), where the node has enough
 time to inform the network about its pending removal.

6.7. Latency

 With the exception of alert-reporting solutions and (to a certain
 extent) queried reporting, U-LLNs are delay tolerant as long as the
 information arrives within a fraction of the smallest reporting
 interval, e.g., a few seconds if reporting is done every 4 hours.
 The routing protocol(s) SHOULD also support the ability to route
 according to different metrics (one of which could, e.g., be
 latency).

7. Security Considerations

 As every network, U-LLNs are exposed to routing security threats that
 need to be addressed.  The wireless and distributed nature of these
 networks increases the spectrum of potential routing security
 threats.  This is further amplified by the resource constraints of
 the nodes, thereby preventing resource-intensive routing security

Dohler, et al. Informational [Page 16] RFC 5548 Routing Requirements for U-LLNs May 2009

 approaches from being deployed.  A viable routing security approach
 SHOULD be sufficiently lightweight that it may be implemented across
 all nodes in a U-LLN.  These issues require special attention during
 the design process, so as to facilitate a commercially attractive
 deployment.
 The U-LLN MUST deny any node that has not been authenticated to the
 U-LLN and authorized to participate to the routing decision process.
 An attacker SHOULD be prevented from manipulating or disabling the
 routing function, for example, by compromising routing control
 messages.  To this end, the routing protocol(s) MUST support message
 integrity.
 Further examples of routing security issues that may arise are the
 abnormal behavior of nodes that exhibit an egoistic conduct, such as
 not obeying network rules or forwarding no or false packets.  Other
 important issues may arise in the context of denial-of-service (DoS)
 attacks, malicious address space allocations, advertisement of
 variable addresses, a wrong neighborhood, etc.  The routing
 protocol(s) SHOULD support defense against DoS attacks and other
 attempts to maliciously or inadvertently cause the mechanisms of the
 routing protocol(s) to over-consume the limited resources of LLN
 nodes, e.g., by constructing forwarding loops or causing excessive
 routing protocol overhead traffic, etc.
 The properties of self-configuration and self-organization that are
 desirable in a U-LLN introduce additional routing security
 considerations.  Mechanisms MUST be in place to deny any node that
 attempts to take malicious advantage of self-configuration and self-
 organization procedures.  Such attacks may attempt, for example, to
 cause DoS, drain the energy of power-constrained devices, or to
 hijack the routing mechanism.  A node MUST authenticate itself to a
 trusted node that is already associated with the U-LLN before the
 former can take part in self-configuration or self-organization.  A
 node that has already authenticated and associated with the U-LLN
 MUST deny, to the maximum extent possible, the allocation of
 resources to any unauthenticated peer.  The routing protocol(s) MUST
 deny service to any node that has not clearly established trust with
 the U-LLN.
 Consideration SHOULD be given to cases where the U-LLN may interface
 with other networks such as a home network.  The U-LLN SHOULD NOT
 interface with any external network that has not established trust.
 The U-LLN SHOULD be capable of limiting the resources granted in
 support of an external network so as not to be vulnerable to DoS.

Dohler, et al. Informational [Page 17] RFC 5548 Routing Requirements for U-LLNs May 2009

 With low computation power and scarce energy resources, U-LLNs' nodes
 may not be able to resist any attack from high-power malicious nodes
 (e.g., laptops and strong radios).  However, the amount of damage
 generated to the whole network SHOULD be commensurate with the number
 of nodes physically compromised.  For example, an intruder taking
 control over a single node SHOULD NOT be able to completely deny
 service to the whole network.
 In general, the routing protocol(s) SHOULD support the implementation
 of routing security best practices across the U-LLN.  Such an
 implementation ought to include defense against, for example,
 eavesdropping, replay, message insertion, modification, and man-in-
 the-middle attacks.
 The choice of the routing security solutions will have an impact on
 the routing protocol(s).  To this end, routing protocol(s) proposed
 in the context of U-LLNs MUST support authentication and integrity
 measures and SHOULD support confidentiality (routing security)
 measures.

8. References

8.1. Normative References

 [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

8.2. Informative References

 [Lu2007]      Lu, JL., Valois, F., Barthel, D., and M. Dohler,
               "FISCO: A Fully Integrated Scheme of Self-Configuration
               and Self-Organization for WSN", 11-15 March 2007,
               pp. 3370-3375, IEEE WCNC 2007, Hong Kong, China.
 [RFC1546]     Partridge, C., Mendez, T., and W. Milliken, "Host
               Anycasting Service", RFC 1546, November 1993.
 [RFC4291]     Hinden, R. and S. Deering, "IP Version 6 Addressing
               Architecture", RFC 4291, February 2006.
 [ROLL-BUILD]  Martocci, J., Ed., De Mil, P., Vermeylen, W., and N.
               Riou, "Building Automation Routing Requirements in Low
               Power and Lossy Networks", Work in Progress,
               February 2009.
 [ROLL-HOME]   Brandt, A. and G. Porcu, "Home Automation Routing
               Requirements in Low Power and Lossy Networks", Work
               in Progress, November 2008.

Dohler, et al. Informational [Page 18] RFC 5548 Routing Requirements for U-LLNs May 2009

 [ROLL-INDUS]  Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T.
               Phinney, "Industrial Routing Requirements in Low Power
               and Lossy Networks", Work in Progress, April 2009.
 [ROLL-TERM]   Vasseur, J., "Terminology in Low power And Lossy
               Networks", Work in Progress, October 2008.

Dohler, et al. Informational [Page 19] RFC 5548 Routing Requirements for U-LLNs May 2009

Appendix A. Acknowledgements

 The in-depth feedback of JP Vasseur, Jonathan Hui, Iain Calder, and
 Pasi Eronen is greatly appreciated.

Appendix B. Contributors

 Christian Jacquenet
 France Telecom R&D
 4 rue du Clos Courtel BP 91226
 35512 Cesson Sevigne
 France
 EMail: christian.jacquenet@orange-ftgroup.com
 Giyyarpuram Madhusudan
 France Telecom R&D
 28 Chemin du Vieux Chene
 38243 Meylan Cedex
 France
 EMail: giyyarpuram.madhusudan@orange-ftgroup.com
 Gabriel Chegaray
 France Telecom R&D
 28 Chemin du Vieux Chene
 38243 Meylan Cedex
 France
 EMail: gabriel.chegaray@orange-ftgroup.com

Dohler, et al. Informational [Page 20] RFC 5548 Routing Requirements for U-LLNs May 2009

Authors' Addresses

 Mischa Dohler (editor)
 CTTC
 Parc Mediterrani de la Tecnologia
 Av. Canal Olimpic S/N
 08860 Castelldefels, Barcelona
 Spain
 EMail: mischa.dohler@cttc.es
 Thomas Watteyne (editor)
 Berkeley Sensor & Actuator Center, University of California, Berkeley
 497 Cory Hall #1774
 Berkeley, CA  94720-1774
 USA
 EMail: watteyne@eecs.berkeley.edu
 Tim Winter (editor)
 Eka Systems
 20201 Century Blvd. Suite 250
 Germantown, MD  20874
 USA
 EMail: wintert@acm.org
 Dominique Barthel (editor)
 France Telecom R&D
 28 Chemin du Vieux Chene
 38243 Meylan Cedex
 France
 EMail: Dominique.Barthel@orange-ftgroup.com

Dohler, et al. Informational [Page 21]

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