Networking Working Group JP. Vasseur, Ed. Internet-Draft Cisco Systems, Inc Intended status: Standards Track M. Kim, Ed. Expires: August 3, 2011 Corporate Technology Group, KT K. Pister Dust Networks N. Dejean Coronis SAS D. Barthel France Telecom Orange January 30, 2011 Routing Metrics used for Path Calculation in Low Power and Lossy Networks draft-ietf-roll-routing-metrics-17 Abstract Low power and Lossy Networks (LLNs) have unique characteristics compared with traditional wired and ad-hoc networks that require the specification of new routing metrics and constraints. By contrast with typical Interior Gateway Protocol (IGP) routing metrics using hop counts or link metrics, this document specifies a set of link and node routing metrics and constraints suitable to LLNs to be used by the Routing for Low Power and lossy networks (RPL) routing protocol. 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]. 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." Vasseur, et al. Expires August 3, 2011 [Page 1] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 This Internet-Draft will expire on August 3, 2011. Copyright Notice Copyright (c) 2011 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 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. Vasseur, et al. Expires August 3, 2011 [Page 2] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Object Formats . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1. DAG Metric Container Format . . . . . . . . . . . . . . . 7 2.2. Use of Multiple DAG Metric Containers . . . . . . . . . . 10 2.3. Metric Usage . . . . . . . . . . . . . . . . . . . . . . . 10 3. Node Metric/Constraint Objects . . . . . . . . . . . . . . . . 11 3.1. Node State and Attributes Object . . . . . . . . . . . . . 11 3.2. Node Energy Object . . . . . . . . . . . . . . . . . . . . 13 3.3. Hop-Count Object . . . . . . . . . . . . . . . . . . . . . 16 4. Link Metric/Constraint Objects . . . . . . . . . . . . . . . . 17 4.1. Throughput . . . . . . . . . . . . . . . . . . . . . . . . 17 4.2. Latency . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.3. Link Reliability . . . . . . . . . . . . . . . . . . . . . 19 4.3.1. The Link Quality Level Reliability Metric . . . . . . 20 4.3.2. The Expected Transmission Count (ETX) reliability object . . . . . . . . . . . . . . . . . . . . . . . . 21 4.4. Link Color Object . . . . . . . . . . . . . . . . . . . . 23 4.4.1. Link Color Object Description . . . . . . . . . . . . 23 4.4.2. Mode of operation . . . . . . . . . . . . . . . . . . 24 5. Computation of Dynamic Metrics and Attributes . . . . . . . . 25 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 6.1. Routing Metric/Constraint Type . . . . . . . . . . . . . . 26 6.2. Routing Metric/Constraint TLV . . . . . . . . . . . . . . 26 6.3. Routing Metric/Constraint Common Header . . . . . . . . . 26 6.4. NSA Object . . . . . . . . . . . . . . . . . . . . . . . . 27 6.5. Hop-Count Object . . . . . . . . . . . . . . . . . . . . . 27 7. Security Considerations . . . . . . . . . . . . . . . . . . . 27 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 9.1. Normative references . . . . . . . . . . . . . . . . . . . 28 9.2. Informative references . . . . . . . . . . . . . . . . . . 28 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 Vasseur, et al. Expires August 3, 2011 [Page 3] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 1. Introduction This document makes use of the terminology defined in [I-D.ietf-roll-terminology]. Low power and Lossy Networks (LLNs) have specific routing characteristics compared with traditional wired or ad-hoc networks that have been spelled out in [RFC5548], [RFC5673], [RFC5826] and [RFC5867]. Historically, IGP such as OSPF ([RFC2328]) and IS-IS ([RFC1195]) have used quantitative static link metrics. Other mechanisms such as Multiprotocol Label Switching (MPLS) Traffic Engineering (TE) (see [RFC2702] and [RFC3209]) make use of other link attributes such as the available reserved bandwidth (dynamic) or link affinities (most of the time static) to compute constrained shortest paths for Traffic Engineering Label Switched Paths (TE LSPs). This document specifies routing metrics and constraints to be used in path calculation by the Routing Protocol for Low Power and Lossy Networks (RPL) specified in [I-D.ietf-roll-rpl]. One of the prime objectives of this document is to define a flexible mechanism for the advertisement of routing metrics and constraints used by RPL. Some RPL implementations may elect to adopt an extremely simple approach based on the use of a single metric with no constraint whereas other implementations may use a larger set of link and node routing metrics and constraints. This specification provides a high degree of flexibility and a set of routing metrics and constraints. New routing metrics and constraints could be defined in the future, as needed. The metrics and constraints defined in this document are carried in objects that are OPTIONAL within RPL. This means that implementations are free to include different subsets of the functions (metric, constraint) defined in this document. Specific sets of metrics/constraints and other optional RPL parameters for use in key environments will be specified as compliance profiles in applicability profile documents produced by the ROLL working group. RPL is a distance vector routing protocol variant that builds Directed Acyclic Graphs (DAGs) based on routing metrics and constraints. DAG formation rules are defined in [I-D.ietf-roll-rpl]: o The Destination Oriented Directed Acyclic Graph (DODAG) root as defined in [I-D.ietf-roll-rpl] may advertise a routing constraint used as a "filter" to prune links and nodes that do not satisfy specific properties. For example, it may be required for the path Vasseur, et al. Expires August 3, 2011 [Page 4] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 to only traverse nodes that are mains powered or links that have at least a minimum reliability or a specific "color" reflecting a user defined link characteristic (e.g the link layer supports encryption). o A routing metric is a quantitative value that is used to evaluate the path cost. Link and node metrics are usually (but not always) additive. The best path is the path that satisfies all supplied constraints (if any) and that has the lowest cost with respect to some specified metrics. It is also called the shortest constrained path (in the presence of constraints). Routing metrics may be categorized according to the following characteristics: o Link versus Node metrics o Qualitative versus quantitative o Dynamic versus static Routing requirements documents (see [RFC5673], [RFC5826] [RFC5548] and [RFC5867]) observe that it must be possible to take into account a variety of node constraints/metrics during path computation. Some link or node characteristics (e.g. link reliability, remaining energy on the node) may be used by RPL either as routing constraints or as metrics. For example, the path may be computed to avoid links that do not provide a sufficient level of reliability (use as a constraint) or as the path offering most links with a specified reliability level (use as a metric). This document provides the flexibility to use link and node characterisics either as constraints and/or metrics. The use of link and node routing metrics and constraints is not exclusive (e.g. it is possible to advertise a "hop count" both as a metric to optimize the computed path and as a constraint (e.g. "Path should not exceed n hops")). Links in LLN commonly have rapidly changing node and link characteristics: thus routing metrics must be dynamic and techniques must be used to smooth out the dynamicity of these metrics so as to avoid routing oscillations. For instance, in addition to the dynamic nature of some links (e.g. wireless but also Powerline Communication (PLC) links), nodes' resources such as residual energy are changing continuously and may have to be taken into account during the path Vasseur, et al. Expires August 3, 2011 [Page 5] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 computation. It must be noted that the use of dynamic metrics is not new and has been experimented in ARPANET 2 (see [[Khanna1989J]). The use of dynamic metrics is not trivial and great care must be given to the use of dynamic metrics since it may lead to potential routing instabilities. That being said, lots of experience has been gained over the years on the use of dynamic routing metrics, which have been deployed in a number of (non IP) networks. Very careful attention must be given to the pace at which routing metrics and attributes values change in order to preserve routing stability. When using a dynamic routing metric, a RPL implementation should make use of a multi-threshold scheme rather than fine granular metric updates reflecting each individual change to avoid spurious and unneccessary routing changes. The requirements on reporting frequency may differ among metrics, thus different reporting rates may be used for each metric. The set of routing metrics and constraints used by an RPL deployment is signaled along the DAG that is built according to the Objective Function (rules governing how to build a DAG) and the routing metrics and constraints are advertised in the DAG Information Option (DIO) message specified in [I-D.ietf-roll-rpl]. RPL may be used to build DAGs with different characteristics. For example, it may be desirable to build a DAG with the goal to maximize reliability by using the link reliability metric to compute the "best" path. Another example might be to use the energy node characteristic (e.g. mains powered versus battery operated) as a node constraint when building the DAG so as to avoid battery powered nodes in the DAG while optimizing the link throughput. The specification of objective functions used to compute the DAG built by RPL is out of the scope of this document. This document defines routing metrics and constraints that are decoupled from the objective function. So a generic objective function could for example specify the rules to select the best parents in the DAG, the number of backup parents, etc and could be used with any routing metrics and/or constraints such as the ones specified in this document. Some metrics are either aggregated or recorded. An aggregated metric is adjusted as the DIO message travels along the DAG. For example, if the metric is the number of hops, each node updates the path cost that reflects the number of traversed hops along the DAG. By contrast, for a recorded metric, each node adds a sub-object reflecting the local valuation of the metric. For example, it might Vasseur, et al. Expires August 3, 2011 [Page 6] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 be desirable to record the link quality level along a path. In this case, each visited node adds a sub-object recording the local link quality level. In order to limit the number of sub-objects, the use of a counter may be desirable (e.g. record the number of links with a certain link quality level), thus compressing the information to reduce the message length. Upon receiving the DIO message from a set of parents, a node might decide according to the OF and local policy which node to choose as a parent based on the maximum number of links with a specific link reliability level, for example. Note that the routing metrics and constraints specified in this document are not specific to any particular link layer. An internal API between the MAC layer and RPL may be used to accurately reflect the metrics values of the link (wireless, wired, PLC). Since a set of metrics and constraints will be used for links and nodes in LLN, it is critical to ensure the use of consistent metric calculation mechanisms for all links and nodes in the network, similarly to the case of inter-domain IP routing. 2. Object Formats 2.1. DAG Metric Container Format Routing metrics and constraints are carried within the DAG Metric Container object defined in [I-D.ietf-roll-rpl]. Should multiple metrics and/or constraints be present in the DAG Metric Container, their use to determine the "best" path can be defined by an Objective Function. The Routing Metric/Constraint objects represent a metric or a constraint of a particular type. They may appear in any order in the DAG Metric Container (specified in [I-D.ietf-roll-rpl]). They have a common format consisting of one or more bytes with a common header: Vasseur, et al. Expires August 3, 2011 [Page 7] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Routing-MC-Type|Res Flags|P|C|O|R| A | Prec | Length (bytes)| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // (object body) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Routing Metric/Constraint object generic format The object body carries one or more sub-objects defined later in this document. Note that an object may carry TLV, which may itself comprise other TLVs. A TLV carried within a TLV is called a TLV in this specification. Routing-MC-Type (Routing Metric/Constraint Type - 8 bits): the Routing Metric/Constraint Type field uniquely identifies each Routing Metric/Constraint object and is managed by IANA. Length: this field defines the length of the object body, in bytes. Flag field (16 bits). The Flag field of the Routing Metric/ Constraint object is managed by IANA. Unassigned bits are considered as reserved. They MUST be set to zero on transmission and MUST be ignored on receipt. The following bits of the Routing Metric/Constraint Flag field object are currently defined: o P flag: the P field is only used for recorded metrics. When cleared, all nodes along the path successfully recorded the corresponding metric. When set, this indicates than one or several nodes along the path could not record the metric of interest (either because of lack of knowledge or because this was prevented by policy). o C Flag. When set, this indicates that the Routing Metric/ Constraint object refers to a routing constraint. When cleared, the routing object refers to a routing metric. o O Flag: The O flag is used exclusively for routing constraints (C flag is set). When set, this indicates that the constraint specified in the body of the object is optional. When cleared, the constraint is mandatory. If the C flag is zero, the O flag MUST be set to zero on transmission and ignored on reception. Vasseur, et al. Expires August 3, 2011 [Page 8] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 o R Flag: The R Flag is only relevant for routing metric (C=0) and MUST be cleared for C=1. When set, this indicates that the routing metric is recorded along the path. Conversely, when cleared, the routing metric is aggregated. A Field (3 bits): The A field is only relevant for metrics and is used to indicate whether the aggregated routing metric is additive, multiplicative, reports a maximum or a minimum. o A=0x00: The routing metric is additive o A=0x01: The routing metric reports a maximum o A=0x02: The routing metric reports a minimum o A=0x03: The routing metric is multiplicative The A field has no meaning when the C Flag is set (i.e. when the Routing Metric/Constraint object refers to a routing constraint) and he only valid when the R bit is cleared. Otherwise, the A field MUST be set to 0x00 and MUST be ignored on receipt. Prec field (4 bits): The Prec field indicates the precedence of this Routing Metric/Constraint object relative to other objects in the container. This is useful when a DAG Metric Container contains several Routing Metric objects. The value 0 means the highest precedence. Example 1: A DAG formed by RPL where all nodes must be mains-powered and the best path is the one with lower aggregated ETX. In this case the DAG Metric container carries two Routing Metric/Constraint objects: one is an ETX metric object with header (C=0, O=0, A=00, R=0) and the second one is a Node Energy constraint object with header (C=1, O=0, A=00, R=0). Note that a RPL instance may use the metric object to report a maximum (A=0x01) or a minimum (A=0x02). If, for example, the best path is characterized by the path avoiding low quality links, then the path metric reports a maximum (A=0x01) (the higher is the ETX the lower link quality is): when the DIO message reporting link quality metric (ETX) is processed by a node, each node selecting the advertising node as a parent updates the value carried in the metric object by replacing it with its local link ETX value if and only if the latter is higher. As far as the constraint is concerned, the object body will carry a node energy constraint object defined in Section 3.1 indicating that nodes must be mains-powered: if the constraint signalled in the DIO message is not satisfied, the advertising node is just not selected as a parent by the node that processes the DIO message. Vasseur, et al. Expires August 3, 2011 [Page 9] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 Example 2: A DAG formed by RPL where the link metric is the link quality level (defined in Section 4) and link quality levels must be recorded along the path. In this case, the DAG Metric Container carries a Routing Metric/Constraint object: link quality level metric (C=0, O=0, A=00, R=1) containing multiple sub-objects. A Routing Metric/Constraint object may also include one or more additional type-length-value (TLV) encoded data sets. Each Routing Metric/Constraint TLV has the same structure: Type: 1 byte Length: 1 byte Value: variable A Routing Metric/Constraint TLV is comprised of 1 byte for the type, 1 byte specifying the TLV length, and a value field. The TLV length field defines the length of the value field in bytes (from 0 to 255). Unrecognized TLVs MUST be silently ignored while still being propagated in DIO generated by receiving node. IANA manages the codepoints for all TLV carried in routing constraint/metric objects. IANA management of the Routing Metric/Constraint objects identifier codespace is described in Section 6. 2.2. Use of Multiple DAG Metric Containers Since the length of RPL options is encoded using 1 octet, they cannot exceed 255 bytes, which also applies to the DAG Metric Container. In the vast majority of cases, the advertised routing metrics and constraints will not require that much space. However, there might be circumstances where larger space is required, should for example a set of routing metrics be recorded along a long path. In this case, in order to avoid overflow, as specified in [I-D.ietf-roll-rpl], routing metrics will be carried using multiple DAG Metric Containers objects. In the rest of this document, this use of multiple DAG Metric Containers objects will be considered as if they were actually just one long DAG Metric Container object. 2.3. Metric Usage When the DAG Metric Container contains a single aggregated metric (scalar value), the order relation to select the best path is implicitly derived from the metric type. For example, lower is Vasseur, et al. Expires August 3, 2011 [Page 10] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 better for Hop Count, Link Latency and ETX. Conversely, for Node Energy or Throughput, higher is better. An example of using such a single aggregated metric is optimizing routing for node energy. The Node Energy metric (E-E field) defined in Section 3.2 is aggregated along paths with an explicit min function (A field), and the best path is selected through an implied Max function because the metric is Energy. When the DAG Metric Container contains several aggregated metrics, they are to be used as tie-breakers according to their precedence defined by their Prec field values. An example of such use of multiple aggregated metrics is the following: Hop-Count as the primary criterion, LQL as the secondary criterion and Node Energy as the ultimate tie-breaker. In such a case, the Hop-Count, LQL and Node Energy metric objects' Prec fields should bear strictly increasing values such as 0, 1 and 2, respectively. If several aggregated metrics happen to bear the same Prec value, the behavior is implementation-dependant. 3. Node Metric/Constraint Objects The sections 3. and 4. specify several link and node metric/ constraint objects. In some cases it is stated that there must not be more than one object of a specific type. In that case, if an RPL implementation receives more than one object of that type, the second objet MUST silently be ignored. In the presence of a constraint and a metric (which may or may not be of the same type), a node MUST update the constraint before advertising the updated metric and constraints. For example, if the constraint is the number of hops (e.g. the maximum number of hops is n) and the path is optimized against the delay: if a node selects a parent advertising a maximum number of hops of n (constraint), it must advertises DIO messages containing a hop count metrics constraint with a field value equal of (n-1) and the newly computed path metric. This applies to the following constraints defined below: hop-count, latency and path ETX. 3.1. Node State and Attributes Object The Node State and Attribute (NSA) object is used to provide information on node characteristics. Vasseur, et al. Expires August 3, 2011 [Page 11] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 The NSA object MAY be present in the DAG Metric Container. There MUST NOT be more than one NSA object as a constraint per DAG Metric Container, and there MUST NOT be more than one NSA object as a metric per DAG Metric Container. The NSA object may also contain a set of TLVs used to convey various node characteristics. No TLV is currently defined. The NSA Routing Metric/Constraint Type is to be assigned by IANA (recommended value=1). The format of the NSA object body is as follows: 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... | Res | Flags |A|O| Optional TLVs +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Figure 2: NSA object body format Res flags (8 bits): Reserved field. This field MUST be set to zero on transmission and MUST be ignored on receipt. Flags field (8 bits). The following two bits of the NSA object are currently defined: o A Flag: data Aggregation Attribute. Data aggregation is listed as a requirement in Section 6.2 of [RFC5548]. Some applications may make use of the aggregation node attribute in their routing decision so as to minimize the amount of traffic on the network, thus potentially increasing its lifetime in battery operated environments. Applications where highly directional data flow is expected on a regular basis may take advantage of data aggregation supported routing. When set, this indicates that the node can act as a traffic aggregator. Further documents MAY define optional TLVs to describe the node traffic aggregator functionality. o O Flag: node workload may be hard to determine and express in some scalar form. However, node workload could be a useful metric to consider during path calculation, in particular when queuing delays must be minimized for highly sensitive traffic considering Medium Access Control (MAC) layer delay. Node workload MAY be set upon CPU overload, lack of memory or any other node related conditions. Using a simple 1-bit flag to characterize the node workload provides a sufficient level of granularity, similarly to the "overload" bit used in routing protocols such as IS-IS. Algorithms used to set the overload bit and to compute paths to Vasseur, et al. Expires August 3, 2011 [Page 12] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 potentially avoid nodes with their overload bit set are outside the scope of this document, but it is RECOMMENDED to avoid frequent changes of this bit to avoid routing oscillations. When set, this indicates that the node is overloaded and may not be able to process traffic. They MUST be set to zero on transmission and MUST be ignored on receipt. The Flag field of the NSA Routing Metric/Constraint object is managed by IANA. Unassigned bits are considered as reserved. 3.2. Node Energy Object It may sometimes be desirable to avoid selecting a node with low residual energy as a router, thus the support for constraint-based routing is needed. In such cases, the routing protocol engine may compute a longer path (constraint based) for some traffic in order to increase the network life duration. Power and energy are clearly critical resources in most LLNs. As yet there is no simple abstraction which adequately covers the broad range of power sources and energy storage devices used in existing LLN nodes. These include mains-powered, primary batteries, energy scavengers, and a variety of secondary storage mechanisms. Scavengers may provide a reliable low level of power, such as might be available from a 4-20mA loop; a reliable but periodic stream of power, such as provided by a well-positioned solar cell; or unpredictable power, such as might be provided by a vibrational energy scavenger on an intermittently powered pump. Routes which are viable when the sun is shining may disappear at night. A pump turning on may connect two previously disconnected sections of a network. Storage systems like rechargeable batteries often suffer substantial degradation if regularly used to full discharge, leading to different residual energy numbers for regular versus emergency operation. A route for emergency traffic may have a different optimum than one for regular reporting. Batteries used in LLNs often degrade substantially if their average current consumption exceeds a small fraction of the peak current that they can deliver. It is not uncommon for self-supporting nodes to have a combination of primary storage, energy scavenging, and secondary storage, leading to three different values for acceptable average current depending on the time frame being considered, e.g. milliseconds, seconds, and hours/years. Vasseur, et al. Expires August 3, 2011 [Page 13] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 Raw power and energy values are meaningless without knowledge of the energy cost of sending and receiving packets, and lifetime estimates have no value without some higher-level constraint on the lifetime required of a device. In some cases the path that exhausts the battery of a node on the bed table in a month may be preferable to a route that reduces the lifetime of a node in the wall to a decade. Given the complexity of trying to address such a broad collection of constraints, this document defines two levels of fidelity in the solution. The simplest solution relies on a 2-bit field encoding three types of power sources: "powered", "battery", "scavenger". This simple approach may be sufficient for many applications. The mid-complexity solution is a single parameter that can be used to encode the energetic happiness of both battery powered and scavenging nodes. For scavenging nodes, the 8 bit quantity is the power provided by the scavenger divided by the power consumed by the application, E-E=P_in/P_out, in units of percent. Nodes which are scavenging more power than they are consuming will register above 100. A good time period for averaging power in this calculation may be related to the discharge time of the energy storage device on the node, but specifying this is out of the scope of this document. For battery powered devices, E-E is the current expected lifetime divided by the desired minimum lifetime, in units of percent. The estimation of remaining battery energy and actual power consumption can be difficult, and the specifics of this calculation are out of scope of this document, but two examples are presented. If the node can measure its average power consumption, then H can be calculated as the ratio of desired max power (initial energy E_0 divided by desired lifetime T) to actual power, E-E=P_max/P_now. Alternatively, if the energy in the battery E_bat can be estimated, and the total elapsed lifetime, t, is available, then H can be calculated as the total stored energy remaining versus the target energy remaining: E-E= E_bat / [E_0 (T-t)/T]. An example of optimized route is max(min(H)) for all battery operated nodes along the route, subject to the constraint that E-E>=100 for all scavengers along the route. Note that the estimated percentage of remaining energy indicated in the E-E field may not be useful in the presence of nodes powered by battery or energy scavengers when the amount of energy accumulated by the device significantly differ. Indeed, X% of remaining energy on a node that can store a large amount of energy cannot be easily compared to the same percentage of remaining energy on a node powered by a tiny source of energy. That being said, in networks where nodes Vasseur, et al. Expires August 3, 2011 [Page 14] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 have relatively close energy storage, such a percentage of remaining energy is useful. The Node Energy (NE) object is used to provide information related to node energy and may be used as a metric or as constraint. The NE object MAY be present in the DAG Metric Container. There MUST NOT be more than one NE object as a constraint per DAG Metric Container, and there MUST NOT be more than one NE object as a metric per DAG Metric Container. The NE object Type is to be assigned by IANA (recommended value=2). The format of the NE object body is as follows: 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... | NE Sub-objects +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Figure 3: NE sub-object format The format of the NE sub-object body is as follows: 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... | Flags |I| T |E| E-E | Optional TLVs +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Figure 4: NE sub-object format The NE sub-object may also contain a set of TLVs used to convey various nodes' characteristics. Flags field (8 bits). The following flags are currently defined: o I (Included): the I bit is only relevant when the node type is used as a constraint. For example, the path must only traverse mains-powered nodes. Conversely, battery operated nodes must be excluded. The I bit is used to stipulate inclusion versus exclusion. When set, this indicates that nodes of the type specified in the node type field MUST be included. Conversely, when cleared, this indicates that nodes of type specified in the node type field MUST be excluded. Vasseur, et al. Expires August 3, 2011 [Page 15] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 o T (node Type): 2-bit field indicating the node type. T=0x00 designates a mains-powered node, T=0x01 a battery-powered node and T=0x02 a node powered by an energy scavenger. o E (Estimation): when the E bit is set for a metric, the estimated percentage of remaining energy on the node is indicated in the E-E 8-bit field. When cleared, the estimated percentage of remaining energy is not provided. When the E bit is set for a constraint, the E-E field defines a threshold for the inclusion/exclusion: if an inclusion, nodes with values higher than the threshold are to be included; if an exclusion, nodes with values lower than the threshold are to be excluded. E-E (Estimated-Energy): 8-bit unsigned integer field indicating an estimated percentage of remaining energy. The E-E field is only relevant when the E flag is set, and MUST be set to 0 when the E flag is cleared. If the NE object comprises several sub-objects when used as a constraint, each sub-object adds or subtracts node subsets as the sub-objects are parsed in order. The initial set (full or empty) is defined by the I bit of the first sub-object: full if that I bit is an exclusion, empty if that I bit is an inclusion. No TLV is currently defined. Future documents may define more complex solutions involving TLV parameters representing energy storage, consumption, and generation capabilities of the node, as well as desired lifetime. 3.3. Hop-Count Object The HoP-Count (HP) object is used to report the number of traversed nodes along the path. The HP object MAY be present in the DAG Metric Container. There MUST NOT be more than one HP object as a constraint per DAG Metric Container, and there MUST NOT be more than one HP object as a metric per DAG Metric Container. The HP object may also contain a set of TLVs used to convey various node characteristics. No TLV is currently defined. The HP routing metric object Type is to be assigned by IANA (recommended value=3) Vasseur, et al. Expires August 3, 2011 [Page 16] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 The format of the Hop Count object body is as follows: 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... | Res | Flags | Hop Count | Optional TLVs +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Figure 5: Hop Count object body format Res flags (4 bits): Reserved field. This field MUST be set to zero on transmission and MUST be ignored on receipt. No Flag is currently defined. Unassigned bits are considered as reserved. They MUST be set to zero on transmission and MUST be ignored on receipt. The HP object may be used as a constraint or a metric. When used as a constraint, the DAG root indicates the maximum number of hops that a path may traverse. When that number is reached, no other node can join that path. When used as a metric, each visited node simply increments the Hop Count field. Note that the first node along a path inserting a Hop-count object MUST set the Hop Count field value to 1. 4. Link Metric/Constraint Objects 4.1. Throughput Many LLNs support a wide range of throughputs. For some links, this may be due to variable coding. For the deeply duty-cycled links found in many LLNs, the variability comes as a result of trading power consumption for bit rate. There are several MAC layer protocols which allow for the effective bit rate of a link to vary over more than three orders of magnitude with a corresponding change in power consumption. For efficient operation, it may be desirable for nodes to report the range of throughput that their links can handle in addition to the currently available throughput. The Throughput object MAY be present in the DAG Metric Container. There MUST NOT be more than one Throughput object as a constraint per DAG Metric Container, and there MUST NOT be more than one Throughput object as a metric per DAG Metric Container. The Throughput object is made of throughput sub-objects and MUST at least comprise one Throughput sub-object. The first Throughput sub- Vasseur, et al. Expires August 3, 2011 [Page 17] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 object MUST be the most recently estimated actual throughput. The actual estimation of the throughput is outside the scope of this document. Each Throughput sub-object has a fixed length of 4 bytes. The Throughput object does not contain any additional TLV. The Throughput object Type is to be assigned by IANA (recommended value=4) The format of the Throughput object body is as follows: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (sub-object) ..... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: Throughput object body format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Throughput | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 7: Throughput sub-object format Throughput: 32 bits. The Throughput is encoded in 32 bits in unsigned integer format, expressed in bytes per second. 4.2. Latency Similarly to throughput, the latency of many LLN MAC sub-layers can vary over many orders of magnitude, again with a corresponding change in power consumption. Some LLN MAC link layers will allow the latency to be adjusted globally on the subnet, on a link-by-link basis, or not at all. Some will insist that it be fixed for a given link, but allow it to be variable from link to link. The Latency object MAY be present in the DAG Metric Container. There MUST NOT be more than one Latency object as a constraint per DAG Metric Container, and there MUST NOT be more than one Latency object as a metric per DAG Metric Container. The Latency object is made of Latency sub-objects and MUST at least Vasseur, et al. Expires August 3, 2011 [Page 18] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 comprise one Latency sub-object. Each Latency sub-object has a fixed length of 4 bytes. The Latency object does not contain any additional TLV. The Latency object Type is to be assigned by IANA (recommended value=5) The Latency object is a metric or constraint. The format of the Latency object body is as follows: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (sub-object) ..... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 8: Latency object body format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Latency | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 9: Latency sub-object format Latency: 32 bits. The Latency is encoded in 32 bits in unsigned integer format, expressed in microseconds. The Latency object may be used as a constraint or a path metric. For example, one may want the latency not to exceed some value. In this case, the Latency object common header indicates that the provided value relates to a constraint. In another example, the Latency object may be used as an aggregated additive metric where the value is updated along the path to reflect the path latency. 4.3. Link Reliability In LLNs, link reliability could be degraded for a number of reasons: signal attenuation, interferences of various forms, etc ... Time scales vary from milliseconds to days, and are often periodic and linked to human activity. Packet error rates can generally be measured directly, and other metrics (e.g. bit error rate, mean time between failures) are typically derived from that. Note that such variability is not specific to wireless link but also applies to PLC Vasseur, et al. Expires August 3, 2011 [Page 19] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 links. A change in link quality can affect network connectivity, thus, link quality may be taken into account as a critical routing metric. A number of link reliability metrics could be defined reflecting several reliability aspects. Two link reliability metrics are defined in this document: the Link Quality Level (LQL) and the Expected Transmission count Metric (ETX). Note that an RPL deployment MAY either use the LQL, the ETX or both. 4.3.1. The Link Quality Level Reliability Metric The Link Quality Level (LQL) object is used to quantify the link reliability using a discrete value, from 0 to 7 where 0 indicates that the link quality level is unknown and 1 reports the highest link quality level. The mechanisms and algorithms used to compute the LQL are implementation specific and outside of the scope of this document. The LQL can either be used as a metric or a constraint. When used as a metric, the LQL metric can only be recorded. For example, the DAG Metric object may request all traversed nodes to record the LQL of their incoming link into the LQL object. Each node can then use the LQL record to select its parent based on some user defined rules (e.g. something like "select the path with most links reporting a LQL value of 3 or less"). Counters are used to compress the information: for each encountered LQL value, only the number of matching links is reported. The LQL object MAY be present in the DAG Metric Container. There MUST NOT be more than one LQL object as a constraint per DAG Metric Container, and there MUST NOT be more than one LQL object as a metric per DAG Metric Container. The LQL object MUST contain one or more sub-object used to report the number of links along with their LQL. The LQL object Type is to be assigned by IANA (recommended value=6) Vasseur, et al. Expires August 3, 2011 [Page 20] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 The format of the LQL object body is as follows: 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... | Res | LQL sub-object +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Figure 10: LQL object body format Res flags (8 bits): Reserved field. This field MUST be set to zero on transmission and MUST be ignored on receipt. When the LQL metric is recorded, the LQL object body comprises one or more LQL Type 1 sub-object. The format of the LQL Type 1 sub-object is as follows 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Val | Counter | +-+-+-+-+-+-+-+-+ Figure 11: LQL Type 1 sub-object format Val: LQL value from 0 to 7 where 0 means undetermined and 1 indicates the highest link quality. Counter: number of links with that value. 4.3.2. The Expected Transmission Count (ETX) reliability object The Expected Transmission Count (ETX) metric is the number of transmissions a node expects to make to a destination in order to successfully deliver a packet. In contrast with the LQL routing metric, the ETX provides a discrete value (which may not be an integer) computed according to a specific formula: for example, an implementation may use the following formula: ETX= 1 / (Df * Dr) where Df is the measured probability that a packet is received by the neighbor and Dr is the measured probability that the acknowledgment packet is successfully received. This document does not mandate the use of a specific formula to compute the ETX value. The ETX object MAY be present in the DAG Metric Container. There MUST NOT be more than one ETX object as a constraint per DAG Metric Container, and there MUST NOT be more than one ETX object as a metric per DAG Metric Container. Vasseur, et al. Expires August 3, 2011 [Page 21] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 The ETX object is made of ETX sub-objects and MUST at least comprise one ETX sub-object. Each ETX sub-object has a fixed length of 8 bits. The ETX object does not contain any additional TLV. The ETX object Type is to be assigned by IANA (recommended value=7) The format of the ETX object body is as follows: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | (sub-object) ..... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 12: ETX object body format 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ETX | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 13: ETX sub-object format ETX: 16 bits. The ETX * 128 is encoded using 16 bits in unsigned integer format, rounded off to the nearest whole number. For example, if ETX = 3.569, the object value will be 457. If ETX > 511.9921875, the object value will be the maximum which is 65535. The ETX object may be used as a constraint or a path metric. For example, it may be required that the ETX must not exceed some specified value. In this case, the ETX object common header indicates that the value relates to a constraint. In another example, the ETX object may be used as an aggregated additive metric where the value is updated along the path to reflect the path quality: when a node receives the aggregated additive ETX value of the path (cummulative path ETX calculated as the sum of the link ETX of all of the traversed links from the advertising node to the DAG root), if it selects that node as its preferred parent, the node updates the path ETX by adding the ETX of the local link between itself and the preferred parent to the received path cost (path ETX) before potentially advertising itself the new path ETX. Vasseur, et al. Expires August 3, 2011 [Page 22] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 4.4. Link Color Object 4.4.1. Link Color Object Description The Link Color (LC) object is an administrative 10-bit link constraint (which may either be static or dynamically adjusted) used to avoid or attract specific links for specific traffic types. The LC object can either be used as a metric or as a constraint. When used as a metric, the LC metric can only be recorded. For example, the DAG may require recording the link colors for all traversed links. A color is defined as a specific set of bit values: in other words, that 10-bit field is a flag field, and not a scalar value. Each node can then use the LC to select the parent based on user defined rules (e.g. "select the path with the maximum number of links having their first bit set 1 (e.g. encrypted links)"). The LC object may also be used as a constraint. When used as a recorded metric, a counter is used to compress the information where the number of links for each Link Color is reported. The Link Color (LC) object MAY be present in the DAG Metric Container. There MUST NOT be more than one LC object as a constraint per DAG Metric Container, and there MUST NOT be more than one LC object as a metric per DAG Metric Container. There MUST be a at least one LC sub-object per LC object. The LC object does not contain any additional TLV. The LC object Type is to be assigned by IANA (recommended value=8) The format of the LC object body is as follows: 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... | Res | LC sub-objects +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... Figure 14: LC object format Res flags (8 bits): Reserved field. This field MUST be set to zero on transmission and MUST be ignored on receipt. When the LC object is used as a recorded metric, the LC object body comprises one or more LC Type 1 sub-objects. Vasseur, et al. Expires August 3, 2011 [Page 23] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 The format of the LC Type 1 sub-object body is as follows: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Color | Counter | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 15: LC Type 1 sub-object format When the LC object is used as a constraint, the LC object body comprises one or more LC Type 2 sub-objects. The format of the LC Type 2 sub-object body is as follows: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Color |Reserved |I| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 16: LC Type 2 sub-object format Res flags (7 bits): Reserved field. This field MUST be set to zero on transmission and MUST be ignored on receipt. I Bit: The I bit is only relevant when the Link Color is used as a constraint. When cleared, this indicates that links with the specified color must be included. When set, this indicates that links with the specified color must be excluded. It is left to the implementer to define the meaning of each bit of the 10-bit Link Color Flag field. 4.4.2. Mode of operation The link color may be used as a constraint or a metric. o When used as constraint, the LC object may be inserted in the DAG Metric Container to indicate that links with a specific color should be included or excluded from the computed path. o When used as recorded metric, each node along the path may insert a LC object in the DAG Metric Container to report the color of the local link. If there is already a LC object reporting a similar color, the node MUST NOT add another identical LC sub-object and MUST increment the counter field. Vasseur, et al. Expires August 3, 2011 [Page 24] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 5. Computation of Dynamic Metrics and Attributes As already pointed out, dynamically calculated metrics are of the utmost importance in many circumstances in LLNs. This is mainly because a variety of metrics change on a frequent basis, thus implying the need to adapt the routing decisions. That being said, care must be given to the pace at which changes are reported in the network. The attributes will change according to their own time scales. RPL controls the reporting rate. To minimize metric updates, multi-threshold algorithms MAY be used to determine when updates should be sent. When practical, low-pass filtering and/or hysteresis should be used to avoid rapid fluctuations of these values. Finally, although the specification of path computation algorithms using dynamic metrics are out the scope of this document, it is RECOMMENDED to carefully design the route optimization algorithm to avoid too frequent computation of new routes upon metric values changes. Controlled adaptation of the routing metrics and rate at which paths are computed are critical to avoid undesirable routing instabilities resulting in increased latencies and packet loss because of temporary micro-loops. Furthermore, excessive route changes will adversely impact the traffic and power consumption in the network, thus potentially impacting its scalability. 6. IANA Considerations IANA is requested to establish a new top-level registry to contain all Routing Metric/Constraint objects codepoints and sub-registries. The allocation policy for each new registry is by IETF review: new values are assigned through the IETF review process (see [RFC5226]). Specifically, new assignments are made via RFCs approved by the IESG. Typically, the IESG will seek input on prospective assignments from appropriate persons (e.g., a relevant Working Group if one exists). New bit numbers may be allocated only by an IETF Review action. Each bit should be tracked with the following qualities: o Bit number o Capability Description o Defining RFC Vasseur, et al. Expires August 3, 2011 [Page 25] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 6.1. Routing Metric/Constraint Type IANA is requested to create a registry for Routing Metric/Constraint objects. Each Routing Metric/Constraint object has a type value (from 1 to 255). Value Meaning Reference 1 Node State and Attribute This document 2 Node Energy This document 3 Hop Count This document 4 Link Throughput This document 5 Link Latency This document 6 Link Quality Level This document 7 Link ETX This document 8 Link Color This document 6.2. Routing Metric/Constraint TLV IANA is requested to create a registry used for all TLVs carried within Routing Metric/Constraint objects. The type field is an 8-bit field whose value can be comprised between 1 and 255. 6.3. Routing Metric/Constraint Common Header IANA is requested to create a registry to manage the Flag field of the Routing Metric/Constraint common header. Several bits are defined for the Routing Metric/Constraint common header in this document. The following values have been assigned: Codespace of the Flag field (Routing Metric/Constraint common header) Bit Description Reference 12-15 Precedence This document 9-11 Additive/Max/Min/Multi This document 8 Recorded/Aggregated This document 7 Optional Constraint This document 6 Constraint/Metric This document 5 P (Partial) This document IANA is requested to create a registry to manage the codespace of the A field of the Routing Metric/Constraint common header. Vasseur, et al. Expires August 3, 2011 [Page 26] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 Codespace of the A field (Routing Metric/Constraint common header) Value Meaning Reference 0 Routing metric is additive This document 1 Routing metric reports a maximum This document 2 Routing metric reports a minimum This document 3 Routing metric is multiplicative This document 6.4. NSA Object IANA is requested to create a registry to manage the codespace of the Flag field of the NSA object. Several bits are defined for the NSA object flag field in this document. The following values have been assigned: Codespace of the Flag field (NSA object) Bit Description Reference 14 Aggregator This document 15 Overloaded This document 6.5. Hop-Count Object IANA is requested to create a registry to manage the codespace of the Flag field of the Hop-count object. No Flag is currently defined. 7. Security Considerations Routing metrics should be handled in a secure and trustful manner. For instance, RPL should not allow a malicious node to falsely advertise that it has good metrics for routing, be added as a router for other nodes' traffic and intercept packets. Another attack may consist of making intermitment attacks on a link in an attempt to constantly modify the link quality and consequently the associated routing metric, thus leading to potential fluctuation in the DODAG. It is thus RECOMMENDED for a RPL implementation to put in place mechanism so as to stop advertising routing metrics for highly unstable links that may be subject to attacks. Some routing metrics may also be used to identify some areas of weaknesses in the network (a highly unreliable link, a node running low in terms of energy, etc.). Such information may be used by a potential attacker. Thus, it is RECOMMENDED to carefully consider which metrics should be used by RPL and the level of visibility that Vasseur, et al. Expires August 3, 2011 [Page 27] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 they provide about the network state or to use appropriate the security measures as specified in [I-D.ietf-roll-rpl] to protect that information. Since the routing metrics/constraints are carried within RPL message, the security routing mechanisms defined in [I-D.ietf-roll-rpl] applies here. 8. Acknowledgements The authors would like to acknowledge the contributions of Young Jae Kim, Hakjin Chong, David Meyer, Mischa Dohler, Anders Brandt, Philip Levis, Pascal Thubert, Richard Kelsey, Jonathan Hui, Alexandru Petrescu, Richard Kelsey, Mathilde Durvy, Phoebus Chen, Tim Winter, Yoav Ben-Yehezkel, Matteo Paris, Omprakash Gnawali, Mads Westergreen, Mukul Goyal, Joseph Saloway and David Culler for their review and valuable comments. Special thank to Adrian Farrel for his thourough review. 9. References 9.1. Normative references [I-D.ietf-roll-rpl] Winter, T., Thubert, P., Brandt, A., Clausen, T., Hui, J., Kelsey, R., Levis, P., Pister, K., Struik, R., and J. Vasseur, "RPL: IPv6 Routing Protocol for Low power and Lossy Networks", draft-ietf-roll-rpl-17 (work in progress), December 2010. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. 9.2. Informative references [I-D.ietf-roll-terminology] Vasseur, J., "Terminology in Low power And Lossy Networks", draft-ietf-roll-terminology-04 (work in progress), September 2010. [Khanna1989J A. Zinky, A. Khanna, and G. Vichniac. "Performance of the Revised Routing Metric for ARPANET and MILNET. Submitted to MILCOM 89, March 1989 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, December 1990. Vasseur, et al. Expires August 3, 2011 [Page 28] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J. McManus, "Requirements for Traffic Engineering Over MPLS", RFC 2702, September 1999. [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001. [RFC5548] Dohler, M., Watteyne, T., Winter, T., and D. Barthel, "Routing Requirements for Urban Low-Power and Lossy Networks", RFC 5548, May 2009. [RFC5673] Pister, K., Thubert, P., Dwars, S., and T. Phinney, "Industrial Routing Requirements in Low-Power and Lossy Networks", RFC 5673, October 2009. [RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation Routing Requirements in Low-Power and Lossy Networks", RFC 5826, April 2010. [RFC5867] Martocci, J., De Mil, P., Riou, N., and W. Vermeylen, "Building Automation Routing Requirements in Low-Power and Lossy Networks", RFC 5867, June 2010. Authors' Addresses JP Vasseur (editor) Cisco Systems, Inc 11, Rue Camille Desmoulins Issy Les Moulineaux, 92782 France Email: jpv@cisco.com Mijeom Kim (editor) Corporate Technology Group, KT 17 Woomyeon-dong, Seocho-gu Seoul, 137-792 Korea Email: mjkim@kt.com Vasseur, et al. Expires August 3, 2011 [Page 29] Internet-Draft draft-ietf-roll-routing-metrics-17 January 2011 Kris Pister Dust Networks 30695 Huntwood Ave. Hayward, CA 95544 USA Email: kpister@dustnetworks.com Nicolas Dejean Coronis SAS Espace Concorde, 120 impasse JB Say Perols, 34470 France Email: nicolas.dejean@coronis.com Dominique Barthel France Telecom Orange 28 chemin du Vieux Chene, BP 98 Meylan, 38243 France Email: dominique.barthel@orange-ftgroup.com Vasseur, et al. Expires August 3, 2011 [Page 30]