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Versions: (draft-mjkim-roll-routing-metrics) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 RFC 6551

Networking Working Group                                JP. Vasseur, Ed.
Internet-Draft                                        Cisco Systems, Inc
Intended status: Standards Track                             M. Kim, Ed.
Expires: June 5, 2011                     Corporate Technology Group, KT
                                                               K. Pister
                                                           Dust Networks
                                                               N. Dejean
                                                             Coronis SAS
                                                              D. Barthel
                                                   France Telecom Orange
                                                        December 6, 2010


    Routing Metrics used for Path Calculation in Low Power and Lossy
                                Networks
                   draft-ietf-roll-routing-metrics-13

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."




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   This Internet-Draft will expire on June 5, 2011.

Copyright Notice

   Copyright (c) 2010 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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.



































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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  . . . . . . . . . . . . . . . . . . 25
   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  . . . . . . . . . . . . . . . . . . . 28
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
     9.1.  Normative references . . . . . . . . . . . . . . . . . . . 28
     9.2.  Informative references . . . . . . . . . . . . . . . . . . 29
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29

















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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.

   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
      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.



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   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
   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.



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   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
   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.




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   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.


    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 2
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
   |     Type=2    |  Option Len   |Routing Metric/Constraint objects
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...

          Figure 1: DAG Metric Container format

   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.  They have a common format consisting of one or
   more bytes with a common header:

















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    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|  Flags  |P|C|O|R| A   |  Prec | Length (bytes)|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        (object body)                        //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 2: 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 of the Routing Metric/Constraint object:

   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.

   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.

   The Flag field of the Routing Metric/Constraint object is managed by



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   IANA.  Unassigned bits are considered as reserved.  They MUST be set
   to zero on transmission and MUST be ignored on receipt.

   A Field: 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: 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, 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.

   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.



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   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.

   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
   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



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   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 objet of that type, the second
   objet MUST silently be ignored.

3.1.  Node State and Attributes Object

   The Node State and Attribute (NSA) object is used to provide
   information on node characteristics.

   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).










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   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 3: 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.

   The following two bits of the NSA object are currently defined:

   o  A Flag: data Aggregation Attribute.  Data fusion involves more
      complicated processing to improve the accuracy of the output data,
      while data aggregation mostly aims at reducing the amount of data.
      This 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.  An implementation MAY
      decide to add optional TLVs (not currently defined) to further
      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
      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.




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   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.

   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



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   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
   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



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   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 4: 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 5: NE sub-object format

   The NE sub-object may also contain a set of TLVs used to convey
   various nodes' characteristics.

   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.

   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



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      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)

   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 6: 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.



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   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-
   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)






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   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 8: 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 9: 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
   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.





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   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 10: 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 11: 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 is degraded by external interference and
   multi-path interference (wireless links).  Multipath typically
   affects both directions on the link equally, whereas external
   interference is sometimes unidirectional.  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 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).



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   Note that an RPL implementation 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 be recorded or aggregated.  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").  By contrast, the LQL link metric may be
   aggregated, in which case the sum of all LQLs may be reported
   (additive metric) or the minimum value may be reported along the
   path.

   When used as a recorded metric, 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)

   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 12: LQL object body format

   Res flags (8 bits): Reserved field.  This field MUST be set to zero



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   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 13: 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.

   When the LQL metric is aggregated, the LQL object body comprises one
   LQL Type 2 sub-object:

   The format of the LQL Type 2 sub-object is as follows

     0                   1
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Aggregated LQL Value     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 14: LQL Type 2 sub-object format

   Aggregated LQL Value: when used as an additive metric (A=0x00), the
   aggregated LQL value reports the sum of all the LQL values for all
   links along the path.  When used to report a minimum (A=0x02), the
   field reports the minimum LQL value of all links along the path,
   ignoring undetermined LQLs (Aggregated LQL Value = 0).  When used to
   report a maximum (A=0x01), the field reports the maximum LQL value of
   all links along the path.  When used to report a multiplication
   (A=0x03), and the LQL field of one of the links along the path is
   undetermined (LQL=0), the undetermined LQL will be ignored and not be
   aggregated (i.e. no reset to Aggregated LQL Value field).

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



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   successfully deliver a packet.  In contrast with the LQL routing
   metric, the ETX provides a discrete value (wich 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.

   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 15: ETX object body format


    0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              ETX              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Figure 16: 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



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   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.

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)







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   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 17: 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.

   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 18: 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 19: 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



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   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.


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.



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   The allocation policy for each new registry is by IETF Consensus: new
   values are assigned through the IETF consensus 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).

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.

   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.

6.3.  Routing Metric/Constraint Common Header

   IANA is requested to create a registry to manage the codespace of the
   A field of the Routing Metric/Constraint common header.

   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

   IANA is requested to create a registry to manage the Flag field of
   the Routing Metric/Constraint common header.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number




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   o  Capability Description

   o  Defining RFC

   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

6.4.  NSA Object

   IANA is requested to create a registry to manage the codespace of the
   Flag field of the NSA object.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:

   o  Bit number

   o  Capability Description

   o  Defining RFC

   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.

   New bit numbers may be allocated only by an IETF Consensus action.
   Each bit should be tracked with the following qualities:




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   o  Bit number

   o  Capability Description

   o  Defining RFC

   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 DAG.  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.

   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,
   Mukul Goyal, Yoav Ben-Yehezkel, Matteo Paris, Omprakash Gnawali, Mads
   Westergreen, Mukul Goyal 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-15 (work in



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              progress), November 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.

   [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.







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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


   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






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