draft-ietf-roll-routing-metrics-08.txt   draft-ietf-roll-routing-metrics-09.txt 
Networking Working Group JP. Vasseur, Ed. Networking Working Group JP. Vasseur, Ed.
Internet-Draft Cisco Systems, Inc Internet-Draft Cisco Systems, Inc
Intended status: Standards Track M. Kim, Ed. Intended status: Standards Track M. Kim, Ed.
Expires: January 10, 2011 Corporate Technology Group, KT Expires: March 9, 2011 Corporate Technology Group, KT
K. Pister K. Pister
Dust Networks Dust Networks
N. Dejean N. Dejean
Coronis SAS Coronis SAS
D. Barthel D. Barthel
France Telecom Orange France Telecom Orange
July 09, 2010 September 5, 2010
Routing Metrics used for Path Calculation in Low Power and Lossy Routing Metrics used for Path Calculation in Low Power and Lossy
Networks Networks
draft-ietf-roll-routing-metrics-08 draft-ietf-roll-routing-metrics-09
Abstract Abstract
Low power and Lossy Networks (LLNs) have unique characteristics Low power and Lossy Networks (LLNs) have unique characteristics
compared with traditional wired and ad-hoc networks that require the compared with traditional wired and ad-hoc networks that require the
specification of new routing metrics and constraints. By contrast specification of new routing metrics and constraints. By contrast
with typical Interior Gateway Protocol (IGP) routing metrics using with typical Interior Gateway Protocol (IGP) routing metrics using
hop counts or link metrics, this document specifies a set of link and hop counts or link metrics, this document specifies a set of link and
node routing metrics and constraints suitable to LLNs. 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 Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
skipping to change at page 1, line 48 skipping to change at page 2, line 4
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 9, 2011.
This Internet-Draft will expire on January 10, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Object formats . . . . . . . . . . . . . . . . . . . . . . . . 7 2. Object formats . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Node Metric/Constraint objects . . . . . . . . . . . . . . . . 9 3. Node Metric/Constraint objects . . . . . . . . . . . . . . . . 9
3.1. Node State and Attributes object . . . . . . . . . . . . . 9 3.1. Node State and Attributes object . . . . . . . . . . . . . 10
3.2. Node Energy object . . . . . . . . . . . . . . . . . . . . 11 3.2. Node Energy object . . . . . . . . . . . . . . . . . . . . 11
3.3. Hop-Count object . . . . . . . . . . . . . . . . . . . . . 14 3.3. Hop-Count object . . . . . . . . . . . . . . . . . . . . . 14
3.4. Node Fanout Ratio object . . . . . . . . . . . . . . . . . 15 3.4. Node Fanout Ratio object . . . . . . . . . . . . . . . . . 15
4. Link Metric/Constraint objects . . . . . . . . . . . . . . . . 16 4. Link Metric/Constraint objects . . . . . . . . . . . . . . . . 16
4.1. Throughput . . . . . . . . . . . . . . . . . . . . . . . . 16 4.1. Throughput . . . . . . . . . . . . . . . . . . . . . . . . 16
4.2. Latency . . . . . . . . . . . . . . . . . . . . . . . . . 17 4.2. Latency . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.3. Link reliability . . . . . . . . . . . . . . . . . . . . . 18 4.3. Link reliability . . . . . . . . . . . . . . . . . . . . . 18
4.3.1. The Link Quality Level reliability metric . . . . . . 19 4.3.1. The Link Quality Level reliability metric . . . . . . 19
4.3.2. The Expected Transmission Count (ETX) reliability 4.3.2. The Expected Transmission Count (ETX) reliability
object . . . . . . . . . . . . . . . . . . . . . . . . 20 object . . . . . . . . . . . . . . . . . . . . . . . . 21
4.4. Link Color object . . . . . . . . . . . . . . . . . . . . 22 4.4. Link Color object . . . . . . . . . . . . . . . . . . . . 22
4.4.1. Link Color object description . . . . . . . . . . . . 22 4.4.1. Link Color object description . . . . . . . . . . . . 22
4.4.2. Mode of operation . . . . . . . . . . . . . . . . . . 23 4.4.2. Mode of operation . . . . . . . . . . . . . . . . . . 24
5. Computation of dynamic metrics and attributes . . . . . . . . 23 5. Computation of dynamic metrics and attributes . . . . . . . . 24
6. Use of multiple DAG Metric Container . . . . . . . . . . . . . 24 6. Use of multiple DAG Metric Container . . . . . . . . . . . . . 25
7. Metric consistency . . . . . . . . . . . . . . . . . . . . . . 24 7. Metric consistency . . . . . . . . . . . . . . . . . . . . . . 25
8. Metric usage . . . . . . . . . . . . . . . . . . . . . . . . . 25 8. Metric usage . . . . . . . . . . . . . . . . . . . . . . . . . 25
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
9.1. Routing Metric/Constraint type . . . . . . . . . . . . . . 26 9.1. Routing Metric/Constraint type . . . . . . . . . . . . . . 26
9.2. Routing Metric/Constraint common header . . . . . . . . . 26 9.2. Routing Metric/Constraint common header . . . . . . . . . 27
9.3. NSA object . . . . . . . . . . . . . . . . . . . . . . . . 27 9.3. NSA object . . . . . . . . . . . . . . . . . . . . . . . . 27
9.4. Hop-Count object . . . . . . . . . . . . . . . . . . . . . 27 9.4. Hop-Count object . . . . . . . . . . . . . . . . . . . . . 28
10. Security considerations . . . . . . . . . . . . . . . . . . . 28 10. Security considerations . . . . . . . . . . . . . . . . . . . 28
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
12.1. Normative references . . . . . . . . . . . . . . . . . . . 28 12.1. Normative references . . . . . . . . . . . . . . . . . . . 29
12.2. Informative references . . . . . . . . . . . . . . . . . . 28 12.2. Informative references . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction 1. Introduction
This document makes use of the terminology defined in This document makes use of the terminology defined in
[I-D.ietf-roll-terminology]. [I-D.ietf-roll-terminology].
Low power and Lossy Networks (LLNs) have specific routing Low power and Lossy Networks (LLNs) have specific routing
characteristics compared with traditional wired or ad-hoc networks characteristics compared with traditional wired or ad-hoc networks
that have been spelled out in [RFC5548], [RFC5673], [RFC5826] and that have been spelled out in [RFC5548], [RFC5673], [RFC5826] and
[RFC5867]. [RFC5867].
Historically, IGP such as OSPF ([RFC2328]) and IS-IS ([RFC1195]) have Historically, IGP such as OSPF ([RFC2328]) and IS-IS ([RFC1195]) have
used quantitative static link metrics. Other mechanisms such as used quantitative static link metrics. Other mechanisms such as
Multiprotocol Label Switching (MPLS) Traffic Engineering (TE) (see Multiprotocol Label Switching (MPLS) Traffic Engineering (TE) (see
[RFC2702] and [RFC3209]) make use of other link attributes such as [RFC2702] and [RFC3209]) make use of other link attributes such as
the available reserved bandwidth (dynamic) or link affinities the available reserved bandwidth (dynamic) or link affinities (most
(static) to compute constrained shortest paths for Traffic of the time static) to compute constrained shortest paths for Traffic
Engineering Label Switched Paths (TE LSPs). Engineering Label Switched Paths (TE LSPs).
This document specifies routing metrics and constraints to be used in This document specifies routing metrics and constraints to be used in
path calculation by the Routing Protocol for Low Power and Lossy path calculation by the Routing Protocol for Low Power and Lossy
Networks (RPL) specified in [I-D.ietf-roll-rpl]. Networks (RPL) specified in [I-D.ietf-roll-rpl].
One of the prime objectives of this document is to propose a flexible One of the prime objectives of this document is to propose a flexible
mechanism for the advertisement of routing metrics and constraints mechanism for the advertisement of routing metrics and constraints
used by RPL. Some RPL implementations may elect to adopt an used by RPL. Some RPL implementations may elect to adopt an
extremely simple approach based on the use of a single metric with no extremely simple approach based on the use of a single metric with no
constraint whereas other implementations may use a larger set of link constraint whereas other implementations may use a larger set of link
and node routing metrics and constraints. This specification and node routing metrics and constraints. This specification
provides a high degree of flexibility and a set of routing metrics provides a high degree of flexibility and a set of routing metrics
and constraints. New routing metrics and constraints could be and constraints. New routing metrics and constraints could be
defined in the future, as needed. defined in the future, as needed.
RPL is a distance vector routing protocol that builds a Directed RPL is a distance vector routing protocol that builds Directed
Acyclic Graph (DAG) based on routing metrics and constraints. DAG Acyclic Graphs (DAGs) based on routing metrics and constraints. DAG
formation rules are defined in [I-D.ietf-roll-rpl]: formation rules are defined in [I-D.ietf-roll-rpl]:
o The DAG root may advertise a routing constraint used as a "filter" o The DAG root may advertise a routing constraint used as a "filter"
to prune links and nodes that do not satisfy specific properties. to prune links and nodes that do not satisfy specific properties.
For example, it may be required for the path to only traverse 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 nodes that are mains powered or links that have at least a minimum
reliability or a specific "color" reflecting a user defined link reliability or a specific "color" reflecting a user defined link
characteristic (e.g the link layer supports encryption). characteristic (e.g the link layer supports encryption).
o A routing metric is a quantitative value that is used to evaluate o A routing metric is a quantitative value that is used to evaluate
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o Link versus Node metrics o Link versus Node metrics
o Qualitative versus quantitative o Qualitative versus quantitative
o Dynamic versus static o Dynamic versus static
It must be noted that the use of dynamic metrics is not new and has It must be noted that the use of dynamic metrics is not new and has
been experimented in ARPANET 2 [Khanna1989], with moderate success. been experimented in ARPANET 2 [Khanna1989], with moderate success.
The use of dynamic metrics is not trivial and great care must be 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 given to the use of dynamic metrics since it may lead to potential
routing instabilities. routing instabilities. it must be noted that the use of dynamic
metrics has been largely experimented and deployed in a number of
(non IP) networks in the past decade.
As pointed out in various routing requirements documents (see As pointed out in various routing requirements documents (see
[RFC5673], [RFC5826] [RFC5548] and [RFC5867]), it must be possible to [RFC5673], [RFC5826] [RFC5548] and [RFC5867]), it must be possible to
take into account a variety of node constraints/metrics during path take into account a variety of node constraints/metrics during path
computation. computation.
It is also worth mentioning that it is fairly common for links in It is also worth mentioning that it is fairly common for links in
LLNs to have fast changing node and link characteristics, which must LLNs to have fast changing node and link characteristics, which must
be taken into account when specifying routing metrics. For instance, be taken into account when specifying routing metrics. For instance,
in addition to the dynamic nature of wireless connectivity, nodes' in addition to the dynamic nature of some links (e.g. wireless but
resources such as residual energy and other link's charatacteristics also Poweline Communication (PLC) links, nodes' resources such as
such as the throughput are changing continuously and may have to be residual energy and other link's charatacteristics such as the
taken into account during the path computation. Similarly, link throughput are changing continuously and may have to be taken into
attributes including throughput and reliability may drastically account during the path computation. Similarly, link attributes
change over time due to multi-path interference. including throughput and reliability may drastically change over time
due to multi-path interference.
Very careful attention must be given when using dynamic metrics and Very careful attention must be given when using dynamic metrics and
attributes that affect routing decisions in order to preserve routing attributes that affect routing decisions in order to preserve routing
stability. Routing metrics and constraints may either be static or stability. Routing metrics and constraints may either be static or
dynamic. When dynamic, a RPL implementation SHOULD make use of a dynamic. When dynamic, a RPL implementation SHOULD make use of a
multi-threshold scheme rather than fine granular metric updates so as multi-threshold scheme rather than fine granular metric updates so as
to avoid constant routing changes. to avoid constant routing changes.
Furthermore, it is a time and energy consuming process to update Furthermore, it is a time and energy consuming process to update
dynamic metrics and recompute the routing tables on a frequent basis. dynamic metrics and recompute the routing tables on a frequent basis.
Therefore, it may be desirable to use a set of discrete values to Therefore, it may be desirable to use a set of discrete values to
reduce computational overhead and bandwidth utilization. Of course, reduce computational overhead and bandwidth utilization. Of course,
this comes with a cost, namely, reduced metric accuracy. In other this comes with a cost, namely, reduced metric accuracy. In other
cases, a set of flags may be defined to reflect a node state without cases, a set of flags may be defined to reflect a node state without
having to define discrete values. having to define discrete values.
Some link or node characteristics (e.g. link reliability flag, energy Some link or node characteristics (e.g. link reliability flag,
remaining on the node) may either be used by RPL as routing remaining energy on the node) may either be used by RPL as routing
constraints or metric. For example, the path may be computed to constraints or metric. For example, the path may be computed to
avoid links that do not provide a sufficient level of reliability avoid links that do not provide a sufficient level of reliability
(use as a constraint) or as the path offering the maximum number of (use as a constraint) or as the path offering the maximum number of
links with a specified reliability level (use as a metric). links with a specified reliability level (use as a metric). The
document provides the flexibility to use link and node charaterisics
either as constraints and/or metrics.
The set of routing metrics and constraints used by an RPL The set of routing metrics and constraints used by an RPL
implementation is signalled along the Directed Acyclic Graph (DAG) implementation is signalled along the Directed Acyclic Graph (DAG)
that is built according to the Objective Function (rules governing that is built according to the Objective Function (rules governing
how to build a DAG) and the routing metrics and constraints how to build a DAG) and the routing metrics and constraints are
advertised in the Dag Information Option (DIO) message specified in advertised in the DAG Information Option (DIO) message specified in
[I-D.ietf-roll-rpl]. RPL may be used to build DAGs with different [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 characteristics. For example, it may be desirable to build a DAG
with the goal to maximize reliability by using the link reliability with the goal to maximize reliability by using the link reliability
metric to compute the "best" path. Another example might be to use metric to compute the "best" path. Another example might be to use
the energy node characteristic (e.g. mains powered versus battery the energy node characteristic (e.g. mains powered versus battery
operated) as a node constraint when building the DAG so as to avoid operated) as a node constraint when building the DAG so as to avoid
battery powered nodes in the DAG while optimizing the link battery powered nodes in the DAG while optimizing the link
throughput. throughput.
Links and nodes routing metrics and constraints are not exclusive. Links and nodes routing metrics and constraints are not exclusive.
The requirements on reporting frequency may differ among metrics, The requirements on reporting frequency may differ among metrics,
thus different reporting rates may be used for each category. thus different reporting rates may be used for each category and are
consequently implementatin-specific.
The specification of objective functions used to compute the DAG The specification of objective functions used to compute the DAG
built by RPL is out of the scope of this document and will be built by RPL is out of the scope of this document. Routing metrics
specified in other documents. Routing metrics and constraints are and constraints are decoupled from the objective function. So a
decoupled from the objective function. So a generic objective generic objective function could for example specify the rules to
function could for example specify the rules to select the best select the best parents in the DAG, the number of backup parents,
parents in the DAG, the number of backup parents, etc. Such etc. Such objective function can be used with any routing metrics
objective function can be used with any routing metrics and/or and/or contraints such as the ones specified in this document.
contraints such as the ones specified in this document.
Some metrics are either aggregated or recorded. In the former case, Some metrics are either aggregated or recorded. In the former case,
the metric is adjusted as the DIO message travels along the DAG. For the metric is adjusted as the DIO message travels along the DAG. For
example, if the metric is the link latency, each node updates the example, if the metric is the link latency, each node updates the
latency metric along the DAG. By contrast, metric may be recorded in latency metric along the DAG. By contrast, a metric may be recorded
which case each node adds a sub-object reflecting the local metric. in which case each node adds a sub-object reflecting the local
For example, it might be desirable to record the link quality level metric. For example, it might be desirable to record the link
along the path. In this case, each visited node adds a sub-object quality level along the path. In this case, each visited node adds a
reporting the local link quality level. In order to limit the number sub-object reporting the local link quality level. In order to limit
of sub-objects, the use of a counter may be desirable (e.g. record the number of sub-objects, the use of a counter may be desirable
the number of links with a certain link quality level). Upon (e.g. record the number of links with a certain link quality level),
thus compressing the information to reduce the message lenght. Upon
receiving the DIO message from a set of parents, a node can decide receiving the DIO message from a set of parents, a node can decide
which node to choose as a parent based on the maximum number of links accoding to the OF and local policy which node to choose as a parent
with a specific link reliability level for example. based on the maximum number of links with a specific link reliability
level for example.
Notion of local versus global metric: some routing objects may have a Note that the routing metrics are constrained specified in this
local or a global significance. In the former case, a metric may be document are not specific to any link layer. Internal API between
transmitted to a neighbor to charaterize a link or a node as opposed the MAC layer and RPL may advantageously be used to accurately
to a path. For example, a node may report information about its reflect the metrics values of the link (wireless, wired, PLC).
local energy without the need to propagate the energy level of all
nodes along the path. In contrast, other metrics such as link
latency metrics are additive and global in the sense that they
characterize a path cost using the latency as a metric. In this
particular example the path latency is an aggregated global and
additive link metric.
2. Object formats 2. Object formats
Routing metrics and constraints are carried within the DAG Metric Routing metrics and constraints are carried within the DAG Metric
Container object defined in [I-D.ietf-roll-rpl]. Container object defined in [I-D.ietf-roll-rpl].
0 1 2 3 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 3 4 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 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
| Type=2 | Option Len | Routing Metric/Constraint objects | Type=2 | Option Len | Routing Metric/Constraint objects
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 1: DAG Metric Container format Figure 1: DAG Metric Container format
The Routing Metric/Contraints objects have a common format consisting The Routing Metric/Contraints objects have a common format consisting
of one or more 8-bit words with a common header: of one or more 8-bit words with a common header:
0 1 2 3 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 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|R|G| A |O|C| Object Length (bytes) | |Routing-MC-Type| Flags |P|C|0|R| A | Prec | Length (bytes)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
// (object body) // // (object body) //
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Routing Metric/Constraint object generic format Figure 2: Routing Metric/Constraint object generic format
The object body carries one or more sub-objects. The object body carries one or more sub-objects.
Note that the Routing Metric/Constraint objects defined in this Note that the Routing Metric/Constraint objects defined in this
document can appear in any order in the DAG Metric Container. document can appear in any order in the DAG Metric Container.
However, for some of them, the order is significant (as described in
Section 8 and Section 3.2, for example).
Routing-MC-Type: (Routing Metric/Contraint Type - 8 bits): the Routing-MC-Type (Routing Metric/Contraint Type - 8 bits): the Routing
Routing Metric/Constraint Type field uniquely identifies each Routing Metric/Constraint Type field uniquely identifies each Routing Metric/
Metric/Constraint object and is managed by IANA. Constraint object and is managed by IANA.
Res flags (2 bits). Reserved field. This field MUST be set to zero Length: this field defines the length of the object body, in bytes.
on transmission and MUST be ignored on receipt.
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.
o C Flag. When set, this indicates that the Routing Metric/ o C Flag. When set, this indicates that the Routing Metric/
Constraint object refers to a routing constraint. When cleared Constraint object refers to a routing constraint. When cleared,
the routing object refers to a routing metric. the routing object refers to a routing metric.
o O Flag: The O flag is used exclusively for routing constraints (C o O Flag: The O flag is used exclusively for routing constraints (C
flag is set) and has no meaning for routing metrics. When set, flag is set). When set, this indicates that the constraint is
this indicates that the constraint is optional. When cleared, the optional. When cleared, the constraint is mandatory. If the C
constraint is mandatory. flag is zero, the O flag MUST be set to zero on transmission and
ignored on reception.
o A Field: The A field is used to indicate whether a routing metric o R Flag: The R Flag is only relevant for routing metric (C=0) and
is additive, multiplicative, reports a maximum or a minimum. 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.
o A Field: The A field is used to indicate whether an aggregated
routing metric is additive, multiplicative, reports a maximum or a
minimum.
* A=0x00: The routing metric is additive * A=0x00: The routing metric is additive
* A=0x01: The routing metric reports a maximum * A=0x01: The routing metric reports a maximum
* A=0x02: The routing metric reports a minimum * A=0x02: The routing metric reports a minimum
* A=0x03: The routing metric is multiplicative * A=0x03: The routing metric is multiplicative
The A field has no meaning when the C Flag is set (i.e. when the 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). Routing Metric/Constraint object refers to a routing constraint)
and MUST be written to 0x00.
o G Flag: When set, the Routing Metric/Constraint object is global.
When cleared it is local (see details below).
o R Flag: The R Flag is only relevant for global routing metric (C=0 o Prec field: The P field indicates the precedence of this Routing
and G=1) and MUST be cleared for all other values of C and G. When Metric/Constraint object. This is useful when a DAG Metric
set, this indicates that the routing metric is recorded along the Container contains several Routing Metric objects. The value 0
path. Conversely, when cleared the routing metric is aggregated. means the highest precedence. The precedence field can be used as
a tie-breaker in the presence of the multiple metrics advertising
the same value.
Example 1: A DAG formed by RPL where all nodes must be mains powered o P field: the P field is only used for recorded metric. When
and the link metric is the link quality characterized by the ETX. In cleared, all nodes along the path managed to recorded the
this case the DAG Metric container carries two Routing Metric/ corresponding link metric. When set, this indicates than one of
Constraint objects: the link metric is the link ETX (C=0, O=0, A=00, more nodes along the path could not record the metric of interest
G=1, R=0) and the node constraint is power (C=1, O=0, A=00, G=0, (either because of lack of knowledge or because this was prevented
R=0). Note that in this example, the link quality is a global by policy).
additive aggregated link metric. Note that a RPL implementation may
use the metric to report a maximum (A=0x01) or a minimum (A=0x02).
If the best path is characterized by the path avoiding low quality
links for example, then the path metric reports a maximum (A=0x02):
when the link quality metric (ETX) is processed each node updates it Example 1: A DAG formed by RPL where all nodes must be main-powered
if the link quality (ETX) is higher than the current value reported and the best path is the one with lower aggregated ETX. In this case
by the link quality metric. 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 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 the best path
is characterized by the path avoiding low quality links for example,
then the path metric reports a maximum (A=0x01) (note that higher
values mean lower link quality): when the link quality metric (ETX)
is processed along a path, each node updates its value if the current
link ETX value is higher than the value carried by the metric object.
Example 2: A DAG formed by RPL where the link metric is the link Example 2: A DAG formed by RPL where the link metric is the link
quality level and link quality levels must be recorded along the quality level and link quality levels must be recorded along the
path. In this case, the DAG Metric Container carries a Routing path. In this case, the DAG Metric Container carries a Routing
Metric/Constraint object: link quality level (C=0, O=0, A=00, G=1, Metric/Constraint object: link quality level metric (C=0, O=0, A=00,
R=1) containing multiple sub-objects. R=1) containing multiple sub-objects.
A Routing Metric/Constraint object may also include one or more type- A Routing Metric/Constraint object may also include one or more type-
length-value (TLV) encoded data sets. Each Routing Metric/Constraint length-value (TLV) encoded data sets. Each Routing Metric/Constraint
TLV has the same structure: TLV has the same structure:
Type: 1 byte Type: 1 byte
Length: 1 byte Length: 1 byte
Value: variable Value: variable
A Routing Metric/Constraint TLV is comprised of 1 byte for the type, A Routing Metric/Constraint TLV is comprised of 1 byte for the type,
1 byte specifying the TLV length, and a value field. 1 byte specifying the TLV length, and a value field. The TLV length
field defines the length of the value field in bytes.
The Length field defines the length of the value field in bytes.
Unrecognized TLVs MUST be ignored. Unrecognized TLVs MUST be ignored.
IANA management of the Routing Metric/Constraint objects identifier IANA management of the Routing Metric/Constraint objects identifier
codespace is described in Section 9. codespace is described in Section 9.
3. Node Metric/Constraint objects 3. Node Metric/Constraint objects
It is fairly common for LLNs to be made of nodes with heterogeneous It is fairly common for LLNs to be made of nodes with heterogeneous
attributes and capabilities (e.g. nodes being battery operated or attributes and capabilities (e.g. nodes being battery operated or
not, amount of memory, etc). More capable and stable nodes may not, amount of memory, etc). More capable and stable nodes may
assist the most constrained ones for routing packets, which results assist the most constrained ones for routing packets, which results
in extension of network lifetime and efficient network operations. in extension of network lifetime and efficient network operations.
This is a typical use of constraint-based routing where the computed This is a typical (but non exclusive) use of constraint-based routing
path may not be the shortest path according to some specified where the computed path may not be the shortest path according to
metrics. some specified metrics. Another use is to find the shortest path
according to a pre-defined metric while avoiding link with a specific
color (for example "non secured link").
3.1. Node State and Attributes object 3.1. Node State and Attributes object
The Node State and Attribute (NSA) object is used to provide The Node State and Attribute (NSA) object is used to provide
information on the nodes characteristics. information on the nodes characteristics.
The NSA object MAY be present in the DAG Metric Container. There The NSA object MAY be present in the DAG Metric Container. There
MUST be no more than one NSA object as a constraint per DAG Metric MUST be no more than one NSA object as a constraint per DAG Metric
Container, and no more than one NSA object as a metric per DAG Metric Container, and no more than one NSA object as a metric per DAG Metric
Container. Container.
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The format of the NSA object body is as follows: The format of the NSA object body is as follows:
0 1 2 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 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 | Res | Flags |A|O| Optional TLVs
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 3: NSA object format Figure 3: NSA object format
Node workload may be hard to determine and express in some scalar Node workload may be hard to determine and expressed in some scalar
form. However, node workload could be a useful metric to consider form. However, node workload could be a useful metric to consider
during path calculation, in particular when queuing delays must be during path calculation, in particular when queuing delays must be
minimized for highly sensitive traffic considering Medium Access minimized for highly sensitive traffic considering Medium Access
Control (MAC) layer delay. Node workload MAY be set upon CPU Control (MAC) layer delay. Node workload MAY be set upon CPU
overload, lack of memory or any other node related conditions. Using overload, lack of memory or any other node related conditions. Using
a simple 1-bit flag to characterize the node workload provides a a simple 1-bit flag to characterize the node workload provides a
sufficient level of granularity, similarly to the "overload" bit used sufficient level of granularity, similarly to the "overload" bit used
in routing protocols such as IS-IS. Algorithms used to set the in routing protocols such as IS-IS. Algorithms used to set the
overload bit and to compute path to potentially avoid node with their overload bit and to compute path to potentially avoid node with their
overload bit set are outside the scope of this document. overload bit set are outside the scope of this document but it is
RECOMMENDED to avoid too frequent changes of that bit to avoid
routing oscillations.
Data Aggregation Attribute: data fusion involves more complicated Data Aggregation Attribute: data fusion involves more complicated
processing to improve accuracy of the output data while data processing to improve accuracy of the output data while data
aggregation mostly aims at reducing the amount of data. This is aggregation mostly aims at reducing the amount of data. This is
listed as a requirement in Section 6.2 of [RFC5548]. Some listed as a requirement in Section 6.2 of [RFC5548]. Some
applications may make use of the aggregation node attribute in their applications may make use of the aggregation node attribute in their
routing decision so as to minimize the amount of traffic on the routing decision so as to minimize the amount of traffic on the
network, thus potentially increasing its life time in battery network, thus potentially increasing its life time in battery
operated environments. Applications where high directional data flow operated environments. Applications where high directional data flow
is expected on a regular basis may take advantage of data aggregation is expected on a regular basis may take advantage of data aggregation
supported routing. supported routing.
The following two bits of the NSA object are defined: The following two bits of the NSA object are currently defined:
o O Flag: When set, this indicates that the node is overloaded and o O Flag: When set, this indicates that the node is overloaded and
may not be able to process traffic. may not be able to process traffic.
o A Flag: When set, this indicates that the node can act as a o A Flag: When set, this indicates that the node can act as a
traffic aggregator. An implementation MAY decide to add optional traffic aggregator. An implementation MAY decide to add optional
TLVs (not currently defined) to further describe the node traffic TLVs (not currently defined) to further describe the node traffic
aggregator functionality. aggregator functionality.
The Flag field of the NSA Routing Metric/Constraint object is managed The Flag field of the NSA Routing Metric/Constraint object is managed
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3.2. Node Energy object 3.2. Node Energy object
Whenever possible, a node with low residual energy should not be Whenever possible, a node with low residual energy should not be
selected as a router, thus the support for constraint-based routing selected as a router, thus the support for constraint-based routing
is needed. In such cases, the routing protocol engine may compute a is needed. In such cases, the routing protocol engine may compute a
longer path (constraint based) for some traffic in order to increase longer path (constraint based) for some traffic in order to increase
the network life duration. the network life duration.
The routing engine may prefer a "longer" path that traverses mains- The routing engine may prefer a "longer" path that traverses mains-
powered nodes or nodes equipped with energy scavenging, rather than a powered nodes in particular for low-critical traffic or nodes
"shorter" path through battery operated nodes. equipped with energy scavenging, rather than a "shorter" path through
battery operated nodes.
Power and energy are clearly critical resources in LLNs. As yet Power and energy are clearly critical resources in most LLNs. As yet
there is no simple abstraction which adequately covers the broad there is no simple abstraction which adequately covers the broad
range of power sources and energy storage devices used in existing range of power sources and energy storage devices used in existing
LLN nodes. These include line-power, primary batteries, energy- LLN nodes. These include main-powered, primary batteries, energy-
scavengers, and a variety of secondary storage mechanisms. scavengers, and a variety of secondary storage mechanisms.
Scavengers may provide a reliable low level of power, such as might 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 be available from a 4-20mA loop; a reliable but periodic stream of
power, such as provided by a well-positioned solar cell; or power, such as provided by a well-positioned solar cell; or
unpredictable power, such as might be provided by a vibrational unpredictable power, such as might be provided by a vibrational
energy scavenger on an intermittently powered pump. Routes which are energy scavenger on an intermittently powered pump. Routes which are
viable when the sun is shining may disappear at night. A pump viable when the sun is shining may disappear at night. A pump
turning on may connect two previously disconnected sections of a turning on may connect two previously disconnected sections of a
network. network.
Storage systems like rechargeable batteries often suffer substantial Storage systems like rechargeable batteries often suffer substantial
degradation if regularly used to full discharge, leading to different degradation if regularly used to full discharge, leading to different
residual energy numbers for regular versus emergency operation. A residual energy numbers for regular versus emergency operation. A
route for emergency traffic may have a different optimum than one for route for emergency traffic may have a different optimum than one for
regular reporting. regular reporting.
Batteries used in LLNs often degrade substantially if their average Batteries used in LLNs often degrade substantially if their average
current consumption exceeds a small fraction of the peak current that current consumption exceeds a small fraction of the peak current that
they can deliver. It is not uncommon for LLN nodes to have a they can deliver. It is not uncommon for battery-operated nodes to
combination of primary storage, energy scavenging, and secondary have a combination of primary storage, energy scavenging, and
storage, leading to three different values for acceptable average secondary storage, leading to three different values for acceptable
current depending on the time frame being considered, e.g. average current depending on the time frame being considered, e.g.
milliseconds, seconds, and hours/years. milliseconds, seconds, and hours/years.
Raw power and energy values are meaningless without knowledge of the Raw power and energy values are meaningless without knowledge of the
energy cost of sending and receiving packets, and lifetime estimates energy cost of sending and receiving packets, and lifetime estimates
have no value without some higher-level constraint on the lifetime have no value without some higher-level constraint on the lifetime
required of a device. In some cases the path that exhausts the 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 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. 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 Given the complexity of trying to address such a broad collection of
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be no more than one HP object as a constraint per DAG Metric be no more than one HP object as a constraint per DAG Metric
Container, and no more than one HP object as a metric per DAG Metric Container, and no more than one HP object as a metric per DAG Metric
Container. Container.
The HP object may also contain a set of TLVs used to convey various The HP object may also contain a set of TLVs used to convey various
node characteristics. No TLV is currently defined. node characteristics. No TLV is currently defined.
The HP routing metric object Type is to be assigned by IANA The HP routing metric object Type is to be assigned by IANA
(recommended value=3) (recommended value=3)
The HP routing metric object is a global routing object that
characterizes a path.
The format of the Hop Count object body is as follows: The format of the Hop Count object body is as follows:
0 1 2 3 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 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 | Res | Flags | Hop Count | Optional TLVs
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 6: Hop Count object format Figure 6: Hop Count object format
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The NFR object may also contain a set of TLVs used to convey various The NFR object may also contain a set of TLVs used to convey various
forwarding load characteristics. No TLV is currently defined. forwarding load characteristics. No TLV is currently defined.
The NFR object Type is to be assigned by IANA (recommended value=9). The NFR object Type is to be assigned by IANA (recommended value=9).
The format of the NFR object body is as follows: The format of the NFR object body is as follows:
0 1 2 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 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 | F R | Optional TLVs | Flags | F R | Optional TLVs
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 7: NFR object format Figure 7: NFR object format
When the data traffic of the application supported by the network is When the data traffic of the application supported by the network is
known a priori, energy depletion in the network can be equalized known a priori, energy depletion in the network can be equalized
simply by controlling the fanout ratio of router nodes. simply by controlling the fanout ratio of router nodes.
Algorithms describing how to compute the FR value and how to use it Algorithms describing how to compute the FR value and how to use it
are outside the scope of this document. are outside the scope of this document.
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Unassigned bits are considered as reserved. They MUST be set to zero Unassigned bits are considered as reserved. They MUST be set to zero
on transmission and MUST be ignored on receipt. on transmission and MUST be ignored on receipt.
4. Link Metric/Constraint objects 4. Link Metric/Constraint objects
4.1. Throughput 4.1. Throughput
Many LLNs support a wide range of throughputs. For some links, this Many LLNs support a wide range of throughputs. For some links, this
may be due to variable coding. For the deeply duty-cycled links may be due to variable coding. For the deeply duty-cycled links
found in many LLNs, the variability comes as a result of trading found in many LLNs, the variability comes as a result of trading
power consumption for bit rate. There are several MAC sub-layer power consumption for bit rate. There are several MAC layer
protocols which allow the effective bit rate and power consumption of protocols which allow for the effective bit rate and power
a link to vary over more than three orders of magnitude, with a consumption of a link to vary over more than three orders of
corresponding change in power consumption. For efficient operation, magnitude, with a corresponding change in power consumption. For
it may be desirable for nodes to report the range of throughput that efficient operation, it may be desirable for nodes to report the
their links can handle in addition to the currently available range of throughput that their links can handle in addition to the
throughput. currently available throughput.
The Throughput object MAY be present in the DAG Metric Container. The Throughput object MAY be present in the DAG Metric Container.
There MUST be no more than one Throughput object as a constraint per There MUST be no more than one Throughput object as a constraint per
DAG Metric Container, and no more than one Throughput object as a DAG Metric Container, and no more than one Throughput object as a
metric per DAG Metric Container. metric per DAG Metric Container.
The Throughput object is made of throughput sub-objects and MUST at The Throughput object is made of throughput sub-objects and MUST at
least comprise one Throughput sub-object. The first Throughput sub- least comprise one Throughput sub-object. The first Throughput sub-
object MUST be the most recently estimated actual throughput. Each object MUST be the most recently estimated actual throughput. The
Throughput sub-object has a fixed length of 4 bytes. actual evaluation of the throughput is outside 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 does not contain any additional TLV.
The Throughput object Type is to be assigned by IANA (recommended The Throughput object Type is to be assigned by IANA (recommended
value=4) value=4)
The Throughput object is a global metric.
The format of the Throughput object body is as follows: The format of the Throughput object body is as follows:
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (sub-object) ..... | (sub-object) .....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Throughput object body format Figure 8: Throughput object body format
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Throughput sub-object format Figure 9: Throughput sub-object format
Throughput: 32 bits. The Throughput is encoded in 32 bits in Throughput: 32 bits. The Throughput is encoded in 32 bits in
unsigned integer format, expressed in bytes per second. unsigned integer format, expressed in bytes per second.
4.2. Latency 4.2. Latency
Similarly to throughput, the latency of many LLN MAC sub-layers can Similarly to throughput, the latency of many LLN MAC sub-layers can
be varied over many orders of magnitude, again with a corresponding vary over many orders of magnitude, again with a corresponding change
change in current consumption. Some LLN MAC link layers will allow in current consumption. Some LLN MAC link layers will allow the
the latency to be adjusted globally on the subnet, or on a link-by- latency to be adjusted globally on the subnet, or on a link-by-link
link basis, or not at all. Some will insist that it be fixed for a basis, or not at all. Some will insist that it be fixed for a given
given link, but allow it to be variable from link to link. link, but allow it to be variable from link to link.
The Latency object MAY be present in the DAG Metric Container. There The Latency object MAY be present in the DAG Metric Container. There
MUST be no more than one Latency object as a constraint per DAG MUST be no more than one Latency object as a constraint per DAG
Metric Container, and no more than one Latency object as a metric per Metric Container, and no more than one Latency object as a metric per
DAG Metric Container. DAG Metric Container.
The Latency object is made of Latency sub-objects and MUST at least 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 comprise one Latency sub-object. Each Latency sub-object has a fixed
length of 4 bytes. length of 4 bytes.
The Latency object does not contain any additional TLV. The Latency object does not contain any additional TLV.
The Latency object Type is to be assigned by IANA (recommended The Latency object Type is to be assigned by IANA (recommended
value=5) value=5)
The Latency object is a global metric or constraint. The Latency object is a metric or constraint.
The format of the Latency object body is as follows: The format of the Latency object body is as follows:
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (sub-object) ..... | (sub-object) .....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Latency object body format Figure 10: Latency object body format
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The Latency object may be used as a constraint or a path metric. For 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 example, one may want the latency not to exceed some value. In this
case, the Latency object common header indicates that the provided case, the Latency object common header indicates that the provided
value relates to a constraint. In another example, the Latency value relates to a constraint. In another example, the Latency
object may be used as an aggregated additive metric where the value object may be used as an aggregated additive metric where the value
is updated along the path to reflect the path latency. is updated along the path to reflect the path latency.
4.3. Link reliability 4.3. Link reliability
In LLNs, link reliability is degraded by external interference and In LLNs, link reliability is degraded by external interference and
multi-path interference. Multipath typically affects both directions multi-path interference (wireless links). Multipath typically
on the link equally, whereas external interference is sometimes uni- affects both directions on the link equally, whereas external
directional. Time scales vary from milliseconds to days, and are interference is sometimes uni-directional. Time scales vary from
often periodic and linked to human activity. Packet error rates can milliseconds to days, and are often periodic and linked to human
generally be measured directly, and other metrics (e.g. bit error activity. Packet error rates can generally be measured directly, and
rate, mean time between failures) are typically derived from that. 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 A change in link quality can affect network connectivity, thus, link
quality may be taken into account as a critical routing metric. Link quality may be taken into account as a critical routing metric. Link
quality metric should be applied to each directional link unless bi- quality metric should be applied to each directional link unless bi-
directionality is one of routing metrics. directionality is one of routing metrics.
A number of link reliability metrics could be defined reflecting A number of link reliability metrics could be defined reflecting
several reliability aspects. Two link reliability metrics are several reliability aspects. Two link reliability metrics are
defined in this document: the Link Quality Level (LQL) and the defined in this document: the Link Quality Level (LQL) and the
Expected Transmission count Metric (ETX). Expected Transmission count Metric (ETX).
Note that an RPL implementation MAY either use the LQL, the ETX or Note that an RPL implementation MAY either use the LQL, the ETX or
both. both.
4.3.1. The Link Quality Level reliability metric 4.3.1. The Link Quality Level reliability metric
The Link Quality Level (LQL) object is used to quantify the link The Link Quality Level (LQL) object is used to quantify the link
reliability using a discrete value, from 0 to 7 where 0 indicates 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 that the link quality level is unknown and 1 reports the highest link
quality level. The mechanisms and algorithms used to compute the LQL quality level. The mechanisms and algorithms used to compute the LQL
is implementation specific and outside the scope of this document. is implementation specific and outside of the scope of this document.
The LQL is global and can either be used as a metric or a constraint. The LQL can either be used as a metric or a constraint. When used as
When used as a metric, the LQL metric can be recorded or aggregated. a metric, the LQL metric can be recorded or aggregated. For example,
For example, the DAG may require to record the LQL for all traversed the DAG may require to record the LQL for all traversed links. Each
links. Each node can then use the LQL to select the parent based on node can then use the LQL to select the parent based on user defined
user defined rules (e.g. "select the path with the maximum number of rules (e.g. "select the path with the maximum number of links
links reporting a LQL value of 3"). By contrast the LQL link metric reporting a LQL value of 3 or less"). By contrast the LQL link
may be aggregated, in which case the sum of all LQL may be reported metric may be aggregated, in which case the sum of all LQLs may be
(additive metric) or the minimum value may be reported along the reported (additive metric) or the minimum value may be reported along
path. the path.
When used as a recorded metric, a counter is used to compress the When used as a recorded metric, a counter is used to compress the
information where the number of links for each LQL is reported. information where the number of links for each LQL is reported.
The LQL object MAY be present in the DAG Metric Container. There The LQL object MAY be present in the DAG Metric Container. There
MUST be no more than one LQL object as a constraint per DAG Metric MUST be no more than one LQL object as a constraint per DAG Metric
Container, and no more than one LQL object as a metric per DAG Metric Container, and no more than one LQL object as a metric per DAG Metric
Container. Container.
The LQL object MUST contain one or more sub-object used to report the The LQL object MUST contain one or more sub-object used to report the
number of links along with their LQL. number of links along with their LQL.
The LQL object Type is to be assigned by IANA (recommended value=6) The LQL object Type is to be assigned by IANA (recommended value=6)
The LQL object is a global object that characterizes the path
reliability.
The format of the LQL object body is as follows: The format of the LQL object body is as follows:
0 1 2 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 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 | Res | LQL sub-object
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 12: LQL object format Figure 12: LQL object format
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The format of the LQL Type 2 sub-object is as follows The format of the LQL Type 2 sub-object is as follows
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Aggregated LQL Value | | Aggregated LQL Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: LQL Type 2 sub-object format Figure 14: LQL Type 2 sub-object format
Aggregated LQL Value: when used an an additive metric (A=0x00), the 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 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 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 field reports the minimum LQL value of all links along the path
ignoring undetermined LQLs (Aggregated LQL Value = 0). When used to ignoring undetermined LQLs (Aggregated LQL Value = 0). When used to
report a maximum (A=0x01), the field reports the maximum LQL value of report a maximum (A=0x01), the field reports the maximum LQL value of
all links along the path. When used to report a multiplication 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 (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 undetermined (LQL=0), the undetermined LQL will be ignored and not be
aggregated (i.e. no reset to Aggregated LQL Value field). aggregated (i.e. no reset to Aggregated LQL Value field).
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Container, and no more than one ETX object as a metric per DAG Metric Container, and no more than one ETX object as a metric per DAG Metric
Container. Container.
The ETX object is made of ETX sub-objects and MUST at least comprise 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 one ETX sub-object. Each ETX sub-object has a fixed length of 8
bits. bits.
The ETX object does not contain any additional TLV. The ETX object does not contain any additional TLV.
The ETX object Type is to be assigned by IANA (recommended value=7) The ETX object Type is to be assigned by IANA (recommended value=7)
The ETX object is a global metric or constraint.
The format of the ETX object body is as follows: The format of the ETX object body is as follows:
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (sub-object) ..... | (sub-object) .....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: ETX object body format Figure 15: ETX object body format
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ETX | | ETX |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: ETX sub-object format Figure 16: ETX sub-object format
ETX: 16 bits. The ETX * 128 is encoded in 16 bits in unsigned ETX: 16 bits. The ETX * 128 is encoded using 16 bits in unsigned
integer format, rounded off to the nearest whole number. For integer format, rounded off to the nearest whole number. For
example, if ETX = 3.569, the object value will be 457. If ETX > 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. 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 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 example, it may be required that the ETX must not exceed some
specified value. In this case, the ETX object common header specified value. In this case, the ETX object common header
indicates that the value relates to a constraint . In another indicates that the value relates to a constraint . In another
example, the ETX object may be used as an aggregated additive metric example, the ETX object may be used as an aggregated additive metric
where the value is updated along the path to reflect to path quality. where the value is updated along the path to reflect to path quality.
4.4. Link Color object 4.4. Link Color object
4.4.1. Link Color object description 4.4.1. Link Color object description
The Link Color (LC) object is an administrative 10-bit static link The Link Color (LC) object is an administrative 10-bit link
constraint used to avoid or attract specific links for specific constraint (which may either be static or dynamically adjusted) used
traffic types. to avoid or attract specific links for specific traffic types.
The LC object can either be used as a metric or as a constraint. 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 When used as a metric, the LC metric can only be recorded. For
example, the DAG may require recording the link colors for all example, the DAG may require recording the link colors for all
traversed links. Each node can then use the LC to select the parent traversed links. Each node can then use the LC to select the parent
based on user defined rules (e.g. "select the path with the maximum 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 number of links having their first bit set 1 (e.g. encrypted
links)"). The LC object may also be used as a constraint. links)"). The LC object may also be used as a constraint.
When used as a recorded metric, a counter is used to compress the When used as a recorded metric, a counter is used to compress the
skipping to change at page 22, line 37 skipping to change at page 23, line 18
Container. There MUST be no more than one LC object as a constraint Container. There MUST be no more than one LC object as a constraint
per DAG Metric Container, and no more than one LC object as a metric per DAG Metric Container, and no more than one LC object as a metric
per DAG Metric Container. per DAG Metric Container.
There MUST be a at least one LC sub-object per LC object. 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 does not contain any additional TLV.
The LC object Type is to be assigned by IANA (recommended value=8) The LC object Type is to be assigned by IANA (recommended value=8)
The LC object may either be local or global.
The format of the LC object body is as follows: The format of the LC object body is as follows:
0 1 2 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 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 | Res | LC sub-objects
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 17: LC object format Figure 17: LC object format
When the LC object is used as a global recorded metric, the LC object When the LC object is used as a recorded metric, the LC object body
body comprises one or more LC Type 1 sub-objects. comprises one or more LC Type 1 sub-objects.
The format of the LC Type 1 sub-object body is as follows: The format of the LC Type 1 sub-object body is as follows:
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Color | Counter | | Link Color | Counter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: LC Type 1 sub-object format Figure 18: LC Type 1 sub-object format
skipping to change at page 23, line 28 skipping to change at page 24, line 15
The format of the LC Type 2 sub-object body is as follows: The format of the LC Type 2 sub-object body is as follows:
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Color |I| | Link Color |I|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: LC Type 2 sub-object format Figure 19: LC Type 2 sub-object format
I Bit: When cleared, this indicates that links with the specified I Bit: The I bits is only relevant when the Link Color is used as a
color must be included. When set, this indicates that links with the constraint. When cleared, this indicates that links with the
specified color must be excluded. specified color must be included. When set, this indicates that
links with the specified color must be excluded.
The use of the LC object is outside the scope of this document. The use of the LC object is outside the scope of this document.
4.4.2. Mode of operation 4.4.2. Mode of operation
The link color may be used as a constraint or a metric. The link color may be used as a constraint or a metric.
o When used as global constraint, the LC object may be inserted in o When used as constraint, the LC object may be inserted in the DAG
the DAG Metric Container to indicate that links with a specific Metric Container to indicate that links with a specific color
color should be included or excluded from the computed path. should be included or excluded from the computed path.
o When used as global recorded metric, each node along the path may o When used as recorded metric, each node along the path may insert
insert a LC object in the DAG Metric Container to report the color a LC object in the DAG Metric Container to report the color of the
of the local link. If there is already a LC object reported a local link. If there is already a LC object reported a similar
similar color, the node MUST NOT add another identical LC sub- color, the node MUST NOT add another identical LC sub-object and
object and MUST increment the counter field. MUST increment the counter field.
5. Computation of dynamic metrics and attributes 5. Computation of dynamic metrics and attributes
As already pointed out, dynamically calculated metrics are of the As already pointed out, dynamically calculated metrics are of the
utmost importance in many circumstances in LLNs. This is mainly utmost importance in many circumstances in LLNs. This is mainly
because a variety of metrics change on a frequent basis, thus because a variety of metrics change on a frequent basis, thus
implying the need to adapt the routing decisions. That being said, 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 care must be given to the pace at which changes are reported in the
network. The attributes will change according to their own time network. The attributes will change according to their own time
scales. RPL controls the reporting rate. scales. RPL controls the reporting rate.
To minimize metric updates, multi-threshold algorithms MAY be used to To minimize metric updates, multi-threshold algorithms MAY be used to
determine when updates should be sent. When practical, low-pass determine when updates should be sent. When practical, low-pass
filtering and/or hysteresis should be used to avoid rapid filtering and/or hysteresis should be used to avoid rapid
fluctuations of these values. Finally, although the specification of fluctuations of these values. Finally, although the specification of
path computation algorithms using dynamic metrics are out the scope path computation algorithms using dynamic metrics are out the scope
of this document, the route optimization algorithm should be designed of this document, it is RECOMMENDED to carefully design the route
carefully to avoid too frequent computation of new routes upon metric optimization algorithm to avoid too frequent computation of new
values changes. routes upon metric values changes.
Controlled adaptation of the routing metrics and rate at which paths Controlled adaptation of the routing metrics and rate at which paths
are computed are critical to avoid undesirable routing instabilities are computed are critical to avoid undesirable routing instabilities
resulting in increased latencies and packet loss because of temporary resulting in increased latencies and packet loss because of temporary
micro-loops. Furthermore, excessive route changes will adversely micro-loops. Furthermore, excessive route changes will adversely
impact the traffic and power consumption in the network. impact the traffic and power consumption in the network, thus
potentially impacting its scalability.
6. Use of multiple DAG Metric Container 6. Use of multiple DAG Metric Container
Since RPL options length are coded using 1 octet, their length cannot Since RPL options length are coded using 1 octet, their length cannot
exceed 256 bytes, which also applies to the DAG Metric Container. exceed 256 bytes, which also applies to the DAG Metric Container.
Although in the vast majority of cases, the advertised routing Although in the vast majority of cases, the advertised routing
metrics and constraints will not require that much space, there might metrics and constraints will not require that much space, there might
be circumstances where larger space will be required, should for be circumstances where larger space will be required, should for
example a set of routing metrics be recorded along a long path. In example a set of routing metrics be recorded along a long path. In
this case, as specified in [I-D.ietf-roll-rpl], routing metrics will this case, as specified in [I-D.ietf-roll-rpl], routing metrics will
be carried using multiple DAG Metric Containers. be carried using multiple DAG Metric Containers.
In the rest of this document, this use of multiple DAG Metric In the rest of this document, this use of multiple DAG Metric
Containers will be considered as if they were actually just one long Containers will be considered as if they were actually just one long
DAG Metric Container. For this to hold, nodes propagating multiple DAG Metric Container.
DAG Metric Containers MUST keep their order unchanged.
7. Metric consistency 7. Metric consistency
Since a set of metrics and constraints will be used for links and Since a set of metrics and constraints will be used for links and
nodes in LLN, it is particularly critical to ensure the use of nodes in LLN, it is particularly critical to ensure the use of
consistent metric calculation mechanisms for all links and nodes in consistent metric calculation mechanisms for all links and nodes in
the network. the network, similarly to the case of inter-domain IP routing.
8. Metric usage 8. Metric usage
This section describes how metrics carried in the DAG Metric This section describes how metrics carried in the DAG Metric
Container shall be used. Container shall be used.
When the DAG Metric Container contains a single aggregated metric When the DAG Metric Container contains a single aggregated metric
(scalar value), the order relation to select the best path is (scalar value), the order relation to select the best path is
implicitely derived from the metric type. For example, lower is implicitly derived from the metric type. For example, lower is
better for Hop Count, Link Latency, ETX and Fanout Ratio. For Node better for Hop Count, Link Latency, ETX and Fanout Ratio. For Node
Energy or Throughput, higher is better. Energy or Throughput, higher is better.
An exemple of using such a single aggregated metric is optimizing An example of using such a single aggregated metric is optimizing
routing for node energy. The Node Energy metric (E-E field) is routing for node energy. The Node Energy metric (E-E field) is
aggregated along pathes with an explicit min function (A field), and aggregated along paths with an explicit min function (A field), and
the best path is selected through an implied Max function because the the best path is selected through an implied Max function because the
metric is Energy. metric is Energy.
When the DAG Metric Container contains several aggregated metrics, When the DAG Metric Container contains several aggregated metrics,
they are to be used as tie-brakers in the order that they appear in they are to be used as tie-breakers according to their precedence
the DAG Metric Container. A node propagating a DAG Metric Container defined by their Prec field values.
MUST keep the order of metric objects unchanged.
An example of such use of multiple aggregated metrics is the An example of such use of multiple aggregated metrics is the
following: Hop-Count as the primary criterion, LQL as the secondary following: Hop-Count as the primary criteria, LQL as the secondary
criterion and Fanout Ratio as the ultimate tie-braker. In such a criteria and Fanout Ratio as the ultimate tie-breaker. In such a
case, the Hop-Count, LQL and Fanout Ratio metric objects need to case, the Hop-Count, LQL and Fanout Ratio metric objects' Prec fields
appear in that order in the DAG Metric Container. should bear strictly increasing values such as 0, 1 and 2,
respectively.
The use of compound metrics, such as a polynomial function of
individual metric values, will be described in a future revision of
this document.
The use of recorded metrics will be described in a future revision of
this document.
9. IANA Considerations 9. IANA Considerations
IANA is requested to establish a new top-level registry to contain IANA is requested to establish a new top-level registry to contain
all Routing Metric/Constraint objects codepoints and sub-registries. all Routing Metric/Constraint objects codepoints and sub-registries.
The allocation policy for each new registry is by IETF Consensus: new The allocation policy for each new registry is by IETF Consensus: new
values are assigned through the IETF consensus process (see values are assigned through the IETF consensus process (see
[RFC5226]). Specifically, new assignments are made via RFCs approved [RFC5226]). Specifically, new assignments are made via RFCs approved
by the IESG. Typically, the IESG will seek input on prospective by the IESG. Typically, the IESG will seek input on prospective
skipping to change at page 27, line 8 skipping to change at page 27, line 36
o Capability Description o Capability Description
o Defining RFC o Defining RFC
Several bits are defined for the Routing Metric/Constraint common Several bits are defined for the Routing Metric/Constraint common
header in this document. The following values have been assigned: header in this document. The following values have been assigned:
Codespace of the Flag field (Routing Metric/Constraint common header) Codespace of the Flag field (Routing Metric/Constraint common header)
Bit Description Reference Bit Description Reference
8 Constraint/metric This document 12-15 Precedence This document
7 Optional Constraint This document 10-11 Additive/Max/Min/Multi This document
5-6 Additive/Max/Min/Multi This document 9 Recorded/Aggregated This document
4 Global/Local This document 8 Optional Constraint This document
3 Recorded/Aggregated This document 7 Constraint/metric This document
6 P (Partial) This document
9.3. NSA object 9.3. NSA object
IANA is requested to create a registry to manage the codespace of the IANA is requested to create a registry to manage the codespace of the
Flag field of the NSA object. Flag field of the NSA object.
New bit numbers may be allocated only by an IETF Consensus action. New bit numbers may be allocated only by an IETF Consensus action.
Each bit should be tracked with the following qualities: Each bit should be tracked with the following qualities:
o Bit number o Bit number
skipping to change at page 28, line 10 skipping to change at page 28, line 38
o Defining RFC o Defining RFC
No Flag is currently defined. No Flag is currently defined.
10. Security considerations 10. Security considerations
Routing metrics should be handled in a secure and trustful manner. Routing metrics should be handled in a secure and trustful manner.
For instance, a malicious node can not advertise falsely that it has For instance, a malicious node can not advertise falsely that it has
good metrics for routing and belong to the established path to have a good metrics for routing and belong to the established path to have a
chance to intercept packets. chance to intercept packets. Since the routing metrics/constraints
are carried within RPL message, the security routing mechanisms
defined in [I-D.ietf-roll-rpl] applies here.
11. Acknowledgements 11. Acknowledgements
The authors would like to acknowledge the contributions of Young Jae The authors would like to acknowledge the contributions of Young Jae
Kim, Hakjin Chong, David Meyer, Mischa Dohler, Anders Brandt, Philip Kim, Hakjin Chong, David Meyer, Mischa Dohler, Anders Brandt, Philip
Levis, Pascal Thubert, Richard Kelsey, Jonathan Hui, Alexandru Levis, Pascal Thubert, Richard Kelsey, Jonathan Hui, Alexandru
Petrescu, Ricahrd Kelsey, Mathilde Durvy, Phoebus Chen, Tim Winter, Petrescu, Richard Kelsey, Mathilde Durvy, Phoebus Chen, Tim Winter,
Mukul Goyal, Yoav Ben-Yehezkel, Matteo Paris, Omprakash Gnawali, Mads Mukul Goyal, Yoav Ben-Yehezkel, Matteo Paris, Omprakash Gnawali, Mads
Westergreen and Mukul Goyal for their review and comments. Westergreen and Mukul Goyal for their review and valuable comments.
12. References 12. References
12.1. Normative references 12.1. Normative references
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226, IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008. May 2008.
12.2. Informative references 12.2. Informative references
[I-D.ietf-roll-rpl] [I-D.ietf-roll-rpl]
Winter, T., Thubert, P., and R. Team, "RPL: IPv6 Routing Winter, T., Thubert, P., and R. Team, "RPL: IPv6 Routing
Protocol for Low power and Lossy Networks", Protocol for Low power and Lossy Networks",
draft-ietf-roll-rpl-10 (work in progress), June 2010. draft-ietf-roll-rpl-11 (work in progress), July 2010.
[I-D.ietf-roll-terminology] [I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy Vasseur, J., "Terminology in Low power And Lossy
Networks", draft-ietf-roll-terminology-03 (work in Networks", draft-ietf-roll-terminology-03 (work in
progress), March 2010. progress), March 2010.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990. dual environments", RFC 1195, December 1990.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
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