draft-ietf-roll-routing-metrics-14.txt   draft-ietf-roll-routing-metrics-15.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: June 16, 2011 Corporate Technology Group, KT Expires: July 18, 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
December 13, 2010 January 14, 2011
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-14 draft-ietf-roll-routing-metrics-15
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 to be used by node routing metrics and constraints suitable to LLNs to be used by
the Routing for Low Power and lossy networks (RPL) routing protocol. the Routing for Low Power and lossy networks (RPL) routing protocol.
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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 June 16, 2011. This Internet-Draft will expire on July 18, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2011 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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
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
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4.2. Latency . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.2. Latency . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.3. Link Reliability . . . . . . . . . . . . . . . . . . . . . 19 4.3. Link Reliability . . . . . . . . . . . . . . . . . . . . . 19
4.3.1. The Link Quality Level Reliability Metric . . . . . . 20 4.3.1. The Link Quality Level Reliability Metric . . . . . . 20
4.3.2. The Expected Transmission Count (ETX) reliability 4.3.2. The Expected Transmission Count (ETX) reliability
object . . . . . . . . . . . . . . . . . . . . . . . . 21 object . . . . . . . . . . . . . . . . . . . . . . . . 21
4.4. Link Color Object . . . . . . . . . . . . . . . . . . . . 23 4.4. Link Color Object . . . . . . . . . . . . . . . . . . . . 23
4.4.1. Link Color Object Description . . . . . . . . . . . . 23 4.4.1. Link Color Object Description . . . . . . . . . . . . 23
4.4.2. Mode of operation . . . . . . . . . . . . . . . . . . 24 4.4.2. Mode of operation . . . . . . . . . . . . . . . . . . 24
5. Computation of Dynamic Metrics and Attributes . . . . . . . . 25 5. Computation of Dynamic Metrics and Attributes . . . . . . . . 25
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
6.1. Routing Metric/Constraint Type . . . . . . . . . . . . . . 25 6.1. Routing Metric/Constraint Type . . . . . . . . . . . . . . 26
6.2. Routing Metric/Constraint TLV . . . . . . . . . . . . . . 26 6.2. Routing Metric/Constraint TLV . . . . . . . . . . . . . . 26
6.3. Routing Metric/Constraint Common Header . . . . . . . . . 26 6.3. Routing Metric/Constraint Common Header . . . . . . . . . 26
6.4. NSA Object . . . . . . . . . . . . . . . . . . . . . . . . 27 6.4. NSA Object . . . . . . . . . . . . . . . . . . . . . . . . 27
6.5. Hop-Count Object . . . . . . . . . . . . . . . . . . . . . 27 6.5. Hop-Count Object . . . . . . . . . . . . . . . . . . . . . 27
7. Security Considerations . . . . . . . . . . . . . . . . . . . 28 7. Security Considerations . . . . . . . . . . . . . . . . . . . 27
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
9.1. Normative references . . . . . . . . . . . . . . . . . . . 28 9.1. Normative references . . . . . . . . . . . . . . . . . . . 28
9.2. Informative references . . . . . . . . . . . . . . . . . . 29 9.2. Informative references . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
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
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document. Note that an object may carry TLV, which may itself 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 comprise other TLVs. A TLV carried within a TLV is called a TLV in
this specification. this specification.
Routing-MC-Type (Routing Metric/Constraint Type - 8 bits): the Routing-MC-Type (Routing Metric/Constraint Type - 8 bits): the
Routing Metric/Constraint Type field uniquely identifies each Routing Routing Metric/Constraint Type field uniquely identifies each Routing
Metric/Constraint object and is managed by IANA. Metric/Constraint object and is managed by IANA.
Length: this field defines the length of the object body, in bytes. Length: this field defines the length of the object body, in bytes.
Flag field of the Routing Metric/Constraint object: Flag field (16 bits). The Flag field of the Routing Metric/
Constraint object is managed by IANA. Unassigned bits are considered
as reserved. They MUST be set to zero on transmission and MUST be
ignored on receipt.
The following bits of the Routing Metric/Constraint Flag field object
are currently defined:
o P flag: the P field is only used for recorded metrics. When o P flag: the P field is only used for recorded metrics. When
cleared, all nodes along the path successfully recorded the cleared, all nodes along the path successfully recorded the
corresponding metric. When set, this indicates than one or corresponding metric. When set, this indicates than one or
several nodes along the path could not record the metric of several nodes along the path could not record the metric of
interest (either because of lack of knowledge or because this was interest (either because of lack of knowledge or because this was
prevented by policy). prevented by policy).
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,
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flag is set). When set, this indicates that the constraint flag is set). When set, this indicates that the constraint
specified in the body of the object is optional. When cleared, specified in the body of the object is optional. When cleared,
the constraint is mandatory. If the C flag is zero, the O flag the constraint is mandatory. If the C flag is zero, the O flag
MUST be set to zero on transmission and ignored on reception. 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 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 MUST be cleared for C=1. When set, this indicates that the
routing metric is recorded along the path. Conversely, when routing metric is recorded along the path. Conversely, when
cleared, the routing metric is aggregated. cleared, the routing metric is aggregated.
The Flag field of the Routing Metric/Constraint object is managed by A Field (3 bits): The A field is only relevant for metrics and is
IANA. Unassigned bits are considered as reserved. They MUST be set used to indicate whether the aggregated routing metric is additive,
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. multiplicative, reports a maximum or a minimum.
o A=0x00: The routing metric is additive o A=0x00: The routing metric is additive
o A=0x01: The routing metric reports a maximum o A=0x01: The routing metric reports a maximum
o A=0x02: The routing metric reports a minimum o A=0x02: The routing metric reports a minimum
o A=0x03: The routing metric is multiplicative o 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) and Routing Metric/Constraint object refers to a routing constraint) and
he only valid when the R bit is cleared. Otherwise, the A field MUST he only valid when the R bit is cleared. Otherwise, the A field MUST
be set to 0x00 and MUST be ignored on receipt. be set to 0x00 and MUST be ignored on receipt.
Prec field: The Prec field indicates the precedence of this Routing Prec field (4 bits): The Prec field indicates the precedence of this
Metric/Constraint object relative to other objects in the container. Routing Metric/Constraint object relative to other objects in the
This is useful when a DAG Metric Container contains several Routing container. This is useful when a DAG Metric Container contains
Metric objects. The value 0 means the highest precedence. 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 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 and the best path is the one with lower aggregated ETX. In this case
the DAG Metric container carries two Routing Metric/Constraint the DAG Metric container carries two Routing Metric/Constraint
objects: one is an ETX metric object with header (C=0, O=0, A=00, 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 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 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). 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 If, for example, the best path is characterized by the path avoiding
low quality links, then the path metric reports a maximum (A=0x01) 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 (the higher is the ETX the lower link quality is): when the DIO
message reporting link quality metric (ETX) is processed by a node, message reporting link quality metric (ETX) is processed by a node,
each node selecting the advertising node as a parent updates the each node selecting the advertising node as a parent updates the
value carried in the metric object by replacing it with its local 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 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 constraint is concerned, the object body will carry a node energy
message is not satisfied, the advertising node is just not selected constraint object defined in Section 3.1 indicating that nodes must
as a parent by the node that processes the DIO message. be mains-powered: if the constraint signalled in the DIO message is
not satisfied, the advertising node is just not selected as a parent
by the node that processes the DIO message.
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 (defined in Section 4) and link quality levels must be quality level (defined in Section 4) and link quality levels must be
recorded along the path. In this case, the DAG Metric Container recorded along the path. In this case, the DAG Metric Container
carries a Routing Metric/Constraint object: link quality level metric carries a Routing Metric/Constraint object: link quality level metric
(C=0, O=0, A=00, R=1) containing multiple sub-objects. (C=0, O=0, A=00, R=1) containing multiple sub-objects.
A Routing Metric/Constraint object may also include one or more A Routing Metric/Constraint object may also include one or more
additional type-length-value (TLV) encoded data sets. Each Routing additional type-length-value (TLV) encoded data sets. Each Routing
Metric/Constraint TLV has the same structure: Metric/Constraint TLV has the same structure:
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respectively. respectively.
If several aggregated metrics happen to bear the same Prec value, the If several aggregated metrics happen to bear the same Prec value, the
behavior is implementation-dependant. behavior is implementation-dependant.
3. Node Metric/Constraint Objects 3. Node Metric/Constraint Objects
The sections 3. and 4. specify several link and node metric/ The sections 3. and 4. specify several link and node metric/
constraint objects. In some cases it is stated that there must not 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 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 implementation receives more than one object of that type, the second
objet MUST silently be ignored. objet MUST silently be ignored.
In the presence of a constraint and a metric (which may or may not be In the presence of a constraint and a metric (which may or may not be
of the same type), a node MUST update the constraint before of the same type), a node MUST update the constraint before
advertising the updated metric and constraints. For example, if the advertising the updated metric and constraints. For example, if the
constraint is the number of hops (e.g. the maximum number of hops is constraint is the number of hops (e.g. the maximum number of hops is
n) and the path is optimized against the delay: if a node selects a n) and the path is optimized against the delay: if a node selects a
parent advertising a maximum number of hops of n (constraint), it parent advertising a maximum number of hops of n (constraint), it
must advertises DIO messages containing a hop count metrics must advertises DIO messages containing a hop count metrics
constraint with a field value equal of (n-1) and the newly computed constraint with a field value equal of (n-1) and the newly computed
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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 2: NSA object body format Figure 2: NSA object body format
Res flags (8 bits): Reserved field. This field MUST be set to zero Res flags (8 bits): Reserved field. This field MUST be set to zero
on transmission and MUST be ignored on receipt. on transmission and MUST be ignored on receipt.
The following two bits of the NSA object are currently defined: Flags field (8 bits). The following two bits of the NSA object are
currently defined:
o A Flag: data Aggregation Attribute. Data fusion involves more o A Flag: data Aggregation Attribute. Data fusion involves more
complicated processing to improve the accuracy of the output data, complicated processing to improve the accuracy of the output data,
while data aggregation mostly aims at reducing the amount of 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 This is listed as a requirement in Section 6.2 of [RFC5548]. Some
applications may make use of the aggregation node attribute in applications may make use of the aggregation node attribute in
their routing decision so as to minimize the amount of traffic on their routing decision so as to minimize the amount of traffic on
the network, thus potentially increasing its lifetime in battery the network, thus potentially increasing its lifetime in battery
operated environments. Applications where highly directional data operated environments. Applications where highly directional data
flow is expected on a regular basis may take advantage of data flow is expected on a regular basis may take advantage of data
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
| Flags |I| T |E| E-E | Optional TLVs | Flags |I| T |E| E-E | Optional TLVs
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 4: NE sub-object format Figure 4: NE sub-object format
The NE sub-object may also contain a set of TLVs used to convey The NE sub-object may also contain a set of TLVs used to convey
various nodes' characteristics. various nodes' characteristics.
The following flags are currently defined: Flags field (8 bits). The following flags are currently defined:
o I (Included): the I bit is only relevant when the node type is 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 used as a constraint. For example, the path must only traverse
mains-powered nodes. Conversely, battery operated nodes must be mains-powered nodes. Conversely, battery operated nodes must be
excluded. The I bit is used to stipulate inclusion versus excluded. The I bit is used to stipulate inclusion versus
exclusion. When set, this indicates that nodes of the type exclusion. When set, this indicates that nodes of the type
specified in the node type field MUST be included. Conversely, specified in the node type field MUST be included. Conversely,
when cleared, this indicates that nodes of type specified in the when cleared, this indicates that nodes of type specified in the
node type field MUST be excluded. node type field MUST be excluded.
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Val: LQL value from 0 to 7 where 0 means undetermined and 1 indicates Val: LQL value from 0 to 7 where 0 means undetermined and 1 indicates
the highest link quality. the highest link quality.
Counter: number of links with that value. Counter: number of links with that value.
4.3.2. The Expected Transmission Count (ETX) reliability object 4.3.2. The Expected Transmission Count (ETX) reliability object
The Expected Transmission Count (ETX) metric is the number of The Expected Transmission Count (ETX) metric is the number of
transmissions a node expects to make to a destination in order to transmissions a node expects to make to a destination in order to
successfully deliver a packet. In contrast with the LQL routing successfully deliver a packet. In contrast with the LQL routing
metric, the ETX provides a discrete value (wich may not be an metric, the ETX provides a discrete value (which may not be an
integer) computed according to a specific formula: for example, an integer) computed according to a specific formula: for example, an
implementation may use the following formula: ETX= 1 / (Df * Dr) implementation may use the following formula: ETX= 1 / (Df * Dr)
where Df is the measured probability that a packet is received by the where Df is the measured probability that a packet is received by the
neighbor and Dr is the measured probability that the acknowledgment neighbor and Dr is the measured probability that the acknowledgment
packet is successfully received. This document does not mandate the packet is successfully received. This document does not mandate the
use of a specific formula to compute the ETX value. use of a specific formula to compute the ETX value.
The ETX object MAY be present in the DAG Metric Container. There 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 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 Container, and there MUST NOT be more than one ETX object as a metric
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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, thus impact the traffic and power consumption in the network, thus
potentially impacting its scalability. potentially impacting its scalability.
6. IANA Considerations 6. 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 review: new
values are assigned through the IETF consensus process (see values are assigned through the IETF review process (see [RFC5226]).
[RFC5226]). Specifically, new assignments are made via RFCs approved Specifically, new assignments are made via RFCs approved by the IESG.
by the IESG. Typically, the IESG will seek input on prospective Typically, the IESG will seek input on prospective assignments from
assignments from appropriate persons (e.g., a relevant Working Group appropriate persons (e.g., a relevant Working Group if one exists).
if one exists).
New bit numbers may be allocated only by an IETF Review action. Each
bit should be tracked with the following qualities:
o Bit number
o Capability Description
o Defining RFC
6.1. Routing Metric/Constraint Type 6.1. Routing Metric/Constraint Type
IANA is requested to create a registry for Routing Metric/Constraint IANA is requested to create a registry for Routing Metric/Constraint
objects. Each Routing Metric/Constraint object has a type value. objects. Each Routing Metric/Constraint object has a type value
(from 1 to 255).
Value Meaning Reference Value Meaning Reference
1 Node State and Attribute This document 1 Node State and Attribute This document
2 Node Energy This document 2 Node Energy This document
3 Hop Count This document 3 Hop Count This document
4 Link Throughput This document 4 Link Throughput This document
5 Link Latency This document 5 Link Latency This document
6 Link Quality Level This document 6 Link Quality Level This document
7 Link ETX This document 7 Link ETX This document
8 Link Color This document 8 Link Color This document
6.2. Routing Metric/Constraint TLV 6.2. Routing Metric/Constraint TLV
IANA is requested to create a registry used for all TLVs carried IANA is requested to create a registry used for all TLVs carried
within Routing Metric/Constraint objects. within Routing Metric/Constraint objects. The type field is an 8-bit
field whose value can be comprised between 1 and 255.
6.3. Routing Metric/Constraint Common Header 6.3. Routing Metric/Constraint Common Header
IANA is requested to create a registry to manage the Flag field of
the Routing Metric/Constraint common header.
Several bits are defined for the Routing Metric/Constraint common
header in this document. The following values have been assigned:
Codespace of the Flag field (Routing Metric/Constraint common header)
Bit Description Reference
12-15 Precedence This document
9-11 Additive/Max/Min/Multi This document
8 Recorded/Aggregated This document
7 Optional Constraint This document
6 Constraint/Metric This document
5 P (Partial) This document
IANA is requested to create a registry to manage the codespace of the IANA is requested to create a registry to manage the codespace of the
A field of the Routing Metric/Constraint common header. A field of the Routing Metric/Constraint common header.
Codespace of the A field (Routing Metric/Constraint common header) Codespace of the A field (Routing Metric/Constraint common header)
Value Meaning Reference Value Meaning Reference
0 Routing metric is additive This document 0 Routing metric is additive This document
1 Routing metric reports a maximum This document 1 Routing metric reports a maximum This document
2 Routing metric reports a minimum This document 2 Routing metric reports a minimum This document
3 Routing metric is multiplicative This document 3 Routing metric is multiplicative This document
IANA is requested to create a registry to manage the Flag field of 6.4. NSA Object
the Routing Metric/Constraint common header.
New bit numbers may be allocated only by an IETF Consensus action. IANA is requested to create a registry to manage the codespace of the
Each bit should be tracked with the following qualities: Flag field of the NSA object.
Several bits are defined for the NSA object flag field in this
document. The following values have been assigned:
Codespace of the Flag field (NSA object)
Bit Description Reference
14 Aggregator This document
15 Overloaded This document
6.5. Hop-Count Object
IANA is requested to create a registry to manage the codespace of the
Flag field of the Hop-count object.
No Flag is currently defined.
7. Security Considerations
Routing metrics should be handled in a secure and trustful manner.
For instance, RPL should not allow a malicious node to falsely
advertise that it has good metrics for routing, be added as a router
for other nodes' traffic and intercept packets. Another attack may
consist of making intermitment attacks on a link in an attempt to
constantly modify the link quality and consequently the associated
routing metric, thus leading to potential fluctuation in the DODAG.
It is thus RECOMMENDED for a RPL implementation to put in place
mechanism so as to stop advertising routing metrics for highly
unstable links that may be subject to attacks.
Some routing metrics may also be used to identify some areas of
weaknesses in the network (a highly unreliable link, a node running
low in terms of energy, etc.). Such information may be used by a
potential attacker. Thus, it is RECOMMENDED to carefully consider
which metrics should be used by RPL and the level of visibility that
they provide about the network state or to use appropriate the
security measures as specified in [I-D.ietf-roll-rpl] to protect that
information.
Since the routing metrics/constraints are carried within RPL message,
the security routing mechanisms defined in [I-D.ietf-roll-rpl]
applies here.
8. Acknowledgements
The authors would like to acknowledge the contributions of Young Jae
Kim, Hakjin Chong, David Meyer, Mischa Dohler, Anders Brandt, Philip
Levis, Pascal Thubert, Richard Kelsey, Jonathan Hui, Alexandru
Petrescu, Richard Kelsey, Mathilde Durvy, Phoebus Chen, Tim Winter,
Mukul Goyal, Yoav Ben-Yehezkel, Matteo Paris, Omprakash Gnawali, Mads
Westergreen, Mukul Goyal, Joseph Saloway and David Culler for their
review and valuable comments. Special thank to Adrian Farrel for his
thourough review.
9. References
9.1. Normative references
[I-D.ietf-roll-rpl]
Winter, T., Thubert, P., Brandt, A., Clausen, T., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., and J.
Vasseur, "RPL: IPv6 Routing Protocol for Low power and
Lossy Networks", draft-ietf-roll-rpl-17 (work in
progress), December 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
9.2. Informative references
[I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy
Networks", draft-ietf-roll-terminology-04 (work in
progress), September 2010.
[Khanna1989J A. Zinky, A. Khanna, and G. Vichniac. "Performance of
the Revised Routing Metric for ARPANET and MILNET.
Submitted to MILCOM 89, March 1989
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, September 1999.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC5548] Dohler, M., Watteyne, T., Winter, T., and D. Barthel,
"Routing Requirements for Urban Low-Power and Lossy
Networks", RFC 5548, May 2009.
[RFC5673] Pister, K., Thubert, P., Dwars, S., and T. Phinney,
"Industrial Routing Requirements in Low-Power and Lossy
Networks", RFC 5673, October 2009.
[RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation
Routing Requirements in Low-Power and Lossy Networks",
RFC 5826, April 2010.
[RFC5867] Martocci, J., De Mil, P., Riou, N., and W. Vermeylen,
"Building Automation Routing Requirements in Low-Power and
Lossy Networks", RFC 5867, June 2010.
Authors' Addresses
JP Vasseur (editor)
Cisco Systems, Inc
11, Rue Camille Desmoulins
Issy Les Moulineaux, 92782
France
Email: jpv@cisco.com
Mijeom Kim (editor)
Corporate Technology Group, KT
17 Woomyeon-dong, Seocho-gu
Seoul, 137-792
Korea
Email: mjkim@kt.com
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
Networking Working Group JP. Vasseur, Ed.
Internet-Draft Cisco Systems, Inc
Intended status: Standards Track M. Kim, Ed.
Expires: July 18, 2011 Corporate Technology Group, KT
K. Pister
Dust Networks
N. Dejean
Coronis SAS
D. Barthel
France Telecom Orange
January 14, 2011
Routing Metrics used for Path Calculation in Low Power and Lossy
Networks
draft-ietf-roll-routing-metrics-15
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."
This Internet-Draft will expire on July 18, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Object Formats . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. DAG Metric Container Format . . . . . . . . . . . . . . . 7
2.2. Use of Multiple DAG Metric Containers . . . . . . . . . . 10
2.3. Metric Usage . . . . . . . . . . . . . . . . . . . . . . . 10
3. Node Metric/Constraint Objects . . . . . . . . . . . . . . . . 11
3.1. Node State and Attributes Object . . . . . . . . . . . . . 11
3.2. Node Energy Object . . . . . . . . . . . . . . . . . . . . 13
3.3. Hop-Count Object . . . . . . . . . . . . . . . . . . . . . 16
4. Link Metric/Constraint Objects . . . . . . . . . . . . . . . . 17
4.1. Throughput . . . . . . . . . . . . . . . . . . . . . . . . 17
4.2. Latency . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.3. Link Reliability . . . . . . . . . . . . . . . . . . . . . 19
4.3.1. The Link Quality Level Reliability Metric . . . . . . 20
4.3.2. The Expected Transmission Count (ETX) reliability
object . . . . . . . . . . . . . . . . . . . . . . . . 21
4.4. Link Color Object . . . . . . . . . . . . . . . . . . . . 23
4.4.1. Link Color Object Description . . . . . . . . . . . . 23
4.4.2. Mode of operation . . . . . . . . . . . . . . . . . . 24
5. Computation of Dynamic Metrics and Attributes . . . . . . . . 25
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
6.1. Routing Metric/Constraint Type . . . . . . . . . . . . . . 26
6.2. Routing Metric/Constraint TLV . . . . . . . . . . . . . . 26
6.3. Routing Metric/Constraint Common Header . . . . . . . . . 26
6.4. NSA Object . . . . . . . . . . . . . . . . . . . . . . . . 27
6.5. Hop-Count Object . . . . . . . . . . . . . . . . . . . . . 27
7. Security Considerations . . . . . . . . . . . . . . . . . . . 27
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 28
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
9.1. Normative references . . . . . . . . . . . . . . . . . . . 28
9.2. Informative references . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
This document makes use of the terminology defined in
[I-D.ietf-roll-terminology].
Low power and Lossy Networks (LLNs) have specific routing
characteristics compared with traditional wired or ad-hoc networks
that have been spelled out in [RFC5548], [RFC5673], [RFC5826] and
[RFC5867].
Historically, IGP such as OSPF ([RFC2328]) and IS-IS ([RFC1195]) have
used quantitative static link metrics. Other mechanisms such as
Multiprotocol Label Switching (MPLS) Traffic Engineering (TE) (see
[RFC2702] and [RFC3209]) make use of other link attributes such as
the available reserved bandwidth (dynamic) or link affinities (most
of the time static) to compute constrained shortest paths for Traffic
Engineering Label Switched Paths (TE LSPs).
This document specifies routing metrics and constraints to be used in
path calculation by the Routing Protocol for Low Power and Lossy
Networks (RPL) specified in [I-D.ietf-roll-rpl].
One of the prime objectives of this document is to define a flexible
mechanism for the advertisement of routing metrics and constraints
used by RPL. Some RPL implementations may elect to adopt an
extremely simple approach based on the use of a single metric with no
constraint whereas other implementations may use a larger set of link
and node routing metrics and constraints. This specification
provides a high degree of flexibility and a set of routing metrics
and constraints. New routing metrics and constraints could be
defined in the future, as needed.
The metrics and constraints defined in this document are carried in
objects that are OPTIONAL within RPL. This means that
implementations are free to include different subsets of the
functions (metric, constraint) defined in this document. Specific
sets of metrics/constraints and other optional RPL parameters for use
in key environments will be specified as compliance profiles in
applicability profile documents produced by the ROLL working group.
RPL is a distance vector routing protocol variant that builds
Directed Acyclic Graphs (DAGs) based on routing metrics and
constraints. DAG formation rules are defined in [I-D.ietf-roll-rpl]:
o The Destination Oriented Directed Acyclic Graph (DODAG) root as
defined in [I-D.ietf-roll-rpl] may advertise a routing constraint
used as a "filter" to prune links and nodes that do not satisfy
specific properties. For example, it may be required for the path
to only traverse nodes that are mains powered or links that have
at least a minimum reliability or a specific "color" reflecting a
user defined link characteristic (e.g the link layer supports
encryption).
o A routing metric is a quantitative value that is used to evaluate
the path cost. Link and node metrics are usually (but not always)
additive.
The best path is the path that satisfies all supplied constraints (if
any) and that has the lowest cost with respect to some specified
metrics. It is also called the shortest constrained path (in the
presence of constraints).
Routing metrics may be categorized according to the following
characteristics:
o Link versus Node metrics
o Qualitative versus quantitative
o Dynamic versus static
Routing requirements documents (see [RFC5673], [RFC5826] [RFC5548]
and [RFC5867]) observe that it must be possible to take into account
a variety of node constraints/metrics during path computation.
Some link or node characteristics (e.g. link reliability, remaining
energy on the node) may be used by RPL either as routing constraints
or as metrics. For example, the path may be computed to avoid links
that do not provide a sufficient level of reliability (use as a
constraint) or as the path offering most links with a specified
reliability level (use as a metric). This document provides the
flexibility to use link and node characterisics either as constraints
and/or metrics.
The use of link and node routing metrics and constraints is not
exclusive (e.g. it is possible to advertise a "hop count" both as a
metric to optimize the computed path and as a constraint (e.g. "Path
should not exceed n hops")).
Links in LLN commonly have rapidly changing node and link
characteristics: thus routing metrics must be dynamic and techniques
must be used to smooth out the dynamicity of these metrics so as to
avoid routing oscillations. For instance, in addition to the dynamic
nature of some links (e.g. wireless but also Powerline Communication
(PLC) links), nodes' resources such as residual energy are changing
continuously and may have to be taken into account during the path
computation.
It must be noted that the use of dynamic metrics is not new and has
been experimented in ARPANET 2 (see [[Khanna1989J]). The use of
dynamic metrics is not trivial and great care must be given to the
use of dynamic metrics since it may lead to potential routing
instabilities. That being said, lots of experience has been gained
over the years on the use of dynamic routing metrics, which have been
deployed in a number of (non IP) networks.
Very careful attention must be given to the pace at which routing
metrics and attributes values change in order to preserve routing
stability. When using a dynamic routing metric, a RPL implementation
should make use of a multi-threshold scheme rather than fine granular
metric updates reflecting each individual change to avoid spurious
and unneccessary routing changes.
The requirements on reporting frequency may differ among metrics,
thus different reporting rates may be used for each metric.
The set of routing metrics and constraints used by an RPL deployment
is signaled along the DAG that is built according to the Objective
Function (rules governing how to build a DAG) and the routing metrics
and constraints are advertised in the DAG Information Option (DIO)
message specified in [I-D.ietf-roll-rpl]. RPL may be used to build
DAGs with different characteristics. For example, it may be
desirable to build a DAG with the goal to maximize reliability by
using the link reliability metric to compute the "best" path.
Another example might be to use the energy node characteristic (e.g.
mains powered versus battery operated) as a node constraint when
building the DAG so as to avoid battery powered nodes in the DAG
while optimizing the link throughput.
The specification of objective functions used to compute the DAG
built by RPL is out of the scope of this document. This document
defines routing metrics and constraints that are decoupled from the
objective function. So a generic objective function could for
example specify the rules to select the best parents in the DAG, the
number of backup parents, etc and could be used with any routing
metrics and/or constraints such as the ones specified in this
document.
Some metrics are either aggregated or recorded. An aggregated metric
is adjusted as the DIO message travels along the DAG. For example,
if the metric is the number of hops, each node updates the path cost
that reflects the number of traversed hops along the DAG. By
contrast, for a recorded metric, each node adds a sub-object
reflecting the local valuation of the metric. For example, it might
be desirable to record the link quality level along a path. In this
case, each visited node adds a sub-object recording the local link
quality level. In order to limit the number of sub-objects, the use
of a counter may be desirable (e.g. record the number of links with a
certain link quality level), thus compressing the information to
reduce the message length. Upon receiving the DIO message from a set
of parents, a node might decide according to the OF and local policy
which node to choose as a parent based on the maximum number of links
with a specific link reliability level, for example.
Note that the routing metrics and constraints specified in this
document are not specific to any particular link layer. An internal
API between the MAC layer and RPL may be used to accurately reflect
the metrics values of the link (wireless, wired, PLC).
Since a set of metrics and constraints will be used for links and
nodes in LLN, it is critical to ensure the use of consistent metric
calculation mechanisms for all links and nodes in the network,
similarly to the case of inter-domain IP routing.
2. Object Formats
2.1. DAG Metric Container Format
Routing metrics and constraints are carried within the DAG Metric
Container object defined in [I-D.ietf-roll-rpl]. Should multiple
metrics and/or constraints be present in the DAG Metric Container,
their use to determine the "best" path can be defined by an Objective
Function.
The Routing Metric/Constraint objects represent a metric or a
constraint of a particular type. They may appear in any order in the
DAG Metric Container (specified in [I-D.ietf-roll-rpl]). They have a
common format consisting of one or more bytes with a common header:
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 1: Routing Metric/Constraint object generic format
The object body carries one or more sub-objects defined later in this
document. Note that an object may carry TLV, which may itself
comprise other TLVs. A TLV carried within a TLV is called a TLV in
this specification.
Routing-MC-Type (Routing Metric/Constraint Type - 8 bits): the
Routing Metric/Constraint Type field uniquely identifies each Routing
Metric/Constraint object and is managed by IANA.
Length: this field defines the length of the object body, in bytes.
Flag field (16 bits). The Flag field of the Routing Metric/
Constraint object is managed by IANA. Unassigned bits are considered
as reserved. They MUST be set to zero on transmission and MUST be
ignored on receipt.
The following bits of the Routing Metric/Constraint Flag field object
are currently defined:
o P flag: the P field is only used for recorded metrics. When
cleared, all nodes along the path successfully recorded the
corresponding metric. When set, this indicates than one or
several nodes along the path could not record the metric of
interest (either because of lack of knowledge or because this was
prevented by policy).
o C Flag. When set, this indicates that the Routing Metric/
Constraint object refers to a routing constraint. When cleared,
the routing object refers to a routing metric.
o O Flag: The O flag is used exclusively for routing constraints (C
flag is set). When set, this indicates that the constraint
specified in the body of the object is optional. When cleared,
the constraint is mandatory. If the C flag is zero, the O flag
MUST be set to zero on transmission and ignored on reception.
o R Flag: The R Flag is only relevant for routing metric (C=0) and
MUST be cleared for C=1. When set, this indicates that the
routing metric is recorded along the path. Conversely, when
cleared, the routing metric is aggregated.
A Field (3 bits): The A field is only relevant for metrics and is
used to indicate whether the aggregated routing metric is additive,
multiplicative, reports a maximum or a minimum.
o A=0x00: The routing metric is additive
o A=0x01: The routing metric reports a maximum
o A=0x02: The routing metric reports a minimum
o A=0x03: The routing metric is multiplicative
The A field has no meaning when the C Flag is set (i.e. when the
Routing Metric/Constraint object refers to a routing constraint) and
he only valid when the R bit is cleared. Otherwise, the A field MUST
be set to 0x00 and MUST be ignored on receipt.
Prec field (4 bits): The Prec field indicates the precedence of this
Routing Metric/Constraint object relative to other objects in the
container. This is useful when a DAG Metric Container contains
several Routing Metric objects. The value 0 means the highest
precedence.
Example 1: A DAG formed by RPL where all nodes must be mains-powered
and the best path is the one with lower aggregated ETX. In this case
the DAG Metric container carries two Routing Metric/Constraint
objects: one is an ETX metric object with header (C=0, O=0, A=00,
R=0) and the second one is a Node Energy constraint object with
header (C=1, O=0, A=00, R=0). Note that a RPL instance may use the
metric object to report a maximum (A=0x01) or a minimum (A=0x02).
If, for example, the best path is characterized by the path avoiding
low quality links, then the path metric reports a maximum (A=0x01)
(the higher is the ETX the lower link quality is): when the DIO
message reporting link quality metric (ETX) is processed by a node,
each node selecting the advertising node as a parent updates the
value carried in the metric object by replacing it with its local
link ETX value if and only if the latter is higher. As far as the
constraint is concerned, the object body will carry a node energy
constraint object defined in Section 3.1 indicating that nodes must
be mains-powered: if the constraint signalled in the DIO message is
not satisfied, the advertising node is just not selected as a parent
by the node that processes the DIO message.
Example 2: A DAG formed by RPL where the link metric is the link
quality level (defined in Section 4) and link quality levels must be
recorded along the path. In this case, the DAG Metric Container
carries a Routing Metric/Constraint object: link quality level metric
(C=0, O=0, A=00, R=1) containing multiple sub-objects.
A Routing Metric/Constraint object may also include one or more
additional type-length-value (TLV) encoded data sets. Each Routing
Metric/Constraint TLV has the same structure:
Type: 1 byte
Length: 1 byte
Value: variable
A Routing Metric/Constraint TLV is comprised of 1 byte for the type,
1 byte specifying the TLV length, and a value field. The TLV length
field defines the length of the value field in bytes.
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
function (A field), and the best path is selected through an implied
Max function because the metric is Energy.
When the DAG Metric Container contains several aggregated metrics,
they are to be used as tie-breakers according to their precedence
defined by their Prec field values.
An example of such use of multiple aggregated metrics is the
following: Hop-Count as the primary criterion, LQL as the secondary
criterion and Node Energy as the ultimate tie-breaker. In such a
case, the Hop-Count, LQL and Node Energy metric objects' Prec fields
should bear strictly increasing values such as 0, 1 and 2,
respectively.
If several aggregated metrics happen to bear the same Prec value, the
behavior is implementation-dependant.
3. Node Metric/Constraint Objects
The sections 3. and 4. specify several link and node metric/
constraint objects. In some cases it is stated that there must not
be more than one object of a specific type. In that case, if an RPL
implementation receives more than one object of that type, the second
objet MUST silently be ignored.
In the presence of a constraint and a metric (which may or may not be
of the same type), a node MUST update the constraint before
advertising the updated metric and constraints. For example, if the
constraint is the number of hops (e.g. the maximum number of hops is
n) and the path is optimized against the delay: if a node selects a
parent advertising a maximum number of hops of n (constraint), it
must advertises DIO messages containing a hop count metrics
constraint with a field value equal of (n-1) and the newly computed
path metric. This applies to the following constraints defined
below: hop-count, latency and path ETX.
3.1. Node State and Attributes Object
The Node State and Attribute (NSA) object is used to provide
information on node characteristics.
The NSA object MAY be present in the DAG Metric Container. There
MUST NOT be more than one NSA object as a constraint per DAG Metric
Container, and there MUST NOT be more than one NSA object as a metric
per DAG Metric Container.
The NSA object may also contain a set of TLVs used to convey various
node characteristics. No TLV is currently defined.
The NSA Routing Metric/Constraint Type is to be assigned by IANA
(recommended value=1).
The format of the NSA object body is as follows:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
| Res | Flags |A|O| Optional TLVs
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 2: NSA object body format
Res flags (8 bits): Reserved field. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
Flags field (8 bits). The following two bits of the NSA object are
currently defined:
o A Flag: data Aggregation Attribute. Data 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.
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
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
per DAG Metric Container.
The NE object Type is to be assigned by IANA (recommended value=2).
The format of the NE object body is as follows:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
| NE Sub-objects
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 3: NE sub-object format
The format of the NE sub-object body is as follows:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
| Flags |I| T |E| E-E | Optional TLVs
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 4: NE sub-object format
The NE sub-object may also contain a set of TLVs used to convey
various nodes' characteristics.
Flags field (8 bits). The following flags are currently defined:
o I (Included): the I bit is only relevant when the node type is
used as a constraint. For example, the path must only traverse
mains-powered nodes. Conversely, battery operated nodes must be
excluded. The I bit is used to stipulate inclusion versus
exclusion. When set, this indicates that nodes of the type
specified in the node type field MUST be included. Conversely,
when cleared, this indicates that nodes of type specified in the
node type field MUST be excluded.
o T (node Type): 2-bit field indicating the node type. T=0x00
designates a mains-powered node, T=0x01 a battery-powered node and
T=0x02 a node powered by an energy scavenger.
o E (Estimation): when the E bit is set for a metric, the estimated
percentage of remaining energy on the node is indicated in the E-E
8-bit field. When cleared, the estimated percentage of remaining
energy is not provided. When the E bit is set for a constraint,
the E-E field defines a threshold for the inclusion/exclusion: if
an inclusion, nodes with values higher than the threshold are to
be included; if an exclusion, nodes with values lower than the
threshold are to be excluded.
E-E (Estimated-Energy): 8-bit unsigned integer field indicating an
estimated percentage of remaining energy. The E-E field is only
relevant when the E flag is set, and MUST be set to 0 when the E flag
is cleared.
If the NE object comprises several sub-objects when used as a
constraint, each sub-object adds or subtracts node subsets as the
sub-objects are parsed in order. The initial set (full or empty) is
defined by the I bit of the first sub-object: full if that I bit is
an exclusion, empty if that I bit is an inclusion.
No TLV is currently defined.
Future documents may define more complex solutions involving TLV
parameters representing energy storage, consumption, and generation
capabilities of the node, as well as desired lifetime.
3.3. Hop-Count Object
The HoP-Count (HP) object is used to report the number of traversed
nodes along the path.
The HP object MAY be present in the DAG Metric Container. There MUST
NOT be more than one HP object as a constraint per DAG Metric
Container, and there MUST NOT be more than one HP object as a metric
per DAG Metric Container.
The HP object may also contain a set of TLVs used to convey various
node characteristics. No TLV is currently defined.
The HP routing metric object Type is to be assigned by IANA
(recommended value=3)
The format of the Hop Count object body is as follows:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
| Res | Flags | Hop Count | Optional TLVs
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 5: Hop Count object body format
Res flags (4 bits): Reserved field. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
No Flag is currently defined. Unassigned bits are considered as
reserved. They MUST be set to zero on transmission and MUST be
ignored on receipt.
The HP object may be used as a constraint or a metric. When used as
a constraint, the DAG root indicates the maximum number of hops that
a path may traverse. When that number is reached, no other node can
join that path. When used as a metric, each visited node simply
increments the Hop Count field.
Note that the first node along a path inserting a Hop-count object
MUST set the Hop Count field value to 1.
4. Link Metric/Constraint Objects
4.1. Throughput
Many LLNs support a wide range of throughputs. For some links, this
may be due to variable coding. For the deeply duty-cycled links
found in many LLNs, the variability comes as a result of trading
power consumption for bit rate. There are several MAC layer
protocols which allow for the effective bit rate of a link to vary
over more than three orders of magnitude with a corresponding change
in power consumption. For efficient operation, it may be desirable
for nodes to report the range of throughput that their links can
handle in addition to the currently available throughput.
The Throughput object MAY be present in the DAG Metric Container.
There MUST NOT be more than one Throughput object as a constraint per
DAG Metric Container, and there MUST NOT be more than one Throughput
object as a metric per DAG Metric Container.
The Throughput object is made of throughput sub-objects and MUST at
least comprise one Throughput sub-object. The first Throughput sub-
object MUST be the most recently estimated actual throughput. The
actual estimation of the throughput is outside the scope of this
document.
Each Throughput sub-object has a fixed length of 4 bytes.
The Throughput object does not contain any additional TLV.
The Throughput object Type is to be assigned by IANA (recommended
value=4)
The format of the Throughput object body is as follows:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (sub-object) .....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Throughput object body format
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Throughput |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Throughput sub-object format
Throughput: 32 bits. The Throughput is encoded in 32 bits in
unsigned integer format, expressed in bytes per second.
4.2. Latency
Similarly to throughput, the latency of many LLN MAC sub-layers can
vary over many orders of magnitude, again with a corresponding change
in power consumption. Some LLN MAC link layers will allow the
latency to be adjusted globally on the subnet, on a link-by-link
basis, or not at all. Some will insist that it be fixed for a given
link, but allow it to be variable from link to link.
The Latency object MAY be present in the DAG Metric Container. There
MUST NOT be more than one Latency object as a constraint per DAG
Metric Container, and there MUST NOT be more than one Latency object
as a metric per DAG Metric Container.
The Latency object is made of Latency sub-objects and MUST at least
comprise one Latency sub-object. Each Latency sub-object has a fixed
length of 4 bytes.
The Latency object does not contain any additional TLV.
The Latency object Type is to be assigned by IANA (recommended
value=5)
The Latency object is a metric or constraint.
The format of the Latency object body is as follows:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (sub-object) .....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Latency object body format
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Latency |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Latency sub-object format
Latency: 32 bits. The Latency is encoded in 32 bits in unsigned
integer format, expressed in microseconds.
The Latency object may be used as a constraint or a path metric. For
example, one may want the latency not to exceed some value. In this
case, the Latency object common header indicates that the provided
value relates to a constraint. In another example, the Latency
object may be used as an aggregated additive metric where the value
is updated along the path to reflect the path latency.
4.3. Link Reliability
In LLNs, link reliability 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).
Note that an RPL deployment MAY either use the LQL, the ETX or both.
4.3.1. The Link Quality Level Reliability Metric
The Link Quality Level (LQL) object is used to quantify the link
reliability using a discrete value, from 0 to 7 where 0 indicates
that the link quality level is unknown and 1 reports the highest link
quality level. The mechanisms and algorithms used to compute the LQL
are implementation specific and outside of the scope of this
document.
The LQL can either be used as a metric or a constraint. When used as
a metric, the LQL metric can only be recorded. For example, the DAG
Metric object may request all traversed nodes to record the LQL of
their incoming link into the LQL object. Each node can then use the
LQL record to select its parent based on some user defined rules
(e.g. something like "select the path with most links reporting a LQL
value of 3 or less").
Counters are used to compress the information: for each encountered
LQL value, only the number of matching links is reported.
The LQL object MAY be present in the DAG Metric Container. There
MUST NOT be more than one LQL object as a constraint per DAG Metric
Container, and there MUST NOT be more than one LQL object as a metric
per DAG Metric Container.
The LQL object MUST contain one or more sub-object used to report the
number of links along with their LQL.
The LQL object Type is to be assigned by IANA (recommended value=6)
The format of the LQL object body is as follows:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
| Res | LQL sub-object
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 10: LQL object body format
Res flags (8 bits): Reserved field. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
When the LQL metric is recorded, the LQL object body comprises one or
more LQL Type 1 sub-object.
The format of the LQL Type 1 sub-object is as follows
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| Val | Counter |
+-+-+-+-+-+-+-+-+
Figure 11: LQL Type 1 sub-object format
Val: LQL value from 0 to 7 where 0 means undetermined and 1 indicates
the highest link quality.
Counter: number of links with that value.
4.3.2. The Expected Transmission Count (ETX) reliability object
The Expected Transmission Count (ETX) metric is the number of
transmissions a node expects to make to a destination in order to
successfully deliver a packet. In contrast with the LQL routing
metric, the ETX provides a discrete value (which may not be an
integer) computed according to a specific formula: for example, an
implementation may use the following formula: ETX= 1 / (Df * Dr)
where Df is the measured probability that a packet is received by the
neighbor and Dr is the measured probability that the acknowledgment
packet is successfully received. This document does not mandate the
use of a specific formula to compute the ETX value.
The ETX object MAY be present in the DAG Metric Container. There
MUST NOT be more than one ETX object as a constraint per DAG Metric
Container, and there MUST NOT be more than one ETX object as a metric
per DAG Metric Container.
The ETX object is made of ETX sub-objects and MUST at least comprise
one ETX sub-object. Each ETX sub-object has a fixed length of 8
bits.
The ETX object does not contain any additional TLV.
The ETX object Type is to be assigned by IANA (recommended value=7)
The format of the ETX object body is as follows:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (sub-object) .....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: ETX object body format
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ETX |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: ETX sub-object format
ETX: 16 bits. The ETX * 128 is encoded using 16 bits in unsigned
integer format, rounded off to the nearest whole number. For
example, if ETX = 3.569, the object value will be 457. If ETX >
511.9921875, the object value will be the maximum which is 65535.
The ETX object may be used as a constraint or a path metric. For
example, it may be required that the ETX must not exceed some
specified value. In this case, the ETX object common header
indicates that the value relates to a constraint. In another
example, the ETX object may be used as an aggregated additive metric
where the value is updated along the path to reflect the path
quality: when a node receives the aggregated additive ETX value of
the path (cummulative path ETX calculated as the sum of the link ETX
of all of the traversed links from the advertising node to the DAG
root), if it selects that node as its preferred parent, the node
updates the path ETX by adding the ETX of the local link between
itself and the preferred parent to the received path cost (path ETX)
before potentially advertising itself the new path ETX.
4.4. Link Color Object
4.4.1. Link Color Object Description
The Link Color (LC) object is an administrative 10-bit link
constraint (which may either be static or dynamically adjusted) used
to avoid or attract specific links for specific traffic types.
The LC object can either be used as a metric or as a constraint.
When used as a metric, the LC metric can only be recorded. For
example, the DAG may require recording the link colors for all
traversed links. A color is defined as a specific set of bit values:
in other words, that 10-bit field is a flag field, and not a scalar
value. Each node can then use the LC to select the parent based on
user defined rules (e.g. "select the path with the maximum number of
links having their first bit set 1 (e.g. encrypted links)"). The LC
object may also be used as a constraint.
When used as a recorded metric, a counter is used to compress the
information where the number of links for each Link Color is
reported.
The Link Color (LC) object MAY be present in the DAG Metric
Container. There MUST NOT be more than one LC object as a constraint
per DAG Metric Container, and there MUST NOT be more than one LC
object as a metric per DAG Metric Container.
There MUST be a at least one LC sub-object per LC object.
The LC object does not contain any additional TLV.
The LC object Type is to be assigned by IANA (recommended value=8)
The format of the LC object body is as follows:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
| Res | LC sub-objects
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 14: LC object format
Res flags (8 bits): Reserved field. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
When the LC object is used as a recorded metric, the LC object body
comprises one or more LC Type 1 sub-objects.
The format of the LC Type 1 sub-object body is as follows:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Color | Counter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: LC Type 1 sub-object format
When the LC object is used as a constraint, the LC object body
comprises one or more LC Type 2 sub-objects.
The format of the LC Type 2 sub-object body is as follows:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Color |Reserved |I|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: LC Type 2 sub-object format
Res flags (7 bits): Reserved field. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
I Bit: The I bit is only relevant when the Link Color is used as a
constraint. When cleared, this indicates that links with the
specified color must be included. When set, this indicates that
links with the specified color must be excluded.
It is left to the implementer to define the meaning of each bit of
the 10-bit Link Color Flag field.
4.4.2. Mode of operation
The link color may be used as a constraint or a metric.
o When used as constraint, the LC object may be inserted in the DAG
Metric Container to indicate that links with a specific color
should be included or excluded from the computed path.
o When used as recorded metric, each node along the path may insert
a LC object in the DAG Metric Container to report the color of the
local link. If there is already a LC object reporting a similar
color, the node MUST NOT add another identical LC sub-object and
MUST increment the counter field.
5. Computation of Dynamic Metrics and Attributes
As already pointed out, dynamically calculated metrics are of the
utmost importance in many circumstances in LLNs. This is mainly
because a variety of metrics change on a frequent basis, thus
implying the need to adapt the routing decisions. That being said,
care must be given to the pace at which changes are reported in the
network. The attributes will change according to their own time
scales. RPL controls the reporting rate.
To minimize metric updates, multi-threshold algorithms MAY be used to
determine when updates should be sent. When practical, low-pass
filtering and/or hysteresis should be used to avoid rapid
fluctuations of these values. Finally, although the specification of
path computation algorithms using dynamic metrics are out the scope
of this document, it is RECOMMENDED to carefully design the route
optimization algorithm to avoid too frequent computation of new
routes upon metric values changes.
Controlled adaptation of the routing metrics and rate at which paths
are computed are critical to avoid undesirable routing instabilities
resulting in increased latencies and packet loss because of temporary
micro-loops. Furthermore, excessive route changes will adversely
impact the traffic and power consumption in the network, thus
potentially impacting its scalability.
6. IANA Considerations
IANA is requested to establish a new top-level registry to contain
all Routing Metric/Constraint objects codepoints and sub-registries.
The allocation policy for each new registry is by IETF review: new
values are assigned through the IETF review process (see [RFC5226]).
Specifically, new assignments are made via RFCs approved by the IESG.
Typically, the IESG will seek input on prospective assignments from
appropriate persons (e.g., a relevant Working Group if one exists).
New bit numbers may be allocated only by an IETF Review action. Each
bit should be tracked with the following qualities:
o Bit number o Bit number
o Capability Description o Capability Description
o Defining RFC o Defining RFC
6.1. Routing Metric/Constraint Type
IANA is requested to create a registry for Routing Metric/Constraint
objects. Each Routing Metric/Constraint object has a type value
(from 1 to 255).
Value Meaning Reference
1 Node State and Attribute This document
2 Node Energy This document
3 Hop Count This document
4 Link Throughput This document
5 Link Latency This document
6 Link Quality Level This document
7 Link ETX This document
8 Link Color This document
6.2. Routing Metric/Constraint TLV
IANA is requested to create a registry used for all TLVs carried
within Routing Metric/Constraint objects. The type field is an 8-bit
field whose value can be comprised between 1 and 255.
6.3. Routing Metric/Constraint Common Header
IANA is requested to create a registry to manage the Flag field of
the Routing Metric/Constraint common header.
Several bits are defined for the Routing Metric/Constraint common 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
12-15 Precedence This document 12-15 Precedence This document
9-11 Additive/Max/Min/Multi This document 9-11 Additive/Max/Min/Multi This document
8 Recorded/Aggregated This document 8 Recorded/Aggregated This document
7 Optional Constraint This document 7 Optional Constraint This document
6 Constraint/Metric This document 6 Constraint/Metric This document
5 P (Partial) This document 5 P (Partial) This document
6.4. 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. A field of the Routing Metric/Constraint common header.
New bit numbers may be allocated only by an IETF Consensus action. Codespace of the A field (Routing Metric/Constraint common header)
Each bit should be tracked with the following qualities: Value Meaning Reference
o Bit number 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
o Capability Description 6.4. NSA Object
o Defining RFC IANA is requested to create a registry to manage the codespace of the
Flag field of the NSA object.
Several bits are defined for the NSA object flag field in this Several bits are defined for the NSA object flag field in this
document. The following values have been assigned: document. The following values have been assigned:
Codespace of the Flag field (NSA object) Codespace of the Flag field (NSA object)
Bit Description Reference Bit Description Reference
14 Aggregator This document 14 Aggregator This document
15 Overloaded This document 15 Overloaded This document
6.5. Hop-Count Object 6.5. Hop-Count 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 Hop-count object. 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:
o Bit number
o Capability Description
o Defining RFC
No Flag is currently defined. No Flag is currently defined.
7. Security Considerations 7. 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, RPL should not allow a malicious node to falsely For instance, RPL should not allow a malicious node to falsely
advertise that it has good metrics for routing, be added as a router advertise that it has good metrics for routing, be added as a router
for other nodes' traffic and intercept packets. Another attack may for other nodes' traffic and intercept packets. Another attack may
consist of making intermitment attacks on a link in an attempt to consist of making intermitment attacks on a link in an attempt to
constantly modify the link quality and consequently the associated constantly modify the link quality and consequently the associated
routing metric, thus leading to potential fluctuation in the DAG. It routing metric, thus leading to potential fluctuation in the DODAG.
is thus RECOMMENDED for a RPL implementation to put in place It is thus RECOMMENDED for a RPL implementation to put in place
mechanism so as to stop advertising routing metrics for highly mechanism so as to stop advertising routing metrics for highly
unstable links that may be subject to attacks. unstable links that may be subject to attacks.
Some routing metrics may also be used to identify some areas of
weaknesses in the network (a highly unreliable link, a node running
low in terms of energy, etc.). Such information may be used by a
potential attacker. Thus, it is RECOMMENDED to carefully consider
which metrics should be used by RPL and the level of visibility that
they provide about the network state or to use appropriate the
security measures as specified in [I-D.ietf-roll-rpl] to protect that
information.
Since the routing metrics/constraints are carried within RPL message, Since the routing metrics/constraints are carried within RPL message,
the security routing mechanisms defined in [I-D.ietf-roll-rpl] the security routing mechanisms defined in [I-D.ietf-roll-rpl]
applies here. applies here.
8. Acknowledgements 8. 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, Richard 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, Mukul Goyal and David Culler for their review and Westergreen, Mukul Goyal, Joseph Saloway and David Culler for their
valuable comments. Special thank to Adrian Farrel for his thourough review and valuable comments. Special thank to Adrian Farrel for his
review. thourough review.
9. References 9. References
9.1. Normative references 9.1. Normative references
[I-D.ietf-roll-rpl] [I-D.ietf-roll-rpl]
Winter, T., Thubert, P., Brandt, A., Clausen, T., Hui, J., Winter, T., Thubert, P., Brandt, A., Clausen, T., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., and J. Kelsey, R., Levis, P., Pister, K., Struik, R., and J.
Vasseur, "RPL: IPv6 Routing Protocol for Low power and Vasseur, "RPL: IPv6 Routing Protocol for Low power and
Lossy Networks", draft-ietf-roll-rpl-16 (work in Lossy Networks", draft-ietf-roll-rpl-17 (work in
progress), December 2010. progress), December 2010.
[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.
9.2. Informative references 9.2. Informative references
[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-04 (work in Networks", draft-ietf-roll-terminology-04 (work in
progress), September 2010. 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 [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.
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J. [RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS", McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, September 1999. RFC 2702, September 1999.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
 End of changes. 35 change blocks. 
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