draft-ietf-roll-routing-metrics-16.txt   draft-ietf-roll-routing-metrics-17.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: July 18, 2011 Corporate Technology Group, KT Expires: August 3, 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
January 14, 2011 January 30, 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-16 draft-ietf-roll-routing-metrics-17
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 July 18, 2011. This Internet-Draft will expire on August 3, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2011 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
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Function. Function.
The Routing Metric/Constraint objects represent a metric or a The Routing Metric/Constraint objects represent a metric or a
constraint of a particular type. They may appear in any order in the 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 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: common format consisting of one or more bytes 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| Flags |P|C|O|R| A | Prec | Length (bytes)| |Routing-MC-Type|Res Flags|P|C|O|R| A | Prec | Length (bytes)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
// (object body) // // (object body) //
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Routing Metric/Constraint object generic format Figure 1: Routing Metric/Constraint object generic format
The object body carries one or more sub-objects defined later in this The object body carries one or more sub-objects defined later in this
document. Note that an object may carry TLV, which may itself document. Note that an object may carry TLV, which may itself
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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:
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. The TLV length 1 byte specifying the TLV length, and a value field. The TLV length
field defines the length of the value field in bytes. field defines the length of the value field in bytes (from 0 to 255).
Unrecognized TLVs MUST be silently ignored while still being Unrecognized TLVs MUST be silently ignored while still being
propagated in DIO generated by receiving node. propagated in DIO generated by receiving node.
IANA manages the codepoints for all TLV carried in routing IANA manages the codepoints for all TLV carried in routing
constraint/metric objects. constraint/metric objects.
IANA management of the Routing Metric/Constraint objects identifier IANA management of the Routing Metric/Constraint objects identifier
codespace is described in Section 6. codespace is described in Section 6.
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
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.
Flags field (8 bits). The following two bits of the NSA object are Flags field (8 bits). The following two bits of the NSA object are
currently defined: currently defined:
o A Flag: data Aggregation Attribute. Data fusion involves more o A Flag: data Aggregation Attribute. Data aggregation is listed as
complicated processing to improve the accuracy of the output data, a requirement in Section 6.2 of [RFC5548]. Some applications may
while data aggregation mostly aims at reducing the amount of data. make use of the aggregation node attribute in their routing
This is listed as a requirement in Section 6.2 of [RFC5548]. Some decision so as to minimize the amount of traffic on the network,
applications may make use of the aggregation node attribute in thus potentially increasing its lifetime in battery operated
their routing decision so as to minimize the amount of traffic on environments. Applications where highly directional data flow is
the network, thus potentially increasing its lifetime in battery expected on a regular basis may take advantage of data aggregation
operated environments. Applications where highly directional data supported routing. When set, this indicates that the node can act
flow is expected on a regular basis may take advantage of data as a traffic aggregator. Further documents MAY define optional
aggregation supported routing. When set, this indicates that the TLVs to describe the node traffic aggregator functionality.
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 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 scalar form. However, node workload could be a useful metric to
consider during path calculation, in particular when queuing consider during path calculation, in particular when queuing
delays must be minimized for highly sensitive traffic considering delays must be minimized for highly sensitive traffic considering
Medium Access Control (MAC) layer delay. Node workload MAY be set Medium Access Control (MAC) layer delay. Node workload MAY be set
upon CPU overload, lack of memory or any other node related upon CPU overload, lack of memory or any other node related
conditions. Using a simple 1-bit flag to characterize the node conditions. Using a simple 1-bit flag to characterize the node
workload provides a sufficient level of granularity, similarly to workload provides a sufficient level of granularity, similarly to
the "overload" bit used in routing protocols such as IS-IS. the "overload" bit used in routing protocols such as IS-IS.
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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 could be degraded for a number of reasons:
multi-path interference (wireless links). Multipath typically signal attenuation, interferences of various forms, etc ... Time
affects both directions on the link equally, whereas external scales vary from milliseconds to days, and are often periodic and
interference is sometimes unidirectional. Time scales vary from linked to human activity. Packet error rates can generally be
milliseconds to days, and are often periodic and linked to human measured directly, and other metrics (e.g. bit error rate, mean time
activity. Packet error rates can generally be measured directly, and between failures) are typically derived from that. Note that such
other metrics (e.g. bit error rate, mean time between failures) are variability is not specific to wireless link but also applies to PLC
typically derived from that. Note that such variability is not links.
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. quality may be taken into account as a critical routing metric.
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 deployment MAY either use the LQL, the ETX or both. Note that an RPL deployment MAY either use the LQL, the ETX or both.
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