draft-ietf-manet-olsrv2-dat-metric-01.txt   draft-ietf-manet-olsrv2-dat-metric-02.txt 
MANET H. Rogge MANET H. Rogge
Internet-Draft Fraunhofer FKIE Internet-Draft Fraunhofer FKIE
Intended status: Experimental E. Baccelli Intended status: Experimental E. Baccelli
Expires: January 23, 2015 INRIA Expires: February 9, 2015 INRIA
July 22, 2014 August 8, 2014
Packet Sequence Number based directional airtime metric for OLSRv2 Packet Sequence Number based directional airtime metric for OLSRv2
draft-ietf-manet-olsrv2-dat-metric-01 draft-ietf-manet-olsrv2-dat-metric-02
Abstract Abstract
This document specifies an directional airtime link metric for usage This document specifies an directional airtime link metric for usage
in OLSRv2. in OLSRv2.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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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 January 23, 2015. This Internet-Draft will expire on February 9, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability Statement . . . . . . . . . . . . . . . . . . . 4 3. Applicability Statement . . . . . . . . . . . . . . . . . . . 4
4. Directional Airtime Metric Rational . . . . . . . . . . . . . 4 4. Directional Airtime Metric Rationale . . . . . . . . . . . . 5
5. Metric Functioning & Overview . . . . . . . . . . . . . . . . 5 5. Metric Functioning & Overview . . . . . . . . . . . . . . . . 5
6. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 6 6. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 6
6.1. Recommended Values . . . . . . . . . . . . . . . . . . . 7 6.1. Recommended Values . . . . . . . . . . . . . . . . . . . 7
7. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 7 7. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 7
8. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 7 8. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Initial Values . . . . . . . . . . . . . . . . . . . . . 8 8.1. Initial Values . . . . . . . . . . . . . . . . . . . . . 8
9. Packets and Messages . . . . . . . . . . . . . . . . . . . . 8 9. Packets and Messages . . . . . . . . . . . . . . . . . . . . 9
9.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 9 9.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 9
9.2. Requirements . . . . . . . . . . . . . . . . . . . . . . 9 9.2. Requirements for using DAT metric in OLSRv2
implementations . . . . . . . . . . . . . . . . . . . . . 9
9.3. Link Loss Data Gathering . . . . . . . . . . . . . . . . 9 9.3. Link Loss Data Gathering . . . . . . . . . . . . . . . . 9
9.3.1. Packet Sequence based link loss . . . . . . . . . . . 9 9.3.1. Packet Sequence based link loss . . . . . . . . . . . 10
9.3.2. HELLO based Link Loss . . . . . . . . . . . . . . . . 10 9.3.2. HELLO based Link Loss . . . . . . . . . . . . . . . . 11
9.3.3. Other Measurement of Link Loss . . . . . . . . . . . 10 9.3.3. Other Measurement of Link Loss . . . . . . . . . . . 11
9.4. HELLO Message Processing . . . . . . . . . . . . . . . . 11 9.4. HELLO Message Processing . . . . . . . . . . . . . . . . 11
10. HELLO Timeout Processing . . . . . . . . . . . . . . . . . . 11 10. Timer Event Handling . . . . . . . . . . . . . . . . . . . . 12
11. Metric Update . . . . . . . . . . . . . . . . . . . . . . . . 11 10.1. HELLO Timeout Processing . . . . . . . . . . . . . . . . 12
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 10.2. Metric Update . . . . . . . . . . . . . . . . . . . . . 12
13. Security Considerations . . . . . . . . . . . . . . . . . . . 12 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 12. Security Considerations . . . . . . . . . . . . . . . . . . . 13
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
15.1. Normative References . . . . . . . . . . . . . . . . . . 13 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
15.2. Informative References . . . . . . . . . . . . . . . . . 14 14.1. Normative References . . . . . . . . . . . . . . . . . . 14
Appendix A. OLSR.org metric history . . . . . . . . . . . . . . 14 14.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix B. Linkspeed stabilization . . . . . . . . . . . . . . 15 Appendix A. OLSR.org metric history . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 Appendix B. Linkspeed stabilization . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
One of the major shortcomings of OLSR [RFC3626] is the missing of a One of the major shortcomings of OLSR [RFC3626] is the lack of a
link cost metric between mesh nodes. Operational experience with granular link cost metric between OLSR routers. Operational
mesh networks gathered since the standardization of OLSR has revealed experience with OLSR networks gathered since the publication of OLSR
that wireless networks links can have highly variable and has revealed that wireless networks links can have highly variable
heterogeneous properties. This makes a hopcount metric insufficient and heterogeneous properties. This makes a hopcount metric
for effective mesh routing. insufficient for effective OLSR routing.
Based on this experience, OLSRv2 [OLSRV2] integrates the concept of Based on this experience, OLSRv2 [RFC7181] integrates the concept of
link metrics directly into the core specification of the routing link metrics directly into the core specification of the routing
protocol. The OLSRv2 routing metric is an external process, it can protocol. The OLSRv2 routing metric is an external process, it can
be any kind of dimensionless additive cost function which reports to be any kind of dimensionless additive cost function which reports to
the OLSRv2 protocol. the OLSRv2 protocol.
Since 2004 the OLSR.org [OLSR.org] implementation of OLSR included an Since 2004 the OLSR.org [OLSR.org] implementation of OLSR included an
Estimated Transmission Count (ETX) metric [MOBICOM04] as a Estimated Transmission Count (ETX) metric [MOBICOM04] as a
proprietary extension. While this metric is not perfect, it proved proprietary extension. While this metric is not perfect, it proved
to be sufficient for a long time for Community Mesh Networks to be sufficient for a long time for Community Mesh Networks
(Appendix A). But the increasing maximum data rate of IEEE 802.11 (Appendix A). But the increasing maximum data rate of IEEE 802.11
made the ETX metric less efficient than in the past, which is one made the ETX metric less efficient than in the past, which is one
reason to move to a different metric. reason to move to a different metric.
This document describes a Directional Airtime routing metric for This document describes a Directional Airtime routing metric for
OLSRv2, a successor of the OLSR.org routing metric for [RFC3626]. It OLSRv2, a successor of the ETX-derived OLSR.org routing metric for
takes both the loss rate and the link speed into account to provide a OLSR. It takes both the loss rate and the link speed into account to
more accurate picture of the mesh network links. provide a more accurate picture of the links within the network.
This experimental draft will allow OLSRv2 deployments with a metric
defined by the IETF Manet group. It enables easier interoperability
tests between implementations and will also deliver an useful
baseline to compare other metrics to.
2. Terminology 2. Terminology
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
NOT','SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED', 'MAY', NOT','SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED', 'MAY',
and 'OPTIONAL' in this document are to be interpreted as described in and 'OPTIONAL' in this document are to be interpreted as described in
[RFC2119]. [RFC2119].
The terminology introduced in [RFC5444], [OLSRV2] and [RFC6130], The terminology introduced in [RFC5444], [RFC7181] and [RFC6130],
including the terms "packet", "message" and "TLV" are to be including the terms "packet", "message" and "TLV" are to be
interpreted as described therein. interpreted as described therein.
Additionally, this document uses the following terminology and Additionally, this document uses the following terminology and
notational conventions: notational conventions:
QUEUE - a first in, first out queue of integers. QUEUE - a first in, first out queue of integers.
QUEUE[TAIL] - the most recent element in the queue. QUEUE[TAIL] - the most recent element in the queue.
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diff_seqno(new, old) - an operation which returns the positive diff_seqno(new, old) - an operation which returns the positive
distance between two elements of the circular sequence number distance between two elements of the circular sequence number
space defined in section 5.1 of [RFC5444]. Its value is either space defined in section 5.1 of [RFC5444]. Its value is either
(new - old) if this result is positive, or else its value is (new (new - old) if this result is positive, or else its value is (new
- old + 65536). - old + 65536).
MAX(a,b) - the maximum of a and b. MAX(a,b) - the maximum of a and b.
UNDEFINED - a value not in the normal value range of a variable. UNDEFINED - a value not in the normal value range of a variable.
Might be -1 for this protocol.
airtime - the time a transmitted packet blocks the link layer, e.g., airtime - the time a transmitted packet blocks the link layer, e.g.,
a wireless link. a wireless link.
ETX - Expected Transmission Count, a link metric proportional to the ETX - Expected Transmission Count, a link metric proportional to the
number of transmissions to successfully send an IP packet over a number of transmissions to successfully send an IP packet over a
link. link.
ETT - Estimated Travel Time, a link metric proportional to the ETT - Estimated Travel Time, a link metric proportional to the
amount of airtime needed to transmit an IP packet over a link, not amount of airtime needed to transmit an IP packet over a link, not
considering layer-2 overhead created by preamble, backoff time and considering layer-2 overhead created by preamble, backoff time and
queuing. queuing.
DAT - Directional Airtime Metric, the link metric described in this DAT - Directional Airtime Metric, the link metric described in this
document, which is a directional variant of ETT. It does not take document, which is a directional variant of ETT. It does not take
reverse path loss into account. reverse path loss into account.
3. Applicability Statement 3. Applicability Statement
The Directional Airtime Metric was designed and tested in wireless The Directional Airtime Metric was designed and tested in wireless
IEEE 802.11 mesh networks. These networks employ link layer IEEE 802.11 [RFC7181] networks. These networks employ link layer
retransmission to increase the delivery probability and multiple retransmission to increase the delivery probability and multiple
unicast data rates. unicast data rates.
The metric must learn about the unicast data rate towards each one- The metric must learn about the unicast data rate towards each one-
hop neighbor from an external process, either by configuration or by hop neighbor from an external process, either by configuration or by
an external measurement process. This measurement could be done by an external measurement process. This measurement could be done by
gathering cross-layer data from the operating system or an external gathering cross-layer data from the operating system or an external
daemon like DLEP [DLEP], but also by indirect layer-3 measurements daemon like DLEP [DLEP], but also by indirect layer-3 measurements
like packet-pair. like packet-pair.
If [RFC5444] control traffic is used to determine the link packet If [RFC5444] control traffic is used to determine the link packet
loss, the administrator should take care that link layer multicast loss, the administrator should take care that link layer multicast
transmission do not not have a higher reception probability than the transmission do not not have a higher reception probability than the
slowest unicast transmission. It might be necessary to increase the slowest unicast transmission. It might, for example in 802.11g, be
data-rate of the multicast transmissions, e.g. set the multicast necessary to increase the data-rate of the multicast transmissions,
data-rate to 6 MBit/s if you use IEEE 802.11g only. e.g. set the multicast data-rate to 6 MBit/s.
The metric can only handle a certain range of packet loss and unicast The Directional Airtime metric can only handle a certain range of
data-rate. Maximum packet loss is "ETX 8" (1 of 8 packets is packet loss and unicast data-rate. The maximum packet loss that can
successfully sent to the receiver, without link layer be encoded into the metric a loss of 7 of 8 packets, without link
retransmissions), the unicast data-rate can be between 1 kBit/s and 2 layer retransmissions. The unicast data-rate that can be encoded by
GBit/s. The metric has been designed for data-rates of 1 MBit/s and this metric can be between 1 kBit/s and 2 GBit/s. This metric has
hundreds of MBit/s. been designed for data-rates of 1 MBit/s and hundreds of MBit/s.
4. Directional Airtime Metric Rationale
4. Directional Airtime Metric Rational
The Directional Airtime Metric has been inspired by the publications The Directional Airtime Metric has been inspired by the publications
on the ETX [MOBICOM03] and ETT [MOBICOM04] metric, but has several on the ETX [MOBICOM03] and ETT [MOBICOM04] metric, but differs from
key differences. both of these in several ways.
Instead of measuring the combined loss probability of a bidirectional Instead of measuring the combined loss probability of a bidirectional
transmission of a packet over a link in both directions, the transmission of a packet over a link in both directions, the
Directional Airtime Metric measures the incoming loss rate and Directional Airtime Metric measures the incoming loss rate and
integrates the incoming linkspeed into the metric cost. There are integrates the incoming linkspeed into the metric cost. There are
multiple reasons for this decision: multiple reasons for this decision:
o OLSRv2 [OLSRV2] defines the link metric as directional costs o OLSRv2 [RFC7181] defines the link metric as directional costs
between nodes. between routers.
o Not all link layer implementations use acknowledgement mechanisms. o Not all link layer implementations use acknowledgement mechanisms.
Most link layer implementations who do use them use less airtime Most link layer implementations who do use them use less airtime
and a more robust modulation for the acknowledgement than the data and a more robust modulation for the acknowledgement than the data
transmission, which makes it more likely for the data transmission transmission, which makes it more likely for the data transmission
to be disrupted compared to the acknowledgement. to be disrupted compared to the acknowledgement.
o Incoming packet loss and linkspeed can be measured locally, o Incoming packet loss and linkspeed can be measured locally,
symmetric link loss would need an additional signaling TLV in the symmetric link loss would need an additional signaling TLV in the
[RFC6130] HELLO and would delay metric calculation by up to one [RFC6130] HELLO and would delay metric calculation by up to one
HELLO interval. HELLO interval.
The Directional Airtime Metric does not integrate the packet size The Directional Airtime Metric does not integrate the packet size
into the link cost. Doing so is not feasible in most link-state into the link cost. Doing so is not feasible in most link-state
routing protocol implementations. The routing decision of most routing protocol implementations. The routing decision of most
operation systems don't take packet size into account. Multiplying operation systems don't take packet size into account. Multiplying
all link costs of a topology with the size of a data-plane packet all link costs of a topology with the size of a data-plane packet
would never change the dijkstra result anyways. would never change the dijkstra result anyways.
The queue based packet loss estimator has been tested extensively in The queue based packet loss estimator has been tested extensively in
the OLSR.org ETX implementation, see Appendix A. The output is the the OLSR.org ETX implementation, see Appendix A. The output is the
average of the packet loss over a configured time period. average of the packet loss over a configured time period.
5. Metric Functioning & Overview 5. Metric Functioning & Overview
The Directional Airtime Metric is calculated for each link set entry, The Directional Airtime Metric is calculated for each link set entry,
as defined in [RFC6130] section 7.1. as defined in [RFC6130] section 7.1.
The metric processes two kinds of data into the metric value, namely The metric processes two kinds of data into the metric value, namely
packet loss rate and link-speed. While the link-speed is taken from packet loss rate and link-speed. While the link-speed is taken from
an external process, the current packet loss rate is calculated by an external process, the current packet loss rate is calculated by
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number of received packets in the queue based on the total time number of received packets in the queue based on the total time
interval the queue represents compared to the total time of the lost interval the queue represents compared to the total time of the lost
HELLO intervals. HELLO intervals.
The average packet loss ratio is calculated as the sum of the 'total The average packet loss ratio is calculated as the sum of the 'total
packets' counters divided by the sum of the 'packets received' packets' counters divided by the sum of the 'packets received'
counters. This value is then divided through the current link-speed counters. This value is then divided through the current link-speed
and then scaled into the range of metrics allowed for OLSRv2. and then scaled into the range of metrics allowed for OLSRv2.
The metric value is then used as L_in_metric of the Link Set (as The metric value is then used as L_in_metric of the Link Set (as
defined in section 8.1. of [OLSRV2]). defined in section 8.1. of [RFC7181]).
6. Protocol Parameters 6. Protocol Parameters
This specification defines the following parameters, which can be This specification defines two constants, agreement on which is
changed without making the metric outputs incomparable with each required, from all the OLSRv2 routers participating in the same
other: deployment. Two routers which use different values for these
constants will not be able to generate metric values which can be
correctly interpreted by both. These constants are:
DAT_MEMORY_LENGTH - Queue length for averaging packet loss. All DAT_MEMORY_LENGTH - Queue length for averaging packet loss. All
received and lost packets within the queue are used to calculate received and lost packets within the queue are used to calculate
the cost of the link. the cost of the link.
DAT_REFRESH_INTERVAL - interval in seconds between two metric DAT_REFRESH_INTERVAL - interval in seconds between two metric
recalculations as described in Section 11. This value SHOULD be recalculations as described in Section 10.2. This value SHOULD be
smaller than a typical HELLO interval. smaller than a typical HELLO interval.
DAT_HELLO_TIMEOUT_FACTOR - timeout factor for HELLO interval at DAT_HELLO_TIMEOUT_FACTOR - multiplier relative to the HELLO_INTERVAL
which point a HELLO is definitely considered lost. The value must (see [RFC6130] Section 5.3.1) after which the DAT metric considers
be a floating point number between 1.0 and 2.0, large enough to a HELLO as lost.
take the delay and jitter for message aggregation into account.
DAT_SEQNO_RESTART_DETECTION - threshold in number of missing packets DAT_SEQNO_RESTART_DETECTION - threshold in number of missing packets
(based on received packet sequence numbers) at which point the (based on received packet sequence numbers) at which point the
router considers the neighbor has restarted. This parameter is router considers the neighbor has restarted. This parameter is
only used for packet sequence number based loss estimation. This only used for packet sequence number based loss estimation. This
number MUST be larger than DAT_MAXIMUM_LOSS. number MUST be larger than DAT_MAXIMUM_LOSS.
6.1. Recommended Values 6.1. Recommended Values
The proposed values of the protocol parameters are for Community Mesh The proposed values of the protocol parameters are for Community Mesh
Networks, which mostly use immobile mesh nodes. Using this metric Networks, which mostly use immobile routers. Using this metric for
for mobile networks might require shorter DAT_REFRESH_INTERVAL and/or mobile networks might require shorter DAT_REFRESH_INTERVAL and/or
DAT_MEMORY_LENGTH. DAT_MEMORY_LENGTH.
DAT_MEMORY_LENGTH := 64 DAT_MEMORY_LENGTH := 64
DAT_REFRESH_INTERVAL := 1 DAT_REFRESH_INTERVAL := 1
DAT_HELLO_TIMEOUT_FACTOR := 1.2 DAT_HELLO_TIMEOUT_FACTOR := 1.2
DAT_SEQNO_RESTART_DETECTION := 256 DAT_SEQNO_RESTART_DETECTION := 256
7. Protocol Constants 7. Protocol Constants
This specification defines the following constants, which cannot be This specification defines the following constants, which define the
changed without making the metric outputs incomparable: range of metric values that can be encoded by the DAT metric. They
cannot be changed without making the metric outputs incomparable and
should only be changed for MANET's with a very slow or very fast
linklayer.
DAT_MAXIMUM_LOSS - Fraction of the loss rate used in this routing DAT_MAXIMUM_LOSS - Fraction of the loss rate used in this routing
metric. Loss rate will be between 0/DAT_MAXIMUM_LOSS and metric. Loss rate will be between 0/DAT_MAXIMUM_LOSS and
(DAT_MAXIMUM_LOSS-1)/DAT_MAXIMUM_LOSS: 8. (DAT_MAXIMUM_LOSS-1)/DAT_MAXIMUM_LOSS: 8.
DAT_MINIMUM_BITRATE - Minimal bit-rate in Bit/s used by this routing DAT_MINIMUM_BITRATE - Minimal bit-rate in Bit/s used by this routing
metric: 1000. metric: 1000.
8. Data Structures 8. Data Structures
This specification extends the Link Set Tuples of the Interface This specification extends the Link Set of the Interface Information
Information Base, as defined in [RFC6130] section 7.1, by the Base, as defined in [RFC6130] section 7.1, by the adding the
following additional elements for each link tuple when being used following elements to each link tuple:
with this metric:
L_DAT_received is a QUEUE with DAT_MEMORY_LENGTH integer elements. L_DAT_received is a QUEUE with DAT_MEMORY_LENGTH integer elements.
Each entry contains the number of successfully received packets Each entry contains the number of successfully received packets
within an interval of DAT_REFRESH_INTERVAL. within an interval of DAT_REFRESH_INTERVAL.
L_DAT_total is a QUEUE with DAT_MEMORY_LENGTH integer elements. L_DAT_total is a QUEUE with DAT_MEMORY_LENGTH integer elements.
Each entry contains the estimated number of packets transmitted by Each entry contains the estimated number of packets transmitted by
the neighbor, based on the received packet sequence numbers within the neighbor, based on the received packet sequence numbers within
an interval of DAT_REFRESH_INTERVAL. an interval of DAT_REFRESH_INTERVAL.
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the links neighbor as signaled by the INTERVAL_TIME TLV [RFC5497] the links neighbor as signaled by the INTERVAL_TIME TLV [RFC5497]
of NHDP messages [RFC6130]. of NHDP messages [RFC6130].
L_DAT_lost_hello_messages is the estimated number of lost hello L_DAT_lost_hello_messages is the estimated number of lost hello
messages from this neighbor, based on the value of the hello messages from this neighbor, based on the value of the hello
interval. interval.
L_DAT_rx_bitrate is the current bitrate of incoming unicast traffic L_DAT_rx_bitrate is the current bitrate of incoming unicast traffic
for this neighbor. for this neighbor.
L_DAT_last_pkt_seqno is the last received packet sequence number
received from this link.
Methods to obtain the value of L_DAT_rx_bitrate are out of the scope Methods to obtain the value of L_DAT_rx_bitrate are out of the scope
of this specification. Such methods may include static configuration of this specification. Such methods may include static configuration
via a configuration file or dynamic measurement through mechanisms via a configuration file or dynamic measurement through mechanisms
described in a separate specification (e.g. [DLEP]). Any Link tuple described in a separate specification (e.g. [DLEP]). Any Link tuple
with L_status = HEARD or L_status = SYMMETRIC MUST have a specified with L_status = HEARD or L_status = SYMMETRIC MUST have a specified
value of L_DAT_rx_bitrate if it is to be used by this routing metric. value of L_DAT_rx_bitrate if it is to be used by this routing metric.
When using packet sequence numbers to estimate the loss rate, the This specification updates the L_in_metric field of the Link Set of
Link Set Tuples get another field: the Interface Information Base, as defined in section 8.1. of
[RFC7181])
L_DAT_last_pkt_seqno is the last received packet sequence number
received from this link.
8.1. Initial Values 8.1. Initial Values
When generating a new tuple in the Link Set, as defined in [RFC6130] When generating a new tuple in the Link Set, as defined in [RFC6130]
section 12.5 bullet 3, the values of the elements specified in section 12.5 bullet 3, the values of the elements specified in
Section 8 are set as follows: Section 8 are set as follows:
o L_DAT_received := 0, ..., 0. The queue always has o L_DAT_received := 0, ..., 0. The queue always has
DAT_MEMORY_LENGTH elements. DAT_MEMORY_LENGTH elements.
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o L_DAT_last_pkt_seqno := UNDEFINED (no earlier packet received). o L_DAT_last_pkt_seqno := UNDEFINED (no earlier packet received).
o L_DAT_hello_time := EXPIRED (no earlier NHDP HELLO received). o L_DAT_hello_time := EXPIRED (no earlier NHDP HELLO received).
o L_DAT_hello_interval := UNDEFINED (no earlier NHDP HELLO o L_DAT_hello_interval := UNDEFINED (no earlier NHDP HELLO
received). received).
o L_DAT_lost_hello_messages := 0 (no HELLO interval without o L_DAT_lost_hello_messages := 0 (no HELLO interval without
packets). packets).
o L_DAT_last_pkt_seqno := UNDEFINED (no earlier RFC5444 packet
received).
9. Packets and Messages 9. Packets and Messages
This section describes the necessary changes of [RFC7181]
implementations with DAT metric for the processing and modification
of incoming and outgoing [RFC5444] data.
9.1. Definitions 9.1. Definitions
For the purpose of this section, note the following definitions: For the purpose of this section, note the following definitions:
o "pkt_seqno" is defined as the [RFC5444] packet sequence number of o "pkt_seqno" is defined as the [RFC5444] packet sequence number of
the received packet. the received packet.
o "interval_time" is the time encoded in the INTERVAL_TIME message o "interval_time" is the time encoded in the INTERVAL_TIME message
TLV of a received [RFC6130] HELLO message. TLV of a received [RFC6130] HELLO message.
9.2. Requirements o "validity_time" is the time encoded in the VALIDITY_TIME message
TLV of a received [RFC6130] HELLO message.
9.2. Requirements for using DAT metric in OLSRv2 implementations
An implementation of OLSRv2 using the metric specified by this An implementation of OLSRv2 using the metric specified by this
document MUST include the following parts into its [RFC5444] output: document SHOULD include the following parts into its [RFC5444]
output:
o an INTERVAL_TIME message TLV in each HELLO message, as defined in o an INTERVAL_TIME message TLV in each HELLO message, as defined in
[RFC6130] section 4.3.2. [RFC6130] section 4.3.2.
9.3. Link Loss Data Gathering 9.3. Link Loss Data Gathering
While this metric was designed for measuring the packet loss based on While this metric was designed for measuring the packet loss based on
the [RFC5444] packet sequence number, some implementations might not the [RFC5444] packet sequence number, some implementations might not
be able to add the packet sequence number to their output. be able to add the packet sequence number to their output. Because
of this the following section contains multiple alternatives to
calculate the packet loss.
9.3.1. Packet Sequence based link loss 9.3.1. Packet Sequence based link loss
An implementation of OLSRv2, using the metric specified by this An implementation of OLSRv2, using the metric specified by this
document with packet sequence based link loss, MUST include the document with packet sequence based link loss, MUST include the
following element into its [RFC5444] output: following element into its [RFC5444] output:
o an interface specific packet sequence number as defined in o an interface specific packet sequence number as defined in
[RFC5444] section 5.1 which is incremented by 1 for each outgoing [RFC5444] section 5.1 which is incremented by 1 for each outgoing
[RFC5444] packet on the interface. [RFC5444] packet on the interface.
For each incoming [RFC5444] packet, additional processing MUST be For each incoming [RFC5444] packet, additional processing MUST be
carried out after the packet messages have been processed as carried out after the packet messages have been processed as
specified in [RFC6130] and [OLSRV2]. specified in [RFC6130] and [RFC7181].
[RFC5444] packets without packet sequence number MUST NOT be [RFC5444] packets without packet sequence number MUST NOT be
processed in this way by this metric. processed in this way by this metric.
The router MUST update the Link Set Tuple corresponding to the The router MUST update the Link Set Tuple corresponding to the
originator of the packet: originator of the packet:
1. If L_DAT_last_pkt_seqno = UNDEFINED, then: 1. If L_DAT_last_pkt_seqno = UNDEFINED, then:
1. L_DAT_received[TAIL] := 1. 1. L_DAT_received[TAIL] := 1.
skipping to change at page 10, line 51 skipping to change at page 11, line 28
1. L_DAT_received[TAIL] := L_DAT_received[TAIL] + 1. 1. L_DAT_received[TAIL] := L_DAT_received[TAIL] + 1.
2. L_DAT_total[TAIL] := L_DAT_total[TAIL] + 1. 2. L_DAT_total[TAIL] := L_DAT_total[TAIL] + 1.
3. L_DAT_lost_hello_messages := 0. 3. L_DAT_lost_hello_messages := 0.
9.3.3. Other Measurement of Link Loss 9.3.3. Other Measurement of Link Loss
Instead of using incoming [RFC5444] packets or [RFC6130] messages, Instead of using incoming [RFC5444] packets or [RFC6130] messages,
the routing daemon can also use other sources to measure the link the routing daemon can also use other sources to measure the link
layer lossrate (e.g. [DLEP]). layer lossrate (e.g. [DLEP]).
To use a source like this with the DAT metric, the routing daemon has To use a source like this with the DAT metric, the routing daemon has
to add incoming total traffic (or the sum of received and lost to add incoming total traffic (or the sum of received and lost
traffic) and lost traffic to the queued elements in the extension of traffic) and lost traffic to the queued elements in the extension of
the Link Set Tuple defined in Section 8 corresponding to originator the Link Set Tuple defined in Section 8 corresponding to originator
of the traffic. of the traffic.
The routing daemon should also set L_DAT_lost_hello_messages to zero The routing daemon should also set L_DAT_lost_hello_messages to zero
every times new packages arrive. every times new packages arrive.
9.4. HELLO Message Processing 9.4. HELLO Message Processing
For each incoming HELLO Message, after it has been processed as For each incoming HELLO Message, after it has been processed as
defined in [RFC6130] section 12, the Link Set Tuple corresponding to defined in [RFC6130] section 12, the Link Set Tuple corresponding to
the incoming HELLO message must be updated. the incoming HELLO message must be updated.
Only HELLO messages with an INTERVAL_TIME message TLVs must be 1. If the HELLO message contains an INTERVAL_TIME message TLV, then:
processed.
1. L_DAT_hello_interval := interval_time. 1. L_DAT_hello_interval := interval_time.
10. HELLO Timeout Processing 2. Otherwise:
1. L_DAT_hello_interval := validity_time.
10. Timer Event Handling
In addition to changes in the [RFC5444] processing/generation code,
the DAT metric also uses two timer events.
10.1. HELLO Timeout Processing
When L_DAT_hello_time has timed out, the following step MUST be done: When L_DAT_hello_time has timed out, the following step MUST be done:
1. L_DAT_lost_hello_messages := L_DAT_lost_hello_messages + 1. 1. L_DAT_lost_hello_messages := L_DAT_lost_hello_messages + 1.
2. L_DAT_hello_time := L_DAT_hello_time + L_DAT_hello_interval. 2. L_DAT_hello_time := L_DAT_hello_time + L_DAT_hello_interval.
11. Metric Update 10.2. Metric Update
Once every DAT_REFRESH_INTERVAL, all L_in_metric values in all Link Once every DAT_REFRESH_INTERVAL, all L_in_metric values in all Link
Set entries MUST be recalculated: Set entries MUST be recalculated:
1. sum_received := sum(L_DAT_total). 1. sum_received := sum(L_DAT_total).
2. sum_total := sum(L_DAT_received). 2. sum_total := sum(L_DAT_received).
3. If L_DAT_hello_interval != UNDEFINED and 3. If L_DAT_hello_interval != UNDEFINED and
L_DAT_lost_hello_messages > 0, then: L_DAT_lost_hello_messages > 0, then:
1. lost_time_proportion := L_DAT_hello_interval * 1. lost_time_proportion := L_DAT_hello_interval *
L_DAT_lost_hello_messages / DAT_MEMORY_LENGTH. L_DAT_lost_hello_messages / DAT_MEMORY_LENGTH.
2. sum_received := sum_received * MAX ( 0, 1 - 2. sum_received := sum_received * MAX ( 0, 1 -
lost_time_proportion); lost_time_proportion);
4. If sum_received < 1, then: 4. If sum_received < 1, then:
1. L_in_metric := MAXIMUM_METRIC, as defined in [OLSRV2] section 1. L_in_metric := MAXIMUM_METRIC, as defined in [RFC7181]
5.6.1. section 5.6.1.
5. Otherwise: 5. Otherwise:
1. loss := sum_total / sum_received. 1. loss := sum_total / sum_received.
2. If loss > DAT_MAXIMUM_LOSS, then: 2. If loss > DAT_MAXIMUM_LOSS, then:
1. loss := DAT_MAXIMUM_LOSS. 1. loss := DAT_MAXIMUM_LOSS.
3. bitrate := L_DAT_rx_bitrate. 3. bitrate := L_DAT_rx_bitrate.
skipping to change at page 12, line 33 skipping to change at page 13, line 18
DAT_MINIMUM_BITRATE). DAT_MINIMUM_BITRATE).
6. remove(L_DAT_total) 6. remove(L_DAT_total)
7. add(L_DAT_total, 0) 7. add(L_DAT_total, 0)
8. remove(L_DAT_received) 8. remove(L_DAT_received)
9. add(L_DAT_received, 0) 9. add(L_DAT_received, 0)
12. IANA Considerations 11. IANA Considerations
This document contains no actions for IANA. This document contains no actions for IANA.
13. Security Considerations 12. Security Considerations
Artificial manipulation of metrics values can drastically alter Artificial manipulation of metrics values can drastically alter
network performance. In particular, advertising a higher L_in_metric network performance. In particular, advertising a higher L_in_metric
value may decrease the amount of incoming traffic, while advertising value may decrease the amount of incoming traffic, while advertising
lower L_in_metric may increase the amount of incoming traffic. By lower L_in_metric may increase the amount of incoming traffic. By
artificially increasing or decreasing the L_in_metric values it artificially increasing or decreasing the L_in_metric values it
advertises, a rogue router may thus attract or repulse data traffic. advertises, a rogue router may thus attract or repulse data traffic.
A rogue router may then potentially degrade data throughput by not A rogue router may then potentially degrade data throughput by not
forwarding data as it should or redirecting traffic into routing forwarding data as it should or redirecting traffic into routing
loops or bad links. loops or bad links.
An attacker might also inject packets with incorrect packet level An attacker might also inject packets with incorrect packet level
sequence numbers, pretending to be somebody else. This attack could sequence numbers, pretending to be somebody else. This attack can be
be prevented by the true originator of the RFC5444 packets by adding prevented by the true originator of the RFC5444 packets by adding a
a [RFC6622] ICV Packet TLV and TIMESTAMP Packet TLV to each packet. [RFC7182] ICV Packet TLV and TIMESTAMP Packet TLV to each packet.
This allows the receiver to drop all incoming packets which have a This allows the receiver to drop all incoming packets which have a
forged packet source, both packets generated by the attacker or forged packet source, both packets generated by the attacker or
replayed packets. replayed packets. The signature scheme described in [RFC7183] does
not protect the additional sequence number of the DAT metric because
it does only sign the RFC5444 messages, not the RFC5444 packet
header.
14. Acknowledgements 13. Acknowledgements
The authors would like to acknowledge the network administrators from The authors would like to acknowledge the network administrators from
Freifunk Berlin [FREIFUNK] and Funkfeuer Vienna [FUNKFEUER] for Freifunk Berlin [FREIFUNK] and Funkfeuer Vienna [FUNKFEUER] for
endless hours of testing and suggestions to improve the quality of endless hours of testing and suggestions to improve the quality of
the original ETX metric for the OLSR.org routing daemon. the original ETX metric for the OLSR.org routing daemon.
This effort/activity is supported by the European Community Framework This effort/activity is supported by the European Community Framework
Program 7 within the Future Internet Research and Experimentation Program 7 within the Future Internet Research and Experimentation
Initiative (FIRE), Community Networks Testbed for the Future Internet Initiative (FIRE), Community Networks Testbed for the Future Internet
([CONFINE]), contract FP7-288535. ([CONFINE]), contract FP7-288535.
The authors would like to gratefully acknowledge the following people The authors would like to gratefully acknowledge the following people
for intense technical discussions, early reviews and comments on the for intense technical discussions, early reviews and comments on the
specification and its components (listed alphabetically): Teco Boot specification and its components (listed alphabetically): Teco Boot
(Infinity Networks), Juliusz Chroboczek (PPS, University of Paris 7), (Infinity Networks), Juliusz Chroboczek (PPS, University of Paris 7),
Thomas Clausen, Christopher Dearlove (BAE Systems Advanced Technology Thomas Clausen, Christopher Dearlove (BAE Systems Advanced Technology
Centre), Ulrich Herberg (Fujitsu Laboratories of America), Markus Centre), Ulrich Herberg (Fujitsu Laboratories of America), Markus
Kittenberger (Funkfeuer Vienna), Joseph Macker (Naval Research Kittenberger (Funkfeuer Vienna), Joseph Macker (Naval Research
Laboratory) and Stan Ratliff (Cisco Systems). Laboratory) and Stan Ratliff (Cisco Systems).
15. References 14. References
15.1. Normative References 14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997. Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC3626] Clausen, T. and P. Jacquet, "Optimized Link State Routing [RFC3626] Clausen, T. and P. Jacquet, "Optimized Link State Routing
Protocol", RFC 3626, October 2003. Protocol", RFC 3626, October 2003.
[RFC5444] Clausen, T., Dearlove, C., Dean, J., and C. Adjih, [RFC5444] Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
"Generalized Mobile Ad Hoc Network (MANET) Packet/Message "Generalized Mobile Ad Hoc Network (MANET) Packet/Message
Format", RFC 5444, February 2009. Format", RFC 5444, February 2009.
[RFC5497] Clausen, T. and C. Dearlove, "Representing Multi-Value [RFC5497] Clausen, T. and C. Dearlove, "Representing Multi-Value
Time in Mobile Ad Hoc Networks (MANETs)", RFC 5497, March Time in Mobile Ad Hoc Networks (MANETs)", RFC 5497, March
2009. 2009.
[RFC6130] Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc [RFC6130] Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc
Network (MANET) Neighborhood Discovery Protocol (NHDP)", Network (MANET) Neighborhood Discovery Protocol (NHDP)",
RFC 6130, April 2011. RFC 6130, April 2011.
[RFC6622] Ulrich, U. and T. Clausen, "Integrity Check Value and [RFC7181] Clausen, T., Jacquet, P., and C. Dearlove, "The Optimized
Timestamp TLV Definitions for Mobile Ad Hoc Networks Link State Routing Protocol version 2", RFC 7181, April
(MANETs)", RFC 6622, May 2012. 2014.
[OLSRV2] Clausen, T., Jacquet, P., and C. Dearlove, "The Optimized [RFC7182] Ulrich, U., Clausen, T., and C. Dearlove, "Integrity Check
Link State Routing Protocol version 2", draft-ietf-manet- Value and Timestamp TLV Definitions for Mobile Ad Hoc
olsrv2-19 , March 2013. Networks (MANETs)", RFC 7182, April 2014.
15.2. Informative References [RFC7183] Ulrich, U., Dearlove, C., and T. Clausen, "Integrity
Protection for the Neighborhood Discovery Protocol (NHDP)
and Optimized Link State Routing Protocol Version 2
(OLSRv2)", RFC 7183, April 2014.
[CONFINE] , "Community Networks Testbed for the Future Internet 14.2. Informative References
[CONFINE] "Community Networks Testbed for the Future Internet
(CONFINE)", 2013, <http://www.confine-project.eu>. (CONFINE)", 2013, <http://www.confine-project.eu>.
[DLEP] Ratliff, S., Berry, B., Harrison, G., Jury, S., and D. [DLEP] Ratliff, S., Berry, B., Harrison, G., Jury, S., and D.
Satterwhite, "Dynamic Link Exchange Protocol (DLEP)", Satterwhite, "Dynamic Link Exchange Protocol (DLEP)",
draft-ietf-manet-dlep-04 , March 2013. draft-ietf-manet-dlep-04 , March 2013.
[MOBICOM03] [MOBICOM03]
De Couto, D., Aguayo, D., Bicket, J., and R. Morris, "A De Couto, D., Aguayo, D., Bicket, J., and R. Morris, "A
High-Throughput Path Metric for Multi-Hop Wireless High-Throughput Path Metric for Multi-Hop Wireless
Routing", Proceedings of the MOBICOM Conference , 2003. Routing", Proceedings of the MOBICOM Conference , 2003.
[MOBICOM04] [MOBICOM04]
Richard, D., Jitendra, P., and Z. Brian, "Routing in Richard, D., Jitendra, P., and Z. Brian, "Routing in
Multi-Radio, Multi-Hop Wireless Mesh Networks", Multi-Radio, Multi-Hop Wireless Mesh Networks",
Proceedings of the MOBICOM Conference , 2004. Proceedings of the MOBICOM Conference , 2004.
[OLSR.org] [OLSR.org]
, "The OLSR.org OLSR routing daemon", 2013, "The OLSR.org OLSR routing daemon", 2013,
<http://www.olsr.org/>. <http://www.olsr.org/>.
[FREIFUNK] [FREIFUNK]
, "Freifunk Wireless Community Networks", 2013, "Freifunk Wireless Community Networks", 2013,
<http://www.freifunk.net>. <http://www.freifunk.net>.
[FUNKFEUER] [FUNKFEUER]
, "Austria Wireless Community Network", 2013, "Austria Wireless Community Network", 2013,
<http://www.funkfeuer.at>. <http://www.funkfeuer.at>.
Appendix A. OLSR.org metric history Appendix A. OLSR.org metric history
The Funkfeuer [FUNKFEUER] and Freifunk networks [FREIFUNK] are OLSR- The Funkfeuer [FUNKFEUER] and Freifunk networks [FREIFUNK] are OLSR-
based [RFC3626] or B.A.T.M.A.N. based wireless community networks based [RFC3626] or B.A.T.M.A.N. based wireless community networks
with hundreds of routers in permanent operation. The Vienna with hundreds of routers in permanent operation. The Vienna
Funkfeuer network in Austria, for instance, consists of 400 routers Funkfeuer network in Austria, for instance, consists of 400 routers
(around 600 routes) covering the whole city of Vienna and beyond, (around 600 routes) covering the whole city of Vienna and beyond,
spanning roughly 40km in diameter. It has been in operation since spanning roughly 40km in diameter. It has been in operation since
2003 and supplies its users with Internet access. A particularity of 2003 and supplies its users with Internet access. A particularity of
the Vienna Funkfeuer network is that it manages to provide Internet the Vienna Funkfeuer network is that it manages to provide Internet
access through a city wide, large scale Wi-Fi mesh network, with just access through a city wide, large scale Wi-Fi MANET, with just a
a single Internet uplink. single Internet uplink.
Operational experience of the OLSR project [OLSR.org] with these Operational experience of the OLSR project [OLSR.org] with these
networks have revealed that the use of hop-count as routing metric networks have revealed that the use of hop-count as routing metric
leads to unsatisfactory network performance. Experiments with the leads to unsatisfactory network performance. Experiments with the
ETX metric [MOBICOM03] were therefore undertaken in parallel in the ETX metric [MOBICOM03] were therefore undertaken in parallel in the
Berlin Freifunk network as well as in the Vienna Funkfeuer network in Berlin Freifunk network as well as in the Vienna Funkfeuer network in
2004, and found satisfactory, i.e., sufficiently easy to implement 2004, and found satisfactory, i.e., sufficiently easy to implement
and providing sufficiently good performance. This metric has now and providing sufficiently good performance. This metric has now
been in operational use in these networks for several years. been in operational use in these networks for several years.
skipping to change at page 15, line 38 skipping to change at page 16, line 30
ranged links with high bitrate (with higher but reasonable loss ranged links with high bitrate (with higher but reasonable loss
ratios). Such conditions, when they occur, can degrade the ratios). Such conditions, when they occur, can degrade the
performance of a network considerably by not taking advantage of performance of a network considerably by not taking advantage of
higher capacity links. higher capacity links.
Because of this the OLSR.org project has implemented the Directional Because of this the OLSR.org project has implemented the Directional
Airtime Metric for OLSRv2, which has been inspired by the Estimated Airtime Metric for OLSRv2, which has been inspired by the Estimated
Travel Time (ETT) metric [MOBICOM04]. This metric uses an Travel Time (ETT) metric [MOBICOM04]. This metric uses an
unidirectional packet loss, but also takes the bitrate into account unidirectional packet loss, but also takes the bitrate into account
to create a more accurate description of the relative costs or to create a more accurate description of the relative costs or
capabilities of mesh links. capabilities of OLSRv2 links.
Appendix B. Linkspeed stabilization Appendix B. Linkspeed stabilization
The DAT metric describes how to generate a reasonable stable packet The DAT metric describes how to generate a reasonable stable packet
loss value from incoming packet reception/loss events, the source of loss value from incoming packet reception/loss events, the source of
the linkspeed used in this document is considered an external the linkspeed used in this document is considered an external
process. process.
In the presence of a layer-2 technology with variable linkspeed it is In the presence of a layer-2 technology with variable linkspeed it is
likely that the raw linkspeed will be fluctuating too fast to be likely that the raw linkspeed will be fluctuating too fast to be
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