draft-ietf-manet-olsrv2-dat-metric-10.txt   draft-ietf-manet-olsrv2-dat-metric-11.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: May 27, 2016 INRIA Expires: June 17, 2016 INRIA
November 24, 2015 December 15, 2015
Packet Sequence Number based directional airtime metric for OLSRv2 Packet Sequence Number based directional airtime metric for OLSRv2
draft-ietf-manet-olsrv2-dat-metric-10 draft-ietf-manet-olsrv2-dat-metric-11
Abstract Abstract
This document specifies an Directional Airtime (DAT) link metric for This document specifies an Directional Airtime (DAT) link metric for
usage in OLSRv2. usage 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 May 27, 2016. This Internet-Draft will expire on June 17, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 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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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 Rationale . . . . . . . . . . . . 5 4. Directional Airtime Metric Rationale . . . . . . . . . . . . 5
5. Metric Functioning & Overview . . . . . . . . . . . . . . . . 6 5. Metric Functioning & Overview . . . . . . . . . . . . . . . . 6
6. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 7 6. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 7
7. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 8 7. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 8
7.1. Recommended Values . . . . . . . . . . . . . . . . . . . 8 7.1. Recommended Values . . . . . . . . . . . . . . . . . . . 8
8. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 8 8. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Initial Values . . . . . . . . . . . . . . . . . . . . . 9 8.1. Initial Values . . . . . . . . . . . . . . . . . . . . . 10
9. Packets and Messages . . . . . . . . . . . . . . . . . . . . 10 9. Packets and Messages . . . . . . . . . . . . . . . . . . . . 10
9.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 10 9.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 10
9.2. Requirements for using DAT metric in OLSRv2 9.2. Requirements for using DAT metric in OLSRv2
implementations . . . . . . . . . . . . . . . . . . . . . 10 implementations . . . . . . . . . . . . . . . . . . . . . 10
9.3. Link Loss Data Gathering . . . . . . . . . . . . . . . . 11 9.3. Link Loss Data Gathering . . . . . . . . . . . . . . . . 11
9.4. HELLO Message Processing . . . . . . . . . . . . . . . . 11 9.4. HELLO Message Processing . . . . . . . . . . . . . . . . 12
10. Timer Event Handling . . . . . . . . . . . . . . . . . . . . 12 10. Timer Event Handling . . . . . . . . . . . . . . . . . . . . 12
10.1. Packet Timeout Processing . . . . . . . . . . . . . . . 12 10.1. Packet Timeout Processing . . . . . . . . . . . . . . . 12
10.2. Metric Update . . . . . . . . . . . . . . . . . . . . . 12 10.2. Metric Update . . . . . . . . . . . . . . . . . . . . . 13
11. Security Considerations . . . . . . . . . . . . . . . . . . . 13 11. Security Considerations . . . . . . . . . . . . . . . . . . . 13
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
13.1. Normative References . . . . . . . . . . . . . . . . . . 14 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
13.2. Informative References . . . . . . . . . . . . . . . . . 15 14.1. Normative References . . . . . . . . . . . . . . . . . . 15
14.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Future work . . . . . . . . . . . . . . . . . . . . 16 Appendix A. Future work . . . . . . . . . . . . . . . . . . . . 16
Appendix B. OLSR.org metric history . . . . . . . . . . . . . . 17 Appendix B. OLSR.org metric history . . . . . . . . . . . . . . 17
Appendix C. Linkspeed stabilization . . . . . . . . . . . . . . 18 Appendix C. Linkspeed stabilization . . . . . . . . . . . . . . 18
Appendix D. Packet loss hysteresis . . . . . . . . . . . . . . . 18 Appendix D. Packet loss hysteresis . . . . . . . . . . . . . . . 18
Appendix E. Example DAT values . . . . . . . . . . . . . . . . . 18 Appendix E. Example DAT values . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction 1. Introduction
One of the major shortcomings of Optimized Link State Routing (OLSR) One of the major shortcomings of Optimized Link State Routing (OLSR)
[RFC3626] is the lack of a granular link cost metric between OLSR [RFC3626] is the lack of a granular link cost metric between OLSR
routers. Operational experience with OLSR networks gathered since routers. Operational experience with OLSR networks gathered since
its publication has revealed that wireless networks links can have its publication has revealed that wireless networks links can have
highly variable and heterogeneous properties. This makes a hopcount highly variable and heterogeneous properties. This makes a hopcount
metric insufficient for effective OLSR routing. metric insufficient for effective OLSR routing.
Based on this experience, OLSRv2 [RFC7181] 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 has
Estimated Transmission Count (ETX) metric [MOBICOM04] as a included an Estimated Transmission Count (ETX) metric [MOBICOM04] as
proprietary extension. While this metric is not perfect, it proved a 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 (see
(Appendix B). But the increasing maximum data rate of IEEE 802.11 Appendix B). 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 ETX-derived routing metric for OLSRv2, a successor of the OLSR.org ETX-derived routing metric for
OLSR. It takes both the loss rate and the link speed into account to OLSR. It takes both the loss rate and the link speed into account to
provide a more accurate picture of the links within the network. provide a more accurate picture of the links within the network.
This experimental draft will allow OLSRv2 deployments with a metric This specification allows OLSRv2 deployments with a metric defined by
defined by the IETF Manet group. It enables easier interoperability the IETF MANET working group. It enables easier interoperability
tests between implementations and will also deliver a useful baseline tests between implementations and targets to deliver a useful
to compare other metrics to. Appendix A contains a few possible baseline to compare with, for experiments with this metric as well as
steps to improve the Directional Airtime Metric. other metrics. Appendix A contains a few possible steps to improve
the Directional Airtime Metric. Coming experiments should also allow
to judge if the DAT metric can be useful for other IETF protocol,
both inside and out of the MANET working group. This could lead
either to moving this draft to Standard Track or to replace it with
an improved document.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
The terminology introduced in [RFC5444], [RFC7181] 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:
DAT - Directional Airtime (Metric), the link metric described in DAT - Directional Airtime (Metric), the link metric specified in
this document, which is a directional variant of ETT. It does not this document, which is a directional variant of ETT. It does not
take reverse path loss into account. take reverse path loss into account.
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.
add(QUEUE, value) - adds a new element to the TAIL of the queue. add(QUEUE, value) - adds a new element to the TAIL of the queue.
remove(QUEUE) - removes the HEAD element of the queue remove(QUEUE) - removes the HEAD element of the queue
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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 successfully transmit an IP packet amount of airtime needed to successfully transmit an IP packet
over a link, not considering layer-2 overhead created by preamble, over a link, not considering layer-2 overhead created by preamble,
backoff time and queuing. backoff time and queuing.
3. Applicability Statement 3. Applicability Statement
The Directional Airtime Metric was designed and tested (see The Directional Airtime Metric was designed and tested (see
[olsrv2_paper]) in wireless IEEE 802.11 OLSRv2 [RFC7181] networks. [COMNET15]) in wireless IEEE 802.11 OLSRv2 [RFC7181] networks. These
These networks employ link layer retransmission to increase the networks employ link layer retransmission to increase the delivery
delivery probability. A dynamic rate selection algorithm selects the probability. A dynamic rate selection algorithm selects the unicast
unicast data rate independently for each neighbor. data rate independently for each neighbor.
As specified in OLSRv2, the metric calculates only the incoming link As specified in OLSRv2, the metric calculates only the incoming link
cost. It does neither calculate the outgoing metric, nor does it cost. It does neither calculate the outgoing metric, nor does it
decide the link status (heard, symmetric, lost). decide the link status (heard, symmetric, lost).
The metric works both for nodes which can send/receive [RFC5444] The metric works both for nodes which can send/receive [RFC5444]
packet sequence numbers and those which do not have this capability. packet sequence numbers and those which do not have this capability.
In the absence of such sequence numbers the metric calculates the In the absence of such sequence numbers the metric calculates the
packet loss based on [RFC6130] HELLO message timeouts. packet loss based on [RFC6130] HELLO message timeouts.
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 via
gathering cross-layer data from the operating system or an external gathering cross-layer data from the operating system, via an external
daemon like DLEP [DLEP], but also by indirect layer-3 measurements daemon like DLEP [DLEP], or via indirect layer-3 measurements like
like packet-pair (see [MOBICOM04]). packet-pair (see [MOBICOM04]).
The metric uses [RFC5444] multicast control traffic to determine the The metric uses [RFC5444] multicast control traffic to determine the
link packet loss. The administrator should take care that link layer link packet loss. The administrator should take care that link layer
multicast transmission do not have a higher reception probability multicast transmission do not have a higher reception probability
than the slowest unicast transmission without retransmission. It than the slowest unicast transmission without retransmission. For
might, for example in 802.11g, be necessary to increase the data-rate example, with 802.11g, it might be necessary to increase the data-
of the multicast transmissions, e.g. set the multicast data-rate to 6 rate of the multicast transmissions, e.g. set the multicast data-rate
MBit/s. to 6 MBit/s.
The metric can only handle a certain range of packet loss and unicast The metric can only handle a certain range of packet loss and unicast
data-rate. The maximum packet loss that can be encoded into the data-rate. The maximum packet loss that can be encoded into the
metric a loss of 7 of 8 packets (87.5%), without link layer metric is a loss of 7 of 8 packets (87.5%), without link layer
retransmissions. The unicast data-rate that can be encoded by this retransmissions. The unicast data-rate that can be encoded by this
metric can be between 1 kBit/s and 2 GBit/s. This metric has been metric can be between 1 kBit/s and 2 GBit/s. This metric has been
designed for data-rates of 1 MBit/s and hundreds of MBit/s. designed for data-rates of 1 MBit/s and hundreds of MBit/s.
4. Directional Airtime Metric Rationale 4. Directional Airtime Metric Rationale
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 differs from on the ETX [MOBICOM03] and ETT [MOBICOM04] metric, but differs from
both of these in several ways. both of these in several ways.
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o OLSRv2 [RFC7181] defines the link metric as directional costs o OLSRv2 [RFC7181] defines the link metric as directional costs
between routers. 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, while
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 specified in this document has
the OLSR.org ETX implementation, see Appendix B. The output is the been tested extensively in the OLSR.org ETX implementation, see
average of the packet loss over a configured time period. Appendix B. The output is the average of the packet loss over a
configured time period.
The metric normally measures the loss of a link by tracking the The metric normally measures the loss of a link by tracking the
incoming [RFC5444] packet sequence numbers. Without these packet incoming [RFC5444] packet sequence numbers. Without these packet
sequence numbers, the metric does calculate the loss of the link sequence numbers, the metric does calculate the loss of the link
based of received and lost [RFC5444] HELLO messages. It uses the based of received and lost [RFC5444] HELLO messages. It uses the
incoming HELLO interval time (or if not present, the validity time) incoming HELLO interval time (or if not present, the validity time)
to decide when a HELLO is lost. to decide when a HELLO is lost.
When a neighbor router resets, its packet sequence number might jump When a neighbor router resets, its packet sequence number might jump
to a random value. The metric tries to detect jumps in the packet to a random value. The metric tries to detect jumps in the packet
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INTERVAL_TIME message TLV is present in the HELLO messages and when INTERVAL_TIME message TLV is present in the HELLO messages and when
each RFC5444 packet contains an interface specific sequence number. each RFC5444 packet contains an interface specific sequence number.
It also adds a number of new data entries to be stored for each It also adds a number of new data entries to be stored for each
RFC6130 Link. RFC6130 Link.
6. Protocol Constants 6. Protocol Constants
This specification defines the following constants, which define the This specification defines the following constants, which define the
range of metric values that can be encoded by the DAT metric (see range of metric values that can be encoded by the DAT metric (see
Table 1). They cannot be changed without making the metric outputs Table 1). They cannot be changed without making the metric outputs
incomparable and should only be changed for MANET's with a very slow incomparable and should only be changed for a MANET with very slow or
or very fast link layer. See Appendix D Appendix E for example very fast link layer. See Appendix E for example metric values.
metric values.
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. (DAT_MAXIMUM_LOSS-1)/DAT_MAXIMUM_LOSS.
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. metric.
+---------------------+-------+ +---------------------+-------+
| Name | Value | | Name | Value |
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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.
7.1. Recommended Values 7.1. 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 routers. Using this metric for Networks, which mostly use routers that are not mobile. Using this
mobile networks might require shorter DAT_REFRESH_INTERVAL and/or metric for mobile networks might require shorter DAT_REFRESH_INTERVAL
DAT_MEMORY_LENGTH. and/or 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
8. Data Structures 8. Data Structures
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received from this link. 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.
The incoming bitrate value should be stabilized by a hysteresis The incoming bitrate value should be stabilized by a hysteresis
filter to improve the stability of this metric. See Appendix B filter to improve the stability of this metric. See Appendix C for
Appendix C for an example. an example.
This specification updates the L_in_metric field of the Link Set of This specification updates the L_in_metric field of the Link Set of
the Interface Information Base, as defined in section 8.1. of the Interface Information Base, as defined in section 8.1. of
[RFC7181]) [RFC7181])
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:
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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)
The calculated L_in_metric value should be stabilized by a hysteresis The calculated L_in_metric value should be stabilized by a hysteresis
function. See Appendix C Appendix D for an example. function. See Appendix D for an example.
11. Security Considerations 11. 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
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loops or bad links. It might also attract traffic for "Man in the loops or bad links. It might also attract traffic for "Man in the
Middle" attacks or traffic analysis. Middle" attacks or traffic analysis.
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 can be sequence numbers, pretending to be somebody else. This attack can be
prevented by the true originator of the RFC5444 packets by adding a prevented by the true originator of the RFC5444 packets by adding a
[RFC7182] 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. The security mechanism described in [RFC7183] does replayed packets. The security mechanism described in [RFC7183] does
not protect the additional sequence number of the DAT metric because not protect the sequence number used by the DAT metric because it
it does only sign the RFC5444 messages, not the RFC5444 packet does only sign the RFC5444 messages, not the RFC5444 packet header
header. (which contains the RFC5444 packet sequence number).
Protection against "Man in the Middle" attacks are out of scope of Protection mechanisms against "Man in the Middle" attacks are
this document. nevertheless out of scope of this document.
12. Acknowledgements 12. IANA Considerations
This document has no actions for IANA.
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), Fabian Nack and Stan Ratliff (Cisco Systems). Laboratory), Fabian Nack (Freie Universitaet Berlin) and Stan Ratliff
(Cisco Systems).
13. References 14. References
13.1. 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.
[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.
[RFC7181] Clausen, T., Jacquet, P., and C. Dearlove, "The Optimized [RFC7181] Clausen, T., Jacquet, P., and C. Dearlove, "The Optimized
Link State Routing Protocol version 2", RFC 7181, April Link State Routing Protocol version 2", RFC 7181, April
2014. 2014.
13.2. Informative References 14.2. Informative References
[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.
[RFC7182] Ulrich, U., Clausen, T., and C. Dearlove, "Integrity Check [RFC7182] Ulrich, U., Clausen, T., and C. Dearlove, "Integrity Check
Value and Timestamp TLV Definitions for Mobile Ad Hoc Value and Timestamp TLV Definitions for Mobile Ad Hoc
Networks (MANETs)", RFC 7182, April 2014. Networks (MANETs)", RFC 7182, April 2014.
[RFC7183] Ulrich, U., Dearlove, C., and T. Clausen, "Integrity [RFC7183] Ulrich, U., Dearlove, C., and T. Clausen, "Integrity
Protection for the Neighborhood Discovery Protocol (NHDP) Protection for the Neighborhood Discovery Protocol (NHDP)
and Optimized Link State Routing Protocol Version 2 and Optimized Link State Routing Protocol Version 2
(OLSRv2)", RFC 7183, April 2014. (OLSRv2)", RFC 7183, April 2014.
[olsrv2_paper] [COMNET15]
C., C., C., C., J., J., J., J., and H. H., "OLSRv2 for Barz, C., Fuchs, C., Kirchhoff, J., Niewiejska, J., and H.
Community Networks: Using Directional Airtime Metric with Rogge, "OLSRv2 for Community Networks: Using Directional
external radios", Elsevier Computer Networks 2015 , Airtime Metric with external radios", Elsevier Computer
September 2015, Networks 2015 , September 2015,
<http://dx.doi.org/10.1016/j.comnet.2015.09.022>. <http://dx.doi.org/10.1016/j.comnet.2015.09.022>.
[CONFINE] "Community Networks Testbed for the Future Internet [CONFINE] "Community Networks Testbed for the Future Internet
(CONFINE)", 2015, <http://www.confine-project.eu>. (CONFINE)", 2015, <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-17 , March 2013. draft-ietf-manet-dlep-17 , October 2015.
[BATMAN] Neumann, A., Aichele, C., Lindner, M., and S. Wunderlich, [BATMAN] Neumann, A., Aichele, C., Lindner, M., and S. Wunderlich,
"Better Approach To Mobile Ad-hoc Networking "Better Approach To Mobile Ad-hoc Networking
(B.A.T.M.A.N.)", draft-wunderlich-openmesh-manet- (B.A.T.M.A.N.)", draft-wunderlich-openmesh-manet-
routing-00 , April 2008. routing-00 , April 2008.
[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.
skipping to change at page 16, line 29 skipping to change at page 16, line 38
[FREIFUNK] [FREIFUNK]
"Freifunk Wireless Community Networks", 2015, "Freifunk Wireless Community Networks", 2015,
<http://www.freifunk.net>. <http://www.freifunk.net>.
[FUNKFEUER] [FUNKFEUER]
"Austria Wireless Community Network", 2015, "Austria Wireless Community Network", 2015,
<http://www.funkfeuer.at>. <http://www.funkfeuer.at>.
Appendix A. Future work Appendix A. Future work
As the DAT metric proved to work reasonable well for non- or slow- As the DAT metric proved to work reasonably well for non- or slow-
moving ad hoc networks [olsrv2_paper], it should be considered as a moving ad hoc networks [COMNET15], it should be considered as a solid
solid first step on a way to better MANET metrics. There are first step on a way to better MANET metrics. There are multiple
multiple parts of the DAT metric that need to be reviewed again in parts of the DAT metric that need to be reviewed again in the context
the context of real world deployments and can be subject to later of real world deployments and can be subject to later improvements.
improvements.
The easiest part of the DAT metric to change and test would be the The easiest part of the DAT metric to change and test would be the
timings parameters. A 1 minute interval for packet loss statistics timings parameters. A 1 minute interval for packet loss statistics
might be a good compromise for some MANETs, but could easily be too might be a good compromise for some MANETs, but could easily be too
large or to small for others. More data is needed to verify or large or to small for others. More data is needed to verify or
improve the current parameter selection. improve the current parameter selection.
The DAT metric considers only the multicast RFC5444 packet loss for The DAT metric considers only the multicast RFC5444 packet loss for
estimating the link loss, but it would be good to integrate unicast estimating the link loss, but it would be good to integrate unicast
data loss into the loss estimation. This information could be data loss into the loss estimation. This information could be
provided directly from the link layer. This could increase the provided directly from the link layer. This could increase the
accuracy of the loss rate estimation in scenarios, where the accuracy of the loss rate estimation in scenarios, where the
assumptions regarding the ratio of multicast vs. unicast loss do not assumptions regarding the ratio of multicast vs. unicast loss do not
hold. hold.
The packet loss averaging algorithm could also be improved. While The packet loss averaging algorithm could also be improved. While
the DAT metric provides a stable sliding time interval to average the the DAT metric provides a stable sliding time interval to average the
incoming packet loss and not giving the recent input too much incoming packet loss and not giving the recent input too much
influence, However, first experiments suggest that the algorithm influence, first experiments suggest that the algorithm tends to be
tends to be less agile detecting major changes of link quality. This less agile in detecting major changes of link quality. This makes it
makes it less suited for mobile networks. A more agile algorithm is less suited for mobile networks. A more agile algorithm is needed
needed for detecting major changes while filtering out random for detecting major changes while filtering out random fluctuations
fluctuations regarding frame loss. However, the current "quere of regarding frame loss. However, the current "queue of counters"
counters" algorithm suggested for DAT outperforms the binary queue algorithm suggested for DAT outperforms the binary queue algorithm
algorithm and the exponential aging algorithms used for the ETX and the exponential aging algorithms used for the ETX metric in the
metric in the OLSR [RFC3626] codebase of Olsr.org. OLSR [RFC3626] codebase of Olsr.org.
Appendix B. OLSR.org metric history Appendix B. 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. [BATMAN] based wireless community based [RFC3626] or B.A.T.M.A.N. [BATMAN] based wireless community
networks with hundreds of routers in permanent operation. The Vienna networks 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
covering the whole city of Vienna and beyond, spanning roughly 40km covering the whole city of Vienna and beyond, spanning roughly 40km
in diameter. It has been in operation since 2003 and supplies its in diameter. It has been in operation since 2003 and supplies its
users with Internet access. A particularity of the Vienna Funkfeuer users with Internet access. A particularity of the Vienna Funkfeuer
skipping to change at page 17, line 42 skipping to change at page 17, line 50
been in operational use in these networks for several years. been in operational use in these networks for several years.
The ETX metric of a link is the estimated number of transmissions The ETX metric of a link is the estimated number of transmissions
required to successfully send a packet (each packet equal to or required to successfully send a packet (each packet equal to or
smaller than MTU) over that link, until a link layer acknowledgement smaller than MTU) over that link, until a link layer acknowledgement
is received. The ETX metric is additive, i.e., the ETX metric of a is received. The ETX metric is additive, i.e., the ETX metric of a
path is the sum of the ETX metrics for each link on this path. path is the sum of the ETX metrics for each link on this path.
While the ETX metric delivers a reasonable performance, it doesn't While the ETX metric delivers a reasonable performance, it doesn't
handle well networks with heterogeneous links that have different handle well networks with heterogeneous links that have different
bitrates. Since every wireless link, when using ETX metric, is bitrates. When using ETX metric, since every wireless link is
characterized only by its packet loss ratio, the ETX metric prefers characterized only by its packet loss ratio, long-ranged links with
long-ranged links with low bitrate (with low loss ratios) over short- low bitrate (with low loss ratios) are preferred over short-ranged
ranged links with high bitrate (with higher but reasonable loss links with high bitrate (with higher but reasonable loss ratios).
ratios). Such conditions, when they occur, can degrade the Such conditions, when they occur, can degrade the performance of a
performance of a network considerably by not taking advantage of network considerably, by not taking advantage of higher capacity
higher capacity links. 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 OLSRv2 links. capabilities of OLSRv2 links.
Appendix C. Linkspeed stabilization Appendix C. Linkspeed stabilization
The DAT metric describes how to generate a reasonable stable packet The DAT metric specifies how to generate a reasonably stable packet
loss value from incoming packet reception/loss events, the source of loss rate value based on incoming packet reception/loss events, but
the linkspeed used in this document is considered an external the source of the linkspeed used in this document is considered an
process. external 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
useful for the DAT metric. useful for the DAT metric.
The amount of stabilization necessary for the linkspeed depends on The amount of stabilization necessary for the linkspeed depends on
the implementation of the mac-layer, especially the rate control the implementation of the mac-layer, especially the rate control
algorithm. algorithm.
Experiments with the Linux 802.11 wifi stack have shown that a simple Experiments with the Linux 802.11 wifi stack have shown that a simple
Median filter over a series of raw linkspeed measurements can smooth Median filter over a series of raw linkspeed measurements can smooth
the calculated value without introducing intermediate linkspeed the calculated value without introducing intermediate linkspeed
values you would get by using averaging or an exponential weighted values one would obtain by using averaging or an exponential weighted
moving average. moving average.
Appendix D. Packet loss hysteresis Appendix D. Packet loss hysteresis
While the DAT metric use a sliding window to calculate a reasonable While the DAT metric uses a sliding window to compute a reasonably
stable frame loss, the implementation might choose to integrate an stable frame loss, the implementation might choose to integrate an
additional hysteresis to prevent the metric flapping between two additional hysteresis to prevent undesirable oscillations between two
values. values (i.e. metric flapping).
In Section Section 10.2 DAT caluclates a fractional loss rate. The In Section Section 10.2 DAT calculates a fractional loss rate. The
fraction of 'loss := sum_total / sum_received' may result in minor fraction of 'loss := sum_total / sum_received' may result in minor
fluctuations in the advertised L_in_metric due to minimal changes in fluctuations in the advertised L_in_metric due to minimal changes in
sum_total or sum_received which can cause undesirable protocol churn. sum_total or sum_received, which can cause undesirable protocol
churn.
A hysteresis function applied to the fraction could reduce the amount A hysteresis function applied to the fraction could reduce the amount
of changes in the loss rate and help to stabilize the metric output. of changes in the loss rate and help to further stabilize the metric
output.
Appendix E. Example DAT values Appendix E. Example DAT values
The DAT metric value can be expressed in terms of link speed (bit/s) The DAT metric value can be expressed in terms of link speed (bit/s)
or used airtime (s). When using the default protocol constants (see or used airtime (s). When using the default protocol constants (see
Section 6), DAT encodes link speeds between 119 bit/s and 2 Gbit/s. Section 6), DAT encodes link speeds between 119 bit/s and 2 Gbit/s.
Table Table 2 contains a few examples for metric values and their Table Table 2 contains a few examples for metric values and their
meaning as a link speed: meaning as a link speed:
skipping to change at page 19, line 21 skipping to change at page 19, line 31
| MINIMUM_METRIC (1) | 2 Gbit/s | | MINIMUM_METRIC (1) | 2 Gbit/s |
| | | | | |
| MAXIMUM_METRIC (16776960) | 119 bit/s | | MAXIMUM_METRIC (16776960) | 119 bit/s |
| | | | | |
| 2000 | 1 Mbit/s | | 2000 | 1 Mbit/s |
+---------------------------+-----------+ +---------------------------+-----------+
Table 2: DAT link cost examples Table 2: DAT link cost examples
A path metric value could also be expressed as a link speed, but this A path metric value could also be expressed as a link speed, but this
would be unintuitive and difficult to understand. An easier way to would be less intuitive. An easier way to transform a path metric
transform a path metric value into a textual representation is to value into a textual representation is to divide it by the hopcount
divide it by the hopcount of the path and express the path cost as of the path and express the path cost as average link speed together
average link speed together with the hopcount (see Table 3). with the hopcount (see Table 3).
+---------+------+---------------+ +---------+------+---------------+
| Metric | hops | average bit/s | | Metric | hops | average bit/s |
+---------+------+---------------+ +---------+------+---------------+
| 4 | 2 | 1 Gbit/s | | 4 | 2 | 1 Gbit/s |
| | | | | | | |
| 4000000 | 6 | 3 kbit/s | | 4000000 | 6 | 3 kbit/s |
+---------+------+---------------+ +---------+------+---------------+
Table 3: DAT link cost examples Table 3: DAT link cost examples
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