Packet Sequence Number based directional airtime metric for OLSRv2
draft-ietf-manet-olsrv2-dat-metric-05
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (manet WG) | |
|---|---|---|---|
| Authors | Henning Rogge , Emmanuel Baccelli | ||
| Last updated | 2015-04-21 | ||
| Replaces | draft-rogge-baccelli-olsrv2-ett-metric | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text xml htmlized pdfized bibtex | ||
| Reviews |
GENART Telechat review
(of
-10)
Ready with Nits
OPSDIR Last Call review
(of
-08)
Has Issues
GENART Last Call review
(of
-08)
Ready with Nits
SECDIR Last Call review
(of
-08)
Has Issues
|
||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-manet-olsrv2-dat-metric-05
MANET H. Rogge
Internet-Draft Fraunhofer FKIE
Intended status: Experimental E. Baccelli
Expires: October 24, 2015 INRIA
April 22, 2015
Packet Sequence Number based directional airtime metric for OLSRv2
draft-ietf-manet-olsrv2-dat-metric-05
Abstract
This document specifies an directional airtime link metric for usage
in OLSRv2.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 24, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Rogge & Baccelli Expires October 24, 2015 [Page 1]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability Statement . . . . . . . . . . . . . . . . . . . 4
4. Directional Airtime Metric Rationale . . . . . . . . . . . . 5
5. Metric Functioning & Overview . . . . . . . . . . . . . . . . 6
6. Protocol Parameters . . . . . . . . . . . . . . . . . . . . . 7
6.1. Recommended Values . . . . . . . . . . . . . . . . . . . 7
7. Protocol Constants . . . . . . . . . . . . . . . . . . . . . 8
8. Data Structures . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Initial Values . . . . . . . . . . . . . . . . . . . . . 9
9. Packets and Messages . . . . . . . . . . . . . . . . . . . . 9
9.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 9
9.2. Requirements for using DAT metric in OLSRv2
implementations . . . . . . . . . . . . . . . . . . . . . 10
9.3. Link Loss Data Gathering . . . . . . . . . . . . . . . . 10
9.4. HELLO Message Processing . . . . . . . . . . . . . . . . 11
10. Timer Event Handling . . . . . . . . . . . . . . . . . . . . 11
10.1. Packet Timeout Processing . . . . . . . . . . . . . . . 11
10.2. Metric Update . . . . . . . . . . . . . . . . . . . . . 12
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
12. Security Considerations . . . . . . . . . . . . . . . . . . . 13
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
14.1. Normative References . . . . . . . . . . . . . . . . . . 14
14.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. OLSR.org metric history . . . . . . . . . . . . . . 15
Appendix B. Linkspeed stabilization . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
One of the major shortcomings of OLSR [RFC3626] is the lack of a
granular link cost metric between OLSR routers. Operational
experience with OLSR networks gathered since the publication of OLSR
has revealed that wireless networks links can have highly variable
and heterogeneous properties. This makes a hopcount metric
insufficient for effective OLSR routing.
Based on this experience, OLSRv2 [RFC7181] integrates the concept of
link metrics directly into the core specification of the routing
protocol. The OLSRv2 routing metric is an external process, it can
be any kind of dimensionless additive cost function which reports to
the OLSRv2 protocol.
Since 2004 the OLSR.org [OLSR.org] implementation of OLSR included an
Estimated Transmission Count (ETX) metric [MOBICOM04] as a
Rogge & Baccelli Expires October 24, 2015 [Page 2]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
proprietary extension. While this metric is not perfect, it proved
to be sufficient for a long time for Community Mesh Networks
(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
reason to move to a different metric.
This document describes a Directional Airtime routing metric for
OLSRv2, a successor of the ETX-derived OLSR.org routing metric for
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.
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
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
NOT','SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED', 'MAY',
and 'OPTIONAL' in this document are to be interpreted as described in
[RFC2119].
The terminology introduced in [RFC5444], [RFC7181] and [RFC6130],
including the terms "packet", "message" and "TLV" are to be
interpreted as described therein.
Additionally, this document uses the following terminology and
notational conventions:
QUEUE - a first in, first out queue of integers.
QUEUE[TAIL] - the most recent element in the queue.
add(QUEUE, value) - adds a new element to the TAIL of the queue.
remove(QUEUE) - removes the HEAD element of the queue
sum(QUEUE) - an operation which returns the sum of all elements in a
QUEUE.
diff_seqno(new, old) - an operation which returns the positive
distance between two elements of the circular sequence number
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
- old + 65536).
MAX(a,b) - the maximum of a and b.
Rogge & Baccelli Expires October 24, 2015 [Page 3]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
UNDEFINED - a value not in the normal value range of a variable.
airtime - the time a transmitted packet blocks the link layer, e.g.,
a wireless link.
ETX - Expected Transmission Count, a link metric proportional to the
number of transmissions to successfully send an IP packet over a
link.
ETT - Estimated Travel Time, a link metric proportional to the
amount of airtime needed to transmit an IP packet over a link, not
considering layer-2 overhead created by preamble, backoff time and
queuing.
DAT - Directional Airtime Metric, the link metric described in this
document, which is a directional variant of ETT. It does not take
reverse path loss into account.
3. Applicability Statement
The Directional Airtime Metric was designed and tested in wireless
IEEE 802.11 [RFC7181] networks. These networks employ link layer
retransmission to increase the delivery probability and multiple
unicast data rates.
As specified in [RFC7181] the metric calculates only the incoming
link cost. It does neither calculate the outgoing metric, nor does
it decide the link status (heard, symmetric, lost).
The metric works both for nodes which can send/receive [RFC5444]
packet sequence numbers and such which do not have this capability.
In the absence of such sequence numbers the metric calculates the
packet loss based on [RFC6130] HELLO message timeouts.
The metric must learn about the unicast data rate towards each one-
hop neighbor from an external process, either by configuration or by
an external measurement process. This measurement could be done by
gathering cross-layer data from the operating system or an external
daemon like DLEP [DLEP], but also by indirect layer-3 measurements
like packet-pair.
The metric uses [RFC5444] multicast control traffic to determine the
link packet loss. The administrator should take care that link layer
multicast transmission do not not have a higher reception probability
than the slowest unicast transmission. It might, for example in
802.11g, be necessary to increase the data-rate of the multicast
transmissions, e.g. set the multicast data-rate to 6 MBit/s.
Rogge & Baccelli Expires October 24, 2015 [Page 4]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
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
metric a loss of 7 of 8 packets, without link layer 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 designed for
data-rates of 1 MBit/s and hundreds of MBit/s.
4. Directional Airtime Metric Rationale
The Directional Airtime Metric has been inspired by the publications
on the ETX [MOBICOM03] and ETT [MOBICOM04] metric, but differs from
both of these in several ways.
Instead of measuring the combined loss probability of a bidirectional
transmission of a packet over a link in both directions, the
Directional Airtime Metric measures the incoming loss rate and
integrates the incoming linkspeed into the metric cost. There are
multiple reasons for this decision:
o OLSRv2 [RFC7181] defines the link metric as directional costs
between routers.
o Not all link layer implementations use acknowledgement mechanisms.
Most link layer implementations who do use them use less airtime
and a more robust modulation for the acknowledgement than the data
transmission, which makes it more likely for the data transmission
to be disrupted compared to the acknowledgement.
o Incoming packet loss and linkspeed can be measured locally,
symmetric link loss would need an additional signaling TLV in the
[RFC6130] HELLO and would delay metric calculation by up to one
HELLO interval.
The Directional Airtime Metric does not integrate the packet size
into the link cost. Doing so is not feasible in most link-state
routing protocol implementations. The routing decision of most
operation systems don't take packet size into account. Multiplying
all link costs of a topology with the size of a data-plane packet
would never change the dijkstra result anyways.
The queue based packet loss estimator has been tested extensively in
the OLSR.org ETX implementation, see Appendix A. 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
incoming [RFC5444] packet sequence numbers. Without these packet
sequence numbers, the metric does calculate the loss of the link
based of received and lost [RFC5444] HELLO messages. It uses the
Rogge & Baccelli Expires October 24, 2015 [Page 5]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
incoming HELLO interval time (or if not present, the validity time)
to decide when a HELLO is lost.
When a neighbor router resets, its packet sequence number might jump
to a random value. The metric tries to detect jumps in the packet
sequence number and removes them from the data set, because the
already gathered link loss data should still be valid. The link loss
data is only removed from memory when a Link times out completely and
its Link Set tuple is removed from the database.
5. Metric Functioning & Overview
The Directional Airtime Metric is calculated for each link set entry,
as defined in [RFC6130] section 7.1.
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
an external process, the current packet loss rate is calculated by
keeping track of packet reception and packet loss events.
Multiple incoming packet loss/reception events must be combined into
a loss rate to get a smooth metric. Experiments with exponential
weighted moving average (EWMA) lead to a highly fluctuating or a slow
converging metric (or both). To get a smoother and more controllable
metric result, this metric uses two fixed length queues to measure
and average the incoming packet events, one queue for received
packets and one for the estimated number of packets sent by the other
side of the link.
Because the rate of incoming packets is not uniform over time, the
queue contains a number of counters, each representing a fixed time
interval. Incoming packet loss and packet reception event are
accumulated in the current queue element until a timer adds a new
empty counter to both queues and remove the oldest counter from both.
In addition to the packet loss stored in the queue, this metric uses
a timer to detect a total link-loss. For every [RFC5444] HELLO
interval in which the metric received no packet from a neighbor, it
scales the number of received packets in the queue based on the total
time interval the queue represents compared to the total time of the
lost HELLO intervals.
The average packet loss ratio is calculated as the sum of the 'total
packets' counters divided by the sum of the 'packets received'
counters. This value is then divided through the current link-speed
and then scaled into the range of metrics allowed for OLSRv2.
Rogge & Baccelli Expires October 24, 2015 [Page 6]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
The metric value is then used as L_in_metric of the Link Set (as
defined in section 8.1. of [RFC7181]).
6. Protocol Parameters
This specification defines two constants, agreement on which is
required, from all the OLSRv2 routers participating in the same
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
received and lost packets within the queue are used to calculate
the cost of the link.
DAT_REFRESH_INTERVAL - interval in seconds between two metric
recalculations as described in Section 10.2. This value SHOULD be
smaller than a typical HELLO interval.
DAT_HELLO_TIMEOUT_FACTOR - multiplier relative to the HELLO_INTERVAL
(see [RFC6130] Section 5.3.1) after which the DAT metric considers
a HELLO as lost.
DAT_SEQNO_RESTART_DETECTION - threshold in number of missing packets
(based on received packet sequence numbers) at which point the
router considers the neighbor has restarted. This parameter is
only used for packet sequence number based loss estimation. This
number MUST be larger than DAT_MAXIMUM_LOSS.
6.1. Recommended Values
The proposed values of the protocol parameters are for Community Mesh
Networks, which mostly use immobile routers. Using this metric for
mobile networks might require shorter DAT_REFRESH_INTERVAL and/or
DAT_MEMORY_LENGTH.
DAT_MEMORY_LENGTH := 64
DAT_REFRESH_INTERVAL := 1
DAT_HELLO_TIMEOUT_FACTOR := 1.2
DAT_SEQNO_RESTART_DETECTION := 256
Rogge & Baccelli Expires October 24, 2015 [Page 7]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
7. Protocol Constants
This specification defines the following constants, which define the
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
metric. Loss rate will be between 0/DAT_MAXIMUM_LOSS and
(DAT_MAXIMUM_LOSS-1)/DAT_MAXIMUM_LOSS: 8.
DAT_MINIMUM_BITRATE - Minimal bit-rate in Bit/s used by this routing
metric: 1000.
8. Data Structures
This specification extends the Link Set of the Interface Information
Base, as defined in [RFC6130] section 7.1, by the adding the
following elements to each link tuple:
L_DAT_received is a QUEUE with DAT_MEMORY_LENGTH integer elements.
Each entry contains the number of successfully received packets
within an interval of DAT_REFRESH_INTERVAL.
L_DAT_total is a QUEUE with DAT_MEMORY_LENGTH integer elements.
Each entry contains the estimated number of packets transmitted by
the neighbor, based on the received packet sequence numbers within
an interval of DAT_REFRESH_INTERVAL.
L_DAT_packet_time is the time when the next RFC5444 packet should
have arrived.
L_DAT_hello_interval is the interval between two hello messages of
the links neighbor as signaled by the INTERVAL_TIME TLV [RFC5497]
of NHDP messages [RFC6130].
L_DAT_lost_packet_intervals is the estimated number of HELLO
intervals from this neighbor the metric has not received a single
packet.
L_DAT_rx_bitrate is the current bitrate of incoming unicast traffic
for this neighbor.
L_DAT_last_pkt_seqno is the last received packet sequence number
received from this link.
Rogge & Baccelli Expires October 24, 2015 [Page 8]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
Methods to obtain the value of L_DAT_rx_bitrate are out of the scope
of this specification. Such methods may include static configuration
via a configuration file or dynamic measurement through mechanisms
described in a separate specification (e.g. [DLEP]). Any Link tuple
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.
This specification updates the L_in_metric field of the Link Set of
the Interface Information Base, as defined in section 8.1. of
[RFC7181])
8.1. Initial Values
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 8 are set as follows:
o L_DAT_received := 0, ..., 0. The queue always has
DAT_MEMORY_LENGTH elements.
o L_DAT_total := 0, ..., 0. The queue always has DAT_MEMORY_LENGTH
elements.
o L_DAT_packet_time := EXPIRED (no earlier RFC5444 packet received).
o L_DAT_hello_interval := UNDEFINED (no earlier NHDP HELLO
received).
o L_DAT_lost_packet_intervals := 0 (no HELLO interval without
packets).
o L_DAT_last_pkt_seqno := UNDEFINED (no earlier RFC5444 packet with
sequence number received).
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
For the purpose of this section, note the following definitions:
o "pkt_seqno" is defined as the [RFC5444] packet sequence number of
the received packet.
Rogge & Baccelli Expires October 24, 2015 [Page 9]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
o "interval_time" is the time encoded in the INTERVAL_TIME message
TLV of a received [RFC6130] HELLO message.
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
document SHOULD include the following parts into its [RFC5444]
output:
o an INTERVAL_TIME message TLV in each HELLO message, as defined in
[RFC6130] section 4.3.2.
o an interface specific packet sequence number as defined in
[RFC5444] section 5.1 which is incremented by 1 for each outgoing
[RFC5444] packet on the interface.
9.3. Link Loss Data Gathering
For each incoming [RFC5444] packet, additional processing SHOULD be
carried out after the packet messages have been processed as
specified in [RFC6130] and [RFC7181].
[RFC5444] packets without packet sequence number MUST NOT be
processed in this way by this metric.
The router updates the Link Set Tuple corresponding to the originator
of the packet:
1. If L_DAT_last_pkt_seqno = UNDEFINED, then:
1. L_DAT_received[TAIL] := 1.
2. L_DAT_total[TAIL] := 1.
2. Otherwise:
1. L_DAT_received[TAIL] := L_DAT_received[TAIL] + 1.
2. diff := seq_diff(pkt_seqno, L_DAT_last_pkt_seqno).
3. If diff > DAT_SEQNO_RESTART_DETECTION, then:
1. diff := 1.
4. L_DAT_total[TAIL] := L_DAT_total[TAIL] + diff.
Rogge & Baccelli Expires October 24, 2015 [Page 10]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
3. L_DAT_last_pkt_seqno := pkt_seqno.
4. If L_DAT_hello_interval != UNDEFINED, then:
1. L_DAT_packet_time := current time + (L_DAT_hello_interval *
DAT_HELLO_TIMEOUT_FACTOR).
5. L_DAT_lost_packet_intervals := 0.
9.4. HELLO Message Processing
For each incoming HELLO Message, after it has been processed as
defined in [RFC6130] section 12, the Link Set Tuple corresponding to
the incoming HELLO message MUST be updated.
1. If the HELLO message contains an INTERVAL_TIME message TLV, then:
1. L_DAT_hello_interval := interval_time.
2. Otherwise:
1. L_DAT_hello_interval := validity_time.
3. If L_DAT_last_pkt_seqno = UNDEFINED, then:
1. L_DAT_received[TAIL] := L_DAT_received[TAIL] + 1.
2. L_DAT_total[TAIL] := L_DAT_total[TAIL] + 1.
3. L_DAT_packet_time := current time + (L_DAT_hello_interval *
DAT_HELLO_TIMEOUT_FACTOR).
10. Timer Event Handling
In addition to changes in the [RFC5444] processing/generation code,
the DAT metric also uses two timer events.
10.1. Packet Timeout Processing
When L_DAT_packet_time has timed out, the following step MUST be
done:
1. If L_DAT_last_pkt_seqno = UNDEFINED, then:
1. L_DAT_total[TAIL] := L_DAT_total[TAIL] + 1.
2. Otherwise:
Rogge & Baccelli Expires October 24, 2015 [Page 11]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
1. L_DAT_lost_packet_intervals := L_DAT_lost_packet_intervals +
1.
3. L_DAT_packet_time := L_DAT_packet_time + L_DAT_hello_interval.
10.2. Metric Update
Once every DAT_REFRESH_INTERVAL, all L_in_metric values in all Link
Set entries MUST be recalculated:
1. sum_received := sum(L_DAT_received).
2. sum_total := sum(L_DAT_total).
3. If L_DAT_hello_interval != UNDEFINED and
L_DAT_lost_packet_intervals > 0, then:
1. lost_time_proportion := L_DAT_hello_interval *
L_DAT_lost_packet_intervals / DAT_MEMORY_LENGTH.
2. sum_received := sum_received * MAX ( 0, 1 -
lost_time_proportion);
4. If sum_received < 1, then:
1. L_in_metric := MAXIMUM_METRIC, as defined in [RFC7181]
section 5.6.1.
5. Otherwise:
1. loss := sum_total / sum_received.
2. If loss > DAT_MAXIMUM_LOSS, then:
1. loss := DAT_MAXIMUM_LOSS.
3. bitrate := L_DAT_rx_bitrate.
4. If bitrate < DAT_MINIMUM_BITRATE, then:
1. bitrate := DAT_MINIMUM_BITRATE.
5. L_in_metric := (2^24 / DAT_MAXIMUM_LOSS) * loss / (bitrate /
DAT_MINIMUM_BITRATE).
6. remove(L_DAT_total)
7. add(L_DAT_total, 0)
Rogge & Baccelli Expires October 24, 2015 [Page 12]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
8. remove(L_DAT_received)
9. add(L_DAT_received, 0)
11. IANA Considerations
This document contains no actions for IANA.
12. Security Considerations
Artificial manipulation of metrics values can drastically alter
network performance. In particular, advertising a higher L_in_metric
value may decrease the amount of incoming traffic, while advertising
lower L_in_metric may increase the amount of incoming traffic. By
artificially increasing or decreasing the L_in_metric values it
advertises, a rogue router may thus attract or repulse data traffic.
A rogue router may then potentially degrade data throughput by not
forwarding data as it should or redirecting traffic into routing
loops or bad links.
An attacker might also inject packets with incorrect packet level
sequence numbers, pretending to be somebody else. This attack can be
prevented by the true originator of the RFC5444 packets by adding a
[RFC7182] ICV Packet TLV and TIMESTAMP Packet TLV to each packet.
This allows the receiver to drop all incoming packets which have a
forged packet source, both packets generated by the attacker or
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.
13. Acknowledgements
The authors would like to acknowledge the network administrators from
Freifunk Berlin [FREIFUNK] and Funkfeuer Vienna [FUNKFEUER] for
endless hours of testing and suggestions to improve the quality of
the original ETX metric for the OLSR.org routing daemon.
This effort/activity is supported by the European Community Framework
Program 7 within the Future Internet Research and Experimentation
Initiative (FIRE), Community Networks Testbed for the Future Internet
([CONFINE]), contract FP7-288535.
The authors would like to gratefully acknowledge the following people
for intense technical discussions, early reviews and comments on the
specification and its components (listed alphabetically): Teco Boot
(Infinity Networks), Juliusz Chroboczek (PPS, University of Paris 7),
Thomas Clausen, Christopher Dearlove (BAE Systems Advanced Technology
Rogge & Baccelli Expires October 24, 2015 [Page 13]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
Centre), Ulrich Herberg (Fujitsu Laboratories of America), Markus
Kittenberger (Funkfeuer Vienna), Joseph Macker (Naval Research
Laboratory) and Stan Ratliff (Cisco Systems).
14. References
14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC3626] Clausen, T. and P. Jacquet, "Optimized Link State Routing
Protocol", RFC 3626, October 2003.
[RFC5444] Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
"Generalized Mobile Ad Hoc Network (MANET) Packet/Message
Format", RFC 5444, February 2009.
[RFC5497] Clausen, T. and C. Dearlove, "Representing Multi-Value
Time in Mobile Ad Hoc Networks (MANETs)", RFC 5497, March
2009.
[RFC6130] Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc
Network (MANET) Neighborhood Discovery Protocol (NHDP)",
RFC 6130, April 2011.
[RFC7181] Clausen, T., Jacquet, P., and C. Dearlove, "The Optimized
Link State Routing Protocol version 2", RFC 7181, April
2014.
[RFC7182] Ulrich, U., Clausen, T., and C. Dearlove, "Integrity Check
Value and Timestamp TLV Definitions for Mobile Ad Hoc
Networks (MANETs)", RFC 7182, April 2014.
[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.
14.2. Informative References
[CONFINE] "Community Networks Testbed for the Future Internet
(CONFINE)", 2013, <http://www.confine-project.eu>.
[DLEP] Ratliff, S., Berry, B., Harrison, G., Jury, S., and D.
Satterwhite, "Dynamic Link Exchange Protocol (DLEP)",
draft-ietf-manet-dlep-04 , March 2013.
Rogge & Baccelli Expires October 24, 2015 [Page 14]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
[MOBICOM03]
De Couto, D., Aguayo, D., Bicket, J., and R. Morris, "A
High-Throughput Path Metric for Multi-Hop Wireless
Routing", Proceedings of the MOBICOM Conference , 2003.
[MOBICOM04]
Richard, D., Jitendra, P., and Z. Brian, "Routing in
Multi-Radio, Multi-Hop Wireless Mesh Networks",
Proceedings of the MOBICOM Conference , 2004.
[OLSR.org]
"The OLSR.org OLSR routing daemon", 2013,
<http://www.olsr.org/>.
[FREIFUNK]
"Freifunk Wireless Community Networks", 2013,
<http://www.freifunk.net>.
[FUNKFEUER]
"Austria Wireless Community Network", 2013,
<http://www.funkfeuer.at>.
Appendix A. OLSR.org metric history
The Funkfeuer [FUNKFEUER] and Freifunk networks [FREIFUNK] are OLSR-
based [RFC3626] or B.A.T.M.A.N. based wireless community networks
with hundreds of routers in permanent operation. The Vienna
Funkfeuer network in Austria, for instance, consists of 400 routers
(around 600 routes) covering the whole city of Vienna and beyond,
spanning roughly 40km in diameter. It has been in operation since
2003 and supplies its users with Internet access. A particularity of
the Vienna Funkfeuer network is that it manages to provide Internet
access through a city wide, large scale Wi-Fi MANET, with just a
single Internet uplink.
Operational experience of the OLSR project [OLSR.org] with these
networks have revealed that the use of hop-count as routing metric
leads to unsatisfactory network performance. Experiments with the
ETX metric [MOBICOM03] were therefore undertaken in parallel in the
Berlin Freifunk network as well as in the Vienna Funkfeuer network in
2004, and found satisfactory, i.e., sufficiently easy to implement
and providing sufficiently good performance. This metric has now
been in operational use in these networks for several years.
The ETX metric of a link is the estimated number of transmissions
required to successfully send a packet (each packet equal to or
smaller than MTU) over that link, until a link layer acknowledgement
Rogge & Baccelli Expires October 24, 2015 [Page 15]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
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.
While the ETX metric delivers a reasonable performance, it doesn't
handle well networks with heterogeneous links that have different
bitrates. Since every wireless link, when using ETX metric, is
characterized only by its packet loss ratio, the ETX metric prefers
long-ranged links with low bitrate (with low loss ratios) over short-
ranged links with high bitrate (with higher but reasonable loss
ratios). Such conditions, when they occur, can degrade the
performance of a network considerably by not taking advantage of
higher capacity links.
Because of this the OLSR.org project has implemented the Directional
Airtime Metric for OLSRv2, which has been inspired by the Estimated
Travel Time (ETT) metric [MOBICOM04]. This metric uses an
unidirectional packet loss, but also takes the bitrate into account
to create a more accurate description of the relative costs or
capabilities of OLSRv2 links.
Appendix B. Linkspeed stabilization
The DAT metric describes how to generate a reasonable stable packet
loss value from incoming packet reception/loss events, the source of
the linkspeed used in this document is considered an external
process.
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
useful for the DAT metric.
The amount of stabilization necessary for the linkspeed depends on
the implementation of the mac-layer, especially the rate control
algorithm.
Experiments with the Linux 802.11 wifi stack have shown that a simple
Median filter over a series of raw linkspeed measurements can smooth
the calculated value without introducing intermediate linkspeed
values you would get by using averaging or an exponential weighted
moving average.
Authors' Addresses
Henning Rogge
Fraunhofer FKIE
Email: henning.rogge@fkie.fraunhofer.de
URI: http://www.fkie.fraunhofer.de
Rogge & Baccelli Expires October 24, 2015 [Page 16]
Internet-Draft Directional airtime metric for OLSRv2 April 2015
Emmanuel Baccelli
INRIA
Email: Emmanuel.Baccelli@inria.fr
URI: http://www.emmanuelbaccelli.org/
Rogge & Baccelli Expires October 24, 2015 [Page 17]