Optimized Link State Routing Protocol: Difference between revisions

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{{Short description|IP routing protocol optimized for mobile ad hoc networks}}
{{Redirect|OLSR|ordinary least squares regression|Ordinary least squares}}

[[File:Olsr-overview.pdf|thumb|460px|Diagram of OLSR data flow.]]

The '''Optimized Link State Routing Protocol''' ('''OLSR''')<ref name=":6">RFC{{cite IETF |title=Optimized Link State Routing Protocol (OLSR) |rfc=3626 |author1=Thomas Heide Clausen |author2=Philippe Jacquet |date=October 2003 |publisher=[[Internet Engineering Task Force|IETF]] |access-date=22 October 2024}}</ref> is an [[Internet Protocol|IP]] routing protocol optimized for [[mobile ad hoc network]]s, which can also be used on other [[wireless ad hoc network]]s. OLSR is a proactive [[link-state routing protocol]], which uses ''hello'' and ''topology control'' (TC) messages to discover and then disseminate link state information throughout the mobile ad hoc network. Individual nodes use this topology information to compute next hop destinations for all nodes in the network using shortest hop forwarding paths.

== Features specific to OLSR ==

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Multipoint relays (MPRs) relay messages between nodes. They also have the main role in [[routing]] and selecting the proper route from any source to any desired destination node.

MPRs advertise link-state information for their MPR selectors (a node selected as a MPR) periodically in their control messages. MPRs are also used to form a route from a given node to any destination in route calculation. Each node periodically broadcasts a Hello message for the link sensing, neighbor detection and MPR selection processes.<ref>''Performance Comparison of Wireless Mobile AdHoc Network Routing'' - Arun Kumar, Lokanatha C. Reddy , Prakash S. Hiremath {{clarify|date=March 2013}}</ref>

== Benefits ==

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The routing overhead generated, while generally greater than that of a reactive protocol, does not increase with the number of routes being created.

Default and network routes can be injected into the system by ''Host and Network Association'' (HNA) messages allowing for connection to the internet or other networks within the OLSR [[MANET]] cloud. Network routes are something reactive protocols do not currently execute well.

Timeout values and validity information is contained within the messages conveying information allowing for differing timer values to be used at differing nodes.

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Being a link-state protocol, OLSR requires a reasonably large amount of [[Bandwidth (computing)|bandwidth]] and CPU power to compute optimal paths in the network. In the typical networks where OLSR is used (which rarely exceed a few hundreds of nodes), this does not appear to be a problem.

By only using MPRs to flood topology information, OLSR removes some of the redundancy of the flooding process, which may be a problem in networks with moderate to large packet loss rates<ref>{{cite journalconference|author1=M. Abolhasan |author2=B. Hagelstein |author3=J. C.-P. Wang |title=Real-world performance of current proactive multi-hop mesh protocols|year=2009|url=http://ro.uow.edu.au/infopapers/736/ |conference=15th Asia-Pacific Conference on Communications}}</ref> – however the MPR mechanism is self-pruning (which means that in case of packet losses, some nodes that would not have retransmitted a packet, may do so).

== Messages ==

OLSR makes use of "Hello" messages to find its one hop neighbors and its two hop neighbors through their responses. The sender can then select its multipoint relays (MPR) based on the one hop node that offers the best routes to the two hop nodes. Each node has also an MPR selector set, which enumerates nodes that have selected it as an MPR node. OLSR uses topology control (TC) messages along with MPR forwarding to disseminate neighbor information throughout the network. ''Host and network association'' (HNA) messages are used by OLSR to disseminate network route advertisements in the same way TC messages advertise host routes.

=== HiHello ===

[[Image:olsr-hello-packet.png]]

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== Other approaches ==

The problem of routing in ad hoc wireless networks is actively being researched, and OLSR is but one of several proposed solutions. To many, it is not clear whether a whole new protocol is needed, or whether [[OSPF]] could be extended with support for wireless interfaces.<ref>{{cite IETF |title=Extensions to OSPF to Support Mobile Ad Hoc Networking, |rfc=5820 |author1=Madhavi Chandra, |author2=Abhay Roy, Mar|date=March 2010 |publisher=[[Internet Engineering Task Force|IETF]] |access-10,date=22 RFCOctober 58202024}}</ref><ref>{{cite IETF |title=Mobile Ad Hoc Network (MANET) Extension of OSPF usingUsing Connected Dominating Set (CDS) Flooding, |rfc=5614|author1=Richard Ogier, |author2=Phil Spagnolo, Aug|date=August 2009 |publisher=[[Internet Engineering Task Force|IETF]] |access-09,date=22 RFCOctober 56142024}}</ref>

In bandwidth- and power-starved environments, it is interesting to keep the network silent when there is no traffic to be routed. Reactive routing protocols do not maintain routes, but build them on demand. As link-state protocols require database synchronisation, such protocols typically use the distance vector approach, as in [[AODV]] and [[DSDV]], or more ad hoc approaches that do not necessarily build optimal paths, such as [[Dynamic Source Routing]].

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== OLSR version 2 ==

OLSRv2 has beenwas published by the IETF in April 2014 as a standards-track protocol.<ref name=":0">RFC{{cite IETF |title=The Optimized Link State Routing Protocol Version 2 |rfc=7181 |author1=Thomas Heide Clausen |author2=Christopher Dearlove |author3=Philippe Jacquet |author4=Ulrich Herberg |date=April 2014 |publisher=[[Internet Engineering Task Force|IETF]] |access-date=22 October 2024}}</ref> It maintains many of the key features of the original including MPR selection and dissemination. Key differences are the flexibility and modular design using shared components: packet format packetbb, and neighborhood discovery protocol NHDP. These components are being designed to be common among next generation IETF MANET protocols. Differences in the handling of multiple address and interface enabled nodes is also present between OLSR and OLSRv2.

== Implementations ==

* [https://web.archive.org/web/20150408143413/http://www.olsr.org/ OLSR.ORG] – Downloadable code for OLSR on Linux, Windows, Mac OS X, FreeBSD, NetBSD and [[OpenBSD]] systems. Features a great deal of documentation, including an informative survey of related work.

* [https://archive.today/20121212232316/http://cs.itd.nrl.navy.mil/work/olsr/index.php NRL-OLSR] – Open source code of NRL-OLSR. Works on Windows, MacOS, Linux, and various embedded PDA systems such as Arm/Zaurus and PocketPC as well as simulation environments [[ns (simulator)|ns2]] and OPNET., http://cs.itd.nrl.navy.mil/focus/ {{Webarchive|url=https://web.archive.org/web/20110910024912/http://cs.itd.nrl.navy.mil/focus/ |date=2011-09-10 }}

* [httphttps://sourceforge.net/projects/wmolsr/ SOURCEFORGE.NET-OLSR] – Created by MOVIQUITY and based on studies within the project Workpad, it offers a code in C# to deploy a MANET (Ad Hoc, Meshnet) with protocol OLSR. Developed for WM 6, Win XP and can be adapted to other platforms using .Net Framework and Compact. httphttps://sourceforge.net/projects/wmolsr/

== See also ==

* [[B.A.T.M.A.N.]], Better Approach To Mobile Adhoc Networking

* [[IEEE 802.1aq]]

* [[TRILL (computing)|TRILL]], TRansparentTransparent Interconnection of Lots of Links

== References ==

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* [https://web.archive.org/web/20040912075427/http://hipercom.inria.fr/olsr/ Optimized Link State Routing], which includes this [https://web.archive.org/web/20051013011753/http://hipercom.inria.fr/olsr/mpr-flooding.html Flash Demo].

* [http://pyramid.metrix.net/ Pyramid Linux] – an embedded distro for [http://metrix.net/ embedded x86 boards] with OLSR, web interface, etc. Primarily used in Community Networks.

* [https://archive.today/20121212030031/http://cs.itd.nrl.navy.mil/focus/ NRL's Networks and Communication Systems Branch] – includes project information and open source networking tools and software developed by the U.S. Naval Research Lab.

{{Routing protocols}}