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The '''Optimized Link State Routing Protocol''' ('''OLSR''')<ref>RFC 3626</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. [[File:Olsr-overview.pdf|thumb|Diagram of OLSR data flow.]]
== Features specific to OLSR ==
Link-state routing protocols such as [[Open Shortest Path First]] (OSPF) and [[IS-IS]] elect a ''designated router'' on every link to perform flooding of topology information. In wireless ad- hoc networks, there is different notion of a link, packets can and do go out the same interface; hence, a different approach is needed in order to optimize the flooding process. Using Hello messages the OLSR protocol at each node discovers 2-hop neighbor information and performs a distributed election of a set of ''[[multipoint relay]]s'' (MPRs). Nodes select MPRs such that there exists a path to each of its 2-hop neighbors via a node selected as an MPR. These MPR nodes then source and forward TC messages that contain the MPR selectors. This functioning of MPRs makes OLSR unique from other link state routing protocols in a few different ways: The forwarding path for TC messages is not shared among all nodes but varies depending on the source, only a subset of nodes source link state information, not all links of a node are advertised but only those that represent MPR selections.
Since link-state routing requires the topology database to be synchronized across the network, OSPF and IS-IS perform topology flooding using a reliable algorithm. Such an algorithm is very difficult to design for ad- hoc wireless networks, so OLSR doesn't bother with reliability; it simply floods topology data often enough to make sure that the database does not remain unsynchronized for extended periods of time.
== Benefits ==
== 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>Extensions to OSPF to Support Mobile Ad Hoc Networking, Madhavi Chandra, Abhay Roy, Mar-10, RFC 5820</ref><ref>MANET Extension of OSPF using CDS Flooding, Richard Ogier, Phil Spagnolo, Aug-09, RFC 5614</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]].
For more information see the [[list of ad- hoc routing protocols]].
== OLSR version 2 ==
* [http://www.olsr.org/ OLSR.ORG] – Downloadable code for OLSR on GNU/Linux, Windows, Mac OS X, FreeBSD and NetBSD systems. Features a great deal of documentation, including an informative survey of related work.
* [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 [[ns2]] and OPNET., http://cs.itd.nrl.navy.mil/focus/
* [http://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. http://sourceforge.net/projects/wmolsr/
== See also ==
* [[B.A.T.M.A.N.]] Better approach to mobile ad- hoc networking
* [[Robin-Mesh]] RO.B.IN – routing batman inside
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