Optimized Link State Routing Protocol: Difference between revisions

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{{Short description|IP routing protocol optimized for mobile ad hoc networks}}

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.]]

{{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. [[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 [[Intermediate System to Intermediate System]] (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.

===Multipoint relays===

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 proactive protocol, OLSR uses power and network resources in order to propagate data about possibly unused routes. While this is not a problem for wired access points, and laptops, it makes OLSR unsuitable for sensor networks that try to sleep most of the time.

For small scale wired access points with low [[Central processing unit|CPU]] power, the open source [https://web.archive.org/web/20150408143413/http://www.olsr.org/ OLSRd] project showed that large scale mesh networks can run with OLSRd on thousands of nodes with very little CPU power on {{val|200|ul=MHz}} embedded devices. {{Citation needed|reason=We need a source for "large scale mesh networks ..." and "very little CPU power" |date=June 2019}}

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|authorauthor1=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 ==

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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 iswas currentlypublished being developed withinby the IETF in April 2014 as a standards-track protocol.<ref name=":0">{{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 GNU/Linux, Windows, Mac OS X, FreeBSD, NetBSD and NetBSD[[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.Net Framework and Compact. httphttps://sourceforge.net/projects/wmolsr/

== See also ==

* [[B.A.T.M.A.N.]], Better approachApproach toTo mobileMobile adAdhoc hoc networkingNetworking

* [[IEEE 802.1aq]]

* [[Robin-Mesh]] RO.B.IN – routing batman inside

* [[TRILL]], Transparent Interconnection of Lots of Links

== References ==

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== External links ==

* [https://web.archive.org/web/20130112003204/http://www.ietf.org/ IETF Home Page] The Internet Engineering Task Force standards body

* [http://olsr.funkfeuer.at olsr.funkfeuer.at] currently advancing the olsr.org implementation to improve scalability

* [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}}