What Port Does The Optimized Link State Routing Service Operate On

The Optimized Link State Routing Protocol (OLSR)^[1] is an IP routing protocol optimized for mobile advertizing-hoc networks, which tin can as well be used on other wireless ad-hoc networks. OLSR is a proactive link-country routing protocol, which uses hello and topology control (TC) messages to observe so disseminate link land information throughout the mobile ad-hoc network. Individual nodes use this topology data to compute side by side hop destinations for all nodes in the network using shortest hop forwarding paths.

Diagram of OLSR information menstruum.

1 Features specific to OLSR
2 Benefits
three Criticisms
iv Messages
- four.1 Hello
- 4.two Topology control (TC)
5 Other approaches
6 OLSR version 2
vii Implementations
eight Encounter too
ix References
10 External links

Features specific to OLSR

Link-land 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 tin can and do go out the same interface; hence, a unlike approach is needed in order to optimize the flooding process. Using How-do-you-do letters the OLSR protocol at each node discovers 2-hop neighbor information and performs a distributed ballot of a set of multipoint relays (MPRs). Nodes select MPRs such that at that place exists a path to each of its two-hop neighbors via a node selected every bit an MPR. These MPR nodes then source and forwards TC messages that contain the MPR selectors. This functioning of MPRs makes OLSR unique from other link state routing protocols in a few dissimilar means: The forwarding path for TC messages is non shared among all nodes merely varies depending on the source, only a subset of nodes source link country information, not all links of a node are advertised just only those that represent MPR selections.

Since link-country routing requires the topology database to exist 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; information technology but floods topology information often enough to make sure that the database does not remain unsynchronized for extended periods of fourth dimension.

Benefits

Being a proactive protocol, routes to all destinations within the network are known and maintained earlier use. Having the routes available inside the standard routing table can be useful for some systems and network applications as there is no route discovery delay associated with finding a new route.

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

Default and network routes tin be injected into the system by HNA letters allowing for connection to the internet or other networks within the OLSR MANET deject. Network routes are something reactive protocols do not currently execute well.

Timeout values and validity information is contained inside the messages carrying information assuasive for differing timer values to be used at differing nodes.

Criticisms

The original definition of OLSR does not include any provisions for sensing of link quality; it simply assumes that a link is upward if a number of hullo packets have been received recently. This assumes that links are bi-modal (either working or failed), which is not necessarily the instance on wireless networks, where links often exhibit intermediate rates of packet loss. Implementations such every bit the open up source OLSRd (unremarkably used on Linux-based mesh routers) take been extended (as of five. 0.4.8) with link quality sensing.

Being a proactive protocol, OLSR uses power and network resources in lodge to propagate data near possibly unused routes. While this is not a problem for wired access points, and laptops, information technology makes OLSR unsuitable for sensor networks that try to sleep most of the time. For small-scale scale wired access points with low CPU power, the open source OLSRd project showed that large scale mesh networks tin run with OLSRd on thousands of nodes with very little CPU power on 200 MHz embedded devices.

Being a link-land protocol, OLSR requires a reasonably large amount of 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 non appear to exist a trouble.

By only using MPRs to flood topology data, OLSR removes some of the redundancy of the flooding process, which may be a problem in networks with moderate to big packet loss rates^[2] – however the MPR mechanism is self-pruning (which ways that in example of packet losses, some nodes that would not have retransmitted a packet, may practise so).

Messages

OLSR makes employ of "Hello" messages to find its 1 hop neighbors and its two hop neighbors through their responses. The sender tin then select its multipoint relays (MPR) based on the ane hop node that offers the all-time routes to the ii 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 clan (HNA) messages are used by OLSR to disseminate network route advertisements in the same way TC messages advertise host routes.

Hi

Topology control (TC)

Other approaches

The problem of routing in ad-hoc wireless networks is actively existence researched, and OLSR is but one of several proposed solutions. To many, information technology is not clear whether a whole new protocol is needed, or whether OSPF could be extended with back up for wireless interfaces.^[three] ^[4]

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

For more information encounter the list of advert-hoc routing protocols.

OLSR version ii

OLSRv2 is currently being adult inside the IETF. It maintains many of the key features of the original including MPR selection and dissemination. Key differences are the flexibility and modular pattern 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 accost and interface enabled nodes is also present betwixt OLSR and OLSRv2.

Implementations

OLSR.ORG – Downloadable code for OLSR on GNU/Linux, Windows, Mac OS Ten, FreeBSD and NetBSD systems. Features a keen deal of documentation, including an informative survey of related work.
NRL-OLSR – Open source code of NRL-OLSR. Works on Windows, MacOS, Linux, and various embedded PDA systems such as Arm/Zaurus and PocketPC every bit well as simulation environments ns2 and OPNET., http://cs.itd.nrl.navy.mil/focus/
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/

References

^ RFC 3626
^ M. Abolhasan, B. Hagelstein, J. C.-P. Wang (2009). Real-globe performance of electric current proactive multi-hop mesh protocols.
^ Extensions to OSPF to Support Mobile Ad Hoc Networking, Madhavi Chandra, Abhay Roy, Mar-x, RFC 5820
^ MANET Extension of OSPF using CDS Flooding, Richard Ogier, Phil Spagnolo, Aug-09, RFC 5614

External links

IETF Home Page The Internet Technology Task Force standards torso
olsr.funkfeuer.at currently advancing the olsr.org implementation to improve scalability
Optimized Link State Routing, which includes this Flash Demo.
Freifunk Firmware (English language folio) – a firmware based on OpenWRT that uses OLSR, designed to build mesh networks out of wireless admission points, due east.g. LinksysWRT54G'due south
Pyramid Linux – an embedded distro for embedded x86 boards with OLSR, web interface, etc. Primarily used in Community Networks.
NRL's Networks and Communication Systems Branch – includes project information and open source networking tools and software adult by the U.S. Naval Enquiry Lab.