Optimized Link State Routing

from Wikipedia, the free encyclopedia

Optimized Link State Routing , or OLSR for short, is a routing protocol for mobile ad-hoc networks that is a version of Link State Routing that is adapted to the requirements of a mobile wireless LAN . The protocol is described in RFC 3626 .

With this distributed and flexible routing method , all nodes (routers) know the network topology so that they can determine the shortest route to the destination on a case-by-case basis. As a proactive routing protocol , it keeps the information required for this ready at all times. Additional connections can be used for redundancy. OLSR can improve performance, especially in dense networks.

The protocol is implemented in olsrd.

OLSR is used, along with other protocols, in Freifunk networks and research.

Overview

A device (node) participating in the network looks for other nodes within range, so-called multipoint relays (MPR), via which messages are then forwarded. A bidirectional connection is a condition for being chosen as MPR. The choice of MPRs is made known to the other nodes, which means that messages are not transmitted to all nodes in range. Thanks to the proactive distribution of route information, each node can calculate the shortest route between two points at any time. Additional information about the topology can be shared between the nodes for redundancy purposes. The protocol works completely decentrally, and a secure transmission of control messages is not necessary, as each node periodically passes on its information and so the loss of individual messages can be coped with. The aim of the MPRs is to reduce redundant messages. It is not specified with which other protocols OLSR is combined.

Working method

With OLSR, topology discovery takes place via two types of messages: HELLO and Topology Control (TC) messages . HELLO messages are used for link sensing, neighbor discovery and notification of the multipoint relay choice. The TC messages are used to distribute the information obtained in this way via possible connections in the network.

A device participating in the network discovers its 1-hop and 2-hop neighbors via the periodically sent HELLO messages. These contain the addresses of the already known 1-hop neighbors as well as the status of the connection to them and are not forwarded. Each node selects multipoint relays (MPRs) from its 1-hop neighbors so that it can use them to reach each of its 2-hop neighbors. The MPRs are the nodes that forward broadcast messages, which makes flooding more efficient. It is also they who compose the TC messages, which contain a list of at least the nodes from which they were chosen as MPRs, so that for each node at least one possibility is known how it can be reached. These TC messages are distributed throughout the network. In this way, each node gets an idea of ​​the network and can create routing tables.

Successor to OLSRv2

The further development of OLSRv2 is described in RFC 7181 , which refers to four previous RFCs, which were written specifically for OLSRv2, and extends them:

  • RFC 6130 . - Mobile Ad Hoc Network (MANET) Neighborhood Discovery Protocol (NHDP) . April 2011. (Updated by RFC 7466  - March 2011 - English).
  • RFC 5444 . - Generalized Mobile Ad Hoc Network (MANET) Packet / Message Format . February 2009. (Updated by RFC 8245  - October 2017 - English).
  • RFC 5497 . - Representing Multi-Value Time in Mobile Ad Hoc Networks (MANETs) - defines TLVs (type-length-value structure) . March 2009. (English).
  • RFC 5148 . - jitter . February 2008. (English).

The main difference to OLSRv1 is the more meaningful link metric instead of the pure hop count.

The protocol is implemented by olsrd2.

Other ad hoc routing protocols

  • AODV
  • BATMAN - further development of OLSRv1. Not every router knows the entire network here.

Web links