The Optimized Link State Routing Protocol (OLSR) [1] is an IP routing protocol optimized for mobile ad hoc networks, which can also be used on other wireless ad hoc networks. 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.
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 relays (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 (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. [2]
Being a proactive protocol, routes to all destinations within the network are known and maintained before use. Having the routes available within 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 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.
The original definition of OLSR does not include any provisions for sensing of link quality; it simply assumes that a link is up if a number of hello packets have been received recently. This assumes that links are bi-modal (either working or failed), which is not necessarily the case on wireless networks, where links often exhibit intermediate rates of packet loss. Implementations such as the open source OLSRd (commonly used on Linux-based mesh routers) have been extended (as of v. 0.4.8) with link quality sensing.
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 CPU power, the open source OLSRd project showed that large scale mesh networks can run with OLSRd on thousands of nodes with very little CPU power on 200 MHz embedded devices. [ citation needed ]
Being a link-state 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 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 [3] – 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).
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.
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. [4] [5]
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.
OLSRv2 has been published by the IETF in April 2014. [6] 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.
Routing is the process of selecting a path for traffic in a network or between or across multiple networks. Broadly, routing is performed in many types of networks, including circuit-switched networks, such as the public switched telephone network (PSTN), and computer networks, such as the Internet.
Open Shortest Path First (OSPF) is a routing protocol for Internet Protocol (IP) networks. It uses a link state routing (LSR) algorithm and falls into the group of interior gateway protocols (IGPs), operating within a single autonomous system (AS).
Link-state routing protocols are one of the two main classes of routing protocols used in packet switching networks for computer communications, the others being distance-vector routing protocols. Examples of link-state routing protocols include Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS).
A wireless mesh network (WMN) is a communications network made up of radio nodes organized in a mesh topology. It can also be a form of wireless ad hoc network.
Ad hoc On-Demand Distance Vector (AODV) Routing is a routing protocol for mobile ad hoc networks (MANETs) and other wireless ad hoc networks. It was jointly developed by Charles Perkins and Elizabeth Royer and was first published in the ACM 2nd IEEE Workshop on Mobile Computing Systems and Applications in February 1999.
Dynamic Source Routing (DSR) is a routing protocol for wireless mesh networks. It is similar to AODV in that it forms a route on-demand when a transmitting node requests one. However, it uses source routing instead of relying on the routing table at each intermediate device.
The OrderOne MANET Routing Protocol is an algorithm for computers communicating by digital radio in a mesh network to find each other, and send messages to each other along a reasonably efficient path. It was designed for, and promoted as working with wireless mesh networks.
The Hazy-Sighted Link State Routing Protocol (HSLS) is a wireless mesh network routing protocol being developed by the CUWiN Foundation. This is an algorithm allowing computers communicating via digital radio in a mesh network to forward messages to computers that are out of reach of direct radio contact. Its network overhead is theoretically optimal, utilizing both proactive and reactive link-state routing to limit network updates in space and time. Its inventors believe it is a more efficient protocol to route wired networks as well. HSLS was invented by researchers at BBN Technologies.
Flooding is used in computer network routing algorithms in which every incoming packet is sent through every outgoing link except the one it arrived on.
A wireless ad hoc network (WANET) or mobile ad hoc network (MANET) is a decentralized type of wireless network. The network is ad hoc because it does not rely on a pre-existing infrastructure, such as routers or wireless access points. Instead, each node participates in routing by forwarding data for other nodes. The determination of which nodes forward data is made dynamically on the basis of network connectivity and the routing algorithm in use.
The Better Approach to Mobile Ad-hoc Networking (B.A.T.M.A.N.) is a routing protocol for multi-hop mobile ad hoc networks which is under development by the German "Freifunk" community and intended to replace the Optimized Link State Routing Protocol (OLSR) as OLSR did not meet the performance requirements of large-scale mesh deployments.
A routing protocol specifies how routers communicate with each other to distribute information that enables them to select paths between nodes on a computer network. Routers perform the traffic directing functions on the Internet; data packets are forwarded through the networks of the internet from router to router until they reach their destination computer. Routing algorithms determine the specific choice of route. Each router has a prior knowledge only of networks attached to it directly. A routing protocol shares this information first among immediate neighbors, and then throughout the network. This way, routers gain knowledge of the topology of the network. The ability of routing protocols to dynamically adjust to changing conditions such as disabled connections and components and route data around obstructions is what gives the Internet its fault tolerance and high availability.
The Wireless Routing Protocol (WRP) is a proactive unicast routing protocol for mobile ad hoc networks (MANETs).
Vehicular Reactive Routing protocol (VRR) is a reactive routing protocol with geographical features which is specifically designed for Wireless Access for the Vehicular Environment (WAVE) standard in vehicular ad hoc networks (VANETs). The protocol takes advantages of the multichannel scheme defined in WAVE and uses the Control Channel (CCH) for signalling, and relies on one of the multiple Service Channels (SCHs) for payload data dissemination.
Topology control is a technique used in distributed computing to alter the underlying network to reduce the cost of distributed algorithms if run over the resulting graphs. It is a basic technique in distributed algorithms. For instance, a (minimum) spanning tree is used as a backbone to reduce the cost of broadcast from O(m) to O(n), where m and n are the number of edges and vertices in the graph, respectively.
Scalable Source Routing (SSR) is a routing protocol for unstructured networks such as mobile ad hoc networks, mesh networks, or sensor networks. It combines source routing with routing along a virtual ring, and is based on the idea of "pushing Chord into the underlay".
IEEE 802.11s is a wireless local area network (WLAN) standard and an IEEE 802.11 amendment for mesh networking, defining how wireless devices can interconnect to create a wireless LAN mesh network, which may be used for relatively fixed topologies and wireless ad hoc networks. The IEEE 802.11s task group drew upon volunteers from university and industry to provide specifications and possible design solutions for wireless mesh networking. As a standard, the document was iterated and revised many times prior to finalization.
Fisheye State Routing (FSR) is a proposal for an implicit hierarchical routing protocol targeted to ad hoc networks. The basic principles of FSR are shared with other proactive, link-state routing protocols. In proactive link-state protocols every network node constantly updates a topology map that makes it possible to compute the shortest path to any destination in the network. The originality of FSR is inspired by the "fisheye" technique to reduce the size of information required to represent graphical data: The eye of a fish captures with high detail the pixels near the focal point, while the detail decreases as the distance from the focal point increases.
A mobile wireless sensor network (MWSN) can simply be defined as a wireless sensor network (WSN) in which the sensor nodes are mobile. MWSNs are a smaller, emerging field of research in contrast to their well-established predecessor. MWSNs are much more versatile than static sensor networks as they can be deployed in any scenario and cope with rapid topology changes. However, many of their applications are similar, such as environment monitoring or surveillance. Commonly, the nodes consist of a radio transceiver and a microcontroller powered by a battery, as well as some kind of sensor for detecting light, heat, humidity, temperature, etc.
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