Optimized Link State Routing Protocol
The Optimized Link State Routing Protocol (OLSR) is a proactive (or table-driven) link-state routing protocol specifically designed for mobile ad hoc networks (MANETs). It can also be utilized in other wireless ad hoc networks. Routes are always available before they are needed because OLSR is a proactive protocol that continuously maintains routing information for all network destinations. This removes route discovery delays and helps applications that need low latency.
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How OLSR Works
OLSR optimizes traditional link-state routing by introducing the notion of Multipoint Relays (MPRs). Here’s a breakdown of its basic mechanisms:
Hello Messages: To find its one-hop and two-hop neighbors, every node sends out “Hello” messages on a regular basis. The MPR selection process depends on this information.
Multipoint Relays (MPRs): Instead of every node retransmitting all control messages, OLSR designates a set of MPRs. By forwarding broadcast messages, these chosen nodes drastically cut down on message redundancy and network overhead. To cover all strict two-hop neighbors with the fewest number of MPRs possible, a node chooses MPRs from its one-hop neighbors based on which neighbors provide the greatest paths to its two-hop neighbors. MPRs also have a key function in routing and selecting the right path from any source to any desired destination. Periodically, they use their control messages to promote link-state information for their MPR selectors, or nodes that have selected them as MPRs.
Topology Control (TC) Messages: MPRs send out TC messages to the network on a regular basis. These messages enable other nodes to construct a comprehensive representation of the network architecture by providing link-state information about their MPR selectors (nodes that have selected them as MPRs). Only links that represent MPR selections are advertised, and only a subset of nodes (MPRs) source link-state information.
Host and Network Association (HNA) Messages: In the same way as TC messages advertise host routes, these messages are used to promote network routes. They make it possible to connect to the OLSR MANET cloud’s other networks or the internet.
Route Calculation: Each node uses the disseminated link-state information to independently calculate the shortest path (in terms of hop count) to all other destinations in the network, typically using an algorithm like Dijkstra’s. These routes are subsequently put in the node’s routing database.
Key Features and Advantages
OLSR offers several benefits for mobile ad hoc networks:
Proactive Nature: Low-latency applications benefit from routes’ constant availability, which removes delays in route discovery.
Reduced Overhead: In comparison to conventional link-state protocols, the MPR method drastically lowers the quantity of control messages that are flooded, conserving bandwidth and reducing the issue of broadcast storms. Although it is often higher than reactive protocols, the routing overhead does not rise as more routes are generated.
Optimized/Shortest Routes: OLSR offers the best routes based on the number of hops.
Scalability: Because of its lower control message overhead, it is typically seen as appropriate for big, dense ad hoc networks.
Decentralized: This protocol is perfect for ad hoc settings because it does not require a central administrative system.
Robustness: It has a reasonable ability to adapt to changes in the dynamic network topology.
Multiple Routes: By identifying several routes between source and destination nodes, OLSR helps improve the resilience and dependability of networks.
Energy Efficiency: Some sources indicate OLSR is meant to be energy-efficient by decreasing broadcast messages and improving the routing process, making it suited for wireless networks with limited battery capacity. But in other situations, this is also mentioned as a drawback.
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Disadvantages of Optimized Link State Routing Protocol
Despite its advantages, OLSR has some drawbacks:
Resource Consumption: Being proactive can require more power, bandwidth, and CPU power than reactive protocols, especially in networks with numerous nodes, occasional communication, or when the network is inactive, as it propagates data about possibly unused routes. Because of this, it is less appropriate for sensor networks that aim to sleep the majority of the time.
Scalability Limits: Although superior to certain protocols, large network sizes (thousands of nodes) can still result in overhead problems and larger routing tables.
Limited QoS Support: Standard OLSR doesn’t automatically provide strong Quality of Service (QoS) guarantees, which might be troublesome for applications requiring specified levels of bandwidth, latency, or packet loss.
Increased Latency: Some sources say OLSR may bring additional latency due to the time it takes to locate and update routes, particularly in real-time applications.
Susceptible to Security Attacks: Due to its dependence on broadcast messages, it is susceptible to security threats such as black hole and spoofing attacks.
Difficulty in Configuration: Because numerous settings must be properly tuned for OLSR to function at its best, it can be difficult to set up, particularly for novices.
Link Quality Sensing: Since links are assumed to be bi-modal (either successful or unsuccessful), which isn’t necessarily the case in wireless networks with different packet loss rates, the original definition omits facilities for link quality sensing. Implementations like OLSRd have been extended with link quality sensing.
Redundancy: Some redundancy of the flooding process is eliminated by relying solely on MPRs for flooding, which could be problematic in networks with moderate to high packet loss rates.
Applications
OLSR is well-suited for various scenarios:
- Mobile Ad Hoc Networks (MANETs): Its primary design focus.
- Community Networks.
- Military Communications: For establishing and maintaining communication links between military vehicles and personnel.
- Disaster Response Networks: For establishing communication links between emergency responders.
- Vehicular Ad Hoc Networks (VANETs).
- Industrial Automation: For communication links between sensors and devices in industrial settings.
- Wireless Sensor Networks.
- Internet of Things (IoT): For managing dynamic networks and communication links between devices.
- Smart Urban Areas: For monitoring and control of city aspects like traffic, pollution, and public safety.
- Wireless Mesh Networks (WMNs).
- Multimedia Streaming: For high-bandwidth communication links.
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