Ad Hoc Routing Protocols

Introduction

Ad hoc routing protocols play a crucial role in wireless ad hoc networks. These protocols are responsible for establishing and maintaining communication paths between nodes in a network where there is no fixed infrastructure. In this topic, we will explore the fundamentals of ad hoc routing protocols and understand the key concepts and principles associated with them.

Key Concepts and Principles

Issues in Designing a Routing Protocol for Ad Hoc Wireless Networks

Designing a routing protocol for ad hoc wireless networks poses several challenges. Some of the key issues include:

• Dynamic Network Topology: Ad hoc networks have a dynamic topology where nodes can join or leave the network at any time. The routing protocol should be able to adapt to these changes.
• Limited Network Resources: Ad hoc networks typically have limited resources such as bandwidth, battery power, and processing capabilities. The routing protocol should optimize the utilization of these resources.
• Scalability: Ad hoc networks can vary in size from a few nodes to hundreds or even thousands of nodes. The routing protocol should scale well with the network size.

Classifications of Routing Protocols

Ad hoc routing protocols can be classified into the following categories:

1. Table-Driven Routing Protocols: These protocols maintain routing tables at each node, which are periodically updated to reflect the changes in the network topology.

2. Source-Initiated On-Demand Approaches: These protocols establish routes on-demand when a node wants to send data to a destination. The routes are maintained as long as there is active communication between the nodes.

3. Signal Stability Routing: These protocols use signal strength as a metric to determine the stability of a link. Routes with higher signal strength are preferred over routes with lower signal strength.

4. Location-Aided Routing: These protocols utilize location information to make routing decisions. Nodes exchange their location information to determine the optimal path to the destination.

5. Power-Aware Routing: These protocols take into account the power levels of nodes when making routing decisions. They aim to minimize energy consumption and prolong the network lifetime.

Table-Driven Routing Protocols

Table-driven routing protocols, also known as proactive protocols, maintain routing tables at each node. These routing tables are periodically updated to reflect the changes in the network topology. Examples of table-driven routing protocols include:

• Destination-Sequenced Distance Vector (DSDV): DSDV is a proactive routing protocol that uses sequence numbers to ensure loop-free routing. It maintains a routing table with the next hop and sequence number for each destination.
• Optimized Link State Routing (OLSR): OLSR is a proactive routing protocol that uses link-state information to construct and maintain a routing table. It uses multipoint relays to reduce the flooding of control messages.

Table-driven routing protocols have the following advantages:

• Low latency: Routes are already established, so there is minimal delay in sending data.
• Robustness: Routes are always available, even if there are no active communications.

However, they also have the following disadvantages:

• High overhead: Maintaining routing tables and updating them periodically consumes network resources.
• Inefficient for large networks: The overhead increases with the network size, making them less suitable for large-scale networks.

Source-Initiated On-Demand Approaches

Source-initiated on-demand approaches, also known as reactive protocols, establish routes on-demand when a node wants to send data to a destination. The routes are maintained as long as there is active communication between the nodes. Examples of source-initiated on-demand approaches include:

• Ad hoc On-Demand Distance Vector (AODV): AODV is a reactive routing protocol that establishes routes on-demand using route discovery and route maintenance mechanisms. It uses sequence numbers to ensure loop-free routing.
• Dynamic Source Routing (DSR): DSR is a reactive routing protocol that uses source routing. The source node includes the complete route in the packet header, and intermediate nodes simply forward the packet based on this route.

Source-initiated on-demand approaches have the following advantages:

• Efficient resource utilization: Routes are only established when needed, reducing the overhead.
• Scalability: They are more scalable than table-driven protocols as they do not require maintaining routing tables for the entire network.

However, they also have the following disadvantages:

• Higher latency: Routes need to be established before data can be sent, resulting in higher delay.
• Route discovery overhead: The process of route discovery consumes network resources and can lead to increased control message overhead.

Signal Stability Routing

Signal stability routing protocols use signal strength as a metric to determine the stability of a link. Routes with higher signal strength are preferred over routes with lower signal strength. Examples of signal stability routing protocols include:

• Signal Stability-based Adaptive Routing (SSA): SSA is a routing protocol that uses signal strength as a metric to select the next hop. It aims to maximize the stability of the route by choosing links with higher signal strength.
• Signal Stability Routing (SSR): SSR is a routing protocol that uses signal strength as a metric to select the next hop. It maintains a routing table with the next hop and signal strength for each destination.

Signal stability routing protocols have the following advantages:

• Better link quality: Routes with higher signal strength are more likely to have better link quality.
• Improved reliability: By selecting routes with higher signal strength, the reliability of the communication can be improved.

However, they also have the following disadvantages:

• Limited applicability: Signal strength may not always be a reliable metric for link stability, especially in environments with interference or fading.
• Increased complexity: Measuring and maintaining signal strength information adds complexity to the routing protocol.

Location-Aided Routing

Location-aided routing protocols utilize location information to make routing decisions. Nodes exchange their location information to determine the optimal path to the destination. Examples of location-aided routing protocols include:

• Geographic Routing Protocol (GRP): GRP is a routing protocol that uses geographic information to make routing decisions. Nodes exchange their location information and use it to determine the next hop.
• Greedy Perimeter Stateless Routing (GPSR): GPSR is a routing protocol that uses greedy forwarding based on geographic information. It selects the next hop that is closest to the destination in terms of Euclidean distance.

Location-aided routing protocols have the following advantages:

• Efficient routing: By utilizing location information, routes can be established more efficiently.
• Better adaptability: Location information can help in adapting to changes in the network topology.

However, they also have the following disadvantages:

• Dependency on location information: If location information is not available or inaccurate, the routing protocol may not perform optimally.
• Increased overhead: Exchanging and maintaining location information consumes network resources.

Power-Aware Routing

Power-aware routing protocols take into account the power levels of nodes when making routing decisions. They aim to minimize energy consumption and prolong the network lifetime. Examples of power-aware routing protocols include:

• Power-Aware Routing in Mobile Ad hoc Networks (PARMAN): PARMAN is a routing protocol that considers the residual energy of nodes when making routing decisions. It selects routes that minimize the energy consumption.
• Energy-Aware Routing (EAR): EAR is a routing protocol that takes into account both the residual energy and the energy consumption rate of nodes. It aims to balance the energy consumption among nodes.

Power-aware routing protocols have the following advantages:

• Extended network lifetime: By minimizing energy consumption, the network lifetime can be prolonged.
• Better utilization of energy: Power-aware routing protocols can help in balancing the energy consumption among nodes.

However, they also have the following disadvantages:

• Increased complexity: Power-aware routing protocols require additional mechanisms to monitor and manage energy levels.
• Trade-off between energy efficiency and other metrics: Optimizing energy consumption may result in suboptimal routing decisions in terms of other metrics such as latency or throughput.

Zone Routing Protocol

The Zone Routing Protocol (ZRP) is a hybrid routing protocol that combines the advantages of proactive and reactive protocols. It divides the network into zones and uses a proactive protocol within each zone and a reactive protocol between zones. ZRP has the following advantages:

• Reduced control message overhead: Proactive protocols are used within zones, reducing the control message overhead compared to a fully proactive protocol.
• Efficient resource utilization: Reactive protocols are used between zones, minimizing the overhead in large-scale networks.

However, ZRP also has the following disadvantages:

• Increased complexity: The combination of proactive and reactive protocols adds complexity to the routing protocol.
• Dependency on zone configuration: The performance of ZRP depends on the configuration of zones.

Conclusion

In conclusion, ad hoc routing protocols are essential for establishing and maintaining communication paths in wireless ad hoc networks. They address the challenges posed by dynamic network topology, limited network resources, and scalability. By understanding the key concepts and principles of ad hoc routing protocols, network designers can choose the right protocol for specific network requirements and optimize the performance of their wireless ad hoc networks.

Summary

Ad hoc routing protocols are crucial for establishing and maintaining communication paths in wireless ad hoc networks. They address the challenges posed by dynamic network topology, limited network resources, and scalability. Ad hoc routing protocols can be classified into table-driven routing protocols, source-initiated on-demand approaches, signal stability routing, location-aided routing, and power-aware routing. Each type of protocol has its advantages and disadvantages, and network designers need to choose the right protocol based on specific network requirements. The Zone Routing Protocol (ZRP) is a hybrid routing protocol that combines the advantages of proactive and reactive protocols. By understanding the key concepts and principles of ad hoc routing protocols, network designers can optimize the performance of their wireless ad hoc networks.

Analogy

Imagine a group of people trying to communicate with each other in a crowded park without any fixed infrastructure like cell towers or Wi-Fi routers. They need to find the best paths to reach each other, taking into account factors like distance, signal strength, and available energy. Ad hoc routing protocols are like the navigation systems that guide them, helping them find the most efficient routes and ensuring reliable communication.