Routing Protocols for MANET
MANET stands for Mobile Adhoc Network also called a wireless Adhoc network or Adhoc wireless network that usually has a routable networking environment on top of a Link Layer ad hoc network.. They consist of a set of mobile nodes connected wirelessly in a self-configured, self-healing network without having a fixed infrastructure. MANET nodes are free to move randomly as the network topology changes frequently. Each node behaves as a router as they forward traffic to other specified nodes in the network.
MANET may operate a standalone fashion or they can be part of larger internet. They form a highly dynamic autonomous topology with the presence of one or multiple different transceivers between nodes.
For Example : Consider a network with nodes N1, N2, N3, N4, N5 & N6 and N1 wants to send data packet N6. So with the help of concept of routing and routing protocols, a shortest path will be defined simultaneously the data packet reaches a particular node.
Route 1: N1 -> N2 -> N3 -> N4 -> N6.
Route 2: N1 -> N2 -> N3 -> N6.
Route 3: N1 -> N2 -> N6.
Here, Route 3 will be the shortest path and packet will be sent through this path only.
Characteristics of MANET –
- Dynamic Topologies:
Network topology which is typically multihop may change randomly and rapidly with time, it can form unidirectional or bi-directional links.
- Bandwidth constrained, variable capacity links:
Wireless links usually have lower reliability, efficiency, stability, and capacity as compared to a wired network
- Autonomous Behavior:
Each node can act as a host and router, which shows its autonomous behavior.
- Energy Constrained Operation:
As some or all the nodes rely on batteries or other exhaustible means for their energy. Mobile nodes are characterized by less memory, power, and lightweight features.
- Limited Security:
Wireless networks are more prone to security threats. A centralized firewall is absent due to the distributed nature of the operation for security, routing, and host configuration.
- Less Human Intervention:
They require minimum human intervention to configure the network, therefore they are dynamically autonomous in nature.
Types of MANET in Computer Network
1. Pro-active routing protocols:
These are also known as table-driven routing protocols. Each mobile node maintains a separate routing table which contains the information of the routes to all the possible destination mobile nodes.
Since the topology in the mobile ad-hoc network is dynamic, these routing tables are updated periodically as and when the network topology changes. It has a limitation that is doesn’t work well for the large networks as the entries in the routing table becomes too large since they need to maintain the route information to all possible nodes.
- Destination Sequenced Distance Vector Routing Protocol (DSDV):
It is a pro-active/table driven routing protocol. It actually extends the distance vector routing protocol of the wired networks as the name suggests. It is based on the Bellman-ford routing algorithm. Distance vector routing protocol was not suited for mobile ad-hoc networks due to count-to-infinity problem. Hence, as a solution Destination Sequenced Distance Vector Routing Protocol (DSDV) came into picture.
Destination sequence number is added with every routing entry in the routing table maintained by each node. A node will include the new update in the table only if the entry consists of the new updated route to the destination with higher sequence number.
2. Global State Routing (GSR):
It is a pro-active/table driven routing protocol. It actually extends the link state routing of the wired networks. It is based on the Dijkstra’s routing algorithm. Link state routing protocol was not suited for mobile ad-hoc networks because in it, each node floods the link state routing information directly into the whole network i.e. Global flooding which may lead to the congestion of control packets in the network.
Hence, as a solution Global State Routing Routing Protocol (GSR) came into the picture. Global state routing doesn’t flood the link state routing packets globally into the network. In GSR, each of the mobile node maintains one list and three tables namely, adjacency list, topology table, next hop table and distance table.
2. Reactive routing protocols:
These are also known as on-demand routing protocol. In this type of routing, the route is discovered only when it is required/needed. The process of route discovery occurs by flooding the route request packets throughout the mobile network. It consists of two major phases namely, route discovery and route maintenance.
- Dynamic Source Routing protocol (DSR):
It is a reactive/on-demand routing protocol. In this type of routing, the route is discovered only when it is required/needed. The process of route discovery occurs by flooding the route request packets throughout the mobile network.
It consists of two phases:
- Route Discovery:
This phase determines the most optimal path for the transmission of data packets between the source and the destination mobile nodes.
- Route Maintenance:
This phase performs the maintenance work of the route as the topology in the mobile ad-hoc network is dynamic in nature and hence, there are many cases of link breakage resulting in the network failure between the mobile nodes.
2. Ad-Hoc On Demand Vector Routing protocol (AODV):
It is a reactive/on-demand routing protocol. It is an extension of dynamic source routing protocol (DSR) and it helps to remove the disadvantage of dynamic source routing protocol. In DSR, after route discovery, when the source mobile node sends the data packet to the destination mobile node, it also contains the complete path in its header. Hence, as the network size increases, the length of the complete path also increases and the data packet’s header size also increases which makes the whole network slow.
Hence, Ad-Hoc On Demand Vector Routing protocol came as solution to it. The main difference lies in the way of storing the path, AODV stores the path in the routing table whereas DSR stores it in the data packet’s header itself. It also operates in two phases in the similar fashion: Route discovery and Route maintenance.
3. Hybrid Routing protocol:
It basically combines the advantages of both, reactive and pro-active routing protocols. These protocols are adaptive in nature and adapts according to the zone and position of the source and destination mobile nodes. One of the most popular hybrid routing protocol is Zone Routing Protocol (ZRP).
The whole network is divided into different zones and then the position of source and destination mobile node is observed. If the source and destination mobile nodes are present in the same zone, then proactive routing is used for the transmission of the data packets between them. And if the source and destination mobile nodes are present in different zones, then reactive routing is used for the transmission of the data packets between them.
Pros and Cons of MANET –
- Separation from central network administration.
- Each node can play both the roles ie. of router and host showing autonomous nature.
- Self-configuring and self-healing nodes do not require human intervention.
- Resources are limited due to various constraints like noise, interference conditions, etc.
- Lack of authorization facilities.
- More prone to attacks due to limited physical security.
As conclusion I would like to say that both proactive and reactive protocols have their own set of pros and cons. Proactive protocols have large amount of data for maintenance with high cost and slow reaction on restructuring and failures, route setup latency is low, not suitable for large highly dynamic network. Reactive protocols have high latency time in route failure, excessive flooding can lead to network clogging, scalability problem, low routing overhead, quick reaction for network restructure and node failure. Hybrid protocols are complex, advantages depend upon the number of nodes activated, low routing overhead, less route setup latency.