Ad-hoc routing protocols for MANET:

• Mobile Ad-hoc networks (MANETs) are collections of mobile nodes dynamically establishing short lived networks in the absence of fixed infrastructure.
• Each mobile node is equipped with a wireless transmitter and a receiver with an appropriate antenna.
• Nodes in MANET are free to move and organize themselves in an arbitrary manner.These nodes are connected bye wireless links and acts as a routers for all other mobile nodes in the network.
• An Ad-hoc routing protocol is a standard that controls how mobile nodes decide which way to route packets better computing devices in a mobile ad-hoc network.
• In MANET, mobile nodes are not familiar with the topology of their network in the beginning;instead, they have to discover it.
• A new node may announce its presence and should listen for announcements broadcast by it neighbors.
• Each node learns about nodes nearby and how to reach the and may announce that it too can reach them.

Ad-hoc network protocols can be classified as follows:

A) Proactive (Table-Driven) Routing protocols:

This type of protocols maintain fresh list of destinations and their routes by periodically distributing routing tables through the network. Example: Destination sequenced distance vector (DSDV) routing protocols.

B) Reactive (On-Demand) Routing protocols:

This type of protocol finds a route on demand by flooding the network with route request packets. Example: Dynamic source routing (DSR) and Ad-hoc on demand distance vector (AODV) routing protocol.

C) Hybrid (Both proactive and reactive) Routing protocols:

This type of protocol combines the advantage of proactive and reactive routing. Example: Zone routing protocols.

D) Hierarchical Routing protocols:

With this type of protocol the choice of proactive and reactive routing depends on hierarchical level where a mobile node resides. Example: Cluster based routing protocol (CBRP)

E) Adaptive (Situation-Aware) Routing protocols:

This type of protocols also combines the advantage of proactive and reactive routing.This routing initially established with same proactively prospected routes and then serves the demand from additionally activated nodes through reactive flooding.Example: Temporally ordered routing algorithm (TORA)

F) Flow oriented Routing protocols:

This type of protocols find a route on demand by following the present flow. example: Preferred link base routing protocol,Multi path On demand routing protocols.