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A Mobile Ad-hoc Network is defined as the group of mobile device without any infrastructure, who tend to share their information collectively for their business purpose. Ad-hoc networks are wireless networks where each mobile node communicates with each other using multi-hop radio links. In MANET there is no stationary infrastructure or base station for communication. Each node itself in MANET acts as a router for forwarding and receiving packets to/from other nodes. Routing in ad-networks has been a challenging task ever since the wireless networks came into existence. The major reason for routing is the regular change in network topology, location because of high degree of node mobility. A number of protocols have been developed for achieve this task. Some of them are discussed in this paper. The node which is leaving / joins the network has routing ability, and allowed them to make multi hop paths which are not within the radio range. The nodes which are in-between the sender / receiver node will act as router and will forward the message to next node which is coming from sender .
In MANET routing will become more challenge task because of no fixed Network Infrastructure, Dynamic Network Configuration, Mobility of Nodes, frequent node Failure and low battery power etc . MANET has its uses in the following areas:
ï‚· Creating Personal Area Network with the help of cell phones, laptops, smart watches and other wireless equipments.
ï‚· Provides with access to real-time information to the mobile user, even when they are away from their home or office.
ï‚· MANET can be extended to places which cannot be wired.
ï‚· MANET can form a temporary network for office, meeting room, or at any place where required without any infrastructure.
ï‚· MANET can use in Military (e.g. to create a network at battle fields), Searching and Reusing of resources.
ï‚· To make intelligent transportation system, Vehicle may use MANET. (where Vehicle will act as mobile node moving from one location to other location) [3, 22].
Routing is the process to moving information / packet from a source node to a destination node in a mobile ad-hoc network. During routing process, at least one intermediate node within the network is encountered. This concept is not new to computer science since routing was used in the networks in early 1970's. But this concept has achieved popularity from the mid-1980. The major reason for this is because the earlier networks were very simple and homogeneous environments; but, now high end and large scale internetworking has become popular with the latest advancements in the networks and telecommunication technology .
Routing protocol in Mobile ad-hoc network is divided into following types:
1) Unicast Routing Protocol
2) Multicast Routing Protocol
3) Broadcast Routing Protocol.
International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) 205
There are many kinds of routing protocol for Unicast, multicast and broadcast routing protocol in the MANET. All routing protocol cannot fit in all different scenarios and traffic patterns so they are further classified into other category.
For examples, reactive routing protocols are good for a large scale, narrow band mobile ad-hoc network  while on other hand proactive routing algorithms works for small scale, broad band mobile ad-hoc network . In this survey paper we will discuss only Unicast routing protocols.
Unicast Routing Protocol in MANET
Reactive Unicast Routing Protocols
Proactive Unicast Routing Protocols
Hybrid Unicast Routing Protocols
Secure Unicast Routing Protocols
Geographical Based Unicast Routing Protocols
Figure1. Classification of various unicast routing protocol in MANET
II. UNICAST ROUTING PROTOCOL
Unicast Routing Protocol: in MANET most of applications are base on Unicast communication. In Unicast source mobile node transmit data packet to destination. While forwarding data packet dispatch node use the destination address in the data packet to look it up in routing table. If the destination address found in routing table the data packet will send to the corresponding next hop. But in such condition every node maintains the routing table in network. So the problem is that how the routing table is created and maintained in MANET. Unicast routing protocols are further divided into two categories:
Proactive Unicast Routing Protocol: In Proactive Unicast routing protocol each node in MANET maintains routing information to every other node in network to compute shortest path from the source to every destination node, which consumes lots of bandwidth. Such routing information is kept in many different types of tables. Such tables are time to time updates if network topology changes or a node moves from network.
Proactive unicast routing protocol are Divided as Optimized Link State Routing Protocol (OLSR), Fishey State Routing Protocol (FSR) and Topology Broadcast Based on Reverse Path Forwarding Routing Protocol (TBRPF).
Optimized Link State Routing Protocol: OLSRâ€-s  main aim is for large and dense Mobile Ad-Hoc Network. OLSR works on Multipoint Relaying flooding techniques to reduced topology broadcast packets. OLSR works according to the following points.
ï‚· Every mobile node broadcast "hello" message periodically to its neighbor. With this hello message every mobile node can obtain topological information for every node in MANET.
ï‚· Now based on topological Information, A node will select a subset of its neighbor to act as multipoint relaying nodes.
ï‚· Every node contains its global topological information and update, shortest path from source node to every other node can computed with dijkstra's Algorithm.
International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013) 206
Fishey State Routing Protocol: FSR was proposed in  for aim at large scale and wit high mobility MANET. Name of this protocol comes from property of eye's fish. Fishey State Routing Algorithm works on following method.
ï‚· Based on distances the network is divided into different scopes. For example if the nodes are in 3 hops distance, they will come in same scope. Other node will come outer scope.
ï‚· The nodes which are in different scope, Routing entries corresponding to these nodes are sent at different frequencies and routing entries for inner nodes are sent at highest frequency and other entries are sent at lower frequency. Because of this reason the nearby node will receive more up to date link state updates compare to the node far away node.
Topology Broadcast Based on Reverse Path Forwarding Routing Protocol: TBRPF was proposed for several hundred of mobile nodes or high mobility in MANET . In TBRPF each mobile node in network keeps incomplete global topological information. To reduce routing overhead TBRPF adopts following optimization steps:
ï‚· â€•helloâ€- messages are exchanged among neighboring nodes periodic and differential. Only the changes of neighbor status are included in â€•helloâ€- message.
ï‚· A part of spanning tree is broadcast to its neighbors if mobile node â€-A â€- finds itself is on the path from its neighbor â€-Bâ€Ÿ to a destination â€-Câ€Ÿ in the â€žAâ€Ÿ rooted spanning tree, it will put node â€žCâ€Ÿ and its adjacent links in the reportable topology sent to neighbors.
ï‚· Whenever required like network topology updated, mobile node mobility etc, it will update with "hello" message.
TABLE I COMPARISON BETWEEN OLSR, FSR & TBRPE Protocol
O(D) or D+2 for link failure
O(N2)+ O(N)+ O(N+V)