In this research I will mainly discuss about the wireless ad-hoc network modelling and performance evaluation problems.
The objective of this project is to:
* Briefly describe the background of wireless ad-hoc network modelling and network performance evaluation.
* Design and simulate a multi-hop ad-hoc network model by using any two routing protocols.
* Evaluate the performance of this model.
In this Literature survey I am discussing the background of the wireless ad-hoc network and multi-hop relay modelling and network performance evaluation. During my survey I found that ad hoc network is a collection of wireless mobile nodes which forms temporary network without the use of any existing network infrastructure or centralized administration. In other words we can say that wireless mobile users may be able to communicate without using any expensive or inconvenient infrastructure by the formation of an ad-hoc network. They communicate with each other by forming a multi hop radio network to maintain connectivity. 
1.4 Working of Wireless ad-hoc networks:
Each node or mobile device is equipped with a transmitter and receiver. This means that each node in a wireless ad hoc network functions as both a host and a router. In which the control of the network is distributed among the nodes. These mobile nodes communicate directly with each other and without the aid of access points, and therefore have no fixed infrastructure. They form an arbitrary topology, where the routers are free to move randomly and arrange themselves as required. 
Ad hoc Routing Protocols
A routing protocol is a protocol that specifies how routers communicate with each other to disseminate information that allows them to select routes between any two nodes on a network. 
Routing protocols between any pair of nodes within an ad hoc network can be difficult because the nodes can move randomly and can also join or leave the network. This means that an optimal route at a certain time may not work seconds later. For this purpose routing protocols were introduced. 
2.2 Routing protocols involved: 
The three types of routing protocols involved in wireless ad hoc networks are:
1. Table Driven Protocols
2. On Demand Protocols
3. Hybrid Protocols
The block diagram showing the various protocols involved in wireless ad hoc networks is shown below: Diagram 1: Ad-hoc Wireless Routing Protocols 
2.2.1. Table Driven Routing Protocols:
In this routing protocol each node uses routing information to store the location information of other nodes in the network and this information is then used to move data among different nodes in the network. This type of protocol is slow to converge and may be prone to routing loops. Fisheye State Routing is an example of a Table Driven Protocol.
2.2.2. On Demand Routing Protocols:
This protocol establishes routes between nodes only when they are required to route data packets. On Demand protocols are generally considered efficient when the route discovery is less frequent than the data transfer because the network traffic caused by the route discovery step is low compared to the total communication bandwidth. An example of an On Demand Protocol is Dynamic Source Routing. 
2.2.3. Hybrid Routing Protocols:
This protocol combines Table Based Routing Protocols with On Demand Routing Protocols. They use distance-vectors for more precise metrics to establish the best paths to destination networks, and report routing information only when there is a change in the topology of the network. 
Ø A routing protocol is used to select any two nodes in a network to communicate.
Ø In ad hoc networks the nodes can move randomly and can also join or leave the network.
Ø An optimal route at a certain time may not work seconds later.
Ø Three routing protocols were introduced.
Wireless multi-hop ad-hoc communication networks represent an infrastructure less generalization of today's wireless cellular phone networks (see fig 3.1). in the ad hoc network which lacks a central control authority in the form of base stations, each end device acts as router and relay packets for other participants. This kind of end to end communications may be via multi hop connections. During these courses, the participating devices need coordination among themselves in order to ensure network connectivity, efficient discovery and execution of end-to-end routes and avoidance of data packet collisions on shared radio channels.
Multi-hopping can be employed to increase the coverage distance as well as improving the overall performance gains of a network if it is used within a defined coverage area.
3.2 Performance evaluation of Multi-Hop Relay network:
There are few parameters to evaluate the performance of the multi-hop relay network:
1. Transmission power
4. Loss rate
3.2.1 Transmission power:
The coverage is always defined by the receiver threshold especially to a fixed transmission power. The receiver threshold is a lower bound on the receiving power of any packet that can be successfully received. On the other hand, the minimum received signal has other criteria or signal-to-noise ratio; the nodes can reduce communication distance and save the amount of power. For this purpose we need to calculate Transmission power. 
It is the rate if sending or receiving data of a computer or a network. Therefore it is very useful to measure he absolute performance of the network, and we frequently will see the internet connections rated in terms of how many bits the pass per second. 
In packet switched network, one-way means the time from the source sending a packet to the destination receiving it. Similarly, round trip means the time from the source sending a packet to the source receiving a response. Latency is measured either one-way or round-trip.
3.2.4 Loss rate
Loss rate is the ratio of system output to system input. Loss rate calculation and units used are the same as gain , except that the output is less than the input. Loss rate is usually expressed as a negative gain or a gain of less than one.
By previous demonstration it is observed that the two-hop relay scheme save on power and at the same time delay, throughput and loss rate are very close to the single hop scheme. Corresponding to the two hop relay, the other multi-hop schemes save on power and have an acceptable delay but the loss rate is very high and the throughput achieved is less than a single hop scheme.
Comparison of Multi-Hop Wireless Ad-Hoc network routing protocols
Due to the limited transmission range of wireless network interfaces, multiple networks "hops" may be needed for one node to exchange data with another across the network. For this purpose a variety of new routing protocols were introduced. . in this chapter we will have a look on the key features of the DSDV, TORA, DSR and AODV protocols
4.2 Studied Ad hoc network routing protocols:
In this section I will describe the particular parameters that we can chose while implementing each protocol. 
4.2.1 Destination-Sequenced Distance Vector (DSDV):
DSDV is a hop-by-hop distance vector routing protocol requiring each node to periodically broadcast routing updates. The main advantage of DSDV is that it guarantees loop-freedom.
Basic mechanism: Each DSDV node maintains a routing table listing the “next hop” for each reachable destination. Each node is the network advertises a monotonically increasing even sequence number for itself. When a node B decides that its route to a destination D has broken, it advertises the route to D with an infinite metric and a sequence number one greater than its sequence number for the route that has broken. This caused any node A routing packets through B to incorporate the infinite-metric route into its routing table until node A routes to D with a higher sequence number.
4.2.2 Temporally-Ordered Routing Algorithm (TORA):
TORA is a distributed routing protocol based on a “link reversal” algorithm. It was designed to discover routes on demand. The actions taken by TORA can be described in terms of water flowing downhill towards a destination node through a network of tubes that models the routing state of the real network. If the tube between nodes A and B becomes blocked such that water can no longer flow through it, the height of A is set to a height greater than that of any neighbours such that water flow back out of A.
Basic mechanism: At each node in a network, a logically separate copy of TORA is run for each destination. When a node needs a route to a particular destination, it broadcasts a QUERY packet containing the address of the destination for which it requires a route. This packet propagates through the network until it reaches either the destination or an intermediate node having a route to the destination.
4.2.3 Dynamic Source Routing (DSR):
DSR uses source routing rather than hop-by-hop routing, with each packet to be routed carrying in its header the complete ordered list of nodes through which the packet must pass. The key advantage of source routing is that intermediate nodes do not need to maintain up to date routing in order to route the packets they forward. 
Basic mechanism: The DSR protocol consists of two mechanisms: Route Discovery and Route Maintenance. Route discovery is the mechanism by which a node S wishing to send a packet to a destination D obtains a source route to D. Route Maintenance is the mechanism by which a packet's sender S detects if the network topology has changed such that it can no longer use its route to the destination D because two nodes listed in the route have moved out of range of each other. 
4.2.4 Ad Hoc On-Demand Distance Vector (AODV):
AODV is essentially a combination of both DSR and DSDV. It borrows the basic on-demand mechanism of Route Discovery and Route Maintenance from DSR. It also makes use of hop-by-hop routing, sequence numbers, and periodic beacons from DSDV. 
Basic mechanism: When a node S needs a route to some destination D, it broadcasts a ROUTE REQUEST message to its neighbours, including the last known sequence number for that destination. 
Securing Wireless Ad hoc Networks
Ad-hoc networks are highly vulnerable to security attacks and dealing with this is one of the main challenges of developers of these networks today . The main reasons for this difficulty are
* Shared broadcast radio channel,
* insecure operating environment,
* lack of central authority,
* lack of association among nodes,
* limited availability of resources,
* Physical vulnerability.
In an ad-hoc network, nodes must act as both terminals and routers for other nodes. Because there are no dedicated nodes, a secure routing protocol is needed. Multi hop routing protocols are usually employed. These can lead to problems due to non-cooperating nodes and denial of service attacks. 
5.2 Security Goals:
Security is an important issue for ad hoc networks, especially for those security sensitive applications. To secure an ad-hoc network we consider the following attributes :
5.2.1 Availability: It ensures the survivability of network services despite denial of service attacks. A denial of service attack could be launched at any layer of an ad-hoc network.
5.2.2 Confidentiality: it ensures that certain information, strategic or tactical military information, is never disclosed to unauthorized entities.
5.2.3 Integrity: It guarantees that the message being transferred is never corrupted. A message could be corrupted because of benign failures such as radio propagation impairment.
5.2.4 Non-repudiation: It ensures that the origin of a message cannot deny having sent the message. It is very much useful info detection and isolation of compromised nodes. 
After researching Ad-hoc networks in depth, I believe that they will be the future of wireless networking. It is true that performance suffers as the number of devices grows and large ad-hoc networks become difficult to route and manage. However, much time is being devoted to achieving routing stability, and a few technical issues need to be solved before they become common place. The area of ad hoc networks is a very fast growing area; need a vast research in them.
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