Mobile Ad Hoc Network (MANET) is a developing area of research. Mobile ad-hoc network is a group of wireless mobile sites forming a temporary network and provides communication between the nodes without any central authority. Efforts have been taken for achieving efficient and reliable routing in Mobile Ad Hoc Networks. Mobile Ad Hoc Networking is an efficient way of exchanging peer-topeer information among devices, such as fixed, portable, and wireless nodes. To provide communication link, a routing protocol must be able to support uni-cast, multicast, and broadcast. Each node in a MANET (Mobile Ad Hoc Network) functions as both a host and a router [4]. The link failure can significantly increase in the network and the performance decreases because link failure may result in packet loss, delay, and may also need global information of the nodes in the network to discover a new route, when no other route is available in route cache. Route maintenance is one of the major challenges in MANET [1]. MANETs are also known as “autonomous system” due its dynamic and unpredictable nature [2]. In order to maintain a steady communication in MANET, route discovery mechanisms must be very efficient in case of node failures or movement [5] . MANET is a special subset of wireless ad hoc network. Hence, it is limited to power and other available resources (bandwidth, range). The paper mainly focuses on the effect and efficiency of protocol to handle node failure in the network. The failure of node results in the failure of link by the way that particular node and this may be due to the consequences of congestion, low energy levels, and unpredictable nature of MANET [10].

The main objectives of this paper are as follows,

• The primary objective of this research is improvement in performance of DSR protocol.
• It will help people in future research in improved performance of DSR protocol.
• It also helps to determine performance of network with the help of various performance metrics.

Routing in MANET is critical because of its energetic topology. Many routing protocols have been proposed for MANET, and these protocols are mainly categorized as,

• Proactive Routing Protocol;
• Reactive Routing Protocol; and
• Hybrid Routing Protocol.

Reactive routing protocols are mostly preferred because of their low frequency of route discovery in comparison with pro-active routing protocols [1] . Figure 1 shows the types of Ad hoc Routing Protocols. DSR is an on-demand reactive routing protocol. It is used to control the bandwidth consumed by control packets in ad hoc wireless networks. It eliminates the periodic table update messages required in the table-driven approach. During the routing construction phase, DSR protocol routes the request packets in the whole network. Whenever destination node gets a packet, it responds by sending a reply packet back which contains the path scanned by the Route Request packet received. The major difference between the DSR protocol and the other on-demand routing protocols is that it is beacon-less, while other are having beacon. Because of this, it does not require periodic hello packet transmissions which are used by a node to inform its neighbours of their presence [3] .

Figure 1. Ad Hoc Routing Protocols

NetSim (Network Simulation) standard version 9 has been used for simulations. Custom code is developed in NetSim using VC++. Visual studio 2010 is used to create the dynamic link loader. The codes for the protocol have been modified as per the requirements and the properties have been setup for simulation scenario. The constant hazard model [6] outputs a notepad file having two columns node id and failure time, which acts as input to NetSim for the DSR protocol to fail the nodes.

Figure 2 shows a network taken up for this study. The results indicate evaluation in performance by taking MANET routing protocol such as DSR. Under this protocol, Throughput (Mbps) is used as performance metrics while packets transmitted, packets errored, and packets collided are used as network metrics. The simulation setup is a network with randomly placed mobile nodes within an area of 100 * 100 (in meters). In the scenario, node 1 and node 10 are used as source node and destination node for sending and receiving data, respectively.

Figure 2. MANET Scenario

The parameters used in the simulation are summarized in Table 1.

Table 1. Parameters and their Values

The parameters on basis of which the protocols are evaluated are the default parameters of the protocols.

There are numbers of metrics using which one can evaluate and compare. In this work, typical metrics are used for design and analysis purpose.

Throughput is an average rate of victorious message delivery over a communication channel [9]. Throughput is defined as the ratio of the total number of packets transmitted per unit time. The network throughput for various numbers of failed nodes is shown in Figure 3. When there is no node failure the value of throughput is 0.635392 Mbps. For 2, 4, 6, 8, and 10 failed nodes value of throughput is 0.618222, 0.596614, 0.591008, 0.581898, and 0.027098, respectively. Throughput decreases exponentially with respect to failed nodes.

Figure 3. Failed nodes v/s Throughput

A packet is a segment of data sent from one computer or device to another over a network. A packet contains the source, destination, size, type, data, and other useful information that helps packet get to its destination and read [11]. Packets transmitted in the healthy network are more as compared to the network containing failed nodes. As the failure nodes increase, packets transmitted will be decreasing. This is because the nodes become inactive and hence they transmit lesser packets to their neighbours, which results in overall lowering of packets. Figure 4 shows the overall trend of packets transmitted with respect to failed nodes. When there is no node failure the packets transmitted are 21048. For 2, 4, 6, 8, and 10 failed nodes packets transmitted are 20723, 19813, 10975, 10260, and 617, respectively.

Figure 4. Failed Nodes v/s Packets Transmitted

Errored packets are the packets which are discarded in the network [8]. By increasing the number of failed nodes known, the transmitted packets get lowered. Due to which, there are lesser number of errored packets. Figure 5 shows the overall trend of packets errored with respect to failed nodes. When there is no node failure the packets errored are 442. For 2, 4, 6, 8, and 10 failed nodes packets errored are 436, 424, 422, 197, and 138, respectively.

Figure 5. Failed Nodes v/s Packets Errored

In the network, whenever two or more mobile sites attempt to transmit a packet across the network at the same time, a packet collision occurs. As by increasing the number of failed nodes known, the transmitted packets get lowered. Due to which there are lesser number of packets get collided. Figure 6 shows the overall trend of packets collided with respect to failed nodes. When there is no node failure the packets transmitted are 442. For 2, 4, 6, 8, and 10 failed nodes packets collided are 436, 424, 27, 0, and 0, respectively.

Figure 6. Failed Nodes v/s Packets Collided

The values for the throughput, packets transmitted, packets errored, packets collided in the healthy scenario as well as by increasing the failed nodes are summarized in Table 2.

Table 2. Value of Different Statistics

In this paper, a node failure model have been developed using Constant Hazard Model (CHM) [7]. The main motive for doing this research was to write custom code for changing the functionalities of the original protocol. The simulation study of this work has been done for DSR routing protocol deployed over MANET analyzing behaviour with respect to throughput, packets transmitted, packets errored, and packets collided. It is found that all the routes to destination might not be available due to node failures. Although, packets have to be routed through a different path, when nodes fail. Due to all these problems, the throughput decreases with increase in number of failed nodes. Motive of doing this simulation was to check the performance of the DSR routing protocols in MANET in normal operating conditions as well as on the occurrence of node failure on the basis of the above mentioned parameters. From the above analysis, it is concluded that, the performance of the network gets decreased with increasing node failure.