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Abstract- Mobile Ad-hoc Networks (MANETs) have attracted a lot of interest in the research community. The Ad Hoc On-demand Distance Vector (AODV) and Dynamic Manet On- Demand(DYMO) are the two most popular reactive routing protocols for MANETs. In this paper AODV and DYMO Routing Protocols are compared using performance metrics Average End to End delay, Throughput, Routing Overhead, Packet Delivery Ratio and packet Loss. Comparison results shows DYMO performs is higher than AODV.
Keywords- MANET, Routing Protocols, AODV, DYMO
A Mobile Ad-hoc Network contains several different protocols. The protocols can be categorized into three types namely Proactive, Reactive and Hybrid. Proactive protocols maintain the routes of all the nodes in the network at all times by broad casting routing updates in the network. Reactive protocols find a route to the destination by sending packets from source to the destination. Hybrid protocols combine proactive and reactive protocols to try and exploit their strengths. One approach is divide the network into zones, and use one protocol within the zone, and another between them.
AODV is an on-demand routing protocoll. The AODV algorithm gives an easy way to get change in the link situation. For example if a link fails notifications are sent only to the affected nodes in the network. This notification cancels all the routes through this affected node. It builds unicast routes from source to destination and that's why the network usage is least. Since the routes are build on demand so the network traffic is minimum. AODV does not allow keeping extra routing which is not in use . If two nodes wish to establish a connection in an ad hoc network then AODV is responsible to enable them to build a multihop route. AODV uses Destination Sequence Numbers (DSN) to avoid counting to infinity that is why it is loop free. This is the characteristic of this algorithm. When a node send request to a destination, it sends its DSNs together with all routing information. It also selects the most favorable route based on the sequence number . AODV requires hosts to maintain only active routes. The advantages of AODV is that it tries to minimize the number of required broadcasts. It creates the routes on an on-demand basis, as opposed to maintain a complete list of routes for each destination. Therefore, the literature on AODV, classifies it as a pure on demand route acquisition system. The usage of the AODV protocol for mobile adhoc networking applications provided consistent results for large scale scenarios.
DYMO has a somewhat simpler design based on, reducing the routing overhead using a path accumulation function, and simplifying the protocolimplementation. Similar to AODV, the basic operations of the DYMO protocol are also route discovery and route maintenance. During route discovery, the originator's DYMO router initiates the dissemination of a RREQ throughout the network to find a route to the destination's DYMO router. Upon receiving the RREQ, each intermediate DYMO router records a route to the originator and rebroadcasts the RREQ including its own information which is called the path accumulation function. When the destination's DYMO router receives the RREQ, it sends a RREP to the originator. When the originator receives the RREP, the route is established. The route maintenance of DYMO is similar to that of AODV. As mentioned above, the path accumulation function of DYMO includes source routing characteristics, thereby allowing nodes listening to routing messages to acquire knowledge about routes to other nodes without initiating route request discoveries themselves. As a result, this path accumulation function can reduce the routing overhead, although the packet size of the routing packet is increased.
The paper is organized as follows. Section 2 represent related work in the modelling of routing protocols. Section 3 presents the performance metrics. Section 4 contains experiments and results. Section 5 concludes this paper.
2. ROUTING PROTOCOLS TECHNIQUES
AODV Routing Protocol
The Ad Hoc On-demand Distance Vector (AODV) and Dynamic Manet On-demand (DYMO) are the two most popular reactive routing protocols for MANETs, where the reactive property means that a route is only requested when needed. In the case of AODV, whenever a source node needs a route to a destination node for which it does not have a route, it broadcasts a route request (RREQ) packet to all its neighbours. A neighbor receiving a RREQ may send a route reply (RREP) packet if it is either the destination or if it has an unexpired route to the destination. Along the path back to the source, intermediate nodes that receive the RREP create forward route entries for the destination node in their routing tables. In order to maintain the routes, AODV normally uses link layer feedback and hello packets. When a link break in an active route is detected by the above mentioned method, the node notifies this link break by sending a route error (RERR) packet to the source node. Upon receiving the RERR packet, the source node newly initiates the procedure for route discovery. However, despite its status as the most popular protocol for reactive MANET routing, AODV has a heavy routing overhead and complexity problem as regards implementation.
2.2 DYMO Routing Protocol
The Dynamic MANET On-demand (DYMO) 
routing protocol is a simple and fast routing protocol for multihop networks. It discovers unicast routes among DY MO routers within the network in an on-demand fashion, offering improved convergence in dynamic topologies. To ensure the correctness of this protocol, digital signatures and hash chains are used . The basic operations of the DYMO protocol are route discovery and route management.
In Route Discovery source needs to send a data packet, it sends an RREQ to discover a route to that particular destination. After issuing an RREQ, the origin DYMO router waits for a route to be discovered. If a route is not obtained within RREQ waiting time, it may again try to discover a route by issuing another RREQ. To reduce congestion in a network, repeated attempts at route discovery for a particular target node should utilize an exponential backoff. Data packets awaiting a route should be buffered by the source's DYMO router. This buffer should have a fixed limited size and older data packets should be discarded first. Buffering of data packets can have both positive and negative effects, and therefore buffer settings should be administratively configurable or intelligently controlled. If a route discovery has been attempted maximum times without receiving a route to the target node, all data packets intended for the corresponding target node are dropped from the buffer and a Destination Unreachable ICMP message is delivered to the source.
When a data packet is to be forwarded and it can not be delivered to the next-hop because no forwarding route for the IP Destination Address exists. Based on this condition, an ICMP Destination Unreachable message must not be generated unless this router is responsible for the IP Destination Address and that IP Destination Address is known to be unreachable. Moreover, an RERR should be issued after detecting a broken link of a forwarding route and quickly notify DYMO routers that a link break occurred and that certain routes are no longer available. If the route with the broken link has not been used recently, the RERR should not be generated.
3. PERFORMANCE METRICS
The following metrics are used to evaluate the performance of AODV and DYMO.
3.1 Average End to End Delay:
It is the average time taken for each data packet to be received by the destination node from the source node. The data packets which were lost in simulation were not recorded for consideration.[5,14]
3.1.1 Record the time the source node sends a datapacket:
start_time[packet_id] = time;
3.1.2 Record the time of destination receives the data packet:
end_time[packet_id] = time;
3.1.3 The end-to-end delay for each data packet:
packet_duration = end - start;
3.1.4. Average end-to-end delay:
Delay = duration_total / packet_number;
The throughput is defined as the total amount of data a receiver actually receives from the sender divided by the time it takes to get the last packet .
Throughput=∑ Receiving packets/End time
The routing overhead describes how many routing packets for route discovery and route maintenance need to be sent in order to propagate the data packets[7,9].
OH=∑ Transmissions of Routing packets
Packet Delivery Ratio:
The fraction of packets sent by the application that are received by the receivers .
PDR= ∑ sending packets/ ∑ Receiving packets
The number of packets dropped during packets send from source to destination.
PL = ∑ Dropping Packets
4. EXPERIMENTS AND RESULTS
4.1 Simulation Environment:
Simulations are created and the comparative results are generated. In the graph X position contaions number of nodes from 5 to 100[11,12,13]. In Y position contains the values of throughput, packetloss, Average end to end delay, Routing Over Head and Packet Delivery Ratio[10,15].
Simulation Environments are created with various
Number of nodes from 5 to 100. First column in the following tables contain nodes details. Second column contains AODV protocol performance metrics values. Third column contains DYMO protocol performance metrics values.
AVERAGE END TO END DELAY
ROUTING OVER HEAD
PACKET DELIVERY RATIO
Figure 1 shows Number of nodes 5 to 60 average end to end delay is low in DYMO. The number of nodes are more than 70 to 100 Average Delay also high in AODV compare to DYMO . In Figure 2 Throughput is slightly high in DYMO and low in large network. Figure 3 produce the result as Overhead is slightly high in AODV and low in other end. In Figure 5 shows Packet Delivery Ratio is low in AODV when compare to DYMO in small and large network. In Figure 5 Packet Loss is high in AODV when compare to DYMO.
Figure 1: Delay
Figure 2: Throughput
Figure 3: Overhead
Figure 4: Packet Delivery Ratio
Figure 5: Packet Loss
AODV and DYMO Performance evaluation Comparisons are done between 5 to 100 nodes. For small network with number of nodes between 5 to 70, the Average End to End Delay for DYMO decreases. Throughput is high in DYMO. Packet Delivery Ratio is high in DYMO. If the number of nodes is between 70 to 100, the Average End to End Delay is lower in AODV. Throughput is high in AODV. Packet Delivery Ratio is high in AODV. AODV Overhead and Packet Loss is high in Small and Large network.
5. DISCUSSION AND CONCLUSION
In this paper AODV and DYMO Reactive Routing Protocols are compared. Performance metrics for comparisons are Average End to End Delay, Throughput, Routing Over Head, Packet Delivery Ratio, Packet Loss.
Results from experiments Number of nodes are low average end to end delay is low in DYMO. If nodes are high Average Delay also high in DYMO when compare to AODV. DYMO protocol give high throughput in number of nodes from 5 to 70. As Number of Nodes increased throughput decreases. Overhead is high in AODV and low in other end. Packet Delivery Ratio is low in AODV when compare to DYMO in small and large network. Packet Loss is high in AODV when compare to DYMO. In overall DYMO protocols performance is high compare to AODV.