Optimization of AODV routing protocol in mobile ad-hoc network by introducing features of the protocol LBAR
GUIDOUM AMINA University of SIDI BEL ABBES
Department of Electronics Communication Networks, Architectures
ALGERIA
guidoum [email protected]
Pr BOUKELIF Aoued University of SIDI BEL ABBES
Department of Electronics Communication Networks, Architectures
ALGERIA [email protected]
Abstract: A mobile ad hoc network is a collection of mobile units; the multi-hop communications in the network are possible through routing protocols, most of these protocols do not take into account the distribution of the load of traffic .In this paper we present a new scheme of distribution of the traffic load for the AODV protocol is implemented at the route discovery process that modifies the RREQ and RREP and adds another cost that is based on the number of packets queued all nodes participating in the establishment of the road . The route selection will be based on the minimum cost and the shortest path to destination. The simulation results show that the proposed approach reduces the time end to end delay, and the overhead and delivery ratio.
Key–Words:ad hoc, AODV, load balancing, RREQ, cost.
1 Introduction
The routing strategy is used in order to discover paths between nodes. There are two main types of rout- ing protocols: protocols based on link state, and oth- ers based on the distance vector. Both methods re- quire periodic updating of routing information that must be shared by different nodes .The routing algo- rithms based on these two methods use the same net- work technology which is the technique of the short- est paths. The characteristics of nodes (mobility, lim- ited resources, etc ...) make the routing in this type of network complex. The AODV protocol (Ad hoc On- Demand Distance Vector Routing Protocol) is a reac- tive routing protocol designed by Charles E . Perkins and Elizabeth M. Royer. [1] It can be considered as a combination of two protocols DSDV [2] and DSR [3]
because it holds its DSR discovery mechanisms and maintenance of routes ”Route Discovery” and ”Route Maintenance”; and DSDV, its routing hops ”hop by hop”, its sequence numbers and the broadcast of up- dates routing tables. It is based on the principle of distance vector routing. Given its characteristics, this protocol has become widely known and has been a lot of research. It is quite suitable for mobile ad hoc net- works to share his support for the mobility of nodes in the network. This protocol allows mobile nodes to ob- tain routes quickly for new destinations without main- taining routes for which there is no active communica- tion. Thus, the establishment of a route is made only when needed. If a source node wants to send data
packets to a destination node, it must establish and maintain and the chosen path is the shortest path with a minimum number of hops as the optimal path with- out any consideration of the traffic that leads to degra- dation performance of the network. The load balanc- ing techniques focus on how to find a path with less traffic load; and the data packets can be routed with a small delay. And to improve the quality of service and optimal routing is essential to take into account the distribution of the traffic load in the routing mech- anism. In this paper we propose a scheme to optimize the AODV protocol which is based on the distribu- tion of traffic load by changing the discovery process and to consider the load of the node and the introduc- tion of a new cost that reflects the size of the queue;
the path selection will be based on the minimum cost and this cost is the sum of all costs of the nodes par- ticipating in the path from the source to the destina- tion and also according to the number of hops; in this way the overloaded nodes and the least congested path will be chosen. This article is organized as follows.
Section2 summarizes the previous work. In section3 implementation. In section4, we study performance evaluation and simulation.
2 PREVIOUS WORK
The family of reactive protocols does not allow a balanced distribution of traffic load on various routes such as AODV, DSR. The technique of load balancing
in ad hoc networks is divided into 3 types, the first on ”delay” where the distribution is achieved by avoiding nodes with a large delay (delay), and the second technique based on ”traffic ”the distribution of traffic is carried on the different nodes of the network and the third technique is hybrid a combination of the above techniques . Protocols LOAD BALANCING focuses on how to find a path with less traffic load
”review of load balanced routing protocol” [7], the mechanisms of load balancing are based on different metrics:
Active path: refers to the number of path sup- ported by a node.
Traffic size: This refers to the traffic load present at a node and its associated neighbors (measured in bytes).
Packets in interface queue: This refers to the total number of packets buffered at both the incoming wireless interfaces.
Channel Access probability: This refers to the like lihood of successful access to the wireless media. It is Also related to the degree of channel contention with neighboring nodes. [8].
Node delay: This refers to the delays incurred for packet queuing, processing, and successful transmis- sion.
Nodal activity: number of active paths passing through the node [4, 8.6].
Load balanced routing in mobile ad hoc networks [10] defined a new metric for routing known as traffic density to represent the degree of contention in the layer control access to the medium. Work Load-Based Adaptive Load-Balancing technology [11] that uses the load of the node that will be compared to a threshold to determine whether a node is overloaded or not at the end to avoid; the value of this threshold dynamically changes depending on the charge status of the node and its workload within a specified period.
DLAR [9]: in this protocol is the destination sends the information of the load attached to the RREP packet to the source; after receipt of the packet by the source, the route less overloaded will be chosen as the active path. In ”load balanced ad hoc wireless routing” Audrey Zhou [4] defined a new metric for routing ”the degree of nodal activity ’for the selection of the least congested routes; its algorithm includes route discovery, route maintenance, connectivity management and the cost.
3 The implementation:
3.1 AODV
For the establishment and maintenance of a route AODV protocol uses three types of messages: RREQ (Route request message), RREP (Route Reply Mes- sage) and RERR (Route Error Message). These packages provide the control traffic routing. When a source node and a destination node does not have a route between them, the source node initiates RREQ to discover the route; the intermediate node or the destination node uses the RREP to respond to the request route discovery; the RERR is used in the case where there has a broken [1] route. The RREQ message contains source address, sequence number, broadcast id, destination address, sequence number, number of hops. Mechanism of AODV protocol consists of 3 phases, the route discovery and maintenance of road connectivity management [1].
For the first phase, a node broadcasts a route request (RREQ), where he would need to know a route to a certain destination and such route is not available.
This can happen if the destination is not known in advance, or if the existing path to the destination has expired its life or if it becomes faulty (the metric as- sociated with it is infinite). After broadcast of RREQ, the source waits for the route reply packet (RREP). If it is not received within a certain period (called RREP WAIT TIME), the source can rebroadcast a new RREQ request. When a transit node (intermediate) sends the request to a neighbor, it also stores the identifier of the node from which the first copy of the request is received. This information is used to construct the reverse path, which will be crossed by RREP in unicast manner (this means AODV only supports symmetric links). Since the route reply packet will be sent to the source, nodes belonging to the return path will change their routing tables following the path contained in the response packet (expiration time, sequence number and next hop).
For the second phase To maintain consistent routes, periodic transmission of the message ”HELLO”
(which is a RREP with TTL 1) is performed. If three messages ”HELLO” are not consecutively received from a neighboring node, the link in question is considered to be faulty. Failures links are generally due to the mobility of the ad hoc network.
Connectivity management: When a node receives a broadcast packet, it updates its local connectivity information to ensure that they include the neighbor.
If no packet is sent to the active neighbors in the last hello interval, a node will send a hello (unsolicited RREP) containing:
3.2 Optimization
The load balancing is a model of quality of service, where a routing protocol is enhanced to meet the requirements of user applications sensitive to a parameter such as delay, bandwidth and jitter. In our work, we are taken to improve quality of service while minimizing delays to satisfy users, who are interested in packet transmission delay,
The AODV protocol does not take into account the distribution of the load, we will add a function that will calculate the cost based on the metric load node and modify the process of route discovery and route selection will according to the minimum cost and the number of hops and we have the rout least congested and shorter.
Route discovery process: the node broadcasts the RREQ packet when it does not have a route to transmit data to another node.
The structure of RREQ is modified carrying the load of nodes crossed during the discovery path and this value of load is the new cost.
Each RREQ packet reception by the node, it calcu- lates the number of packets in its queue and compares it with the cost if its value is greater than the packet is discarded; in this way the considered overloaded node will be avoided else adds value to the cost and rebroadcasts the RREQ until it reaches the destination.
The destination chose the path that has the minimum cost and also less number of hops.
The algorithm works as follows:
1-we transmit length of interface queue from MAC to AODV.
2-Receive RREQ (package) If (getlengt ()> cost) Free package Else (update cost) Cost = cost + getlengt ()
Insert idbroadcast ( Update therouting table ) If the destination node
Cost = sum cost
3-Select min cost and min hop cont.
Send reply with new cost . Update routing table.
4 Simulation
In this section the performance of the improved version of the protocol is evaluated and compared with the basic version of the protocol. The simulation environment is described and simulation results are presented and discussed.
4.1 Simulation Environnent
All simulations are made using NS [14] which is a powerful tool for the simulation based around the TCL programming language, mobility model waypoint mobility model. The protocoleIEEE802.11 is used.
Type of file management or tail drop Tail (FIFO) The maximum number of packets in the buffer is 50 packets. We used applications that are sources of CBR traffic type that transmits packets at regular intervals. The source transmits packets of size 512 bytes at a rate of 4 packages per second. The simu- lation of the two protocols under NS2 generates log files containing the whole course of the simulation (number of packets sent, received, number of failed links).
On this statistics we could analyze the results of the simulation and we could assess changes before and after the modification of the AODV protocol; we look at the following metrics:
Delivery ratio: This rate is calculated by dividing the number of packets received by the packets sent by the sources of applications.
End to end delay: is the average time needed to deliver data packets from the source to the destination successfully including latencies in queues storage time in buffer.
Normalized Routing: The overhead is calculated by dividing the number of data packets received by the control packets.
For each scenario we varied the main parameter that can influence the behavior and the simulation results is that the pause time for each node representing the immobility time before moving again.
End to end delay:
The results of each scenario for this metric based on Pause- Time are shown in the following graph:
The modified AODV is more efficient than AODV. It carries a lower delay than the AODV in scenarios 3 and 4 we have less load on the nodes in the network and the waiting time at each node has decreased.
When there is less mobility AODV is better than AODV modified because the number of communicat- ing nodes is limited, there have less control packets;
delay decrease .time of latencies is lower in AODV modified compared AODV.
Delivery ratio:
The results of each scenario for this metric based on Pause- Time are shown in the following graph:
The delivery ratio is influenced by the deletion of packets if the queue fills up and reaches the maximum number of packets; in our simulation the maximum number of packets in the queue is 50 packets.
In the first scenario we have 10 nodes communicate less control packets; then the rate reached 100 % at pause time 600 sec.
For scenarios 2,3 and 4 AODV- modified is better than AODV because we used the cost of load balancing.
High mobility means more packet loss, which leads to a small pdf at the pause time 300 and 600.
Overhead:
We note from the results of the simulation that as
the number of nodes communicating in 20.30.40 scenarios increase, the network is less congested;
but in the scenario1 AODV modified don’t shows its effectiveness against AODV. Concernant mobility, in high mobility (0 ... 120) we have a load increase. In terms of overload AODV modified is more efficient than AODV.
5 Conclusion
We introduced a new load balancing mechanism that has been applied to AODV and has been evaluated through various simulation scenarios. The simulation results show that our protocol has a better end to end delay and a higher rate of delivery than AODV.
In terms of load, it is more efficient in large ad hoc networks.
As perspective, we propose to combine our approach with that limit the number of active paths to improve
the performance of AODV protocol.
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