Extended Abstract: File Transfer in Vehicular Ad-hoc Networks

Kifayat Ullaha, Luz Marina Santosb*, João Michelina, Edson dos Santos Moreiraa

a ICMC - Universidade de São Paulo, Brazil b Grupo Ciencias Computacionales - Universidad de Pamplona, Colombia

Emails: {kifayat, lsantosj, joaolmm, edson}@icmc.usp.br

Abstract—A large amount of file transfer systems in use today are designed to operate in wired networks. In the context of vehicular ad-hoc networks, these systems may behave improperly, due to the inherent characteristics of wireless networks and mobility of vehicles. This work proposes and implements a model for transferring files using basic client-server architecture, with focus on its operation in vehicular networks. We performed two different sets of experiments. The first experiment was performed to evaluate the performance of the system with different number of clients and servers while the purpose of second experiment was to validate the application behavior in an outdoor environment. The results show that the system is able to perform file transfers. It is concluded that the number of clients has a great impact on performance of the system.

Keywords—client-server file transfer; VANET; V2I; UDP

I. INTRODUCTION

Vehicular ad-hoc network (VANET) is a sub category of mobile ad-hoc network (MANET) in which vehicles act as mobile nodes. VANET provides Vehicle to Vehicle (V2V) and Vehicle to Infrastructure (V2I) communications [1]. Increasing interest in VANET leads to a large demand for a variety of data transmission applications [2].

Several studies contribute to the file transfer in VANETs. The proposals in [3-6] were tested in simulated environments, while the works presented in [7] and [8] were tested in a real world environment. These studies considered Peer to Peer (P2P) file transfer architecture. In contrast, we proposed a novel client-server file transfer scheme for V2I communications with focus on data integrity.

II. FILE TRANSFER SCHEMEIn this section we present our file transfer scheme in details.

A. System Architecture There are three possible architectures for developing the

system; client-server, Peer to Peer (P2P) and hybrid. We use client server scheme, in which clients are considered to be vehicles, while the servers will act like Road Side Units. Fig.1 shows the basic architecture of our system. We assumed that the files to be downloaded are available in all Road Side Units (RSUs).

In VANETs, vehicle will move with high speeds, which make the use of TCP inappropriate. Therefore, we choose UDP protocol, since it will not require establishing a connection among moving vehicles and RSUs. Our system also provides

location transparency, which enables resources to be accessed without knowledge of their physical or network location [9].

Fig. 1. Architecture of the file transfer in VANETs

B. Size and division of the file in chunks The file transfer is made in several chunks or pieces. The

number total of chunks can be calculated by the following equation:

Where x is the number of chunks to be transferred and t is the size of the file being transferred, with t and t > 0. Size of each chunk is 256 bytes.

C. File TransferProcess The transfer process is based on two basic steps. First step

is to obtain information of the file which the client wants and second is to calculate how many pieces the file has to transfer. The client can request a maximum of 32 chunks at a given time

III. EXPERIMENTAL SETUPTo carry out experiments, we developed an application in C

language and implement 802.11 g protocol in four notebooks.

A. Performance Evaluation We evaluate performance of our system by considering

execution time as a response variable. The size of file was 691,943 bytes (i.e. 675.73 KB approximately).

Table I. Factors and Levels

Factors LevelsNumber of clients One client

Two clients

Number of servers One server

Two servers

* Currently on Leave for a Doctoral Program at University of São Paulo,Brazil

x = 1 + (t +1) (1) 256

2013 III Brazilian Symposium on Computing Systems Engineering

2324-7894/14 $31.00 © 2014 IEEE

DOI 10.1109/SBESC.2013.16

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Fig. 2 shows the time taken (in seconds) for receiving the complete file by each case.

Fig. 2. Results varying of number of clients and servers

In the second case (i.e. single client and two servers) the transfer time is almost double as compared to the first case (i.e. single client and single server). This is due to the duplicate messages, generated by the servers. It has a direct consequence on the implementation of location transparency. However, in real world scenarios, better distribution of RSUs along the roads can reduce this effect.

The case of two clients and single server is less efficient than the case of two servers and single client. This is because of the fact that server needs to serve more clients. This leads to the conclusion that in real world scenarios, the number of vehicles can affect the performance.

Fig. 3 shows the influence of the factors on the results. The number of clients shows greatest influence (82.39%) on the transfer time of a file.

Fig. 3. Influence of the factors in the file transfer

B. Location Transparency The second experiment was performed in an outdoor

environment. To perform this experiment, we use three notebooks. The size of file was 1.34 MB (about 1404422 bytes). In this experiment, the servers were placed at adistance of 280m from each other (As presented in Fig. 4).

The client was moving from RSU1 to RSU2. At certain points, the distance between moving client and fixed server become higher than the coverage range of 802.11g (i.e. 140m), which leads to packet lose.

IV. CONCLUSIONS AND FUTURE WORK

We proposed a client-server based file transfer system for V2I communications. In order to evaluate the performance and show location transparency, we conduct experiments . Our results show that increasing the amount of clients and servers

has a great impact on the performance of system. The work presented in this paper is in the initial stages. In the future we will perform simulation based studies, in order to provide file transfer using client-server architecture.

Fig.4. Experiment of location transparency

ACKNOWLEDGMENT

The authors are thankful to The World Academy of Sciences-TWAS, Italy and to the National Counsel of Technological and Scientific Development-CNPq, Brazil for providing financial support under the grant number 190275/2011-1. The authors would also like to thank the National Science and Technology Institute for Critical Embedded Systems (INCT-SEC, Brazil) for funding this work by means of the following agencies: CAPES, CNPq (grant # 573963/2008-8) and FAPESP (grant # 2008/57870-9).

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