Protocols in Realistic Physical Layer
Hassan Faouzi1(&), Hicham Mouncif2, and Mohamed Lamsaadi2
1 FST, Sultan Moulay Slimane University, Beni Mellal, Morocco faouzi.hassan.mi@gmail.com
2 FP, Sultan Moulay Slimane University, Beni Mellal, Morocco {hmouncif,lamsaadima}@yahoo.fr
Abstract. A mobile ad hoc network or MANET (Mobile Ad hoc NETwork) is an autonomous system of mobile platforms called nodes that are free to move about freely. This system can be isolated or have gateways or interfaces con- necting it to afixed network. Most performance evaluation models of routing protocols for ad hoc networks based on the assumption of an ideal radio channel, implying that the underlying physical phenomena are neglected. We propose to use a realistic physical layer by integrating the probability of transmission error characterized by a two-state Markov model in the different radio propagation modes. We measure the impact of such modeling to evaluate-the performance of Proactive and Reactive MANET protocols.
Keywords: Mobile ad-hoc network Routing protocols NS2(Simulator)
Radio channelThroughputDelayPacket delivery ratioControl overhead
Markov chainGilbert-Elliot model
1 Introduction
There is a lot of research studying the performance of routing protocols in ad hoc networks. However, their performance evaluation is based on an ideal radio channel hypothesis: no transmission error, no interference.
In this article we try to evaluate and compare the performance of four routing protocols for mobile ad hoc networks, DSDV [1], AODV [2], DSR [3] and OLSR [4]
using the NS-2 network simulator [5] taking into consideration all the problems related to the transmission media. Packet Delivery Ratio, Average End-to-End Delay, Nor- malized Routing Load and Throughput are the four common measures used for the comparison of the performance of above protocols.
The rest of the paper is organized as follows: Sect. 2 presents the definition of Routing and protocol classification. Section3we study the media transmission error by using a two-state Markov Model. Section 4 gives an overview of different radio propagation models. The simulation environment and then the results are presented in Sect.5. Finally, Sect. 6concludes the paper.
©Springer International Publishing Switzerland 2015
A. Bouajjani and H. Fauconnier (Eds.): NETYS 2015, LNCS 9466, pp. 496–500, 2015.
DOI: 10.1007/978-3-319-26850-7_38
2 Routing and Protocol Classification
Routing protocols in ad hoc networks are essential for communication between two stations that are not in direct contact. Generally the routing protocols can be separated into two categories, proactive and reactive protocols. Proactive protocols establish routes in advance based on the periodic exchange of the routing tables, while the reactive protocols seek routes to the request.
3 Media Transmission Error
A number of researchers have studied the behavior of wireless channels. Among them, Gilbert and Elliot proposed a Discrete Time Markov Chain (DTMC) model, called the Gilbert-Elliot model [6,7], which consists of two states (i.e., a good state and a bad state) and uses a two-by-two transition matrix to specify the state transition probabilities.
The state transition is described by the probabilities of changing from the Good state to the bad state pg=band from the bad state to the good state pb=g. This is illustrated in Fig.1.
The matrix transition can be expressed by:
P¼ pg=g pg=b pb=g pb=b
¼ 1p p
q 1q
ð1Þ
The parameters p and q can be derived from experimental observations. Real measurements show that qp. For example, measurements of errors on the wireless link, given in [8], show pb=g ¼ 0:3820 and pg=b¼ 0:0060 we obtain:
P¼ 0:994 0:006 0:382 0:618
ð2Þ
The probability of being in a good statepg or in a bad state pb can be calculated using a steady state:
pP¼P ð3Þ
Fig. 1. Markov chain of errors on a link
Therefore
pg pb
½ ¼½pg pb 1p p
q 1q
ð4Þ
And
Xp¼1 ð5Þ
Than
pg ¼ p
pþq ð6Þ
and
pb ¼ q
pþq ð7Þ
When a channel is in error-state, any IP packets sent would be either lost or corrupted. In the error-free state all packets are successfully transmitted over the wireless link.
4 Radio Propagation Models
Propagation models are used to predict the propagation characteristics such as received signal power of each packet. At the physical layer of each wireless node, there is a receiving threshold. When a packet is received, if its signal power is below the receiving threshold, it is marked as error and dropped by the MAC layer. In general there are three main propagation models, firstly the Free Space model assumes the propagation conditions as ideal, and the radius of the radio signal propagation is in the form of disc, within which the reception is perfect, and that beyond no further com- munication is possible; secondly the Two-Ray Ground model considers the direct path propagation in addition to the reflection caused by the ground; and thirdly the Shad- owing model is more realistic, since several propagation phenomena are considered, namely, reflection, diffusion and absorption, in addition, the communication radius is no longer considered a perfect disc.
5 Simulation and Results
5.1 Simulation Environment
There Simulation environment in NS2 consists of 30 mobile nodes which are placed uniformly and forming a Mobile Ad-hoc Network with nodes max moving speed of 10.0 m/s and the pause between movements is 20 s about over a 1000×1000 m area for 150 s of simulated time.
5.2 Simulation Results See Fig.2.
6 Conclusion
This paper presents the comparative study and performance evaluation of the routing protocols DSDV, AODV, DSR and OLSR. In the ideal condition of transmission we note that the protocols give good results but in reality we can’t achieve them because the wireless links are characterized by high error rates caused by a variety of trans- mission impairments such as multi-path fading and background noise so it’s normal that we note the decrease in performance of routing protocols if we take into account these effects. Make a comparison in ideal conditions don’t always give the real result so we had to simulate transmission problems in wireless networks in order to get the most useful and reliable results that’s why we integrated the Markov model in our simula- tion. Simulation results (Fig.2(a–h)) show that all types of radio propagation models, AODV performs optimally because is a reactive protocol, which uses routing table one route per destination, sequence number to maintain route and when links break AODV causes the affected set of nodes to be notified so that they are able to invalidate the routes using the lost link, these are the major reasons for it having a good result in average Packet Delivery Ratio, End-to-End DeLay and Throughput, but has a higher Routing load because it generates more control packets. Our future work will include
Fig. 2. Simulation Results
the modification to the basic AODV routing protocol to reduce the number of the control packets.
References
1. Perkins, C.E., Bhagwat, P.: Highly dynamic destination sequenced distance-vector routing (DSDV) for mobile computers. In: ACM SIGCOMM, pp. 234–244, August 1994
2. Perkins, C.E., Belding-Royer, E.M., Das, S.: Ad hoc On-Demand Distance Vector (AODV) Routing. Internet Request For Comments RFC 3561, Internet Engineering Task Force, July 2003
3. Johnson, D.B., Maltz, D.A., Hu, Y.-C.: The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks (DSR). Internet Draft–draft-ietf-manet-dsr-09.txt, April 2003
4. Clausen, T., Jacquet, P.: Optimized Link State Routing Protocol (OLSR). Internet Request For Comments RFC 3626, Internet Engineering Task Force, October 2003
5. http://www.isi.edu/nsnam/ns/
6. Elliott, E.O.: Estimates of error rates for codes on burst-error channels. Bell Syst. Tech. J.42, 1977–1997 (1963)
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