Characteristics Of Mobile ADHOC Networks Computer Science Essay

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Wireless networks are becoming popular in last few decades, particularly from the 1990s when the networks being adopted to enable mobile behaviour of wireless devices. The popularity of mobile devices (MDs) and wireless networks significantly increased over the past 30 years. Mobile Adhoc Networking Working Group was established in 1991. Mid and late 1990 JTRS (Joint Tactical Radio System) in 1996, and IETF (Internet Engineering Task Force) published several drafts about routing protocols of MANET(mobile adhoc network), 2000 and IEEE Workshop on Mobile Adhoc Networking and Computing was organized in 2000 [1, 2].

The concept of commercial adhoc networks arrived with notebook computers and other viable communications devices based on radio waves concept of commercial adhoc networks has emerged. The idea of an infrstructureless collection of mobile hosts was proposed in two conference papers [3, 4] and the IEEE 802.11 subcommittee adopted the term "adhoc networks." The concept of commercial (non-military) adhoc networking had arrived. Meanwhile, the IEEE 802.11 subcommittee standardized a medium access protocol that was based on collision avoidance and tolerated hidden terminals, for building mobile adhoc network prototypes out of notebooks and 802.11 PCMCIA (Personal Computer Memory Card International Association) cards.

Mobile adhoc network has now become one of the most vibrant and vigorous fields of wireless communication and networking research. The wireless networks can be subdivided into two classes, class first is infrastructure and class second is infrastructureless networks [8, 9]. These classes of networks are described as follows:

Class first: Class first networks known as infrastructure networks with fixed and wired gateways. They have fixed base stations connected to other base stations through wires or wireless. Typical applications of this type of "one-hop" wireless network include wireless local area networks (WLANs) as shown in figure 1.1 (a). The Cellular networks come under this category.

Class Second: Class second networks is known as the infrastructureless mobile network. These types of networks do not have fixed routers and all nodes are capable of movement and can be connected dynamically in an arbitrary manner, commonly known as the MANET shown in figure 1.1 (b). A mobile adhoc network (MANET), sometimes called a mobile mesh network, is a self-configuring network of mobile devices connected by wireless links [5, 6]. In an adhoc networks there are no supporting infrastructure like base stations, access points or wireless switching canters.

Figure 1.1 (a) Infrastructure Network

Figure 1.1 (b) Infrastructureless Network

This network can be established as soon as two or more nodes are within each other's transmission range. Nodes within range communicate directly, while nodes further apart rely on other nodes to relay messages for them. If the nodes in the network are mobile, then the topology of the network frequently changes. It is usually referred to a decentralized autonomous system.

This chapter is organised as- section 1.1 characteristics of mobile adhoc networks, 1.2 applications and challenges in mobile adhoc networks, section 1.3 simulation tools for MANET, section 1.4 scenario generation tools, section 1.5 objective of present work and finally section 1.6 organization of Thesis.

1.1 Characteristics of Mobile Adhoc Networks

The characteristics of self connectivity and easy deployment of mobile adhoc networks (MANETs), play an increasingly important role in future civilian and military application, where wireless access to a wired backbone is either ineffective or impossible then it becomes useful in battlefield communications, emergency, surveillance situations, rescue operations and civilian applications like smart homes, patient monitoring while they and staff roam in hospital, environmental control, etc. Mobile adhoc networks have several salient characteristics like self-creation, self-organization and self administration, autonomous and infrastructure less, limited physical security [7, 9, 10, 27] and some others characteristics are shown in figure 1.2.

Figure 1.2 Mobile Adhoc Network Characteristics

1.2 Applications and Challenges in MANET

Present and future MANET applications and their scenario based services are summarized in table 1.1 [8, 10-15].

Table 1.1 Mobile Adhoc Network Applications

S.no.

Applications

Scenario Based offered Services

1

Home and enterprise

Home/office wireless networking

Conferences, meeting rooms

Personal area networks (PANs), personal networks (PN)

Networks at construction sites

2

Education

Universities and campus settings

Virtual classrooms

Ad hoc communications during meetings or lectures

3

Entertainment

Multi-user games

Wireless P2P networking

Outdoor internet access

Robotic pets

Theme parks

4

Commercial and civilian environments

E-commerce: electronic payments anytime and anywhere

Business: dynamic database access, mobile offices

Vehicular services: road or accident guidance, transmission of road and weather conditions, taxi cab network, inter-vehicle networks

Sports stadiums, trade fairs, shopping malls

Networks of visitors at airports

5

Sensor networks

Home applications: smart sensors and actuators embedded in consumer electronics

Body area networks (BANs)

Data tracking of environmental conditions, animal movements, chemical/biological detection

6

Context aware services

Follow-on services: call-forwarding, mobile workspace

Information services: location specific services, time dependent services

Infotainment: touristic information

7

Coverage extension

Extending cellular network access

Linking up with the Internet, intranets, etc.

8

Emergency services

Search and rescue operations

Disaster recovery

Replacement of fixed infrastructure in case of environmental disasters

Policing and fire fighting

Supporting doctors and nurses in hospitals

9

Tactical networks

Military communication and operations

Automated battlefields

The main problem in MANET is to construct and maintain a multi-hop route between the source and the destination in a dynamic environment. For example, if all the intermediate nodes of an initiated route are moving, the route stability will be affected by the nodes mobility. The route maintenance will become easier if the nodes mobility can be predicted in advanced. The specific characteristics and complexities, which are summarised, impose many design challenges to the network protocols [11].

Limited wireless transmission range

Broadcast nature of the wireless medium

Packet losses due to transmission errors

Mobility-induced route changes

Mobility-induced packet losses

Battery constraints

Potentially frequent network partitions

Increased attention is paid to aspects such as routing security

Mobility is a big challenge in MANET, this specific characteristic is solved by appropriate prediction of the node movement through a mobility model. The aim of mobility model is to make an attempt to mimic the movements of real MNs (mobile nodes). MANET protocols must maintain complex network functionalities and logical operations that determine reliable routes in a highly dynamic environment. MANET performance depends largely on multi-hop routing governed by routing protocols. Mobility plays significant role for affecting the MANET routing protocols. Mobility is a major hindrance to the smooth operation of a MANET protocol. It increases link distraction which results higher network activity and exerting more pressure on protocol performance, therefore, in this thesis mobility is considered as key problem for understanding its impact on routing performance in MANET.

Simulation Tools for MANET

In communication and computer network research, network simulation is a technique where a programme module behaviour of networks either by calculating interaction between the network entities (host/routers, data link, packets etc) using the mathematical formula, or actually capturing and playing back observation from a network. The behaviour of the network, various applications, services and their supports can be observed through simulation. Various attributes of the environment can also modify in a controlled manner to assess how the network would behave under different scenario [16].

Network simulation

A real time network establishment is very cost effective. One time establishment of network may not be a good estimation for desired performance of the network, therefore, it may lead further changing of network peripherals. It is always better to have a simulation of network using some simulators like NS-2.34, Qualnet, OPNET, GlomoSim etc. These simulators are helpful for evaluating the performance of networks with low cost involvement. NS 2.34 version is used in this thesis for simulation purpose.

1.3.2 Overview of NS-2

Network Simulator (NS) [17, 18] is a discrete event simulator targeted at networking research, developed at the UC Berkeley that simulates variety of internet protocol (IP) networks. It is constantly under development by an active community of researchers. Network simulator (NS) is based on two languages: an object oriented simulator, written in C++ and Otcl (an object oriented extension of Tcl) interpreter, used to execute user's command script.

A tool command language (TCL) created by John Ousterhout. It is used by millions of people in the world. It has s very simple syntax and allows very easy integration with other languages. The characteristics of these languages are;

Supports rapid development

Provides graphical interface

Compatible with many platform

Flexible for integration

Open source and ease in use

C++ and Otcl have support for both wired and wireless networks and can simulate several network protocols such as TCP (Transmission Control Protocol), UDP (User Datagram Protocol), multicast routing, etc. More recently, support has been added for simulation of large satellite and adhoc wireless networks. The NS project is now a part of the VINT (Virtual Inter-Network Test Bed) project that develops tools for simulation results display, analysis and converters that convert network topologies generated by well-known generators to NS formats [17].

NS (version 2.34) written in C++ and OTCL (TCL script language with Object-oriented extensions developed at MIT) is used in this thesis for all simulation works. As shown in figure 1.3, NS simulator library which has event scheduler objects, network component objects and network setup helping modules (Plumbing modules). In NS (network simulator) user write program in OTCL script language then this script interpreted and initiates an event scheduler, setup network topology and tells traffic sources when to start and stop transmitting packets.

Figure 1.3 Simplified User's View of NS [19]

The simulated results is visualized with NAM (network animator) and analyzed by some filter tools written in some scripts as shown in figure 1.3.

Why NS-2?

NS-2 is an open source, works under UNIX and Window system platform. The main advantage of the NS-2 is low cost of development and implementation in comparison to experimental tests in real environment.

Architectural View of NS-2

The architecture of network simulator constitute five components;

Event Scheduler

Network component

Tclcl 1.19

Otcl 1.13 library

Tcl 8.4.18 script language

Figure 1.4 Architectural View of NS-2[19]

Event scheduler: Figure 1.4 shows the architectural View of NS-2.34. To drive the execution of the simulation, to process and schedule simulation events, NS makes use of the concept of discrete event schedulers [19]. In NS, network components that simulate packet-handling delay or that need timers use event schedulers. If network object issues an event, it has also to handle the event later at scheduled time. There are two different types of event schedulers i.e. non-real-time and real-time schedulers:

Non-Real-Time Schedulers (NRTS) - in Non real-time scheduler, there are three implementations (List, Heap and Calendar); the default is Calendar.

Real Time Scheduler (RTS)- it is used for emulation and allowed the simulator to interact with a real time network

Network Component: NS-2.34 models all network elements with a class library. This class library has a hierarchy; the TclObject class is the superclass of all OTcl library objects (network components, event scheduler, timers and others) [20]. Subclasses of TclObject, NsObject again are the super class of all basic network component objects that handle packets. Network objects, such as nodes and links can then be composed of this basic network component. Moreover, NsObject has two subclasses, Connector and Classifier. Connector is the super class of all basic network objects that have only one output data path and Classifier is the superclass of all switching objects that have possible multiple output data paths. Network objects can now be composed of all basic network component objects that are under the NsObject class [21]. Brief descriptions of these classes are defined below.

Tcl 8.4.18: Tcl (tool command language) is a scripting language of version 8.4.18 which is used for NS -2.34.

Otcl 1.13: Object TCL, is an extension to TCL/TK (Tool Command Language/ Toolkit ) scripting language for object-oriented programming developed at MIT. OTcl is used to express the definition, configuration and control of the simulation in NS. OTcl script creates an event scheduler, sets up the network topology with nodes and likes between them, creates traffic, inserts errors and sets tracing options.

Tclcl 1.19: It is used to implement the Otcl 1.13 linkage.

Figure 1.5 Internal mechanism of NS2 for routing in MANETs [20]

Scenario Generation Tools

Before starting the simulation of any network, it is required a network scenario. In this regard, there are many scenario generator tools but in present work Setdest, BonnMotion-1.5 and Mobility Generator Tool are used. The generated scenario of these tools is compatible with NS2.34.

Setdest Tool: To generate the node traces of only Random Waypoint model the "setdest" tool [22] is used by CMU Monarch group. This tool is included in the network simulator (NS-2) by L. Breslau et al. in 2000 [23]. The node movement files are generated using CMU's scenario generator to be found under ~ns/indep-utils/cmu-scen-gen/setdest. This tool randomly generates a RWP mobility scenario and dumps it in form of TCL scripts. TCL script is used in NS-2 later. The arguments passed are the number of nodes, simulation time, width and height of the simulation area, pause time and node speed.

BonnMotion-1.5 Tool: BonnMotion-1.5 [24] is Java software which creates and analyses mobility scenarios. It is developed within the communication systems group at the Institute of Computer Science 4 of the University of Bonn, Germany, where it serves as a tool for the investigation of mobile adhoc network characteristics. The scenarios can also be exported for the network simulators NS-2, GloMoSim/QualNet, COOJA, MiXiM and ONE.

Mobility Generator Tool: This tool is introduced by F.Bai et al. at University of Southern California in 2004 [25]. This mobility generator tool is very useful for generating the MNs (mobile nodes) patterns. This mobility generator tool is used to generate a rich set of mobility scenarios used to evaluate the protocol performance in mobile adhoc network. The trace files generated by this tool are compatible with the format required by NS-2.

Other Analysis Filters/Tools

Some of other Filters/ Tools like grep command, awk and perl scripts are mainly used to extract important statistics information from NS-2 generated results (trace file) which include detailed information about received and transmitted packets and allow post run processing with these tools.

GREP: It is used in Unix/Linux to "filter" patterns of a file. This is important because some NS-2.34 generated trace files are enormous hence needs to be filtered.

AWK: awk is a powerful UNIX command, using AWK, a command file or an input file should be given. A command file can be a file or a command line input. The command file would tell awk how to deal with the input file. It is composed of patterns and actions. AWK normally parse the file line by line. This utility filter allows doing simple operations on

NS-2 traces file such as averaging the values of a given column, summing or multiplying term by term between several columns. It is useful for analyzing the performance metrics.

PERL: Perl is a programming language developed by Larry Wall in 1987 [26] as a general-purpose UNIX scripting language to make report processing easier, especially for processing text. Due to its strong text processing abilities, Perl has become one of the most popular language for writing CGI (common gateway interface) scripts and other internet applications. Perl is an interpretive language which makes it easy to build and test simple programs. Perl is used for graphics programming, system administration, network programming, finance, bioinformatics, and other applications.

Objective of present work

The objectives of this thesis are to classify mobility models, describe mobility matrices class and impact assessment of mobility metrics on routing performance metrics as well as building block of routing protocols in MANET. The present work carried out to achieve this objective is divided into;

Classification and analysis mobility metrics categories i.e. direct metrics and derived metrics. Further classification and description of mobility models based on mobility matrices class i.e. random based movement, temporal dependencies, spatial dependencies, geographical restriction and hybrid structure has been carried out.

Evaluation of direct metrics for mobility pattern differentiation and justification of category of mobility model.

Assessment of effect of the mobility pattern over derived metrics (connectivity graph) between the mobile nodes and links.

Finally, analysis of mobility pattern impact over routing performance metrics and the protocols building blocks is analysed to understand the behaviour of the protocols in the present task.

Organization of Thesis

The organization of thesis is as follows; chapter 1 gives the introductory background of wireless adhoc networks, their characteristics, applications, challenges and simulators used in brief, chapter 2 classification and analysis of mobility model for mobile adhoc network, chapter 3 performance evaluation of direct metrics for mobility pattern differentiation in mobile adhoc networks, chapter 4 impact analysis of mobility patterns on derived metrics (connectivity graph), chapter 5 impact of mobility models on routing performance metrics and building blocks of MANET routing protocols and finally, chapter 6 concludes the present work and scope for future work.

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