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CHAPTER 1 INTRODUCTION TO WIRELESS NETWORKS 1.1 Introduction Computer network consists of two or more autonomous computers that are linked together in order to share the resources and allow electronic communication to increase the productivity. There are two broad categories of computer networks, namely, wired networks and wireless networks. In wired networks the connecting medium of all computing devices is some kind of cables. Wires are subjected to physical damage. In wireless network the connecting medium is some form of wireless facility. The wired networks are slowly getting replaced by wireless networks. Instead of wired connectivity, telecommunication equipments are connected with electromagnetic waves in wireless networks. The advantage of a wireless network is the mobility and freedom from the restriction of wires or a fixed connection. The signal travels as electromagnetic waves through the air. Wireless network has made a network extremely portable because of digital modulation, adaptive modulation, information compression, and access multiplexing. Rapid advances in mobile devices and wireless networking have converged to enable ubiquitous computing where mobile devices can access services, run programs, utilize resources, and harvest computing power anytime and anywhere. Wireless networks enable the delivery of services that are no longer bound by time or location barriers [1]. Wireless networks allow the user to use the network devices anywhere in an office or home. Wireless networking is available in public “hotspots,” such as businesses, and airports. With the advent of cellular phones, laptops, palmtops and PDAs, one can get connected to the global internet. The challenges posed by wireless networks are different from traditional wired computer networks. Mobile and wireless communication provide greater flexibility and ease of access, they rely on an open and public transmission media over which eavesdropping, unauthorized access, user tracking, and other security threats can be carried out more effectively in comparison with wired networks [2]. The key differences between the wired network and wireless network are shown in Table 1.1. 1 Table 1.1 Differences between wired and wireless network Sl. No. 1 WIRED NETWORK WIRELESS NETWORK 2 3 4 5 6 7 8 9 Communicates through data cables (i.e., Ethernet-based) Need more bandwidth Number of users is usually known Identity of users is controllable Less cost Reliability is high Performance is very good Mobility is limited No interference below network layer 10 Inflexible Communicates through radio waves Need less bandwidth Number of users is not predictable Identity of users is difficult to control More cost Reliability reasonably high Good Unlimited Interference can occur at the physical layer Flexible (expect a lot of technical change within the network) 1.2 Components of wireless networks The wireless networks have a set of components that are different from wired networks. The components of wireless network are [3, 4]: Wireless hosts: As in the case of wired networks, hosts are the end-system devices that run applications. A wireless host might be a laptop, palmtop, PDA and desktop computer. The hosts themselves may or may not be mobile. Wireless links: A host connects to a base station or to another wireless host through a wireless communication link different wireless link technologies have different transmission rates and can transmit over different distances. Base station: The base station is a key part of the wireless network infrastructure which has no counterpart in a wired network. It is responsible for sending and receiving data to and from a wireless host that is associated with that base station. A base station will often be responsible for coordinating the transmission of multiple wireless hosts with which it is associated. When a wireless host is associated with a base station, it means that the host is within wireless communication distance of the base station and the host uses the base station to relay data between it and the larger network. 2 1.3 Characteristics of wireless networks Apart from various characteristics mentioned so far, the wireless networks also have the following characteristics [5] that make them significantly different from wired networks. Dynamic network topology: The network nodes are mobile and thus the topology of the network may change frequently. Infrastructure less: Central servers, specialized hardware, and fixed routers are absent. Multi-hop: Packets follow multichip routes and pass through different mobile nodes before arriving at their final destination. Amorphous: Node mobility and wireless connectivity allow nodes to enter and leave the network spontaneously, to form and break links unintentionally. Therefore, the network topology has no fixed form regarding both its size and shape, i.e., it changes frequently. Power limitation: Ad hoc enabled mobile hosts are small and lightweight, and they are often supplied with limited power resources, such as small batteries. Memory and computation power limitation: Ad hoc enabled mobile nodes have limited storage devices and weak computational capabilities. Consequently, high complex security solution such as symmetric or asymmetric data encryption, are difficult to implement. Mobile devices physical vulnerability: Mobile devices used in Mobile Ad hoc Networks (MANETs) are lightweight and portable. This represents vulnerability, since the devices and the information stored in the devices can be easily stolen. Mechanisms for protecting both devices and information should be employed. [6] Hostile environment: The devices in an Ad hoc network are autonomous units, which roam around in a hostile environment. Devices lack physical protection and are always under the threat of being captured and compromised. Further, a device is always under the threat of being attacked by other malicious or compromised devices in the network. This means that every device should be prepared to operate in a mode that trusts no peer. 3 1.4 Types of wireless network Wireless networks utilizes spread-spectrum or OFDM depends on the technology which is using. Wireless network enable a user to move about within a wide coverage area and still be associated to the network [4, 6, 7]. The various types of wireless networks are: 1. IEEE 802.11 Wireless LAN (Wi-Fi) 2. IEEE 802.15 Wireless Personal Area Network 2.1 IEEE 802.15.1 (Bluetooth Certification) 2.2 IEEE 802.15.2 (Zigbee Certification) 3. IEEE 802.16 Broadband Wireless Access (WiMax Certification) 4. Mobile Ad hoc Network (MANET) 5. Wireless Sensor Network (Base Network) 6. Wireless Mobile Ad hoc Sensor Network (MASN – Hybrid) 7. Wireless Metropolitan Area Network (WMAN) IEEE 802.11 Wireless LAN (Wi-Fi) provide wireless network contact using radio signal instead of traditional network cabling. They provide highest data-transfer rate with 802.11 terminologies. WLANs offering various benefit for user such as mobility, condensed Cost-of-Ownership, installation speed and flexibility and scalability. IEEE 802.15 Wireless Personal Area Network (WPAN) is used to provide connectivity to personal devices separated by up to 10 meters. This network is a lowpower, short-range, low-rate “cable-replacement” technology for interconnecting notebooks, peripheral devices, cellular phones and PDAs. Bluetooth belongs to this network category. Any Bluetooth enabled device could search for other Bluetooth devices and could communicate with them [5]. IEEE 802.16 Broadband Wireless Access (WiMax Certification) provides full worldwide interoperability for microwave access, communication technology for wirelessly delivering high-speed Internet service to large geographical areas. WiMAX would operate similar to WiFi but at higher speeds, over greater distances and for a greater number of users. WiMAX has the ability to provide service even in areas that are difficult for wired infrastructure to reach and the ability to overcome the physical limitations of traditional wired infrastructure. 4 Mobile Ad hoc Network (MANET) is a collection of wireless mobile nodes dynamically forming a temporary network without the use of existing network infrastructure or centralized administration. Due to the limited transmission range of wireless network interfaces, multiple network hops may be needed for one node to exchange data with another across the network. In such a network, each mobile node operate not only as a host but also as a router, forwarding packets for other mobile nodes in the network, that may not be within the direct reach wireless transmission range of each other. Each node participates in an ad hoc routing protocol that allows it to discover multi hop paths through the network to any other node. The idea of an ad hoc network is sometimes also called an infrastructure-less networking, since the mobile nodes in the network dynamically establish routing among themselves to form their own network on the fly. Some examples of the possible use of ad hoc networks include students using laptop computers to participate in an interactive lecture, business associates sharing information during a meeting, soldiers relaying information for situational awareness on the battlefield, and emergency disaster relief personnel coordinating efforts after a hurricane or earthquake. MANET the chosen area of this research is explained in detail in Chapter 2. Wireless Sensor Network (WSN) is an emerging technology that shows great promise for various futuristic applications both for mass public and military. The sensing technology combined with processing power and wireless communication makes it lucrative for being exploited in abundance in future [8]. The basic idea of sensor network is to disperse tiny sensing devices; which are capable of sensing some changes of incidents/parameters and communicating with other devices, over a specific geographic area for some specific purpose. Wireless Mobile Ad hoc Sensor Network (WASN) combines the advantages of sensor networks and MANETs. Wireless Metropolitan Area Network (WMAN) is fast communicating networks within the vicinity of a metropolitan area and span up to 50km. WMAN designed for a larger geographical area than a LAN. The standard of MAN is DQDB which cover up to 30 miles with the speed of 34 Mbit/s to 155 Mbit/s. WMAN is a certified name by the IEEE 802.16 that functioning on Broadband for its wireless metropolitan. 5 1.5 Advantages of wireless network The technical advantages of the wireless networks result in various other consequential advantages in business and management. A few are listed below: Reduced cost of installation in the organizations Flexible configuration that easily accommodate growth, change and scalability Allowance of mobile employees Increased productivity and streamlined processes due to convenient information access No need to knock holes in walls Adaptability as a stand-alone solution or to compliment a traditional wired network 1.6 Limitations of wireless network Despite a wide range of technical, organizational, financial and operational advantages offered by the wireless networks, a few limitations still exist which are listed below. The potential for radio interference due to weather, other wireless devices, or obstructions like walls. The range of a wireless network is limited and a typical wireless device will only allow individuals within 150 to 300 feet to access the network. Wireless networks are typically inexpensive, but can cost up to four times more to set up a wireless network than to set up a wired network in some cases. Wireless networks can be accessed by any computer within range of the network's signal so information transmitted through the network (including encrypted information) may be intercepted by unauthorized users. Wireless networks are typically slower than wired networks, sometimes even up to 10 times slower. 6 1.7 Summary A wireless network connects the computing devices without wires. Wireless technologies make use of electromagnetic microwaves in the ultra high frequency band to send data from one node to another. This chapter discussed the different types of wireless networks, their characteristics, advantages and limitations. The domain of the research is Mobile Ad hoc network (MANET) which is a part of wireless network. The following chapter deals with the MANETs. 7