Ad-Hoc Network Management Ad Hoc Network Mobile hosts and wireless networking hardware are becoming widely available, andextensive work has been done recently in integrating these elements into traditionalnetworks such as the Internet. However, mobile users will want to communicate insituations in which no fixed wired infrastructure such as this is available, eitherbecause it may not be economically practical or physically possible to provide thenecessary infrastructure or because the expediency of the situation does not permit itsinstallation. For example, a class of students may need to interact during a lecture,friends or business associates may run into each other in an airport terminal and wishto share files, or a group of emergency rescue workers may need to be quicklydeployed after an earthquake or flood. In such situations, a collection of mobile hostswith wireless network interfaces may form a temporary network without the aid of anyestablished infrastructure or centralized administration. This type of wireless networkis known as an ad hoc network. General Network Concepts A wireless network is comprised of devices with wireless adapters communicating witheach other using radio waves. These wireless devices are called nodes in thisdissertation. The signal transmitted can be received only within a certain distancefrom the sender, which is called the range of the node. A base station (BS) is a specialnode in the network that is not mobile and is located in a central location. Wirelessnetworks differ in the duplexing mechanism and the network architecture. Network Architecture: Based on the network architecture, wireless networks can belogically divided into two classes: distributed and centralized. Distributed Wireless Networks: Distributed wireless networks, also called ad-hocnetworks, are wireless terminals communicating with one another with no pre-existinginfrastructure in place; therefore, they are also called infrastructure-less networks. Atypical ad hoc network is illustrated in figure.
Figure: Adhoc Network Wireless terminals have a wireless interface (RF or infrared) and exchange informationbetween one another in a distributed manner. An ad hoc network has no centraladministration, thus ensuring that the network does not collapse when one of theterminals is powered down or moves away. In a distributed network all datatransmission and reception has to be in the same frequency band since there are nospecial nodes to translate the transmission from one frequency band to another.Therefore, all ad hoc networks operate in TDD mode. Centralized Wireless Networks: Figure: Centralized wireless network Centralized wireless networks: Centralized wireless networks, also known as last-hop networks, are extensions to wireline networks with wireless in the last section of the network. These networks have a base station that acts as the interface between wireless and wireline networks. In centralized networks the downlink transmissions (from base station to wireless nodes) are broadcast and can be heard by all the deviceson the network. The uplink (from wireless terminals to the BS) is shared by all the nodes and is therefore a multiple access channel. The existence of a central node like a BS gives a great degree of flexibility in the design of MAC protocols. The BS can control the uplink transmissions by allowing access according to QoS requirements. The system architecture of a centralized network is shown in above figure. A centralized network can operate both in TDD mode or FDD mode.