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working connectivity on rough scenarios like “disaster relief areas, battle fields” etc, and considered as best alternative where environmental conditions are another factor that changes the network topology. Using the location of nodes and the availability of direct communication between each pair of nodes the network topology is described.

2.1 Ad-hoc networks:

Centralized networks, such as GSM, cannot be used in all situations. Significant examples of such scenarios where ad hoc networks can be used include establishing survivable, efficient, dynamic communication for rescue operations, disaster relief efforts and military networks. These kinds of networks cannot rely on centralized and organized connectivity and can be considered as applications of MANETs. MANETs has several set of diverse applications which range from ‘small static networks restrained by power sources, to large mobile networks which are highly dynamic’.

All nodes should be able to act as routers for each other, in order to enable multi-hop communication in a distributed manner (See Figure 2.1). Nodes help each other in conveying information to and fro and thereby creating a virtual set of connections between each other. Ad hoc network can only exist and operate if its nodes demonstrate a cooperative behavior.

Routing protocol sets up and maintains the Routes. Routing protocols play a vital role in the creation and maintenance of these connections. In contrast to wired networks, each node in an ad-hoc networks acts like a router. As these routers are usually on the move, standard intra-router protocols cannot be immediately adapted to ad-hoc networks. MANET routing protocol design is a complex issue considering the possible rapidly changing topology of such networks.
Hassene Bouhouch, Sihem Guemara EL Fatmi, “QoS In Ad Hoc Networks by Integreting Activity in the OLSR.
Leila Boukhalfa, Pascale Minet and Serge Midonnet, “QoS support in a MANET based on OLSR and CBQ.
Many different types of routing protocols have been developed for ad hoc networks and have been classified into two categories
Reactive
Proactive

In reactive routing protocols, in order to preserve precious node battery, routes are only discovered when required, while in proactive routing protocols routes are established before usage and hence avoid the delays incurred while discovering new routes in the reactive routing protocols. Reactive protocols set up traffic routes on-demand, whilst proactive protocols attempts to dynamically maintain a full understanding of the topology.

2.1.1 Wireless communication

Ad-hoc networks are not restricted to any special hardware. But today such networks are most likely to consist of nodes utilizing so-called WLAN interfaces . These are wireless interfaces operating according to IEEE specifications 802.11a, 802.11b or 802.11g. Throughout this document it is assumed that an ad-hoc network consists of links made up by either WLAN or Ethernet interfaces.

Figure: 2-1, A traditional base station scheme compared to ad-hoc multi-hop network.

IEEE 802.11 does not support multi-hop communication by it self. Two modes are defined for communication using WLAN devices:
Infrastructure mode: The wireless network consists of at least one access point and a set of wireless nodes. Such configuration is known as Bas本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。