Reliable Communication Using Topology Control in Mobile Ad-hoc Network

The measurability of Mobile ad hoc network (MANET) is the precondition of its management, performance optimization and network resources re-allocations. The traditional network interior measurement technique performs measurement on the nodes or links directly, and obtains the node or link performance through analyzing on the measurement sample, which usually is used in the wired networks measurement based on the solid infrastructure. However, MANET is an infrastructure-free, multi-hop, and self-organized temporary network, comprised of a group of mobile nodes with wireless communication devices. Not only does its topology structure vary with time going by, but also the communication protocol used in its network layer or data link layer is diverse and non-standard. Specially, with the limitation of node energy and wireless bandwidth, the traditional interior network measurement technique is not suited for the measurement requirement of MANET .A mobile ad hoc network is an autonomous collection of mobile devices (laptops, smart phones, sensors, etc.) that communicate with each other over wireless links and cooperate in a distributed manner in order to provide the necessary network functionality in the absence of a fixed infrastructure. This type of network, operating as a stand-alone network or with one or multiple points of attachment to cellular networks or the Internet, paves the way for numerous new and exciting applications. Application scenarios include, but are not limited to: emergency and rescue operations, conference or campus settings, car networks, personal networking, etc. AD HOC NETWORK In general, mobile ad hoc networks are formed dynamically by an autonomous system of mobile nodes that are connected via wireless links without using the existing network infrastructure or centralized administration. The nodes are free to move randomly and organize themselves arbitrarily; thus, the networks wireless topology may change rapidly and unpredictably. Such a network may operate in a standalone fashion, or may be connected to the larger Internet. Mobile ad hoc networks are infrastructureless networks since they do not require any fixed infrastructure, such as a base station, for their operation. In general, routes between nodes in an ad hoc network may include multiple hops, and hence it is appropriate to call such networks as ‘‘multi-hop wireless ad hoc networks’’. Each node will be able to communicate directly with any other node that resides within its transmission range. 1.1 Ad Hoc Network System Architecture According to Ad Hoc network inherent characteristics, such as self-organization,wireless multi-hop routing, dynamic topology, limitation of wireless bandwidth andenergy and low security, its system architecture could be divided as the five layers as described in figure 1(a), such as physical layer, data link layer, network layer, transportation layer and application layer. In the figure 1(a), physical layer mainly is in charge of wireless frequency choice, signal detection, transmission and reception, modulation/demodulation, wireless channel encryption/decryption. It also adopts wireless spread spectrum technique to implement wireless signal transmission and reception, such as DSSS and FHSS. Data link layer is divided into logical link control layer (LLC) and medium access control layer (MAC) again. The LLC has the function of assembling the data frame, checkout, flow and error control from point to point. In recent years, the MAC mainly adopts four mechanisms to control the shared wireless channel access which is chosen by mobile nodes. The first one is stochastic competition technique, i.e., CSMA/CA. The second one is sub-channel access mechanism, such as TDMA, FDMA, CDMA and SDMA, and so on. The last two mechanisms are polling method and dynamic adjusting method. Network layer mainly takes charge of neighbor discovering, routing choice and congestion control. The transportation layer could provide different processes in application layer with reliable or unreliable data transmission service. At present, transportation layer mainly adopts the traditional communication protocol, such as TCP, UDP or special protocols. Application layer provides different application service with the its application interface concerned. (a) Ad Hoc network system architecture (b) Ad Hoc network adaptive system architecture Figure.1. Ad Hoc network system architecture Sunil Deokule et al, / (IJCSIT) International Journal of Computer Science and Information Technologies, Vol. 5 (2) , 2014, 991-993