计算机专业英语期末论文.doc

淮海工学院计算机工程院实验报告书课程名： 计算机专业英语 题 目： Ad Hoc网络 班 级： 学 号： 姓 名： 评语：成绩： 指导教师： 批阅时间： 年 月 日Flash animation in web pages on the Ad Hoc NetworkAbstract: Ad Hoc network with the rapid development of wireless communication technology and the emergence of a new type network. This paper introduces the Ad Hoc network concept, features, applications, and other mobile communication system difference and network management issues.Keywords:Ad Hoc network Mobile IP Network management0 IntroductionAlong with the people to get rid of the wired network, whenever and wherever possible bound can be freely communication desire, in recent years, wireless network communication has been developing rapidly. People can be equipped with wireless interface of the portable computer or personal digital assistant for mobile communication. The present mobile communication mostly need wired infrastructure ( such as base station ) to support implementation. In order to be able to communicate without fixed base station place, one kind of new network technology - Ad Hoc network technology emerge as the times require. Ad Hoc network need not be wired infrastructure support through a mobile host free network communication. Ad Hoc network has promoted people achieve in any environment free communication process, at the same time it also for military communications, disaster relief and temporary communication provides an effective solution.1 The concept of Ad Hoc networkAd Hoc network is a kind of no cable infrastructure to support mobile network, the nodes in the network by the mobile host. Ad Hoc network is initially applied in the military field, it originated from the study of battlefield environment of packet radio network data communication project, the project financed by the DARPA, thereafter, again in 1983 and 1994 were survivable adaptable network SURAN ( Survivable Adaptive Network ) and global mobile information system GloMo ( Global Information System ) research project. Because the wireless communication and the terminal technology unceasing development, the Ad Hoc network in civil environment has also been developed, such as the need in the absence of wired infrastructure areas for temporary communication, can be conveniently through the platform of Ad Hoc network.In Ad Hoc network, when two mobile host in each others communication coverage range, they can communicate directly. But the mobile host communication limited coverage, if two are far apart from the host to communicate between them, needs through the mobile host B forwarding can be achieved. Therefore in the Ad Hoc network, a host or router, charged with looking for routing and forwarding message work. In Ad Hoc network, each host communications limited range, so the routing generally by multi-hop, data through multiple host forwarding to reach the destination. The Ad Hoc network is also known for multi-hop wireless networks.Ad Hoc networks can be regarded as a mobile communication and computer network of the cross. In Ad Hoc network, using computer network packet switching mechanism, rather than circuit switching mechanism. Communications in the host is generally a portable computer, a personal digital assistant ( PDA ) and mobile terminal equipment. Ad Hoc network differs from the current Internet environment in mobile IP network. In the mobile IP network, mobile host can pass through the fixed wired network, a wireless link and dial-up line access network, while in the Ad Hoc network exists only in a connection mode of wireless link. In the mobile IP network, mobile host through the adjacent base station cable infrastructure to support communication, the base station and the base station ( agents and agents) between the wired network are, still use the traditional Internet routing protocols. While the Ad Hoc network without the support facilities. In addition, in mobile IP networks of mobile hosts that do not have the routing function, just a general communication terminal. When the mobile hosts move from one area to another area does not change the network topology, and Ad Hoc networks of mobile hosts move would lead to changes in topology.2. The characteristic of Ad Hoc networkAd Hoc network as a new network mode, has the following characteristics. 2.1 The network s independenceAd Hoc network relative to conventional communication network, the biggest difference is that may at any time, any place without a hardware network infrastructure support, rapid construction of a mobile communication network. Its establishment is not dependent on the existing network communication facilities, have certain independence. Ad Hoc network is very suitable for the characteristics of disaster relief, remote communication application.2.2 Dynamic change of the network topologyIn Ad Hoc network, mobile host can optionally move in network. The mobile host can lead to host a link between increased or disappear, relationships between hosts changing. In ad hoc network, the host may simultaneously or router, therefore, the mobile will make the network topology changes, and changes in the mode and speed are unpredictable. For the conventional network, topological structure of the network are relatively stable.2.3 The limited bandwidth of wireless communicationsIn the Ad Hoc network without cable infrastructure support, therefore, the communication between host through wireless transmission to complete. Due to the physical property of wireless channel, it provides the network bandwidth relative cable channel is much lower. Besides, considering the competition shared radio channel produced by collisions, signal attenuation, noise and other factors, the mobile terminal can obtain the actual bandwidth is far less than the maximum bandwidth value theory.2.4 Host energy LimitedIn Ad Hoc network, the host is a number of mobile devices, such as PDA, portable computer or pda. The host may be in constant state of mobile, host energy is mainly supplied by the battery, so the Ad Hoc network has the characteristics of energy limited.2.5 The network distributed characteristicsIn the Ad Hoc network without central control node, the host through the distributed protocol internet. Once the network of a certain node fails, the rest of the node and can still work normally.2.6 Short life cycleAd Hoc network is mainly used for temporary communication needs, relative to the cable network, its time to live is short.2.7 Limited physical securityMobile network is usually better than the fixed network more vulnerable to physical security attacks, susceptible to eavesdropping, deceit and denial of service attack. The existing link security technology have been applied to a wireless network to reduce security attacks. But Ad Hoc network distributed characteristics compared with the centralized network has certain invulnerability.3. Ad Hoc network applicationsAd Hoc network application scope is very broad, on the whole, it can be used in the following situations:A ) no wired communication facilities, such as the absence of hardware communications facilities or wired communication facilities damaged.B ) requires distributed characteristics of the network communication environment.C ) the existing wired communication facilities is insufficient, need temporary quickly set up a communication network environment.D ) be a strong backup network survivability.Ad Hoc network technology research is the first to meet the needs of military application, military communication system is needed, since the group of survivability and mobility. During the war, the communication system is easy to be attacked by enemies, therefore, requires communication system is able to withstand a certain degree of attack. If the use of centralized communication system, once the communication center is destroyed, will cause the entire system paralysis. Distributed system can guarantee that part of a communication node or link is disconnected, the rest can continue to work. During the war, war is very difficult to guarantee reliable wired communication facilities, therefore, through the communication node own combination, comprising a communication system is very necessary. In addition, maneuverability is an important part of the battle effectiveness of the army, this requires communication system according to the needs of the war the rapid formation and removal.Ad Hoc network to meet the demand of the military communication system. Ad Hoc networks using distributed technology, no central control node management. When the network some node or link failure occurs, the other nodes can also be through the relevant technology to communication. Ad Hoc network by mobile nodes themselves free combination, not dependent on cable television equipment, therefore, have stronger group, very suitable for battlefield bad communication environment. Ad Hoc network is simple to build, high maneuverability. At present, some developed countries to combat personnel equipped with state-of-the-art personal communication system, in bad battlefield environment, difficult through wired communication mechanism or mobile IP mechanism to complete the communication task, but through the Ad Hoc network. Therefore, research on Ad Hoc network in military communication system development has important application value and long-term significance.In recent years, Ad Hoc network research in the civil and commercial field is valued. In civilian areas, Ad Hoc network can be used for disaster relief. In case of flood, earthquake, wired communication facilities are likely to suffer damage to the normal communication, through the Ad Hoc network can quickly establish emergency communication network, ensure the rescue work carried out smoothly, complete emergency communication needs task. The Ad Hoc network can be used for remote or undeveloped area communication. In these regions, due to the cost, geographical and other causes are often not wired communication facilities, Ad Hoc network can solve these environmental issues of communication in. The Ad Hoc network can also be used for temporary communication needs, such as business meetings in mutual communication among the participants, in the existing wired communication system can not meet the communication needs of the situation, through the Ad Hoc network to complete the communication task.Ad Hoc network in the study area is also very popular, in recent years network international conferences are the basic Ad Hoc network subject, with the mobile technology and the continuous development of the growing free communication needs, Ad Hoc network will be more attention, get more rapid development and popularization of.4.Comparison with other mobile communication system4.1 Cellular systemCellular system is the most extensive coverage of the land public mobile communication system. In cellular systems, covering the area is generally divided into a plurality of cells similar to cellular. Within each cell of a fixed set of base station, to provide users with access and message forwarding service. Between mobile users and mobile users and mobile communications between users are required to pass the base station. The base station is generally through the wire is connected to the main body by the exchange of a backbone network. Cellular system is a connected network, once a channel is allocated to a user, usually this channel has been the user. Cellular systems are generally used for voice communication.4.2 Cluster systemCluster system and cellular system is similar, is also a connected network, generally belong to the private network, scale is not large, mainly for mobile users to provide voice communication.4.3 Satellite communication systemSatellite communication system is the most extensive, to every corner of the globe provide communication services. In this system, a satellite base station plays with similar functions. Satellite communications system by satellite location can be divided into geostationary orbit, orbit and the lower orbit in 3. Satellite communication system has high cost, large transmission time delay, such as lack of limited transmission bandwidth.The mobile communication systems require the wired network communication infrastructure support, such as a base station, switches, such as satellite. Establishment and operation of these facilities requires considerable human and material resources, therefore the cost is relatively high, at the same time, construction cycle is long. Ad Hoc network base stations is not required by the host their own support, networking, therefore, the network built low cost, while at the same time short, generally only a few seconds or minutes. The communication system, mobile terminal is not direct communication between mobile terminals, and only with the transceiver function, does not have the forwarding function. While the Ad Hoc network by the mobile host, between the mobile host can communicate directly, while the mobile host not only to send and receive data, but also transmit data. Furthermore the present mobile communication system is mainly to provide users with a voice communication function, usually using a circuit switching, topology structure is stable. While the Ad Hoc networks using packet forwarding technology, mainly to provide users with data communication services, topology structure is easy to change.5 Combination of Mobile IP and Ad Hoc networkThe realization of mobile and IP is one of the two big trends of the development of network. With the mobile phone use is increasingly extensive and people on the move of the information provided by the increasingly high demand, the hope that more people can access to the Internet whenever and wherever possible.For Ad Hoc network, network is readily generated and have easy compositionality, does not require prior existing network to support, therefore, a wide range of applications is also very simple. However, this network has a strong independence, it can exist alone, its characteristics and the active, on-demand driven routing protocol makes it difficult to communication with the Internet, to achieve the purpose of mutual information. In order to meet the Ad Hoc network to the mobile host can differ in Ad Hoc network between mobile and ready access to the Internet, we use the mobile IP protocol can be in different network roaming characteristics, combined with mobile IP and Ad Hoc network, MIPMANET, provides a Ad Hoc network using on-demand driven routing mechanism, mobile IP proxy address and reverse tunnel Ad Hoc network to access the Internet solution.6.Problems of Managing the Ad Hoc network Ad Hoc network determines the characteristics of management than the wired network complex many, because the dynamic change of network topology, network management and automatic dynamic configuration requirements. To take into account the mobile node constraints, such as energy limited, the link state change and limited storage capacity, therefore, will bring to the whole network management protocol load into consideration. Finally we should consider to network management on various environmental suitability.Specific Ad Hoc network management needs to solve the problem as follows:A ) Network management protocol is an important task is to know the network topology structure of network. In a wired network, because the network does not change frequently, so it is easy to do. But in the mobile network, and mobile node causes the topology changes too frequently, network management needs to regularly collect node connection information, which will undoubtedly increase the load of network.B ) Most nodes using battery power, so to guarantee the load of network management is restricted to a minimum in order to save energy. To minimize the transmission and processing of the number of nodes, but