【With the explosive popularity of mobile devices,we have witnessed a steady increase in demand for mobile data services.In addit

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问题 【With the explosive popularity of mobile devices,we have witnessed a steady increase in demand for mobile data services.In addition,mobile users also expect to connect to the Internet for communication and access to services through the best suitable connection,anywhere and at anytime.
Although the seamless roaming capability is well supported in conventional cellular communication networks,roaming and interworking technologies are still immature in heterogenous wireless networks.Seamless roaming over heterogenous wireless networks will be an ongoing and improved process,due to the requirements from both end users and network administrators.From the perspective of mobile users,due to the availability of numerous neighboring wireless access networks belonging to different administrative domains,mobile users cannot always identify at every instance which network is the best one to access for their services.It is highly demanded to establish a network architecture which can facilitate mobile terminals to access the appropriate networks in a cost—effective way.If a mobile user wants to move from one network to another with continuous services,the terminals have to cope with network changes to maintain services seamlessly.Quality of service is a maj or issue that the end users should be provided with the satisfying service,while the network workload and cost should not be too much increased.In addition,since end users are provided with numerous services ranging from Voice-over-IP to Video-on-Demand services,it is expected that users can experience the same quality for all the different services.Therefore,the network architecture need to be designed in such a way that the quality mechanism is incorporated so that users are served according to their individual QoS requirements.】
Based on the paragraph above,at present,seamless roaming over heterogenous wireless networks is(98)in conventional cellular communication networks.   
Because of(99),mobile users cannot always identify at every instance which network is the best one to access for their services.
To satisfy the users’QoS requirements,the network architecture design should include(100).】
(100)

选项 A、Voice-over-IP
B、the quality mechanism
C、workload
D、Video.on.Demand

答案B

解析 本题考查移动通信方面的基本知识。
【随着移动设备的爆炸性普及,我们已经见证了移动数据业务的需求稳步增长。此外,移动用户还期望通过最合适的连接,在任何地点和任何时间,实现连接到互联网的通信和接入服务。虽然传统的蜂窝通信网络对无缝漫游的支持是非常好的,但在异构无线网络中,漫游和互通技术仍不成熟。由于终端用户和网络管理员要求的不断提高,异构无线网络的无缝漫游将是一个不断的改进和完善过程。从移动用户的角度来看,由于许多相邻的无线接入网络属于不同的管理域,在每个实际的环境中,移动用户在接入网络时并不能以最佳的方式接入网络的业务。它要求建立一个网络体系结构,可以帮助移动终端以积极有效的方式接入合适的网络。如果一个移动用户想要从一个网络移动到另一个同时保证业务的不间断,终端必须应对网络的变化,以保持服务的无缝链接。服务质量是一个主要问题,在保证用户满意度的同时,网络的工作量和成本不应该增加太大。此外,由于向终端用户提供了大量的业务,从IP话音到视频点播服务,预计用户可以在实现不同业务时,感受到相同的服务质量。因此,在设计网络体系结构需要考虑包含质量机制,以使用户实现具有个人特点的服务质量要求的业务。】
根据上段内容可知,目前异构无线网络的无缝漫游质量不如传统的蜂窝通信网络。由于不同的网络管理域,在每个实际情况中,网络并不能总是为用户提供最好的业务接入。为了满足用户的服务质量要求,网络结构设计应包括质量机制。
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