【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).】
(98)

选项 A、better than
B、maturer than
C、as good as
D、not as good as

答案D

解析
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