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马克．吐温的作品，《竞选州长》的体裁是（）
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共用题干题A Next Generation Network（NGN） is a （1） network ，which is able to provide Telecomunication Services ti users and to make use of multiple broadband， QoS-enable transport technologies and in which service-related functions are （2） of the underlying transport-related technologies. 括号（1）应填入的是（）。
共用题干题With the explosive popularity of mobile devices， we have witnessed a steady increase in demand for mobile date service. In addition mobile users also expect to connect to the Internet for communicate 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 wireless access networks belonging todifferent administrative domains， mobile users cannot always identify at every instance which network is the best one to access for their service. It is highly demanded to establish a network architecture which can facilitate mobile terminals to access the appropriate network in a cost-effective way. If a mobile user wants to move from one network to another with continuous service， the terminals have to cope with network change to maintain service seamlessly. Quality of service is a major issue that the end users should be provided with the satisfying service， while the network workload and cost should not too much increased. In addition， since end users are provided with numerous service ranging from Voice-over-IP to Video-on-Demand services， it is expected that users can experience the same quality for all the different service. 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 network is （3） in conventional cellular communication networks， Because of （4）， 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 （5） 括号（3）应填入的是（）。
通信科技人员职业道德的两重性，是指通信科技人员应遵守（）两方面的职业道德。
某单位创建自己专用的校园网络，使用内网专用的IP地址段172.16.0.0/12。 该公司一个分支机构的局域网整体搬迁到另外一个城市，系统采用的IPSec VPN通过因特网将分支机构与园区网互联，采用ESP协议，IPSec VPN工作在网络参考模型的哪一层？针对本案例，应当采用ESP的传输模式还是隧道模式？列出除IPSec VPN之外两种其他VPN技术？
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