某公司希望为其客户提供全国统一的客服电话，并让客户免费拨打，该公司可以使用()业务。

50.

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 to different 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 () in conventional cellular communication networks, Because of (), 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 ()

49.

To maintain a telephone conversation over the Internet. The voice packets must arrive at their destination in ()

A Next Generation Network(NGN) is a (上题选择) 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 () of the underlying transport-related technologies.

A Next Generation Network(NGN) is a () 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 (下题选择) of the underlying transport-related technologies.

The VoIP gateway can perform the digitization, () and encapsulation required, and it controls the setup of VoIP calls between the calling device and the called device

“认证”英文通常翻译为()。

802.11n is a WLAN standard approved by the (), which can be used ti support data rate uo to 600Mbps

在通信专业中，TCP的英文全称是()