正确答案: C

数据链路层

题目：7号信令系统中的信令链路控制级对应OSI参考模型的（）。

解析：C

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举一反三的答案和解析：

[单选题]以下关于数字数据网DDN的叙述中，（）是错误的。

采用统计时分复用技术

[单选题]移动通信网特有，而固定通信网不提供的服务是（ ）。

位置相关业务

[单选题]冯诺伊曼体系结构特点不包括（）。

机器以控制器为中心，数据传送都经过控制器

[多选题]虚拟私有网（VPN）从IETF的角度分为（）

拨号VPN

虚拟专线

路由VPN

局域网VPN

解析：ABCD

[多选题]【A popular service that has attercted the interest of companies and has home users alike is the sending of voice signals over an IP-based network, such as the Internet. The practice of making telephone calls over the internet has had a number of different names, including packet voice, voice over packet, voice over the internet, internet telephone, and Voice over Ip（Voip）. But it appears the industry has settled on the term”Voice ove IP” in reference to the internet protocol, which controls the transfer of data over the internet. There are currently three ways to deliver VoIp to users, the first technique is found at the corporate level. Many companies are offering VoIP systerms that operate over a local area network. These systems involve a fair amount of equipment, such as VoIP servers, special IP-enabled telephones, and routers that can direct telephone calls. Today a large portion of corporate sites have converted their older internal telephone systems to VoIP systems that opreate over a LAN, thus converging two systems into one. A second common solution is the one often encountered at home. Using existing telephones, a special converter is added between the telephone and a high speed internet（DSL or cable modem）connection. The converter digitizes the voice signal and creates a stream of packets that are then sent over an ip connection.The third technique involves smart cell phones. Never cell technologies are all packet-based, thus requiring a telephone call to be converted to digital packets and sending those packets over IP networks.】From the paragraph above，a popular service that has attracetd the interest of companies and home users,is termed as （） . The data transfer over the Internet is controlled by the （） . At corporate level, many companies have replaced their older internal telephone systerms with （） that oprerate over a local area network.

voice over the internet B、voice over packet

Voice over IP

industry

VoIP servers

解析：C,B,A