TCP functions at the Open System Interconnection(OSI)(61)layer, or Layer 4. Its chief responsibility is to ensure(62)end-to-end 

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问题 TCP functions at the Open System Interconnection(OSI)(61)layer, or Layer 4. Its chief responsibility is to ensure(62)end-to-end connectivity. IP, located one layer down, at the OSI network layer, or Layer 3, communicates the addresses of each(63)sender and receiver to the routers along the way. Routers and Layer 3 switches can read IP and other Layer 3(64). This information, combined with routing tables and other network intelligence, is all it takes to get(65)the room or around the world via TCP/IP.

选项 A、across
B、up
C、off
D、rid

答案A

解析 TCP在开放系统互联(OSI)的传输层或第四层起作用,其主要功能是确保可靠的端对端的连接。位于下一层的IP在OSI的网络层或第三层,把每个分组的发送者和接收者的地址沿着路线传送给路由器。路由器和第三层交换机可以读IP和其他第三层协议。这些信息与路由表和其他网络智能结合在一起,就是它通过TCP/IP能跨越空间,周游世界。
本题考察的是ISOOSI模型的第三层和第四层的简单功能问题,只要熟悉该模型,问题就变得十分简单了。本题C小题空的前面有each,后面只能接单数,所以,②packets和④ packets’ 肯定不对。同时,所缺单词作为sender and receiver 的定语,因此,正确答案是packet’s。
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