| 单词 | Internet |
| 释义 | Internet A massive, global network of packet data networks based on the Internet Protocol (IP) suite.The Internet is grounded in the U.S. Department of Defense ARPANET (Advanced Research Projects Agency NETwork), which began in 1969 as a means of linking personnel and systems involved in various computer science and military research projects. The Internet since has grown to comprise more than 400 million hosts connected to more than 60,000 academic, business, and governmental networks in more than 150 countries. The Internet also has evolved to support not only data, but also voice, image, video, facsimile, audio, and multimedia communications. Fundamental to the Internet is the Internal Protocol (IP) suite, which, in the context of the OSI Reference Model, includes the Internet Protocol (IP) at the Network Layer and Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) at the Transport Layer. At the Application Layer are File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP), Simple Network Management Protocol (SNMP), and Telecommunications Network (TELNET). The physical infrastructure has evolved into one that is largely broadband in nature, comprising extremely high speed transmission systems and routers.The physical topology is organized in a hierarchical manner, as follows: Level 1: Network Access Points (NAPs) and MAEs serve as points of interconnection where national and regional carriers exchange traffic Level 2: National backbones comprising facilities-based, long haul carriers Level 3: Regional carriers comprising facilities-based, long haul carriers operating in a single state or province 74570c09.qxd 9/11/07 12:22 PM Page 247 |
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