ATM网络中使用信元作为传输数据的单位，当信元从用户端进入网络中第一个交换机后，信元头中修改的部分是(51)。信元传输采用(52)。当进行VP交换时，VPI和VCI的变化情况是(53)。当需要传输压缩的视频流数据时，采用的服务类别最好是(54)。当AAL层采用AAL5协议传输数据时，可以达到的有效数据传输率(除去开销)为(55)。

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Multipurpose Internet Mail Extension(MIME)is a(71)document messaging standard in the Internet enviroment, with MIME, users can send(72)Email messages that include audio, video, graphices, and text to any other user of a TCP/IP network. Richtext information can also be(73)into messages. It defines the fonts, formats, and(74)features of a document so the document can be easily(75)on many different types of systems.

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For each blank, choose the best answer from the four choices and write down on the answer sheet.

(66)is a six bytes OSI layer 2 address which is burned into every networking device that provides its unique identity for point to point communication.

(67)is a professional organization of individuals in multiple professions which focuses on effort on lower-layer protocols.

(68)functions with two layers of protocols. It can connect networks of different speeds and can be adapted to an environment as it expands.

(69)is the popular LAN developed under the direction of the IEEE 802.5.

(70)is the popular backbone technology for transmitting information at high speed with a high level of fault tolerance which is developed under the direction of ANSI.

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