在使用路由器R的TCP/IP网络中，两主机通过一路由器互联，提供主机A和主机 B应用层之间通信的层是(21)，提供机器之间通信的层是(22)，具有IP层和网络接口层的设备(23)；在A与R和R与B使用不同物理网络的情况下，主机A和路由器R之间传送的数据帧与路由器R和主机B之间传送的数据帧(24)，A与R之间传送的IP数据报和R与B之间传送的IP数据报(25)

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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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