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发布时间：2006-06-28 04:52     点击：

　　　　C．1010110001101　　　　D．1010111101010

　　　　E．1010111011001　　　　F．1010110001100

　　●Typically,these are concerm with the establishment of ＿(66)＿ the network and with the control of the flow of messages across this channel. The provision of such facilities is only part of the network requirements,however,since  in many applications the communicating computers may be of different types. This means that they may use different programming languages and,more importantly,different forms of ＿(67)＿ interface between user(application) prograrma，normally referred to,as application processes or APs,and the underlying communication services may be ＿(68)＿ For example，one computer may be a smaall single- user computer,while another may be alarge ＿(69)＿ system.In the earlier days of computer communication,these issues meant  that only closed communities of computers(that is,from the same manufacturer) could communicate with each other in a meaningful way. IBM's Systems Network Architecture(SNA) and DEC's Digital Network Architecture (DNA) are just two examples of communication software packages produced by manufacturers to allow their systems to be int ercormected together.These proprietary  packages, however, of which there am still many inexistence, do not address the problem of universal interconnect ability, or open systems interconnection. In an attempt to alleviate this problem,＿(70)＿,in the late 1970s,formulated a reference model to provide a common basis (or the coordination of standards developments and to allow existing and evolving standards acivities to be  placed into perspective with one another.

　　(66)A．communication channel access　　B．protocols

　　　　C．datachanneI　　　　　　　　　　 D．public communieation

　　(67)A．database　　　　　　　　　　　　B．data representation

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