2. 计算机
  3. Typically,　these　are　concern　with　the　establishment　of(66)the　network　and　with　the　control　　of　the　flow　of　messages　across　this　

Typically,　these　are　concern　with　the　establishment　of(66)the　network　and　with　the　control　　of　the　flow　of　messages　across　this　

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问题 Typically,　these　are　concern　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)program,　normally　referred　to,　　as　application　processes　or　APs,　and　the　underlying　communication　services　may　be(68)For　example,　one　computer　may　be　a　small　single　-user　computer,　while　another　may　be　a　large(69)system.　In　the　earlier　days　of　computer　communication,　these　issues　meantthat　　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 erconnected 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 activities to beplaced into perspective with one another.
选项 A、communication　channel　access
B、protocols
C、data　channel
D、public　communication
答案A
解析 communication　channel　access：通信通道接入。
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