今天先对管理员与用户之间的信息交流问题进行了总体分析，然后进一步把用户之间点对点信息交换的应用协议给定了下来，按下面这样约定：

主类别号   说明       子类别号  说明       孙类别号    说明

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12          点对点      1          留言 

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                           2          文件传输

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                           3          聊天          1           邀请对话

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                                                      2           答应对话

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                                                      3           谢绝对话

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                                                      4           因忙，谢绝对话

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