文档介绍:                                                                     (        )
A互联网                                                        
                                                                                      (          )
                                                                
              层.                                                                                          (              )
                                                                                     
                                                                     (             )
@                      @       C.@           
                                                                                      (            )
                                             C.                  
  将网络划分为星型网、总线型网、环型网和树型网                        (             )
                                 
                                                 
                                       (           )
                                                        
,最低层和最高层分别是                               (