88    1      

  . -     -
      -
  ,  ,     ,
      100 /.    
,   ,   -
       on-line.

   Wide Area Networks (WAN)   
 ,       
.         -
   ,       -
  ,      .
,         
  . -       -
  (   )     -
  ,    ,   
,    .    -
         -
,      ,  
 .  ,     
  ,        
       .

  (  )  Metropolitan Area Networks (MAN) 
    .    
.        
.           -
       ,  -
      ,   
    ,     -
 .      ,
 ,    45 /,    
          -
.        ,  
    ,     
  . .     -
  .   ,   -
        - 
    .      
       ,   -
        , -
    SMDS  .   
 ,      ,  
 ()    .

1.4.2.     

        . 
         ,  
,         80- ,  