476     6   

6.2.2.   

        -
 ,     ,  
      TDM,    2. -
         -
 (  ,    )  
(Plesiochronic Digital Hierarchy, PDH)      
  (Synchronous Digital Hierarchy, SDH).   
SDH   SONET.

    PDH

        -
 60-   AT&T      -
    .    , 
    -,      -
     .   FDM  -
   12  60    
,          -
        .  ,
        , -
     ,    -
       ,   .

       1,   
  ,    ( 
)  24 .    -  -
  ,        ,
  1       8000 
     -  (Pulse Code
Modulation, PCM).       -
   64 /. ^)   Tl -
    _^, , 
        ^
   Ti       -
  2,     6,312 /,    2 
   ,     44,736 /. -
 Tl, T2      ,  -
         .

  70-   ,    Tl, -
        , -
     .  Tl,    
 T2       ,    , -
   ,   ,  ,
  . .

      CCITT.  
     ,     -
     .   -