68     1      

    .       -
  ,     , 
    .

        
  .     -
 ,     ,  -
         
  ,      -
   -.    -
    ,      
,  . . (     -
        ,    ,   
 .) ,   , 
,         -.
        (. 1.26).


 3-                          

	 3	  3	3	
 2-		 1	1	
	 2	 3	  3	3	 2	
	 1-		^ J	^		
			  2			
	 1	 2	 3	  3	 3	 2	 1	

^
  1

. 1.26.    

      -,   
         .
       , 
   ,       -
   .

    (message)    , -
        
.   ISO    ,    
  ,      
(Protocol Data Unit, PDU).      -
   :  (frame),  (packet), -
 (datagram),  (segment).

  OSI     .    -
  (connection-oriented)    
      , ,  -
  ,       -
.        .  
  ,    .