6.4.            547

 Cell Loss Ratio (CLR)    ;       ',
 Cell Transfer Delay (CTD)    ; \
 Cell Delay Variation (CDV)    .

      ,  
   ,      .  -
    ,     
  PCR,    .  
        
    .    
 ,        -
   .

          -
    QoS.    
    (  RCR, SCR, MCR,
MBS),    (CTD  CDV),    -
   (CLR).     
          
 QpS,      .  QpS
     CTD, CDV  CLR.   
  ,       -
,   ,    .

       --
.     ,    frame relay,
       ,  -
         -
  ,      .   frame
relay   ,      
.

 ,      ( 
 QpS)      , 
        
  .

     ,     
       .    
    X,      , 
       QpS, -
   -.

        -
  QpS,        ,  
Best Effort     .    
       Unspecified Bit Rate, UBR.

  -,     -
 ,        , -
   .   UBR   
 ,   ,       -
  ,    
.