6.3.              515

  .    IDI    15 -
 ,   DSP    40 4).

    PSTN     
.163 - 42,      ,  43,  
    .    IDI  (
 12  ,   DSP    26 .

        
ISO DCC (Digital Country Codes)  38,     -
 ,  39,       .
   IDI  4)0  3   ( ),  
DSP    35 .

   .     IDI 
  ,      DSP.
        
 IDI.       IDI    
  ,       DSP.

          
 ISDN  :  ISDN  , , -
  ISDN   .25,      .25.  
  .       
  ISDN       -
 ,    ISDN,     -
  ,       
.

     ISDN

  ISDN (. 6.19)    :    D 
   .

  D       .
      .25.    D -
   :    
1.430/431,   LAP-D   Q.921,   
    0,931,    
      ,   
.25        LAP-D   .25  -
 ISDN    .25.

   D   ISDN     '
    7 (Signal System Number 7, SS7). 
SS7         -
    .       ISDN.
 SS7      OSI. , -
   ,    SS7   -
   .

        .  
 OSI        ISDN   
    1.430/431.     -