 
 
 
  
  
  
  
 Switch
 
  
  
  
  
 Local exchange
 
  
  
   
   
   
   
   
   
   
   
   
   
   
   
  
  
  
 
  
  
  
 
  
  
  
  
  
 
  
  
  
 
  
  
  
  
  
  
  
  
 
 
 ETC: Exchange terminal circuit
 IN: Intelligent network
  
 conference calls, call waiting, broadcasting ...
 Signaling (SS7) with users and 
 other exchanges
 
  
  
  
  
  
  
   
 Traffic concentration
 
  
  
  
  
  
  
 
 - Operation & maintenance support
 (Q.513) 
 - Charging
 - Supplementary (IN) services 
 - Subscriber data, switch control
  
 
  
  
   
  
  
  
  
 Control
 
  
  
  