|  | 
   
    |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
    | n | Over-voltage
    protection 
 |  |  
    |  |  
    | n | Test equipment
    to connect to monitor the line condition 
 |  
    |  | faults 
 |  |  
    |  |  
    | n | Voltage feed 
 |  |  
    |  |  
    |  | n | ringing 
 |  |  
    |  |  
    |  | n | telephone
    current supply 
 |  |  
    |  |  
    | n | Detection of 
 |  |  
    |  |  
    |  | n | hook stage,
    pulse generated, or dual-tone receiver 
 |  |  
    |  |  
    | n | The hybrid
    junction (2 wire - 4 wire interface) 
 |  |  
    |  |  
    | n | An A/D
    converter (uses PCM techniques at 64 kbps) 
 |  |  |  |