- Interfaces local-loop (end-points), trunks to CO's/PBX

1. Battery - power to local end-points -48v DC off-hook, AC voltage on-hook (ringer)
2. Current detector - detects off-hook closed circuit
3. Dial-tone generator - after off-hook detection dial tone is provided
4. Dial-register - receives dialed digits (pulse/DTMF) from end-point
5. Ring generator - incoming call, generates ring tone (AC voltage) to end-point


Typical CO