ERECA, a digital telecommunication company specialising in optical fibre based system provides an optical fibre architecture for emergency call box systems. Using an optical bus structure, 50 couples of Emergency Telephone (100 Emergency telephones) can be managed by one EROS end optical interface. Each field optical interface remains autonomous and the dynamic range of the optical equipment allows for the self healing of the network. The End optical interface manages the network and realises a systematic control of all the optical interfaces on the bus at each communication. The digital transmission techniques employed ensure a high audio quality and allows multi-communication (3 concurrent conversations) on the same optical bus. Interface setting (alarm level, output audio volume) is done directly on the call box by a PC setting tool also able to check the optical power received by each field equipment. No electronic are necessary present in the call boxes by using the underground housing for emergency telephone interface, to ease maintenance on call boxes. Securitisation principle, using optical couplers ensures the functioning of the network in case of call box failure or optical cable fracture. PDF DOCUMENT