Jeirdus 1Pair 1 Channel PCM Voice Telephone Fiber Optical Media Converters Extender Adapter Single Mode FC Fiber Optic Port with 10/100M Ethernet (per network port) full duplex, half duplex fully adaptive, transmission distance of the telephone signals up to 20Km. Strong anti-interference ability, built-in lightning protection. High quality voice call chip, clear voice calls, Support caller ID showing and fax function. High quality PCM voice telephone Modular design, Plug and play, no need on-site debugging. high integration, stable and reliable performance. Made of metallic baking paint, corrosion resistant, porous heat dissipation on both sides to ensure stable operation.