Some Avaya phones models are special which require microphone amplification on headset. This headset comes with circuit box on cable to make sure microphone voice is loud enough for the other end to be heard.
Compatible with below models
16xx or 96xx series:
J139, J169, J179, 1608, 1616, 9608, 9610, 9611, 9611G, 9620, 9620C, 9620L, 9621, 9630, 9630G, 9640, 9640G, 9641, 9641G, 9650, 9650G, 9650C, 9670