We have an IPO 406 4.2 With a VCM 8 installed. We have 6 Avaya IP phones on the system, 5610, 5602 and 5620SW. I am always able to make and receive calls, and can always hear the other person, but they cannot always hear me. It seems to effect all the phones at the same time. Is this a bad VCM? I don't understand why it only effects traffic one way and isn't consistent, also doesn't seem to be related to traffic volume because it happens when there is no traffic as well as during peak. When it's not working it sounds completely dead at the far end and is not even able to send dtmf tones.