I have a Cisco 7920, a WiFi VoIP phone, connected to a terminal of Cisco 870 router. Everything is on a remote site connected via SDSL lines. This remote site configuration is repeated over 50 times (include more than 50 remote sites).
My problem is that some phone has a background noise, sound very low and everything behind a terrible crackle which makes communication virtually impossible.
I tried to replace the telephones in 7920, but the problem returned and most phones do not seem to have the problem when connected elsewhere. I tested the router, but nothing seems malfunctioning because they are also up for a data network that has no problem.
So, if you have any ideas for my problem then please help?