So we installed our first TA900 (2nd-gen) for a customer who switched to us from another provider that had installed a TA900e 2nd-gen. The FXS ports are punched down into a Toshiba phone system, and we pretty much just lifted the previous provider's 924e out and dropped our 912 in its place (customer only needs 8 trunks).
They have been telling us that the party on the other end of the call has been complaining to them about "white noise" in the background that did not used to be there before they switched. At first the description sounded like comfort noise resulting from VAD, but I have VAD turned off. I called in to see what they are talking about, and I heard it too. It is not continuous but sporadic, and apparently only I hear it...they don't on their side of the call (the FXS side of the Adtran). When it happens, it happens for short bursts of time...a second here, 2-3 seconds there, and it happens regardless of whether they are talking or not. What I would describe it as is that suddenly the background noise floor level goes up and I hear a lot of "hiss", but it's not like tape hiss, it's more like there is a fan gently blowing into the microphone on their handset. They said others who alerted them to the problem described it as if somebody was outside with their cell phone on a windy day. Neither side had the other on speakerphone. If I couldn't still hear their voice speaking to me during these events, I *might* have thought "packet loss", but I don't think that's what's going on here. The quality of the voice audio itself sounds fine...not choppy or smoothed-over/stretched-out in time as you would expect with a missing audio sample.
We're using PCM/U, and I'm 99.9% sure the previous carrier was, too. All voice users are set pretty much to stock defaults...no VAD, no PLC, but echo cancellation and NLS are both on. I wondered if there was some kind of auto-gain control (AGC) going on, but I found the "ALC" setting which I'm guessing is synonymous with AGC, and it too is off (the default). The FXS interfaces are also all at stock as well (gain levels, impedance adjustments, etc.).
So what the heck are we looking at here? Any ideas?
EDIT: Forgot to mention we are running R11.4.6.E.
Message was edited by: Nathan Anderson
Nathan, this is likely to be a complex issue that is going to involve packet captures and DSP captures. As such, I would recommend opening up a ticket with support for the quickest resolution. Thanks
Is the incoming SIP feed on a T-1? Look for clock slips or slip-seconds on the interface. In 99% of the cases the TA900 should be set to have a system timing-source of the incoming T-1 interface.