Troubleshooting echo on internal calls

Need a little guidance or docs with some echo troubleshooting sugestions.

We have about 10 VOIP phones (Grandstream 1405s 1414s and 2124’s.) We also have three FSX units with 48 ports each. (Grandstream GXW4248)

The issue I’m having is when a FXS user calls a voip phone, the VOIP user is hearing themselves back in the call delayed. The FXS user doesn’t hear any echo. If we run an echo test (*43) from either device the echo is nearly instant.

The FXS units and the voip phones are on the same switch, an HP procurve only handeling voice traffic. No other data is on it. Responce times from the FSX and VOIP phones is <1ms.

The issue isn’t consistant but fairly regular. I’m not sure how to begin troubleshooting this.

You levels are too high on the analog channels.

Both the TX and RX gain are at 0db, should i pad these down?

Is there a balance procedure for the hybrid on your gateway? Essentially a milliwatt tone is placed on the loaded pair and the hybrid is nulled. This removes and out of phase artifacts.

If not process exists you will have to do it by ear. Start with the TX gain toward the handset and reduce in 1.5 db increments.