Problem: Hollow Sound
This is generally due to a high level of echo with a small amount of delay. For example, if an IP phone was connected over a LAN to a VoIP gateway then the delay would be very small. Echo that occurred on the trunk side of the gateway may cause "hollowness" in the IP Phone.
Impact
Users may report that calls sound "hollow", "cavelike" or "tunnel-like".
Resolution
Initially try and locate the source of echo - often on the analog loop connected to a gateway. The echo canceller in the gateway should compensate for echo however may not operate correctly if misconfigured or if the loss plan is incorrect.
If the problem seems to be associated with a particular telephone handset then it may be due to internal feedback - consider using a different handset.
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