User A notices echo on a call with user B. Both users are using Cisco VoIP phones. User B is using a headset, and user A is using a handset. What is the most likely source of the echo?

User A's handset uses physical design characteristics that isolate the earpiece from the microphone, making it far less likely to generate acoustic echo compared to a headset.

Because User A hears the echo, the signal causing it originates at the far end - User B's side. Headsets are susceptible to acoustic coupling where audio playing through the earpiece leaks back into the microphone, creating an echo path. A handset, by contrast, uses physical separation and design characteristics that inherently reduce this acoustic leakage, making the headset the most likely source.

Disabled echo cancellation on User A's phone profile would affect echo originating at User A's side being returned to User A, not echo arriving from User B's end of the call.

While disabled echo cancellation on User B's phone could allow the echo to pass uncanceled, the physical source generating the echo is the headset hardware itself, not the cancellation setting.