Hi Juan,
Has the device ever been configured and worked in this environment before, or is this a new installation?
How is customer attempting to make internal calls, please describe in detail?
Do inbound calls work without problem?
I doubt the issue is related to QoS. QoS usually results in choppy audio, also called jitter.
Does the customer have a firewall enabled? If so, please disable and test for one-way audio again.
One-way audio is usually related to NAT and or SPI firewalls that don't allow the seemingly unsolicited RTP through.
Regards,
Patrick
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