I tried most of the combinations of below settings, but the result the same: when the RTP stops to be received from Cisco Gateway, also it is stopped towards iPhone.

Maybe I am missing the right combinations of parameters?

<action application="set" data="bridge_generate_comfort_noise=true"/>
<!--
<action application="set" data="rtp_disable_vad_in=true"/>
<action application="set" data="rtp_disable_vad_out=true"/>
-->
<action application="set" data="record_waste_resources=true"/>
<action application="set" data="rtp_enable_vad_in=false"/>
<action application="set" data="rtp_enable_vad_out=false"/>