Places the calling channel in delayed audio loopback mode.It simply returns all audio sent, including voice, DTMF, etc after the specified delay [ms].
It is generally useful for checking if RTP audio path works both ways. Normal echo app can fail when tested on speaker phone.
From the Dialplan
<action application="delay_echo" data="1000"/>
This example repeats back any audio it receives after a 1 second (1000 millisecond) delay.