When call was transferred at phone[9001], the call is established but no audio

Asterisk Asterisk SIP
1

I have an asterisk 16 based ip-pbx like this.

PSTN — GATEWAY — Asterisk 16 — Phone[9001]

inbound call & outbound call is no problem with phone 9001.
But, I set the phone[9001] to be transferred to my cell-phone.

so, inbound call --> Phone[9001] > transferred --> my cell-phone
but in this case, I can’t hear anything!

image

what did I check it?

2

Calls without audio are typically related to NAT firewalls that aren’t configured to handle the audio (RTP) packets correctly.

3

Thanks for your replay.

inbound + outbound call is no problem in my case.
but If i transfered call, this cause issue(no audio).
is this a NAT issue?