How to capture twinkle packets by GNU Radio

I installed Asterisk & Twinkle on a PC and installed Twinkle on another PC, I successfully made a call between the 2 PCs ( let we call them PC1 & PC4) . Now instead of that , I want to use 2 additional PCs which have GNU Radio installed. (let them PC2 & PC3)
I want also to make the call between PC1 & PC4 but when they are not directly connected [No internet or direct ethernet connection )as in this Picture said:

PC1(end-user has Asterisk & Twinkle) will call PC4 but :
PC2 (has an ofdm TX implemented on GNU Radio ) will take the packets from PC1 via Ethernet.
PC2 will process the packets then sends them as RF via USRPs to PC3(has an ofdm RX implemented on GNU Radio).
PC3 will process the real time voice packets and sends them via Ethernet to PC4(end-user has Twinkle and wants to hear the voice of the end-user of PC1)

The problem is how can PC2 receive the voice packets from PC1 while it is the call is between PC1 & Pc4?
Also how can PC3 sends voice packets to Twinkle on PC4 while it is not the caller and not registered?

I installed twinkle on PC2 & I registered to asterisk(which is on PC1) by same username & password of twinkle of PC4 . I connected PC1 & PC2 by Ethernet . I killed Twinkle of PC2 from terminal so that it leaves the sip port to be used by GNU Radio . Then , I sent call invitation from PC1 to PC2 while , in GNU Radio of PC2 , I tried to capture invitation packets coming from SIP port (of Twinkle of PC2) during invitation .
But I found in Twinkle of PC1 “503 service unavailable” written.
And I don’t found any packets captured by GNU Radio in Pc2 but when I try to open twinkle in PC2 it said that sip port is already in use which means that GNU Radio try to capture the packets coming from this port.
[Note that , when I tried before to make a call between pc1 & pc4 using Ethernet there was no problem.]
Why it said service unavailable in PC1 ? Is there any other method to make Pc2 capture packets from PC1 while Pc1 tries to direct packets to pc4 not pc2 ?
I will face the same problem between PC3 & PC4 .

Here is the full output on terminal:
I gave to pc1 as an ip & 101 as username while I gave pc2 as ip & 100 as username
Here are the packets captured by wireshark when I send call invitation from pc1 to pc2 :

Thanks in advance :smile: