...thru.
The calls are thru IP (ECMAV2). You can check the image below
Here's reg format as well
ADD-BUEND:507,"OS4000 -> X8 ",60 ,0 ,* ,2 ,ON ,0 ,0 ,NEUTRAL;
ADD-TDCSU:NEW ,1-01-085-0,202,203,0,0,200,1,1," ",250 ,ECMAV2,8,,NONE,,,,GDTR,N,TIE,NONE,N,0...