Asterisk Expert Required

Step 1 :- A server ------> Invite --->> Bserver ------->> Invite ------->> PSTN Step 2:- A server <------ 100 trying <<--- Bserver <<------- 100 trying <<------- PSTN Step 3:- A server <------ 183 session Progress <<--- Bserver <<------- 183 session Progress <<------- PSTN Step 4:- A server <------ 183 session Progress <<--- Bserver <<------- 180 Ringing <<------- PSTN A Server >>> Installed Asterisk with Freepbx B Server >>> Installed Asterisk with Freepbx PSTN (SIP) attached with Server B An extension 123 created on Server B On Server A created a SIP Trunk with configuration of extension 123 that was created on Server B Also connected server B with the server A via chain_SIP Trunking. Now created a Extension 321 created on server A and configured in soft-phone like zoiper and dialling call on XXXXXXXXXX number. Now the problem is in Step 4 where I am not getting same 180 Ringing that I am getting from PSTN on Server B. How I can get same signal on Server A that are getting on Server B from PSTN.