<div dir="ltr"><div>I use kamilio but I think it works in the same way for Opensips.</div><div><br></div><div>Well, I saw similar questions in the list already but looks like nobody has answer.</div><div><br></div><div>Please look at REFER below.</div><div><br></div><div>Kamilio gets REFER from MS and sends it to FS node. Next, FS node try to make 3th call for some reason.I expect that FS will not do 3th call and just will connect Alice and Bob itself.<br></div><div><br></div><div><br></div><div>2020/05/14 12:32:00.637027 KAM_IP:5060 -> FS_IP:5060<br>REFER sip:Alice_number@FS_IP:5060;transport=udp SIP/2.0<br>FROM: Customer1<sip:MS_TRUNK_NUMBER@sip.pstnhub.microsoft.com:5061;user=phone>;tag=a860c50a3fb54d08b4e5740fa2dfb3d6<br>TO: <sip:Alice_number@FQDN_OF_TRUNK:5061>;user=phone;tag=e8ct9S6ty13va<br>CSEQ: 4 REFER<br>CALL-ID: 2c71b2a6669b5343a231e1244b19c945<br>MAX-FORWARDS: 50<br>Via: SIP/2.0/UDP FQDN_OF_TRUNK:5060;branch=z9hG4bK10ae.2c42897feca117121a23bf0c8d54cd19.0;i=c<br>VIA: SIP/2.0/TLS 52.114.75.24:5061;branch=z9hG4bK7e3e8998<br>CONTACT: <sip:api-du-a-euwe.pstnhub.microsoft.com:443;x-i=6b68e7aa-f5e2-44ec-9edf-0bacbabfce07;x-c=2c71b2a6669b5343a231e1244b19c945/d/8/b68f86794a8e44d19543f8edbee6b2fc<br>CONTENT-LENGTH: 0<br>REFER-TO: <sip:Bob_number@sip.pstnhub.microsoft.com:5061;user=phone;transport=tls><br>REFERRED-BY: <sip:sip.pstnhub.microsoft.com:5061;x-m=8:orgid:21bc47d3-c050-4292-8234-46f7005b97aa;x-t=fb788ef8-3c4c-455a-8d62-f3c20832c0d3;x-ti=6b68e7aa-f5e2-44ec-9edf-<br>acbabfce07;x-tt=aHR0cHM6Ly9hcGktZHUtYS1ldXdlLnBzdG5odWIubWljcm9zb2Z0LmNvbS92MS9uZ2MvY2FsbG5vdGlmaWNhdGlvbj9kY2k9YzIxMjE3MzEyNTQ2NDk1ZjlhYTcwODliYTkwNGIxZGQ%3D><br>USER-AGENT: Microsoft.PSTNHub.SIPProxy v.2020.5.6.2 i.EUWE.4<br>ALLOW: INVITE,ACK,OPTIONS,CANCEL,BYE,NOTIFY<br>P-ASSERTED-IDENTITY: <tel:MS_TRUNK_NUMBER>,<<a href="mailto:sip%3Acustomer1@m365x587912.onmicrosoft.com" target="_blank">sip:customer1@m365x587912.onmicrosoft.com</a>><br>PRIVACY: id<br>X-AUTH-IP: 52.114.75.24<br>X-AUTH-PORT: 3136<br></div><div><br></div><div><br></div><div>Any advice? </div></div>