There are four domain that interact while routing calls from an FCSDK application to another SIP entity.
SIP Registration Domain - This is the domain value specified in the user's voice section in the JSON provisioning request sent to the Gateway. This value is specified in the sipDomain tag of the fusionweb-db.xml for the sample FCSDK application.
Outbound SIP Server - This value is specified in the Web Plugin Framework Gateway Administration
Dialled Domain - This is the domain part of the SIP URI dialed by the client's application, e.g. sip:user@domain. The FCSDK automatically sets the domain to be that of the callers Registration domain if one isn't included in the dialed number.
FAS Controlled Domains - These are the values of the Controlled Domains of FAS, from the Admin Console.
This table shows the outcome given combinations of domains set for these values; note that the FAS Controlled Domain is always x.com:
It's worth noting you cannot route calls externally without the Outbound Sip Server value set.
Also, lines marked with Container cannot route this request may cause the Fusion Sample Application to stall rather than throw an error to the user.