US Patent 11936694 Cross-domain routing based on session initiation protocol information

Methods, devices, and system related to cross-domain routing of communication session requests in Internet Protocol (IP) Multimedia Subsystem are disclosed. In one example aspect, a method for routing a call initiated in an IP Multimedia Subsystem (IMS) includes receiving, by a Breakout Gateway Control Function (BGCF) node operating in a first domain, a first message from a caller requesting an establishment of a communication session. The method includes determining, by the BGCF node based on header information of the first message, that the caller is located in a second domain different than the first domain, and generating, by the BGCF node, a second message based on a preconfigured rule for the second domain.