Patent ID: 8855082

Claim:
A method comprising: receiving, at a network device, a first domain message from a first domain, the first domain message being associated with a user device, wherein the user device is identified with a universal identifier included in the first domain message and determined by the first domain, wherein the universal identifier includes an international mobile subscriber identity (IMSI); assigning the first domain message to a specific server based on the universal identifier, wherein the first domain message includes a first session initiation protocol (SIP) message; receiving, at the network device, a second domain message from a second domain, wherein the second domain message is associated with the user device and the second domain message includes a second SIP message, wherein the second domain is separate from the first domain and the second domain communicates through a different protocol than the first domain, wherein the second domain message did not include the universal identifier when it was received by the second domain and the second domain uses an interworking function to encapsulate the second domain message and interwork the encapsulated message into a protocol used by the first domain to communicate with a home subscriber server in the first domain to determine the universal identifier; and assigning the second domain message to the specific server based on the universal identifier.