Patent ID: 8243725

Claim:
A method for implementing a fallback procedure from a packet switched (PS) radio access technology (RAT) to a circuit switched (CS) RAT, comprising: receiving a paging message at a wireless transmit/receive unit (WTRU) via the PS RAT, the paging message including a WTRU identifier and a domain indicator, wherein the domain indicator indicates whether the paging message is related to a service on the CS RAT; determining whether the WTRU identifier in the paging message matches a stored identifier of the receiving WTRU; performing a fallback procedure to the CS RAT on a condition that the WTRU identifier in the paging message matches the stored identifier of the receiving WTRU; and responding to the paging message using a CS RAT-based identifier assigned to the WTRU, wherein the CS RAT-based identifier is an international mobile subscriber identity.