A system and method for performing SRNS relocation in a communications system transmits radio resource information including a ciphering parameter from a source RNC to a target RNC, modifies the ciphering parameter to coincide with a deciphering parameter which a user terminal uses when out-of-sequence data is received, ciphers a data unit based on the modified ciphering parameter, and transmits the ciphered data unit from the target RNC to the user terminal. The method may be modified to operate in UM mode or AM mode and to transmit data over one of several radio bearers. In accordance with another embodiment, the system and method transmits radio resource information from a source RNC to a target RNC and then transmits a data unit from the target RNC to a user terminal. In this case, the data unit including a transmission sequence number which consecutively follows a transmission sequence number of a data unit last transmitted from the source RNC to the user terminal. In accordance with another embodiment, the system and method resets ciphering and state variables in a target RNC and then transmits a message instructing a user terminal to reset a deciphering and state variables to the same or similar values. All the embodiments are advantageous because they ensure successful communications will take place between the target RNC and user terminal after a serving radio network sub-system relocation procedure is performed.