A target gateway operating in a target wireless network receives a request for transferring wireless service of a wireless device from a source access network to the target access network. The target gateway sends a handover initiate message comprising key information including an uplink key to a source gateway operating in the source access network. In response to the handover initiate message, the target gateway receives a handover acknowledgement message that includes user session information including session reference identifiers (SR-IDs) associated with multiple Internet Protocol (IP) addresses of the wireless device. Subsequently, the target gateway forwards a packet of uplink communication by encrypting using the uplink key to a gateway server.