The Design and Implementation of IEEE 802.21 and Its Application on Wireless VoIP

Supporting a multimode mobile device to seamlessly switch its connections between various wireless access networks, such as WiMAX, Wi-Fi, and LTE, is an important research issue in 4G communications. The IEEE 802.21 working group defines the Media Independent Handover (MIH) standard to provide cross layer control and the information of network environment and services to optimize the handoff process. This work designs and implements the MIH middleware in a Linux platform to provide MIH event services (MIH-ES), MIH command services (MIH-CS) and MIH information services (MIH-IS). Based on the MIH software, we develop a high quality VoIP system which integrates Stream Control Transmission Protocol (SCTP), two MIH-IS based user motion detection (UMD) services and an adaptive QoS playout algorithm (AQP). The MIH services, multi-homing capability and dynamic address configuration extension of SCTP are applied in the VoIP system to perform seamless handoffs. Moreover, AQP adjusts the playout buffer by using the retransmission of partial reliable SCTP (PR-SCTP) and the MIH-ES to reduce the packet loss rate and improve speech quality. The experiment results indicate that MIH can enhance the performance of the handoff process and the quality of wireless VoIP services.