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A new method to support UMTS/WLAN integrating using stream control transmission protocol Ma, Li


Third generation (3G) wide area wireless networks and wireless local area networks (WLANs) possess complementary characteristics. The performance and flexibility of wireless services would be dramatically improved if users could seamlessly roam across these two types of networks. In recent years, Stream Control Transmission Protocol (SCTP) developed by the Internet Engineering Task Force (IETF) has gained significant popularity in the studying of next generation IP networks. SCTP has also been selected as a standard signaling protocol for service control in 3G wireless network. Its multi-streaming, multi-homing and partial reliable (PR) data transferring features are especially attractive for applications that have stringent performance and high reliability requirements. In this research, we propose a new method to facilitate seamless vertical handovers (VHOs) between 3G Universal Mobile Telecommunication System (UMTS) cellular networks and WLANs using SCTP. The multi-homing capability and dynamic address reconfiguration (DAR) extension of SCTP are applied in the UMTS/WLAN overlay architecture to decrease the VHO delay and improve the throughput performance. We develop the UMTS/WLAN bi-directional VHO procedures and study the different scenarios employing a single-homing and a dual-homing fixed server configurations to support the VHO. We compare the performance of these two possible configurations using the ns-2 simulation tool and recommend the better one for our further study. Unlike mobility solutions of network or application layer, SCTP-based vertical handover does not require additional components to be added into the existing networks. Therefore, the proposed scheme provides a network independent solution that is preferred by service providers. In addition, we propose a new scheme that we call Sending-buffer Multicast with Fast Retransmission (SMART-FRX) to allow the sender to enter into the slow start process when handover loss (FEL) occurs in the WLAN link, and retransmit the error loss (EL) caused by multi-path fading over the wireless channel to the same destination IP address. According to the current SCTP link failure detection and recovery process as described in the specification, during a link failure detection period, timeouts and backoffs on the primary link may result in the poor throughput of the whole system. The proposed SMART-FRX scheme multicasts the buffered and new data on both UMTS and WLAN links to subdue the effect of handover loss (HL), and avoid unnecessary long delays of retransmitting lost packets due to UMTS transmission errors over the alternate possibly unreachable WLAN destination address. Consequently, the throughput performance is increased significantly. Moreover, we develop a new analytical model to study the SCTP performance during the VHO. By comparing numerical results for the analytical model with simulation results, we demonstrate that our model is able to accurately predict SCTP throughput. The analytical model provides a useful tool to estimate the SCTP throughput performance.

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