No abstract

With the help of Mobile IP/IPv6 and soft handoff, on-going TCP sessions can remain active and handoff packet loss can be avoided. However, TCP still faces several performance degradation issues due to the disparities in bandwidth and propagation delay between different access networks. Particularly, during vertical handoffs, some undesirable phenomenons may erroneously trigger TCP congestion control actions and thus degrade TCP performance. In this paper, we tackle the spurious timeout problem frequently associated with handovers from fast to slow links. We propose three network-layer schemes: Fast ACK, Slow ACK and ACK Delaying. These schemes require only minor modifications to the network layer of mobile receivers and no change to the TCP protocol and the TCP sender. Simulation results show that these schemes can effectively improve TCP performance during soft vertical handoffs.

No abstract

With the availability of various wireless link-layer technologies, such as Bluetooth, WLAN and GPRS, in one wireless device, ubiquitous communications can be realized through managing vertical handoff in the environment of wireless overlay networks. In this paper, we develop a ubiquitous video streaming system through wireless overlay networks. One of the main features of the developed system is that it can support seamless communications. In other words, the developed system enables wireless devices to roam among different wireless networks without affecting the ongoing multimedia applications. Another feature is that our developed video streaming application can be adaptively adjusted to match the significant change of wireless link characteristics due to vertical handoff. Our contribution lies in the integration of various existing techniques to build a real system.

No abstract