Adaptive semi-soft handoff for Cellular IP networks

Rapid advances in wireless networking have led to more mobile phones, PDAs, and other digital mobile devices becoming ubiquitously connected to the Internet. As the demand of delay sensitive real-time applications for these portable devices increases, providing seamless connectivity to wireless networks becomes a critical issue. For this reason, a number of micro-mobility protocols, such as Cellular IP, have been proposed to complement the Mobile IP protocol. However, providing fast and reliable handoff is still a major obstacle to enabling seamless micro-mobility in wireless access networks. Cellular IP semi-soft handoff has been proposed to address such challenge. Evaluations have been performed which show that semi-soft handoff yields better performance than the conventional hard handoff. However, these studies are based on symmetrical network topologies and loads. In practice, network topology varies and the network load fluctuates depending on numerous parameters (e.g., number of mobile nodes, amount of traffic in the network, etc.). Semi-soft handoff uses fixed delay device and semi-soft delay values for stream synchronization and mobile host’s tune-in timing. Such scheme may work well for the evaluated symmetrical setup. However, this will not be the case with unbalanced and dynamically changing networks, as what are typically found in real life. This paper describes a novel adaptive protocol (Adaptive-SS), which is proposed as an extension to the current Cellular IP semi-soft handoff protocol to address such issue by assigning delay device and semi-soft delay values dynamically based on the present network condition. The simulation results show that Adaptive-SS significantly reduces network traffic and packet losses and duplications during handoff, while still minimizing handoff latency.