A Fast Adaptation Scheme for TFRC over Vertical Handovers

The next generation of mobile communication systems will be an integration of complementary wired and wireless network technologies. A mobile user equipped with multiple interfaces that support different technologies should be able to switch between them when needed without losing its connection to the system. This is called a vertical handover. A vertical handover may cause abrupt changes in the throughput and delay experienced by the mobile user because of the differences in the characteristics and conditions on the old and new networks. This is an issue for all rate/congestion control mechanisms, especially slow responsive ones such as TFRC. TFRC was designed for a smooth transmission rate, therefore it can not follow closely the sudden change in the available bandwidth. Significant change in the end-to-end delay may also cause false no feedback timeout or packet reordering and affect the sending rate calculation. In this paper we propose a fast adaptation mechanism that tries to solve all these problems in a systematic and unified way. We show that our mechanism can greatly reduce the adaptation time and packet loss during TFRC vertical handover between any technologies, while preserving the original TFRC behavior otherwise. It is also designed to be robust in a lossy environment, in case of bad wireless link quality or network congestion.