Effect of Vertical Handovers on Performance of TCP-Friendly Rate Control
Andrei Gurtov
Jouni Korhonen
ACM Mobile Computing and Communications Review, 8(3):73-87, July 2004
[Full Text in PDF Format, 340KB]
Abstract
An intersystem or vertical handover is a key enabling mechanism for next
generations of mobile communication systems. A vertical handover can
cause an abrupt change of up to two orders of magnitude in link
bandwidth and latency. It is hard for end-to-end congestion control to
adapt promptly to such changes. This is especially a concern for slowly
responsive congestion control algorithms, such as TCP-Friendly Rate
Control (TFRC). TFRC is designed to provide a smooth transmission rate
for real-time applications and, therefore, is less responsive to changes in
network conditions than TCP. Using measurements and simulation, we show
that TFRC has significant difficulties adapting after a vertical
handover. TFRC receives only a fraction of TCP throughput over a fast
link, but can be grossly unfair to concurrent TCP flows after handover
to a slow link. We show that two proposals based on overbuffering and an
explicit handover notification are effective solutions to these
problems. Using them, TFRC can quickly adapt to new link
characteristics after a handover, while otherwise maintaining a smooth
transmission rate.