New Cross-Layer Channel Switching Policy for TCP Transmission on 3G UMTS   Downlink
  In 3G UMTS, two main transport channels have been provided for downlink data transmission: a common FACH channel and a dedicated DCH channel. The performance of TCP in UMTS depends much on the channel switching policy used. In this paper, we propose and analyze three new basic threshold-based channel switching policies for UMTS that we name as QS (Queue Size), FS (Flow Size) and QSFS (QS & FS combined) policy. These policies significantly improve over a modified threshold policy in [1] by about 17% in response time metrics. We further propose and evaluate a new improved switching policy that we call FS-DCH (at-least flow-size threshold on DCH) policy. This policy is biased towards short TCP flows of few packets and is thus a cross-layer policy that improves the performance of TCP by giving priority to the initial few packets of a flow on the fast DCH channel. Extensive simulation results confirm this improvement for the case when number of TCP connections is low. 
Dinesh Kumar (INRIA Sophia Antipolis), Dhiman Barman, Eitan Altman   (INRIA Sophia Antipolis), Jean-Marc Kelif (FT R&D)