On the TCP Minimum Retransmission Timeout in a High-speed Cellular Network
Mats Folke, Sara Landstroem, Ulf Bodin · 2005
Abstract: HS-DSCH is a high-speed shared radio chan-nel extension for WCDMA which is used for cellular mo-bile telephony. The algorithm for distributing the chan-nel resources together with the characteristics of the radio medium result in delay variations. The TCP minimum re-transmission timeout interval has effectively alleviated de-lay variations in its range from deteriorating TCP perfor-mance. But recently, this bound has been shortened in modern widely spread TCP implementations. The aim of our study is to find out how a shorter minimum retrans-mission timeout affects TCP performance over HS-DSCH. We have implemented a model of HS-DSCH in the net-work simulator ns-2. Our simulations cover a wide range of different minimum retransmission timeout settings and loads, two types of schedulers (Round-Robin and Signal-to-Interference-Ratio (SIR) scheduling) and two versions of TCP (SACK and NewReno). Our results show that the number of spurious timeouts increase with the load. The SIR scheduler causes fewer spurious timeouts than the RR scheduler for shorter min-imum retransmission timeout settings, however, for longer settings the RR scheduler causes fewer spurious timeouts compared to the SIR scheduler. The minimum retransmis-sion timeout has consequences for goodput fairness, but it does not affect the total system throughput. Both TCP ver-sions produced similar results.