Effect of physical layer bandwidth variation on TCP performance in cdma2000

A cdma2000™ end user can experience wide variations in the physical layer bandwidth allocated to him. This happens as a result of a high rate supplemental channel (SCH) being allocated and deallocated to the user in a bursty manner. This swing of physical layer rates can have an adverse effect on the end-end TCP operation, i.e., this rate variation can cause TCP timeouts and retransmissions even though no packet was lost on the physical layer. In this paper, we study this effect in detail. First, we propose a simple model for TCP over cdma2000. Using this model and subsequent analysis, we study the effects of different TCP parameters and different burst parameters (rate and duration) on the operation of TCP. We perform extensive lab tests to investigate how different TCP parameters and physical layer data rates affect the TCP throughput. Although the studies are done for a cdma2000 system, the results and conclusions hold in general for any system running TCP over a physical layer with varying bandwidth.