A Measurement Based Performance Study of TCP over GSM/GPRS

Abstract: In this thesis, the performance of the wireless Internet is studied with a focus on TCP over GSM/GPRS. To this end, we have developed a GSM/GPRS test bed for TCP measurements. We present measurements conducted in the test bed with TCP over both GSM and GPRS. The GSM measurements show that TCP interacts efficiently with the radio link layer in GSM, also under very poor radio conditions. The only cases when some inefficiency is detected occur due to sudden variations in delay. In GPRS, delay is, among other things, caused by buffering in intermediate nodes and by dynamic resource sharing. The GPRS measurements indicate that if the buffers in intermediate nodes are reduced, then the delay can be decreased significantly with almost retained throughput. Dynamic resource sharing is often configured to give preemptive priority to voice calls, which implies that all GPRS resources may be lost. Measurements with preemptive priority indicate that TCP performance is degraded more than necessary due to inefficient buffer management. The situation would improve if data was buffered during preemption and if the data was transmitted immediately as GPRS resources become available again