Micro- and Macroscopic Analysis of RTT Variability in GPRS and UMTS Networks

We study the data from a passive TCP/IP traffic measurement from a Finnish operator’s GPRS/UMTS network. Of specific interest is the variability of Round Trip Times (RTTs) of TCP flows. The RTTs are analysed at micro- and macroscopic level. The microscopic level involves detailed analysis of the RTTs of individual flows, and we are able to detect, e.g., periodic behavior (via Lomb periodogram) and rate changes in the radio channel. At the macroscopic level we focus on the impact of so called self-congestion caused by bandwidth sharing at the mobile device itself, and it is shown how this seriously affects the RTTs observed by a given flow, both in GPRS and in UMTS.