Measurement and Modelling of Internet Traffic over 2.5 and 3G Cellular Core Networks

THE task of modeling data traffic in networks is as old as the first commercial telephony systems. In the recent past in mobile telephone networks the focus has moved from voice to packetswitched services. The new cellular mobile networks of the third generation (UMTS) and the evolved second generation (GPRS) offer the subscriber the possibility of staying online everywhere and at any time. The design and dimensioning is well known for circuit switched voice systems, but not for mobile packet-switched systems. The terms user expectation, grade of service and so on need to be defined. To find these parameters it is important to have an accurate traffic model that delivers good traffic estimates. In this thesis we carried out measurements in a live 3G core network of an Austrian operator, in order to find appropriate models that can serve as a solid basis for traffic simulations. A requirement for this work was a measurement system, which is able to capture and decode network traffic on various interfaces of the mobile core network. Such a system was established within the METAWIN system. Our results are based on this setup. The work can be split into three parts. First, we studied the service usage on a per user and session base separately for UMTS and GPRS. This analysis revealed that the service usage for UMTS and GPRS is gradually becoming more and more similar and that the main application in terms of transfered bytes is HTTP. Nevertheless, the main application in terms of handsets is WAP. As seen in many network measurements a small fraction of the subscribers generates the majority of the traffic. In a second step we derived traffic models at flow level for UDP/TCP, HTTP, WAP 1.x and WAP 2.0. The TCP and HTTP flows follow a heavy-tailed behavior as expected from wireline measurements. However, UDP andWAP flows showed no heavy-tail effects. Many properties of the mobile flows follow the same distributions as in wireline networks. Third, we designed several source level traffic models. These models allow a better understanding of the user interaction and network settings. In the case of HTTP and FTP we updated the parameters of existing models in order to meet our requirements. The mobile Internet access features high RTTs, so we modified existing e-mail models to reproduce traffic at a better granularity. In order to provide models for upcoming applications we designed three models for online games and a push to talk implementation.