Multi-layer protocol tracing in a GPRS network

The paper presents a performance evaluation of GPRS accomplished by a combination of measurement at the end hosts and tracing inside the network. The multi-layer tracing approach allows not only observing, but also understanding of, the network performance. With end-to-end measurements, we assess data rates, latency, and buffering experienced by users in a live GPRS network. Comparing the results to our previous measurements shows a notable improvement in the network and terminals over the previous two years. Mobility tests while driving in an urban environment quantify the interval, duration and data loss caused by cell reselections. In the test lab, multi-layer tracing of radio, link and transport protocols gives a closer picture of GPRS performance. For instance, TCP interacts inefficiently with resource allocation at the RLC (radio link control) layer and fragmentation at the LLC (logical link control) layer. Finally, we illustrate delay spikes and data losses during cell reselection by tracing signaling messages during cell update and routing area update procedures.