The emerging technologies in the field of telecommunications enable us to access high speed data services through mobile handsets and portable modems over the mobile networks. The recent statistics also shows the use of mobile broad band services are increasing and gaining popularity. In this thesis we have investigated the impact of payload size and data rate on one-way delay and packet loss in operational 3G mobile networks, through network level measurements. To collect the network level traces an experimental testbed is developed. For accurate measurement Endace DAG cards together with GPS synchronization is implemented. Results are gathered from three different commercial mobile operators in Sweden. From the results it is concluded that the combination of maximum payload size and data rate resulted in minimum one-way delay. It is also observed within the big payload size category, that the percentage of packet loss is less as compared to the smaller payload sizes. Such findings will improve efficiency of application developers to meet the challenges of UMTS network conditions.