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The availability of synchronized packet-level traces captured at different links allows the extraction of one-way delays for the network section in between. Delay statistics can be used as quality indicators to validate the health of the network and to detect global performance drifts and/or localized problems. Since packet delays depend not only on the network status but also on the arriving traffic rate, the delay analysis must be coupled with the analysis of the traffic patterns at short time scales. In this work we report on the traffic and delay patterns observed at short timescales in a 3G cellular mobile network. We show that the aggregate traffic rate exhibits large impulses and investigate on their causes. Specifically, we find that high- rate sequential scanners represent a common source of traffic impulses, and identify the potential consequences of such traffic onto the underlying network. This case-study demonstrates that the microscopic analysis of delay and traffic patterns at short time-scales can contribute effectively to the task of troubleshooting IP networks. This is particularly important in the context of 3G cellular networks given their complexity and relatively recent deployment.