Characterizing Wireless Link Throughput with eBPF and Hardware Timestamps.

With a growing user base and the deployment of new systems, such as 5G and Starlink, a deep understanding of the varying link throughput for wireless systems is highly important. While detailed analysis of link throughput can be done on packet traces, collecting extensive packet traces often faces storage and privacy challenges. Instead, we propose using traces of link-wide inter-packet delay (IPD) to enable highly granular link throughput characterization on a wider scale. To this end, we present an eBPF-based tool designed to capture IPDs, and evaluate the accuracy of captured IPDs with the IPD tool and tcpdump, both with and without access to hardware timestamps. While hardware provided timestamps provide accurate IPDs, we find that software based timestamps lead to IPD values which are very inaccurate, but still useful in aggregate form to characterize throughput at millisecond timescales. Furthermore, we show that concurrent packet processing incurs a significant amount of packet reordering, which necessitates the consideration of several previous packets when computing the link-wide IPD. Finally we present an example use case of IPD collection, characterizing frequent silent periods during a speedtest over a 5G link.