We are all treated equal, aren't we? - Flow-level performance as a function of flow size

Recent Internet studies have reported on continued traffic growth, changes in applications usage, and a proliferation in the adoption of high-speed access links. Any adverse impact that these observed trends may have on Internet traffic flows can result in sub par performance, which in turn results in unsatisfactory user experience. To study such adverse impacts, we examine in this paper the flow-level performance of popular applications across a range of size-based flow-classes and applications. We use out-of-sequence packets, retransmissions, throughput, and RTTs as key flow performance metrics. Leveraging data sets collected from two complementary network environments, we compare these metrics for popular applications and for the up/downstream directions. We show that irrespective of the direction, flows are severely impacted by the specifics of the network, e.g., DSL or CDN and application behavior. We also find that, in general, this impact differs markedly across the different flow-classes. In particular, contrary to popular belief, the small flows from all applications, which make up the majority of flows, experience significant retransmissions, while the very large flows, although small in number, experience very limited retransmissions. In terms of application-related performance, we observe that especially when compared to HTTP, apart from large flows, P2P flows suffer from continuously high retransmissions and low throughput. As for the root cause of these retransmissions, we identify the access part of the network as the main culprit and not the network core.