Examining TCP Short Flow Performance in Cellular Networks Through Active and Passive Measurements

In this study we examine the conditions in a current cellular network by examining data passively collected in the core of a cellular operator during a 24-hour period. More than 2 billion traffic measurement data points from over 500,000 cellular users are analyzed. The analysis characterizes the Time-of-Day (ToD) variations for traffic intensity and session length and serves as a complement to the active measurements also performed. A comprehensive active measurement campaign was completed in the HSDPA+ and LTE networks of the four major Swedish operators. We collect around 50,000 data points from stationary cellular modems and analyze the ToD variation pattern for underlying network layer metrics such as delay and throughput. In conjunction with the time-varying session size distribution obtained from the passive measurements, we then analyze the ToD impact on TCP flows of varying sizes. The ToD effects are examined using time series analysis with Lomb-Scargle periodograms and differential Bayesian Information Criterion to allow comparison of the relative impact of the network ToD effects. The results show that ToD effects are predominantly impacting longer-running flows, and although short flows are also impacted they are mostly constrained by other issues such as protocol efficiency.