D. Use of both vs. best interface
Finally, we examine the parameter regime (i.e. bit-rate ratio, packet size, etc.) for which striping across multiple interfaces is beneficial.
Fig. 8 summarizes the comparison of sending through the best vs. sending through both interfaces for different file download sizes and different data rate ratios
of the edge Wi-Fi links. The z-axis plots the ratio of file transfer completion times of sending through the best interface to using both the available Wi-Fi interfaces at the client.
The gray plane cutting across the plot is at z=1. Ratios higher than 1 indicate striping is advantageous as it results in lower completion times.
From the plot, we can draw two interesting observations: Firstly, if the request is too small, the application actually suffers a performance degradation due to striping and
secondly, the benefit of multihoming decreases as the disparity in data rates of the two interfaces increases.
This motivates the use of a soft threshold for the flow size and the data rate
disparities below/above which the routers would decide to use the best interface.