C. Effect of backpropagation threshold on performance
Next we investigate the effect of the back-propagation threshold (referred to as H in Sec. II) on the performance of the striping algorithm, with the client having two Wi-Fi interfaces of physical data rates 54Mbps and 6Mbps respectively,requesting a 200MB file from the server (other parameters remaining the same as before).
In Fig. 7, we see that the file transfer completion time is highest for H=1.
This is because when H is set to 1, a router starts accepting a chunk, only when
it has been able to successfully transfer the previous chunk downstream and therefore waits idle until it receives the next chunk from upstream.
Higher the value of H, larger is the time required for completion as the striping router keeps sending chunks equally across both the interfaces (instead of the ideal
rate of 6 : 54) for a longer time, until the ack-withholding starts, as shown in
Fig. 7.
At the same time, the lower the value of H, lesser would be the reordering at the application, as the striping router would be able interpret the data rates faster,
with the minimum being at H=1.
For the chosen chunk size and delay bandwidth products of the upstream and downstream
links at each router, the value of 2 appears to be ideal.
For a different network configuration, a suitable value of H could be chosen based on similar analysis.