Setting the Timeout in TCP

Question

the timeout interval dynamically changes depending on the network. It is generally represented by TimeoutInterval = EstimatedRTT + 4*DevRTT

But why do we you 4*DevRTT?

Why can't it be 2*DevRTT??

Answer 1

You could set it to that, but you would be decreasing the amount of cushion you are giving variations in RTT by half.

If you have wide variances in RTT, which can happen in more situations than you realize, then you would be setting the timeout value relatively low.

Because this timeout controls the re-transmission of data, setting this level lower almost certainly means that the number of re-transmission will increase in certain scenarios. The concern would be that these re-transmissions are unnecessary, and possibly increase utilization of an already saturated network.