A poor implementation of TCP’s sliding-window protocol can lead to extremely poor performance. There

is a phenomenon known as the Silly Window Syndrome (SWS), which can easily cause degradation in

performance by several factors of 10. As an example of SWS, consider an application that is engaged in a

lengthy file transfer, and that TCP is transferring this file in 200-octet segments. The receiver initially

provides a credit (i.e., the receive window size) of octets. The sender uses up this window with 5

segments of 200 octets. Now suppose that the receiver returns an acknowledgement to each segment

providing an additional credit of 200 octets for every received segment. From the receiver’s point of

view, this opens the window back up to 1000 octets. However, from the sender’s point of view, if the

first acknowledgement arrives after five segments have been sent, a window of only 200 octets

becomes available. Assume that at some point, the sender has a window of 200 octets available but has

only 50 octets to send until it reaches a “push” point. It therefore sends 50 octets in one segment,

followed by 150 octets in the next segment, and then resumes transmission of 200-octet segments.

a) What might now happen to cause a performance problem? (3 points)

b) State the SWS in more general terms. (3 points)