The TCP window is calculated after some sending activity. It reflects the amount of data that can be transmitted in one shot without hurting other TCP flows at the bottleneck.<p>Reusing TCP windows after a while does not reflect the actual state of the network as things would have changed. In fact, there have been proposals about CWND reset[1] that adress this issue.<p>[2] <a href="http://www.ietf.org/rfc/rfc2861.txt" rel="nofollow">http://www.ietf.org/rfc/rfc2861.txt</a>