You work for a large banking firm headquartered in New York

You work for a large banking firm headquartered in New York. Your internetwork consists of more than 100 primary servers and about 3,000 clients scattered along the east coast of the United States. Over the past month, you have been looking at the performance statistics of the network and the critical devices. Today, you are examining the file transfer traffic to and from one of your main servers. You notice that the window size is very small in all the file transfers to and from this device. What could be the reason? How can you investigate further?

Solution

The reason for window size being small is frequent packet loss. In TCP protocol for file transfer, if there is a packet loss (sender does not receive an acknowledgement from the receiver), it exponentially reduces the window size assuming that there is a congestion in the network. However, the window size is then increased linearly, but again a packet loss can reduce the window size exponentially.

Further investigation would need monitoring the traffic to detect the packet losses. The packet drops at the interfaces along the network path needs to be determined. If there is a single point where there is a congestion it needs to be rectified by more bandwidth or additional hardware. I any component (trunk cables, interfaces, ports) shows high packet error rate along the network path, then they should be tested and replaced if needed.