The Microsoft Windows SDK also contains a tool that can read the so called ESTATS of an open TCP connection.
When running, you get a listing of all current TCP connections. Then you can click on one and see statistics about it in a new window. You can get a throughput history, find out where most time is spent during the connection. This is good to find out performance bottlenecks of an already running application, without interrupting it.
Unfortunately to install this tool you need to download and install the whole SDK (the ISO image is a whopping 1.3GB), as there is no separate installation available.
More information is available here.
– Main.ChrisWelti - 12 Jan 2010