Remote Desktop 6.0 leverages a new feature called auto-tuning for the TCP/IP receive window that could be causing the trouble. What is auto-tuning for the TCP/IP receive window? Well, the new Microsoft TCP/IP stack supports Receive Window Auto-Tuning. Receive Window Auto-Tuning continually determines the optimal receive window size by measuring the bandwidth-delay product and the application retrieve rate, and adjusts the maximum receive window size based on changing network conditions.

In Vista, Receive Window Auto-Tuning enables TCP window scaling by default, allowing up to a 16 MB window size. As the data flows over the connection, the TCP/IP stack monitors the connection, measures the current bandwidth-delay product for the connection and the application receive rate, and adjusts the receive window size to optimize throughput. The new TCP/IP stack no longer uses the TCPWindowSize registry values which many third-party utilities used to “tweak”.

Receive Window Auto-Tuning has a number of benefits. It automatically determines the optimal receive window size on a per-connection basis. In Windows XP, the TCPWindowSize registry value applies to all connections. Applications no longer need to specify TCP window sizes through Windows Sockets options. And IT administrators no longer need to manually configure a TCP receive window size for specific computers.

Here is what you need to do if you have the same issue:

– Run a command prompt (cmd.exe) as an Administrator
– Type: netsh interface tcp set global autotuninglevel=disabled

If you want to to re-enable it:
– Type: netsh interface tcp set global autotuninglevel=normal

In some cases you may need to use this command in addition to the above, but I didn’t have to:
– Type: netsh interface tcp set global rss=disabled

Original article:http://blog.tmcnet.com/blog/tom-keating/microsoft/remote-desktop-slow-problem-solved.asp