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Microsoft have implemented their own homemade congestion provider as an alternative to the standard TCP congestion provider. It is called Compound TCP (CTCP) and attempts to solve the following conflict in finding the proper RWIN size:

• High bandwidth connections requiring very large receive windows (RWIN)
• Lossy connections requires lots of retransmission if the RWIN is too large.

These types of connection are becoming more common, as more international companies want to connect their different long distance offices with high speed connections.

To change the congestion provider to CTCP (default on Windows 2008):

netsh interface tcp set global congestionprovider=ctcp

To revert the congestion provider to default TCP (default on Windows Vista):

netsh interface tcp set global congestionprovider=none

More Info Wiki - Compound TCP
More Info Microsoft Research - Document about CTCP
More Info Cable Guy - Compound TCP
More Info MS KB 949316 (Hotfix for Win2k3 enables CTCP)

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