Select Start > Run, type Regedit, and then select OK.Įxpand the registry subkey specific to your version of Windows:įor Windows 2000, expand the following subkey: To set the receive window size to a specific value, add the TcpWindowSize value to the registry subkey specific to your version of Windows. In previous versions of Windows NT, the window size for an Ethernet connection was 8,760 bytes, or six 1460-byte segments. These two options increase the TCP header size to more than 20 bytes, which results in less room for data. The window size may reduce when a connection is established to a computer that supports extended TCP head options, such as Selective Acknowledgments (SACKS) and Timestamps.
The window size is adjusted to four times the MSS, to a maximum size of 64 K, unless the window scaling option (RFC 1323) is used.įor Ethernet connections, the window size will normally be set to 17,520 bytes (16K rounded up to twelve 1460-byte segments).
When the connection is established, the receive window size is rounded up to an even increment of the MSS. The first connection request sent to a remote host advertises a receive window size of 16K (16,384 bytes). The receive window size is determined in the following manner: Adjusting the receive window to even increments of the MSS increases the percentage of full-sized TCP segments used during bulk data transmissions. The MSS is negotiated during connection setup. Instead of using a hard-coded default receive window size, TCP adjusts to even increments of the maximum segment size (MSS). The Windows TCP/IP stack is designed to self-tune itself in most environments, and uses larger default window sizes than earlier versions. The sending host can send only that amount of data before it must wait for an acknowledgment and window update from the receiving host. The TCP receive window size is the amount of receive data (in bytes) that can be buffered during a connection. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base: 322756 How to back up and restore the registry in Windows TCP window size Then, you can restore the registry if a problem occurs. For added protection, back up the registry before you modify it. Therefore, make sure that you follow these steps carefully. 
However, serious problems might occur if you modify the registry incorrectly. The following sections, methods, or tasks contain steps that tell you how to modify the registry.
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