Windws XP/2K window size

binarysoul

What's the TCP window size on WinXP/W2K and Windows 2003 server? I guess it's 64 KB except for Windows 2000 that are not on SP3/SP4. Is that correct?

dtlokee

It probably depends on the protocol in question, telnet is much smaller than FTP, but I would guess it to be a maximum of 8-16k from what I have seen. Also as frames are lost (due to congestion or whatever),of ir the hosts are capiable of ECN, it will cause TCP to lower the window size.

sprkymrk

I didn't have a clue, so I googled it:

http://support.microsoft.com/kb/224829

TCP window size
The TCP receive window size is the amount of receive data (in bytes) that can be buffered during a connection. 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 Windows TCP/IP stack is designed to self-tune itself in most environments, and uses larger default window sizes than earlier versions.

Instead of using a hard-coded default receive window size; TCP adjusts to even increments of the maximum segment size (MSS), which is negotiated during connection setup. Adjusting the receive window to even increments of the MSS increases the percentage of full-sized TCP segments utilized during bulk data transmissions.

The receive window size is determined in the following manner:1. The first connection request sent to a remote host advertises a receive window size of 16K (16,384 bytes).
2. When the connection is established, the receive window size is rounded up to an even increment of the MSS.
3. The window size is adjusted to 4 times the MSS, to a maximum size of 64K, unless the window scaling option (RFC 1323) is used.

JDMurray

The TCP receive window size can be discovered and adjusted using the DrTCP tool.

http://www.dslreports.com/drtcp

FAQ: http://www.dslreports.com/faq/578