Office Office Exchange Server. Not an IT pro? Windows Server TechCenter. Sign in. United States English. Ask a question. Quick access. Search related threads. Remove From My Forums. Answered by:. Instead of using a hard-coded default receive window size, TCP adjusts to even increments of the maximum segment size MSS. The MSS is negotiated during connection setup. Adjusting the receive window to even increments of the MSS increases the percentage of full-sized TCP segments used during bulk data transmissions.
For Ethernet connections, the window size will normally be set to 17, bytes 16K rounded up to twelve byte segments. These two options increase the TCP header size to more than 20 bytes, which results in less room for data. In previous versions of Windows NT, the window size for an Ethernet connection was 8, bytes, or six byte segments. To set the receive window size to a specific value, add the TcpWindowSize value to the registry subkey specific to your version of Windows.
To do so, follow these steps:. This value isn't present by default. When you add the TcpWindowSize value, it overrides the default window size algorithm discussed above.
TcpWindowSize can also be added to the Parameters key to set the window size globally for all interfaces. Previously, TCP options were used primarily for negotiating maximum segment sizes.
Kind: 3 Length: 3 Option: Window Scale Option Description: Identifies the scaling factor to be used when using window sizes larger than 64k. For more efficient use of high-bandwidth networks, a larger TCP window size may be used. The TCP window size field controls the flow of data and is limited to 2 bytes, or a window size of 65, bytes.
Since the size field can't be expanded, a scaling factor is used. TCP window scale is an option used to increase the maximum window size from 65, bytes to 1 Gigabyte. The window scale option is used only during the TCP three-way handshake. The window scale value represents the number of bits to left-shift the bit window size field.
The window scale value can be set from 0 no shift to If the window size is 65, bytes with a window scale factor of 3. The window size used in the actual three-way handshake isn't the window size that's scaled, per RFC section 2.
It means that the first data packet sent after the three-way handshake is the actual window size. If there's a scaling factor, the initial window size of 65, bytes is always used. The window size is then multiplied by the scaling factor identified in the three-way handshake.
Posting enough user receive buffers by increasing the value passed to the -a option reduces TCP copying. You should not excessively post user receive buffers because the first buffers that are posted would return before you need to use other buffers. It is best to bind each set of threads to a logical processor the second delimited parameter in the -m option.
This provides good performance on a low-latency network. In contrast, for high-latency networks or for 10 GB adapters, the default TCP window size value for NTttcp yields less than optimal performance. Connect and share knowledge within a single location that is structured and easy to search.
I think it's bytes, but I'm not sure. Also note that the window size is not necessarily the same size as the MTU. It may be significantly larger - autotuning decides the best size for the network state. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
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