Tweak And Tune Your TCP Window Scaling For Performance On Network

The TCP Window Scaling feature adds support for the Window Scaling option in RFC 1323. A larger window size is recommended to improve TCP performance in network paths with large bandwidth, long-delay characteristics that are called Long Fat Networks (LFNs) . This TCP Window Scaling enhancement provides that support.
The example settings here will provide enhanced performance:

More details can be found on these sites:Tcp1323Opts

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters Determines whether TCP uses the timestamping and window scaling features described in RFC 1323, TCP Extensions for High Performance.

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.

The TCP receive window size is the amount of receive data (in bytes) that can be buffered at one time on a connection. The sending host can send only that amount of data before waiting for an acknowledgment and window update from the receiving host. The Windows 2000 TCP/IP stack was designed to 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) negotiated during connection setup. Matching the receive window to even increments of the MSS increases the percentage of full-sized TCP segments used during bulk data transmission.

Windows Server 2003 TCP/IP supports TCP time stamps, as described in RFC 1323. Like SACK, time stamps are important for connections using large window sizes. Time stamps assist TCP in accurately measuring round-trip time (RTT) to adjust retransmission time-outs.

The primary reason for the window is congestion control. The whole network connection, which consists of the hosts at both ends, the routers in between and the actual connections themselves (be they fiber, copper, satellite or whatever) will have a bottleneck somewhere that can only handle data so fast. Unless the bottleneck is the sending speed of the transmitting host, then if the transmitting occurs too fast the bottleneck will be surpassed resulting in lost data. The TCP window throttles the transmission speed down to a level where congestion and data loss do not occur.

The Bandwidth*Delay Product, or BDP for short determines the amount of data that can be in transit in the network. It is the product of the availalbe bandwidth and the latency, or RTT. BDP is a very important concept in a Window based protocol such as TCP. It plays an especially important role in high-speed / high-latency networks, such as most broadband internet connections. It is one of the most important factors of tweaking TCP in order to tune systems to the type of network used.