There are some significant performance enhancements in the Next Generation TCP/IP stack that comes with Windows Vista and Windows Server 2008. One of my teammates, Chris Henley, has recorded a great screencast all about how the TCP/IP stack has been improved and how you can benefit from it.
Here are a few areas he talks about that have been improved as well as links below to his video and the PowerPoint slide deck he references:
Receive Window Auto-Tuning
The Receive Window Auto-Tuning feature lets the operating system continually monitor routing conditions such as bandwidth, network delay, and application delay. Therefore, the operating system can configure connections by scaling the TCP receive window to maximize the network performance. To determine the optimal receive window size, the Receive Window Auto-Tuning feature measures the products that delay bandwidth and the application retrieve rates. Then, the Receive Window Auto-Tuning feature adapts the receive window size of the ongoing transmission to take advantage of any unused bandwidth.
For TCP connections with a large receive window size and a large bandwidth-delay product, Compound TCP (CTCP) in the Next Generation TCP/IP stack aggressively increases the amount of data sent at a time by monitoring the bandwidth-delay product, delay variations, and packet losses. CTCP also ensures that its behavior does not negatively impact other TCP connections. In testing performed internally at Microsoft, large file backup times were reduced by almost half for a 1 Gigabit per second connection with a 50 millisecond round-trip time. Connections with a larger bandwidth-delay product can have even better performance.
Explicit Congestion Notification (ECN)
When a TCP segment is lost, TCP assumes that the segment was lost due to congestion at a router and performs congestion control, which dramatically lowers the TCP sender’s transmission rate. With Explicit Congestion Notification (ECN) support (RFC 3168) on both TCP peers and the routers in the routing infrastructure, routers experiencing congestion mark the packets as they forward them. TCP peers receiving marked packets lower their transmission rate to ease congestion and prevent segment losses. Detecting congestion before packet losses are incurred increases the overall throughput between TCP peers. Windows Server 2008 and Windows Vista support ECN, but it is disabled by default.
View his video here, I'd recommend double-clicking on the video below to view in fullscreen mode. Click HERE to to download the PowerPoint he mentions at the end of the video.