Companies that deploy Windows Server 2008 and Windows Vista in tandem could see more than a threefold increase in networking performance for file transfers, downloading roaming profiles for mobile users and accessing files on a portal, according to a Microsoft-commissioned study conducted by the Tolly Group.

In a 38-page white paper set for publication Wednesday and titled "Enhanced Network Performance with Microsoft Windows Vista and Windows Server 2008," the Tolly Group compares the networking performance for file access on WANs and LANs using various configurations of Windows Server 2003 R2 or 2008 on the backend and XP SP2 or Vista on the frontend.

Not surprisingly, the combination of the newest operating systems brings the best gains in network performance in large part, Tolly concludes, because of an upgraded TCP/IP stack and updates to the file-sharing Server Message Block (SMB) protocol.

The report was commissioned by Microsoft, which raises questions about the value of the results, but the conclusions should at least provide some benchmarks for corporate users testing the software as part of their adoption evaluations.

Microsoft has been touting the networking benefits of its new operating systems on the client and server, and this study finally attaches numbers to those claims.

"We think the gains that we showed are considerable," says Kyle Sim, director of engineering for Tolly. "Because just by changing the OS on the client or server [or both], you can see performance enhancements of two to three times."

The Tolly study found that just by upgrading to Vista, users can see throughput gain of two to three times over XP and a reduction in time-to-completion (the time it takes to download a 10MB Office file over a simulated 10Mbps WAN) of 60 percent. The study shows that Vista in combination with Windows Server 2008 can yield gains of as much as 3.3 times in throughput and 3.5 times in time-to-completion over Windows Server 2003 and XP.

Tolly ran the tests over a variety of simulated LAN and WAN configurations taking into account bandwidth and latency The tests included sending SMB Copy and Open file commands, copying Roaming Profiles (including all elements on a user's desktop) and executing an Open file command on a SharePoint Services portal across the WAN and performing Office Open and Copy files commands across the LAN.

On the WAN side the connections ranged from satellite-type connections at 512KB per second with 300 milliseconds of latency to 10MB per second with 50-millisecond latency. On the LAN, the connections were 1000MB per second with 1-millisecond delay and 100MB per second with a 5-millisecond delay.

In one sample test, Windows Server 2003 R2 server was able to copy to an XP client a 10MB Office file at an average throughput of .9MB per second in 93.07 seconds using a simulated 2MB per second WAN link with 150 milliseconds of latency. In contrast, the Windows Server 2008/Vista combination had a throughput rate of 2MB per second and a completion time of 42.85 seconds, doubling throughput and cutting the download time by more than half.

"If you go back to the 3270 days with IBM, it recognized that users had large investments in applications, so they continued to fine-tune and wring performance out of those 3270 and VTAM-type applications," says Charlie Bruno, Tolly's executive editor of the white paper. "This is Microsoft's recognition that with these latest operating systems that they need to continue to give users greater performance to protect that large investment in applications they have out there."

Tolly found most of the performance gains could be linked to an upgrade in the TCP/IP stack called Receive Window Auto-Tuning and to support for SMB 2.0, a protocol for sharing files, printers, serial ports and communications between computers.

Receive Window Auto-Tuning automatically adjusts the size of the TCP window up to 16MB and monitors the network connection to optimize throughput.

"It will scale up and scale back dynamically; it won't saturate the network," says Jason Leznek, senior product manager for the Vista team at Microsoft. "I like to say we are using the network more efficiently."

The Receive Windows feature uses standard TCP extensions outlined in the IETF's RFC 1323 and works in conjunction with Compound TCP (CTCP) a new feature in the Microsoft TCP/IP stack, which adjusts the send windows to align with the size of the receive window. The CTCP function is enabled by default in Windows Server 2008.

The SMB 2.0 protocol improvements allow multiple actions in a single request, which reduces the number of round trips the client needs to make to the server.

Leznek says performance gains are greatest with SMB, but that HTTP gets a slight improvement, including the Background Intelligent Transfer Service (BITS) file transfer protocol that runs on top of HTTP.

"The secret sauce behind these tests is the enhancements we have done in the networking layer," said Ian Hameroff, a senior product manager for security and access at Microsoft. "The enhancements almost need to be treated as an 'Intel Inside' type of approach, because most people won't realize that their performance has improved because of networking functionality. They will assume that Internet Explorer is wired better or applications are running better because of some other aspect outside of raw TCP/IP improvements."