New Windows Operating Systems Put to the Speed Test

Published: November 28, 2007

by Alex Woodie

Some serious changes have been made to the TCP/IP stacks in Windows Server 2008 and Windows Vista, and Microsoft wants you to know about it. To that end, the software giant recently commissioned the Tolly Group to conduct speed tests comparing the new versions of the client and server operating systems with Windows XP and Windows Server 2003, and to publish its findings. The results? The new operating systems sport download speeds that are three to four times faster, according to Tolly.

Microsoft has made wide and deep changes to the network stack with Windows Server 2008 and Windows Vista. And while the networking improvements haven't been at the forefront of Redmond's marketing machine--where better security seems to be the key motivational factor--the folks in the Windows Server Division decided it was worth highlighting the improvements in networking by reminding us, in a blog posting, about a February Tolly Group report that you might have missed the first time around.

Let's review some of the significant changes Microsoft has made to the TCP/IP stack, both in the upcoming release of Windows Server 2008, due out early next year, and in Windows Vista, which has already been in use for a year.

Near the top of Microsoft's list is the "TCP receive window auto-tuning" capability, which boosts performance by continually measuring the bandwidth delay and the application retrieve rate, and adjusting the receive windows based upon fluctuations in those network conditions.

Compound TCP, or CTCP, also improves network speed by automatically widening the TCP send window for connections with large TCP receive windows and with large bandwidth delays. (This feature is turned off by default in Windows Vista, but will be turned on by default in Windows Server 2008.) Explicit Congestion Notification (ECN) is another speed-inducing feature that alleviates congested TCP connections by attaching a special marker to packets that alert routers of the congestion, thereby enabling the routers to lower their transmission rates, which prevents segment loss and has the effect of boosting overall throughput, according to Microsoft.

Neighbor Unreachability Detection is another new feature designed to address "high-loss" networking environments. Microsoft built support for this feature into its stack for IP version 4 networks; it's already a part of IPv6. Support for "fail-back to default gateway" and support for a series of algorithms, such as the NewReno Modification to TCP's Fast Recovery Algorithm, an extension to the Selective Acknowledgement (SACK) option for TCP, and the Forward RTO-Recovery (F-RTO) algorithm, also boosts throughput and speed downloads for the new operating systems.

Improvements outside of the TCP/IP stack have also been made. For example, support for the Server Message Block (SMB) 2.0 protocol in Windows Server 2008 and Windows Vista provides a significant boost when sharing Windows files across a network. An older version of SMB (which is also known as the Common Internet File System [CIFS]), called SMB 1.0, was used in Windows Server 2003 and Windows XP. SMB 2.0 has many advantages over SMB 1.0, including the capability to send multiple commands in a single packet, support for much larger buffer sizes, better scalability, and more durability on shaky networks, among other benefits.

Taken together, the TCP/IP stack improvements and support for SMB 2.0 have the effect of significantly boosting the network performance of the new operating system, according to Microsoft and Tolly.

But how much of an improvement? To test this, Tolly rolled out ConNIE, or the "Converged Network Impairment Emulator," a testing tool developed by Spirent Communications to simulate various network speeds and latencies, and the Wireshark network protocol analyzer to capture traffic between clients and servers. Then, the group measured how long it took to send 10 MB files--including Office documents and user profiles--across simulated WANs and LANs.

All combinations of operating systems were tested, and across the board, the new operating systems were able to download and open--or open from afar--Office files and user profiles faster than the older operating systems.

The biggest improvements came when pairing Window Server 2008 with Windows Vista. When these two products are used, total throughout was increased by a factor of 3.3, while completion of task metric augmented performance by a factor of 3.5. But even the pairing of Windows Vista with Windows Server 2003, and Windows Server 2008 with Windows XP, provided improvements over the combination of Windows Server 2003 and Windows XP, the study found.

"By relying on the improvements in the TCP/IP stack, users will realize performance gains and time to completion improvements that make more efficient usage of WAN And LAN connections, and keep end users satisfied," Tolly concluded.

Readers can down the PDF-based white paper, titled "Enhanced Network Performance with Microsoft Windows Vista and Windows Server 2008," at this Web site.

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