Vista over the WAN: good but not great

Here's the skinny on how Microsoft's new client operating system handles WAN optimization

Windows Vista has users buzzing about network performance improvements, but industry watchers caution that the new client operating system is no WAN-optimization cure-all.

In certain scenarios, the improvements implemented in Vista and slated for Windows Server 2008 (Longhorn) will alleviate the problems of latency and inefficient protocols that have hampered application performance over the WAN. But the improvements will have limited or no effect on performance until PC hardware is upgraded, applications are reworked and Microsoft Vista or Longhorn machines sit at both ends of a WAN link.

From a communications perspective, Longhorn and Vista are works in progress, says Joe Skorupa, a Gartner research vice president. "There's a lot to like, but don't dash to deploy Vista just to get these features. As well tested as it has been, you'll want to make sure you take a measured approach to deployment."

Although the vast majority of enterprises plan to adopt Vista, most are in waiting mode, according to a recent survey conducted by Walker Information in collaboration with CDW. Among 753 IT buyers, 1% have deployed Vista, 25% are implementing it and 61% plan to do so within the next 12 months or more.

Respondents acknowledged Vista's potential performance improvement; 56% cited that as a key perceived benefit.

Vista’s performance-boosting trio

With these three targets, Microsoft aims to boost application performance over the WAN:

Updated TCP/IP stack

Impact: Enhancements include autotuning of the receive window's size to optimize throughput on long-distance links, a new Compound TCP (CTCP) algorithm for moderating TCP flow control from the transmitting end, and the ability to detect default-router failures and improperly configured maximum-transmission unit settings.

Limitations: CTCP is best used for high-speed Longhorn server-to-server data replications.

New Common Internet File System (CIFS) implementation

Impact: Support for Microsoft's Server Message Block (SMB) 2.0 protocol in computers running Vista or Longhorn enables the sending of multiple commands within a packet, reducing the number of round trips between a client and server. SMB 2.0 supports larger buffer sizes than SMB 1.0 does, and can withstand short interruptions in network availability.

Limitations: SMB 2.0 will improve performance when file servers are accessed across a WAN, but only between Vista clients and Longhorn servers.

QoS enhancements

Impact: Tools to set application- and transaction-level QoS via Active Directory policies could simplify configuration and management for users.

Limitations: QoS controls aren't detailed enough yet, and asymmetrical QoS requires a homogenous Vista and Longhorn environment.

Source: Gartner

Protocol improvements

For the most part, Vista's performance gains are directed at file-sharing over WANs, which has become an important New Data Center issue for enterprises as the number of employees working in remote offices climbs. Most significant, Vista features a rewritten TCP/IP stack and improvements to Common Internet File System (CIFS), the native Windows access protocol that enables file- and print-sharing among devices.

For the new TCP/IP stack, Microsoft changed its congestion-control algorithms so more data is sent at higher speeds. "It does some autotuning things, and it takes advantage of large window sizes -- stuff the research has been pointing to for a while that will make TCP run a lot better in high-bandwidth, high-latency environments," Skorupa says.

Microsoft based its Vista implementation of CFIS on a new version of the Server Message Block (SMB) protocol that lets multiple data blocks be sent over the WAN simultaneously instead of requiring blocks be sent individually and waiting for acknowledgment that each has been received.

These CIFS and TCP improvements will have the most positive impact on long file-transfers, such as large media files that have been compressed as much as they can be, says Eric Siegel, a senior analyst at Burton Group. But don't count on Vista to do data-reduction-based compression as dedicated WAN-optimization appliances can, he says. Nor will Vista's performance enhancements have much effect on Web-based applications, Skorupa adds.

"They're not going to take a badly structured, browser-based app that does 70 round trips on the network to paint a screen down to five round trips," he says. "Vista also doesn't do anything to provide optimization specifically for HTTPS-encrypted traffic."

Another consideration is that companies won't benefit fully from the TCP and CIFS enhancements unless they have Longhorn or Vista machines on both ends of a link.

Further complicating the CIFS issue is that a number of third-party and homegrown applications, because they were developed specifically for the LAN, never took advantage of some of the advanced features in SMB 1.0. Getting these applications to take advantage of the improvements in SMB 2.0, on which the Vista CIFS implementation is based, is not an attractive prospect for many IT departments, Skorupa says. Deploying WAN-optimization gear is much quicker and far less painful than restructuring an application, he says.

Not fully baked yet

Another performance feature Microsoft has focused on in Vista is QoS, incorporating management tools that let administrators link application policies to user profiles via Active Directory. Using Active Directory information about employees' and groups' access rights as the base, administrators potentially could make decisions as fine-grained as giving a particular finance employee high-priority access to SAP applications during the last two weeks of a quarter.

"If you can do all that through Active Directory and put it out through group policy, and lock it down so that the person on the end station can't change it . . . that becomes a really powerful system to have," Skorupa says. To date, he adds, the policy-based QoS features in Vista don't allow that level of detail. "You can't say, 'Do this for this application running over Port 80.' It's not enough to have a huge impact yet. But it's a start."

On the whole, Microsoft has made great strides to improve application performance over the WAN, but Vista's enhancements are not going to wipe out the market for specialized WAN-optimization gear any time soon. "There's a lot of cleanup here, and it took Microsoft a long time to do it. But that said, it's good stuff," Skorupa says.

For enterprises, taking advantage of all the good stuff will require hardware upgrades. Most existing desktop machines lack the processing power, memory and graphics capabilities to take advantage of Vista, Skorupa says. "This is not a no-cost upgrade."

Significant software testing is required, too. "Enterprises have hundreds, and in some cases thousands, of in-house applications that they have to test," Skorupa says.

That's a serious consideration for Hyundai Information Services North America. David Jung, who is technical lead for infrastructure engineering security at the automaker's Irvine, Calif., IT unit, is running Vista on his work PC, but says Hyundai has no immediate plans to implement Vista companywide. The appeal of performance enhancements is outweighed by the daunting reality of how a client operating-system upgrade could break dozens of existing applications, Jung says.

"One of the big issues is that we need to verify all the applications will keep working on Vista. It will take some time," he says. In addition, he says, the CPU and memory required to run Vista is a factor for waiting.

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