Microsoft Reaches Network Speeds Near 1 Gbps

Microsoft Corp. recently tested proprietary jumbo frames technology in a Windows NT 4.0 environment and saw network performance run away to 920 Mbps on a single Gigabit Ethernet NIC. Microsoft officials claim the lab test shows that the operating system is ready to compete with Unix in terms of handling network bandwidth. Analysts and others in the industry applaud Microsoft’s efforts but caution that the reality of the situation is more complicated.

"The proof is in the pudding," says Peter Ford, Microsoft program manager lead for Windows networking. "Nine-hundred-twenty Mbps pretty much fills up a gigabit link. This will allow customers the ability to plug a gigabit adapter into the bottom of an NT 4.0 system and expect that they’re getting what they pay for."

At this point, that networking card would need to come from Alteon Networks (San Jose, Calif., The tests were conducted using the Alteon ACEnic server adapter, which uses jumbo frames. Alteon was releasing the adapter’s driver this month. By comparison, the same Alteon card reached lab speeds of 960 Mbps on a Unix Sun Solaris 2.6 system, says David Callisch, Alteon’s director of market communications. Another Microsoft lab test using two of the cards in a Windows NT 4.0 system reached network speeds of 1.3 Gbps.

Microsoft officials say they have fought a long battle to show that the operating system could reach such speeds. "When we released NT 4.0, it really wasn’t possible to prove that 4.0 would scale up. We’re really very happy that the operating system has been able to track the hardware," says Mike Zintel, Microsoft development lead, Windows networking. Microsoft’s Ford adds, "We’re working with sort of a stock NT 4.0 system [with Service Pack 3]. We haven’t really done any major performance work on the [TCP/IP] stack per se. We essentially wanted to see how much NT throughput we could get."

Most of Microsoft’s tuning to achieve the performance took place in the form of optimizing the Alteon driver and card for NT and adjusting the TTCP Winsock benchmark application to work better at high speed, says Reza Baghai, Microsoft performance lead, Windows networking.

Alteon’s Callisch confirms the Microsoft claim that most of the optimization concerned components external to the operating system’s TCP/IP stack: "Jumbo frames are for the most part transparent to the operating system."

Others in the Gigabit Ethernet industry are pleased by the news. "The general consensus would be that it’s positive for the whole Gigabit Ethernet industry," says Brian MacLeod, a member of the steering committee for the Gigabit Ethernet Alliance (Palo Alto, Calif., "I’ve got to give Microsoft high marks for jumping on things."

The main sticking point is that jumbo frames, while transparent to the operating system, aren’t transparent to the network. Alteon positions its products mainly for server-to-server connections with proprietary Alteon cards at both ends. Standard frames in TCP/IP networks contain 1.5 KB of data each. Jumbo frames carry six times that much: 9 KB.

While the larger frames make little difference in speed out on the wire, jumbo frames can go a long way toward improving performance if the bottleneck occurs in the PCI bus or the operating system’s protocol stack. The stack and bus deal with the data frame-by-frame, taking about the same amount of time to pump out, for example, 10 of the 9-KB frames as 10 of the 1.5-KB frames. That helps show how NT 4.0 performance can improve so markedly from a former lab maximum of 582 Mbps on a single card using standard frames to 920 Mbps using jumbo frames without significant changes to the stack.

MacLeod, who is also director of marketing for Packet Engines Inc. (Spokane, Wash.,, is not surprised Microsoft went to jumbo frames to post the performance gains. "I think it’s just something that’s available to them," MacLeod says. "They’re looking for any indication of speed and performance that they can get."

Microsoft’s Baghai says a series of improvements being built into NT 5.0 will boost performance of Gigabit Ethernet NICs using standard frames as well. Some of those enhancements include offloading TCP/IP check sums and deserialization to optimize multiprocessor environments.

Analyst Paul Zagaeski of Giga Information Group (Cambridge, Mass.) sees another angle to Microsoft’s work with jumbo frames. Zagaeski says the networking industry in general has been critical of jumbo frame technology because of compatibility problems with TCP/IP. "But customers have been willing to use the jumbo frame technologies available from some of the vendors," he says. Microsoft’s test is "making legitimate the point of view that says customers do want the ability to modify the data framing so that they can improve the performance of these devices."

Meanwhile, Zagaeski recommends that IT managers take the Microsoft benchmark numbers with an "enormous" grain of salt: "The fact that Microsoft has a lab setup that runs at this speed is of no value to real customers with real networks. What will be of value is when Microsoft can say, ‘We have installed this in 50 customer sites.’"