Gigabit Ethernet Cards

Now that 100-Mbps desktop Ethernet connections have become commonplace, network administrators are looking for the next silver bullet to improve network performance. Gigabit Ethernet, also known as 1000BaseT, running at ten times the speed of 100BaseT, promises to be that silver bullet. Alas, today’s Mac CPUs can’t achieve Gigabit’s full potential. Even on a Power Mac G3, the fastest speed attainable with Gigabit Ethernet is barely twice the speed of 100-Mbps Ethernet. Still, as CPUs gain speed, they’ll be able to take advantage of improved network performance. To that end, we checked out three Gigabit Ethernet PCI cards: Asanté Technologies’ AsantéFast 1000 GigaNIC, Farallon’s PN9000-SX, and Team ASA’s Stallion GE-II.

All three products are easy to install: just plug in the card, load the drivers, and reboot. Hooking up the cards’ fiber-optic connections is as simple as with copper Ethernet, but you can run the wires much farther: up to 500 meters.

The CPU speed limits Gigabit Ethernet performance because of the processing overhead. Standard Ethernet packets are a maximum of 1,500 bytes long, which means a computer must process more than 80,000 packets every second to achieve Gigabit Ethernet’s full throughput. It turns out that a Power Macintosh G3 can process only about a fifth of that, limiting performance to less than 100 Mbps. To circumvent this problem, Gigabit Ethernet supports larger packets–called jumbo frames–of up to 9,000 bytes each. With these larger frames, theoretically even a G3 Mac can move data at a gigabit per second. Unfortunately, the Mac OS doesn’t yet support jumbo frames, so this capability is largely unusable. Team ASA bundles a utility that lets you transfer files using jumbo frames, but you can’t mount volumes or copy files through the Finder, and the program won’t run under Mac OS 8.6.

All three products provide performance-boosting aids, including offloaded TCP/IP checksum generation and full-duplex communication. Asanté supports the Ethernet 802.3 p and 802.3 q quality-of-service standards, especially useful in multimedia networks. Team ASA’s card ships with Mac OS X drivers.

On-board diagnostic aids are a big help in troubleshooting network woes. Asanté’s GigaNIC excels here, with six status indicators for power, link, transmit, receive, bus type, and flow control.

The most common application for Gigabit Ethernet is in high-volume servers; a single 1000BaseT card is easier to configure and manage than multiple 100BaseT cards and has the potential for better performance. With that in mind, we tested each card using a mix of client-server file transfers (see “Faster, but Not by Much”). Team ASA had the best showing, hitting 91 Mbps, with the Asanté card a close second. The Farallon card was somewhat slower. However, keep in mind that gigabit performance is largely a function of overall system speed. On faster CPUs, you’ll see better throughput.

January 2000 page: 36

Faster, but Not by Much