Gigabit Ethernet - the FAQs

• Tags:
• 1000Base-X,
• 802.3ab,
• 1000Base-T,
• Ethernet

Rupert Goodwins ZDNet.co.uk

Published: 27 Nov 2002 10:09 GMT

• 
• 
• 
• 
• 

What is Gigabit Ethernet?
Gigabit Ethernet is a networking standard based on Ethernet-standard packets of information sent over optical fibres or ordinary twisted-pair cabling at up to 1000 megabits per second. The standard goes by a couple of names, 1000Base-T for ordinary copper cabling, or 1000Base-X for fibres or special balanced cables. Also known as 802.3z and 802.3ab, Gigabit Ethernet uses the same signalling speed as 100 megabit Ethernet but uses all four pairs of wires in the cable and a more efficient modulation scheme to get ten times the performance. To use Gigabit Ethernet, you'll need new network interface cards and hubs, switches and/or routers. The rest of the Ethernet standard is as before.

What cables does Gigabit Ethernet need?
There is some discussion over this. Officially, Cat 5e is recommended -- that's much the same as the ubiquitous Cat 5 but enhanced -- hence the e -- by making sure it sticks to a tighter specification. In practice, if 100 megabit Ethernet was running successfully over the cabling then 1000Base-T will too, and some vendors say that Cat 5 will in almost all cases be fine. If you have a large installation, you should do a preliminary check for return loss and crosstalk on the existing cabling: the Gigabit Ethernet Alliance reckons that only 10% of professional Cat 5 installations will need work. Cat 3 is right out.

Beware of Cat 6 (250MHz) and Cat 7 (600MHz) cabling, if you choose to recable. Neither standard has been approved yet, and neither is necessary for Gigabit Ethernet, so you run the risk of an expensive re-cable that won't be compatible with whatever happens next.

Does Gigabit Ethernet need new topology rules?
Again, if you're running 100 megabit Ethernet then Gigabit Ethernet should work perfectly well in the same topology. Both have the same maximum cable run length -- 100 metres -- and run with nearly the same rules for collision detection and media access.

Do I need Gigabit Ethernet for my desktop systems?
Almost certainly not, despite the hype from suppliers. Some applications -- such as medical imaging, scientific database analysis and engineering work on large models -- will benefit, but average desktop use will see no difference. There have been attempts to sell Gigabit Ethernet on the back of voice over IP or streamed video requirements, but as such applications take up a vanishingly small amount of bandwidth even on 100 megabit Ethernet the move to gigabit speeds isn't required. However, Dell has announced that all its more powerful computers will come with Gigabit Ethernet as standard, so the movement over to the higher speed will probably be accomplished as much by stealth as anything else.

In server farms, Gigabit Ethernet is proving popular as a low-cost, high-speed storage unit interconnect, and in its fibre forms it is being promoted as a good backbone protocol for metropolitan area networks and the like.

Will a Gigabit Ethernet PC work on an older network?
Yes, all Gigabit Ethernet systems detect 10 or 100 Mbps Ethernet networks and adjust their speed automatically

Will my existing PC be able to use Gigabit Ethernet?
Yes, but the standard 32-bit PCI bus in most desktop PCs doesn't have enough bandwidth to handle Gigabit Ethernet in full duplex mode. 32 and 64-bit PCI network interface cards will work, but you'll need the 64-bit bus to make the most of it. In general, a 32-bit PCI bus will run out of steam at around 500 Mbps transmit, 800 Mbps receive. As for software, there are almost no issues: providing your new Gigabit Ethernet adaptor comes with Windows drivers, which it will, then all your existing software will work perfectly well over it.

What are these 'jumbo frames' I keep hearing about with Gigabit Ethernet?
Standard ethernet frames -- packets -- can be up to 1518 bytes long. Jumbo frames can be up to 9216 bytes long. Frames that long on slower Ethernet systems could block fair access to the network by hogging the wire for too long: that's not so much of a problem with Gigabit Ethernet. However, the shorter standard frames can be delivered up to 80,000 times a second with Gigabit Ethernet, and as each frame generates an interrupt this can load a server far more than the same information delivered in larger but fewer frames. If your drivers can handle jumbo frames, you may see a significant server performance improvement on a heavily loaded network

And LOM?
LOM -- LAN On Motherboard -- is a term that some manufacturers are using to specify network interface card (NIC) components integrated with the rest of the main circuit. The term's introduction concurrent with Gigabit Ethernet is purely a coincidence. Not to be confused with LOTR, Lord Of The Rings, a popular film which by another coincidence used Gigabit Ethernet to link the computer animation workstations with the server farms.

---

• 
• 
• 
• 

• Share this article:
• Digg
• Slashdot
• Del.ici.ous
• Stumble
• Reddit