Article on Gigabit Ethernet from ZD Net
Gigabit Ethernet offers new fix for speed cravings
By Dave Kosiur
May 18, 1998
Internet Computing
If you're already running an Ethernet network (and who isn't?), then Gigabit Ethernet may be the answer to your bandwidth woes. But plan carefully--there are a few hidden "gotchas."
Ethernet's been around since the early 1980s and it's certainly the most popular LAN networking technology on the market today: market research from International Data Corp. estimates that more than 80 percent of all network connections are Ethernet. Since its introduction, Ethernet has gone from shared media and coaxial cable to switched architectures and unshielded twisted-pair (UTP), all at 10Mbps.
It was only four years ago that the first significant improvement on speed occurred--100Mbps Fast Ethernet. Even that hasn't proven sufficient for network backbones, so now 1Gbps Ethernet, or Gigabit Ethernet, has come to market. Gigabit Ethernet may be in its infancy, but it's developing rapidly and may prove the solution to some of your networking problems.
Aside from the fact that it's faster than previous incarnations of Ethernet, Gigabit Ethernet works essentially the same as earlier Ethernet types. This allows network managers to continue working with something they already know. For instance, Gigabit Ethernet preserves the frame formats, full-duplex operation, and flow control methods of its lower-speed brothers, eliminating the need for any translation between different flavors of Ethernet traffic.
But there are some features in Gigabit Ethernet that are new, which can lead to problems in its deployment.
Cabling caveats
In networking, it's impossible to get something for nothing. In the case of Gigabit Ethernet, the transmission speeds and interpacket timing place rather severe constraints on what cabling you can use and the lengths of cable between devices. This factor, more than anything else, may limit how you can use Gigabit Ethernet in your network.
Gigabit Ethernet has been designed initially for transmission over either single-mode or multimode optical fiber. The 1000BaseSX specification addresses transmitting Ethernet signals over multi-mode fiber using shortwave lasers. The 1000BaseLX specification covers Ethernet transmissions over either single-mode or multimode fiber using long-wave lasers. Initially the most common mode for Gigabit Ethernet employs conventional 62.5-micron/125-micron multimode fiber with LED-generated light sources. And that will limit link distances to 260 meters.
The main differences between the use of long-wave and shortwave technologies are cost and distance. Shortwave lasers are readily available because they're used in CD players. Although the shortwave lasers cost less, they traverse a shorter distance. In contrast, long-wave lasers are more expensive but can traverse longer distances. Since the shortwave lasers are more readily available, many of the first Gigabit Ethernet products support 1000BaseSX.
The 62.5-micron fiber is most often seen in vertical campus and building cable plants: it's been used for Ethernet, Fast Ethernet, and fiber distributed data interface (FDDI) backbone traffic. But the new limits on link distances imposed by Gigabit Ethernet may still force you to reconfigure your network or install new fiber. Running large corporate networks on Gigabit Ethernet might even require installing the more expensive single-mode fiber.
Another standard, 1000BaseCX, has been developed for network transmissions over copper cable, but it's a very specialized cable--balanced shielded 150-ohm copper cable (Twinax)--not the UTP cables so often found in current wiring plants. This short-haul copper, which is limited to 25-meter distances for Gigabit Ethernet, is useful as a short jumper to interconnect closets or computer rooms.
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