Options for Gigabit Ethernet over copper
 
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Last week, we considered some of the attractions of running Gigabit Ethernet over fiber-optic cable. In this issue, we'll look at options becoming available for copper cabling.
By next year, customers should have two options for copper Gigabit Ethernet cabling. The first copper cable option - already standardized but not widely available - is known as 1000Base-CX. It involves low-cost, twinaxial cable. This option supports distances only up to 25 meters, positioning it as "jumper" cables within the wiring closet or the data center. Over such short distances, there's no need for high-quality fiber-optic cable and laser transmitters, so such inexpensive copper cabling is appropriate.
The second copper cabling option - not yet standardized but likely to be readily available - involves four-pair Category 5 unshielded twisted pair cable. The standard for Gigabit Ethernet over Category 5 cable, known as 1000Base-TX, is expected to be completed sometime next year. Such a standard may provide several important benefits over fiber-optic cable. First, many customers currently use Category 5 cable for their Fast Ethernet connections, so upgrading to Gigabit Ethernet could be made much easier if the cabling infrastructure could remain intact. Second, the RJ-45 connectors used for Category 5 cable are small enough to allow multiple connectors to fit on a single adapter. This conservation of space could be especially helpful for servers and switches.
By contrast, the size of fiber-optic interfaces usually mandates that only a single fiber port will fit on a given network adapter. Thus, providing redundant server connections with fiber-optic cable most likely means using twice as many server slots.
Also, building high-density switches can be made easier by such smaller interfaces. A plug-in switch module that formerly supported, for example, four multimode fiber-optic interfaces might now support eight or 10 RJ-45 1000Base-TX ports.
While all of this may seem encouraging, remember that 1000Base-CX has yet to become readily available. Most Gigabit Ethernet connections are still 1000Base-SX (short-wave laser) and a very few are 1,000Base-LX (long-wave laser). In fact, The Tolly Group has not yet received a single 1,000Base-CX product for testing, although it has already tested SX and LX products. Also keep in mind that 1000Base-TX won't be standardized until next year. That means that, for now, fiber-optic cable is still an attractive alternative for customers that are ready to deploy Gigabit Ethernet.
RELATED LINKS
Gigabit Ethernet over copper.
A white paper from the Gigabit Ethernet Alliance
Ethernet turns 25
Network World, 5/18/98
Switching grows up: Layer 3 switching completes a circle, giving us pause to relect on where switching has brought us and where it's headed.
Network World, 5/4/98
