The Copper Alternative

FRAMINGHAM (03/20/2000) - Network executives now have the option of using ordinary unshielded twisted-pair copper cabling for Gigabit Ethernet switch connections for short distances at half the cost of fiber.

The IEEE 802.3ab Task Force ratified the 1000Base-T copper interface standard last June, and some vendors have begun offering the necessary copper-based physical interfaces on their Gigabit Ethernet switches. The good news is that Category 5 cable is installed in most buildings in the U.S., which means there's no cable installation cost, except for the new connection itself.

There are two catches, however. First, the existing Cat 5 cabling you have in your LAN may be adequate for carrying Ethernet and Fast Ethernet, but it may not be up to snuff when it comes to Gigabit Ethernet. The cable connections in the wiring closet may not meet the new standard, the cables may be improperly installed or there may be other kinds of wiring problems that never came up when you were running electrical signals far below a gigabit.

If your cabling is up to spec, the other catch is that you can only use copper cable at gigabit speeds for runs of 100 meters (328 feet) or less.

There are, however, many types of installations that fall within that 100-meter limit, including horizontal runs between wiring closets on the same floor; vertical risers between floors, within wiring closets and data centers to interconnect multiple workgroup switches; and backbone switches, to connect servers and to connect high-performance workstations to switches. In that case, for example, Cat 5 cable would be connected to a 1000Base-T port on the switch and a 1000Base-T port on the workstation network interface card (NIC).

Fiber-optic cable is still required for horizontal or vertical building connections that exceed the 100-meter limit. Typically, this would be vertical backbone risers between a data center on one floor and wiring closets on other floors.

Unfortunately, deployment has been slowed by the lack of availability of these copper Gigabit Ethernet interfaces, which is due to semiconductor manufacturers not producing enough copper Gigabit Ethernet interface chips to meet the growing demand.

But switch and NIC vendors are beginning to announce copper interfaces on their existing gigabit products as add-ons and also on new products.

Alteon WebSystems has introduced a 10/100/1000Base-T NIC, which autonegotiates to the highest speed and supports Jumbo Frames for improved server performance.

Its copper ACEnic costs $500, about half the cost of fiber NICs.

Extreme Networks Inc. has a copper-based Gigabit Ethernet switch, the Summit7i Internet Data Center Switch. The Summit7i is available with 28 1000-Base-T ports for Cat 5 at about $700 per copper port. Extreme also has an announced an eight-port 1000Base-T module for its Black Diamond core backbone switch.

And Foundry Networks has a 1000Base-T interface module for existing Foundry switches. Foundry also introduced its FastIron II GC 1000Base-T workgroup switch, available with 16 or 24 1000Base-T ports, and its high-density FastIron II Plus GC switch with 64 1000Base-T ports. Foundry's system-level price for a 1000Base-T switch is $650 per port, well below the price of its fiber ports.

State of the WAN

On the WAN side, fiber cabling is necessary for the transmission of high-speed traffic over extended distances within a building or campus, and for long distances over thousands of kilometers to interconnect WANs and metropolitan-area networks (MAN).

There are two basic types of fiber-optic cable: multimode and single-mode.

Multimode is suitable for short-haul connections, while single-mode fiber cable is required for long-haul connections. The IEEE 802.3Z Gigabit Ethernet standard specifies a maximum cable length of 550 meters (1,800 feet) for multimode fiber and a maximum cable length of five kilometers (three miles) for single-mode fiber.

For distances beyond three miles, there are transceivers that connect to single-mode fiber cable and can support cable distances of more than 100 kilometers.

On the LAN side, GigaBit Interface Converters (GBIC) are becoming popular for connecting switch ports to fiber cables. A GBIC contains the interface optics for fiber cabling and is essentially a transceiver that converts electrical interface signals to light signals and the converse. It plugs in to a 1000Base-X switch port and connects to a fiber cable. GBICs that provide 1000Base-SX, -LX and LH (long haul - 70 kilometers or more) optical interfaces are readily available.

GBICs benefit the switch vendor by providing the flexibility to populate the switch with any mix of interface types, eliminating the need to configure the switch with a fixed number of ports for each interface type. It also reduces the manufacturing cost of a switch. GBICs benefit users by giving them the flexibility to configure a switch according to their needs and to change the configuration to satisfy future applications, extending the life of the switch.

GBICs also provide fault tolerance by enabling users to replace a faulty GBIC with an operable spare. GBIC prices currently average $400 for an SX port, $1,400 for an LX port and $5,500 for a 70-kilometer LH port.

The price of fiber-optic switch ports is steadily declining. 1000Base-SX ports initially priced as high as $3,000 when the technology was new, are now available for as low as $1,000 per port, while 1000Base-LX ports, initially priced as high as $5,000, are now priced as low as $3,000 per port.

The rising demand for copper interfaces will undoubtedly impact the LAN fiber market. Users will elect to go with copper wherever the application allows them to decrease equipment and installation costs. The cost of copper ports is roughly half the cost of short-haul fiber ports. Since the demand for copper will pressure vendors to drop the price of short-haul optical interfaces, copper will erode the price of optical interfaces as copper interfaces become abundantly available.

On the fiber side, a strong market exists for fiber applications that copper cannot address - vertical risers in buildings; campus backbones; network-to-network connections such as enterprise networks connected to MANs; service providers or carriers; and wide-area optical networks. WAN- and MAN-related applications are heating up, so that's potentially a very strong market for fiber cable. An increasing demand for long-haul fiber transceivers should drop prices as they become readily available from multiple sources.

Now that Ethernet is poised to take another giant leap from one gigabit to 10 gigabits, the question arises of whether 10 Gigabit Ethernet will ever run over copper. The 802.3ab Task Force had to implement heroic digital signal processing techniques to get signals to run over copper cable at 1G bit/sec.

With 10G bit/sec signaling, the signaling rate is 10 times the gigabit signaling rate, which would require extraordinary engineering to develop the technology to run over copper cable.

It might be possible to develop a 10G bit/sec technology for copper cable using Cat 6 or 7 cabling, but it is doubtful whether Cat 5 copper cable could carry 10G bit/sec signaling. According to the IEEE 802.3 experts, it should be possible to run 10G bit/sec over good Cat 6 cable up to 100 meters, and maybe some distance over Cat 5-enhanced cable. Some of these experts believe the best approach is to follow modem technology and create a multirate system with a line-quality rate setting process as part of the start-up routine that would negotiate the data rate up or down at gigabit increments between one and 10 gigabits. It is likely that some Cat 5 installations could support at least 2.5G bit/sec, which would improve performance over copper horizontal wiring.

Probable applications are linking switches, a high-capacity storage-area network technology and switch-to-server technology. It could also be used to increase the performance on horizontal copper links.

Axner is president of DAX Associates, a networking consultancy in the Philadelphia area.

He can be reached at daxner@earthlink.net.

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