Gigabit Ethernet: Coming Down the Network--Fast

With protocols changing to support the higher data rates from the backbone all the way to the desktop, management information system (MIS) managers are looking at their network infrastructures for ways to leverage their current investment and still keep up with the demand for higher speeds.

Paul Kolesar, Lucent Technologies

Steve Swanson, Corning Inc.

With protocols changing to support the higher data rates from the backbone all the way to the desktop, management information system (MIS) managers are looking at their network infrastructures for ways to leverage their current investment and still keep up with the demand for higher speeds.

One possible solution is Gigabit Ethernet. With Ethernet networks accounting for more than 80% of all current installations, it makes sense to stay with the familiar, protect one`s corporate investment in Ethernet network interface cards--most of which will not be affected during backbone upgrades--and simply increase the speeds of existing backbone networks.

Envisioned first as a backbone protocol, Gigabit Ethernet could ultimately run all the way to the desktop. The ieee 802.3z committee of the Institute of Electrical and Electronics Engineers (New York, NY) is developing the standard that will determine how this will work.

The standard is scheduled to be released in early 1998, and it is likely that Gigabit Ethernet will initially be primarily an optical-fiber effort. The ieee 802.3z committee recommended to the organization`s last plenary session that the effort to develop a 100-meter solution for unshielded twisted-pair (UTP) cable be completed as a separate project. This means the UTP solution will not be subject to the 1998 deadline for a final standard. For optical-fiber networks, however, MIS managers will be able to choose from a range of solutions, depending on the physical layout of their networks, including the following:

- 62.5-micron multimode fiber--Using this medium, 300-meter transmission distances are possible using short-wavelength (850-nanometer) vertical-cavity surface-emitting lasers or CD lasers. And 550-meter transmission distances are possible using long-wavelength 1300-nm lasers.

- 50-micron multimode fiber--With this medium, 550-meter transmission distances are possible using either short- or long-wavelength lasers.

- Singlemode fiber--Transmission of 3 kilometers can be accomplished using long-wavelength lasers.

These distance targets show that multimode fiber has sufficient capability for intrabuilding networks using either traditional hierarchical star wiring or the new centralized cabling architecture. The 300-meter distance capability over multimode fiber directly supports the architecture and requirements established by TIA TSB-72 Centralized Optical Fiber Cabling Guidelines and the technology recommendations of the TIA Fiber Optic LAN Section. It is expected that singlemode fiber will be required in most campus backbones.

Keep in mind that this is the current thinking. A variety of Gigabit Ethernet products are already hitting the market, even though the standard is not out, and the task force may issue additional recommendations as more information is obtained.

The most important Gigabit Ethernet factors for network managers are the range of fiber-optic solutions being supported and the choice of short- and long-wavelength lasers. To the extent that existing fiber networks meet the distance guidelines established for the draft standard, MIS managers will be able to support the new protocol without pulling new cable. This should keep upgrades cost-effective and relatively trouble-free.

This bodes well for the companies that have installed glass optical fiber to run their current Ethernet networks, and it supports the decisions of those companies that are currently planning a fiber upgrade or rebuild. With a clear pathway toward Gigabit Ethernet, multimode fiber for intrabuilding applications, along with singlemode fiber for the campus backbone, still offers network planners the most flexible cabling infrastructure, which also has the most headroom over the long term.

Paul Kolesar of Lucent Technologies and Steve Swanson of Corning Inc. are their companies` representatives to the ieee 802.3z Gigabit Ethernet Group and members of the Fiber Optic LAN Section (fols) of the Telecommunications Industry Association (Arlington, VA). Other fols members include 3M, AMP, Berk-Tek, Belden Wire & Cable, CommScope, Siecor, Spectran, Sumitomo, and Allied Telesyn.

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