Steve Bartolutti,
Lucent Technologies
Great enhancements have been made over recent years in the handling and routing of fiber-optic cables and the connectors that tie these cables to destination points. Fiber advocates say it is the most universal medium--capable of carrying voice, data, and video communications simultaneously with less signal enhancement than that required with copper cable. Furthermore, fiber enthusiasts point out that fiber is sufficiently robust to withstand the bends and stresses prevalent in the horizontal portion of the local area network (lan) environment in addition to the fiber backbone.
So if fiber can perform effectively as part of the lan backbone infrastructure, why isn`t it enjoying greater growth in use in the horizontal, the portion of the lan that ties directly to the desktop?
Better-performing copper
Introduced in 1990, high-performance (Category 5) unshielded twisted-pair (utp) copper now makes up about 70% of horizontal lan cabling. This suggests that end-users have chosen high-performance copper as the preferred medium in horizontal lan applications. While fiber remains the leading cabling medium in building and campus backbones due to its high bandwidth and distance advantages, horizontal applications have not driven bandwidth demand to the point of requiring fiber-to-the-desk. utp`s proven ability to handle bit rates as high as 155 megabits per second is sufficient to support even the most demanding horizontal applications. And utp`s ability to provide high-speed transmission was strengthened two years ago with the introduction of 622-Mbit/sec high-speed cable solutions.
The introduction of even higher-speed copper cable offerings, which deliver performance at 1 gigabit per second--six times faster than standard Category 5 copper cabling--may encourage end-users to use copper in the horizontal until well past the year 2000. Thus, end-user preference for fiber in the backbone and high-performance utp cable in the horizontal may continue for at least the next several years. Combinations of 10Base-T switching and Fast Ethernet are likely to use existing copper infrastructure in the horizontal while enhancing fiber`s use in the backbone network.
Fiber`s proliferation in building riser and campus backbone applications means it has a strong place in the private network. It is likely that end-users will support an increased role for singlemode fiber in campus backbones where long distances and high bit rates are factors. But fiber also has a place in the horizontal. It will continue to appeal to customers in the areas of education, medicine, government, science, and engineering, whose demands are not driven solely by bandwidth considerations. "Fiber drivers" for these users may be demands for enhanced distance, security, centralization of electronics, or immunity from lightning and electromagnetic interference.
So, will the industry see any substantial changes in the premises network market in the immediate future? Probably not. We now see a predominance of high-performance copper in the horizontal segment of the market. End-users have a vested interest in supporting their copper infrastructure and, for the short term, may be comfortable with a high-performance copper solution in the horizontal. Gigabit Ethernet, which has received a tremendous amount of media attention, is, today, exclusively for fiber and may remain a point-to-point switched technology used for server and switch-to-switch interconnection for some time. This will extend the life of copper-based connections in the horizontal. As a result, end-users may not see shared-media Gigabit Ethernet, especially over utp, for at least the next several years.
LAN speeds continue to increase
The impact on customers of increasing lan speeds and the development of system applications that necessitate higher performance are impossible to predict. The processing capabilities of personal computers have increased at a rate unforeseen even in the information technology industry, doubling approximately every 18 months since 1991.
lan technology should support the demand for networks that can accommodate more-powerful computer processors and higher-bandwidth applications. These factors will eventually require higher- performance lans, with initial demand for 1-Gbit/sec service to the desk by the end of this decade and demand for multigigabit-per- second transmission to the desk in 10 to 15 years.
Historically, improved performance has fueled demand for higher speed throughout the industry. As a rule of thumb, one million instructions per second (mips) of processor performance has the capability to load 1 Mbit of traffic on a network. Higher demand will come with improved central processing units--beyond Pentiums--that process 200, 300, 400, or 500 mips, along with ever-more-demanding applications.
This article is reprinted from the September 1997 issue of Lightwave magazine, another PennWell publication.
Steven Bartolutti is a distinguished member of the technical staff and new business development manager, global private systems, for Lucent Technologies (Norcross, GA).
