Will fiber go to the desktop?

Will fiber go to the desktop? Declining optical component costs are helping to make fiber at the desktop a reality BY SHARON HALL Hewlett-Packard Co. Lightwave Components Optical Communication Div. San Jose, CA The debate over whether optical fiber or copper is the more suitable transmission medium for the desktop has flared up with the appearance of new networking technologies. These include high-speed Ethernet, asynchronous transfer mode (ATM), Fiber Distributed Data Interface (FDDI), and Fibre Channel. Fanning the flames is the shift in the political winds toward creating a nationwide information superhighway. Until recently, optical fiber has had a clear advantage in only one part of the overall local-area network architecture–the backbone. Here, fiber's tremendous bandwidth, noise immunity, and transmission distances have made it practically indispensable. This has left copper cabling as the medium of choice for the remainder. Within the past year, however, the gap between the cost of bringing optical fiber all the way to the desktop and of higher-speed copper-based solutions has narrowed considerably. Now, tremendous competition is heating up in the final 100 m from the cabling closet to the desktop as copper and fiber technologies converge from opposite directions to address the next step in networking–the 100-Mbit/s LAN. On the one hand, the lure of copper remains strong as vendors extend the capabilities of copper wire to carry these higher data rates. On the other hand, thanks to increasing volumes and improved manufacturing processes, manufacturers of optical cable, connectors, and components are bringing costs down to compete with copper-based products. Reducing component costs Over the past few years, designers of active fiber-optic components have made significant strides in lowering the cost of the basic ingredients that go into fiber-optic hubs, bridges, routers, and network interface cards. For example, the first FDDI transceiver, introduced in 1990, employed a package and pinout specification originally promoted by Hewlett-Packard, AT&T, and Siemens. It cost approximately $500 each in small quantities. Today, through the evolution of transceiver design and manufacturing, fiber-optic transceivers of similar performance have fallen in price to about $125 in small quantities–a 75% reduction in just three years. In volume, these prices have fallen to below $100 each. As a result, FDDI adapter prices have now dropped below $1,000 per connection, and are rapidly converging on the price per connection for the different emerging 100-Mbit/s Ethernet technologies. One of the most significant factors in this substantial cost reduction is the evolution of design from the original fiber-optic FDDI transceiver. This device comprised a 2 x 11 pinout, costly die-cast housing, and expensive MIC/R connectors or the alternative ST simplex transceiver modules. The new FDDI and ATM duplex transceivers have a 1 x 9 pinout with SC connectors and a cheaper, plastic, injection-molded housing capable of offering equal or better electromagnetic and radio-frequency shielding. The new devices are approximately 60% the size of the older versions, allowing designers to install more transceivers in a given space and thus reduce cost (see Fig. 1). At the same time, the internal printed circuit has been made smaller, and has changed from an expensive ceramic substrate to a more cost-effective, multilayer, glass-epoxy substrate. Figure 2 shows both SC duplex transceivers and ST-style transmitters and receivers from AMP Inc. Data rates are 125 Mbits/s (FDDI) and 156 Mbits/s (ATM) for the 9-pin SC duplex transceiver. For the 16-pin transmitter and receiver, data can be transmitted at 125 Mbits/s (FDDI) and 156 and 194 Mbits/s (ATM). Better transceiver shielding has another, less obvious effect in reducing network equipment costs. Hubs, routers, switches, and other network equipment may have multiples of eight or ten transceivers in a single chassis. The emissions generated by all these transceivers is cumulative, and the total can quickly escalate. To meet FCC regulations, designers of such equipment need to spend significant time and effort to contain these emissions. By limiting individual transceiver emissions, the overall emission level of any particular system will be reduced. Hewlett-Packard's 1 x 9 duplex SC transceivers, for example, are specified to meet FCC Class B emission levels with a typical margin of 10 dB when tested in free air. This extra margin results not only in reduced design time to attain system-level FCC Class B compliance, but also reduced manufacturing costs for shielding, gasketing, and other methods to prevent radiation from escaping. These savings, of course, can be directly reflected in lower end-user costs. Significant savings in optical component manufacturing have also been realized through the reduced cost of the ICs within the fiber-optic transceiver. In addition, designers have two other options for providing lower-cost fiber-optic solutions. One option is to change to a different, higher transmitting frequency (shorter wavelength of light), something that is being reviewed by several of the 100-Mbit/s-or-greater standards organizations. Typical of these devices is the HFBR-5104/-5203 fiber-optic transceiver from Hewlett-Packard which operates at 850 nm (see Fig. 3). Priced at $95, it lowers the cost of FDDI and ATM connection with duplex SC ports to bring high-speed data to the desktop. Ninety-five percent of all desktop connections have a distance requirement of less than 100 m. In light of this, it becomes reasonable to ask why a technology capable of transmitting data reliably up to 2,000 m should be used when something just as reliable over a shorter distance would suffice. This is precisely the question prompting the standards committee to evaluate the option of using lower-cost, shorter-wavelength transceivers to address this need. Such devices are available with 800-nm LEDs at a significantly reduced cost. The dividing line between the use of 800- and 1,300-nm transmission devices can be seen in Fig. 4. Traditional FDDI transceivers use 1,300-nm LEDs to achieve the 2-km specification in the current standard. But the cost of a 1 x 9 FDDI or ATM transceiver with an 800-nm LED is 25% less than that of one based on a 1,300-nm LED, primarily because the production quantity of 800-nm LEDs is an order of greater magnitude. Both the reliability and performance of 800-nm technology have been well proven over time as all Ethernet and Token Ring fiber-optic backbone connections currently in use are based on this technology. Therefore, although limited as it is to hundreds of meters when operating at the 125- to 155-Mbit/s FDDI and ATM data rates now becoming popular, 800-nm technology is more than adequate for the vast majority of desktop connections. Network integration The second option open to network equipment designers striving to reduce optical components costs is to design with discrete ICs and optical ports. Optical transceivers integrate an LED driver IC and quantizer IC into the package along with the LED and optical elements. Savings of up to an additional 25% can be realized by using discrete ICs and separate optical ports as in Hewlett-Packard's HFBR-0300 and HFBR-0400 series of 1,300- and 820-nm devices. Designing with discrete ICs and optical ports requires more engineering effort by the designer, but with readily available printed circuit board layouts from component vendors, that effort is minimized. In addition, as volumes increase, the piece-part cost savings can more than offset the additional engineering effort. Today, most Ethernet and Token Ring fiber-optic links use the 820-nm discrete component approach and benefit from substantial savings. Cabling conundrum Network hardware accounts for only 25% of the total cost of a typical network installation, whether copper or fiber-optics based. The remaining 75% of the cost is due to labor (35%), cabling (20%), and connectors (20%). Until now, the general perception has been that fiber is more costly to install than copper. Now, however, fiber-optic component prices are falling. At the same time,copper requirements (EIA/TIA-568 Standard Category 5) are more stringent, therefore increasing the cost of copper. These requirements address the higher emissions inherent in 100-Mbit/s data rates and have resulted in increased costs associated with copper plant components, installation, and testing. Upgrading existing copper networks to support 100-Mbit/s data rates often requires significant cable plant redesign with higher-grade cable (to upgrade from Category 3 or lower, which forms the bulk of twisted-pair (UTP) cable installed today), electronics, labor, testing and warranty costs. Nearly all 100-Mbit/s networks require Category 5 unshielded, UTP cable and connectors. The sole exception is the 100Base-VG standard, which can operate over Category 3 UTP. This standard is being promoted by Hewlett-Packard, IBM, and AT&T for Ethernet and Token Ring LANs. In addition, both ANSI and EIA/TIA specifications for Category 5 UTP place stringent requirements on how the cable is pulled and terminated. Because both specifications require that pairs not be untwisted by more than 1/2 in. at termination points, they limit how hard the cable can be pulled during installation to 25 lb. Fiber-optic cable, despite its reputation as being fragile, can withstand more than 150 lb of pull, with some cable designed for horizontal applications able to withstand up to 225 lb. Meeting FCC emission limits and providing adequate crosstalk isolation at 100 Mbits/s can also require the installation of new wall outlets and patch panels. Outlets and patch panels meeting the new Category 5 requirements cost significantly more than their predecessors and have been available only since January 1993. As a result, any Category 5 cabling installed prior to that date with Category 3 or 4 apparatus will need to be retrofitted before it can support 100-Mbit/s data rates. Testing and certification requirements also become more stringent when copper is used at high data rates. Tests for crosstalk, impedance mismatches, cable length, and near-end crosstalk should be conducted at each cable end. The tests apply to all components of the system. CAPTIONS: Fig. 1. The SDM4123 1 x 9 SC duplex transceiver from Sumitomo Electric Fiber Optics Corp. (Tarrytown, NY) is one-third the area of an FDDI-MIC transceiver. The transmit power into multimode fiber is -16 dBm and optical receiver sensitivity is -35 dBm. Fig. 2. These SC duplex transceivers and ST-style transmitters and receivers from AMP Inc. (Harrisburg, PA) suit both FDDI and ATM data transmission schemes. Fig. 3. The HFBR-5104/-5203 fiber-optic transceiver operates at 820 nm and lowers the cost of FDDI and ATM connection with duplex SC ports to bring high-speed data to the desktop. Fig. 4. A typical Premises/ATM fiber-optic network is easily capable of converting and routing multiple protocols seamlessly over long and short distances. The part numbers indicated are for typical products available from Hewlett-Packard. For more information from AMP Inc Hewlett-Packard xxx Sumitomo Electric xxx OVERLINE: Fiber-optic transceivers