View Graph 1: "Issues and Opportunities for the Installed 62.5 um Fiber Base" Paul Kolesar Lucent Technologies View Graph 2: "Overview" @ Private Network Distance Requirements @ Current Distance Capability at 1250 Mbaud @ Possible Distance Improvement Techniques View Graph 3: "Private Network Distance Requirements" A table showing distance requirements for cabling systems as follows: Horizontal <= 100 m Building (horizontal + riser) <= 300 m Campus <= 2000 m View Graph 4: "Building Cabling Distance Distribution (Outlet to Equipment Room)" This is a graph showing the statistal distribution of builing cabling (i.e. from the outlet to the main equipment room) for both small and large businesses. The data was gathered by AT&T in the 1980's using Time Domain Reflectometer measurements of over 10,000 copper lines at 79 sites in the U.S.A. The distribution for both small and large businesses reaches about the 95th percentile at 200 m with a nearly flat slope of 2 percentage points per 100 m additional distance above 200 m. Based on this, the selection of 300 m for building cabling provides coverage for over 95% of all runs surveyed. The additional 100 m buffer provides margin to account for the possibly longer distance scenarios of fiber compared to copper. View Graph 5: "62.5 Distance vs Bandwidth at 1250 Mbaud" This is a graph showing the relationship between bandwidth limited distance and fiber modal bandwidth for sped-up 1.062 Gbaud Fibre Channel transceivers. Using worst case Fibre Channel parameters for center wavelength (770 nm) and spectral width (4 nm RMS), and scaling the transition time parameters in inverse proportion to the baud rate increase (Ttx = 0.31 ns, Trx = 0.51 ns from 20-80%), the supportable distance is found to be 190 m on the installed base of 62.5 um fiber. The installed base has a minimum modal bandwidth of 160 MHz-km at 850 nm, but theory predicts a ~20% lower bandwidth at 770 nm (125 MHz-km). Thus, for sources with 850 nm center wavelenghts, the bandwidth limited distance increases to 240 m. The less-than-linear shape of the curve is a result of chromatic dispersion effects which become more dominant as the modal bandwidth of the fiber is increased. This explains why a fiber with double the modal bandwidth does not double the supportable distance. View Graph 6: "Distance Improvement Techniques For Installed 62.5 um Fiber Base" The preceding graph indicates that the supportable distance on the installed base of fiber is insufficient to address the 300 m distance requirements of building cabling. This table lists the possible distance improvment techniques that can be used to improve the range of optical solutions. The techniques are grouped in columns to show that they apply to the transceiver alone, transceiver and fiber, or fiber alone. Each of these options is examined in the following view graphs. Transceiver Trans/Fiber Fiber ----------- ----------- ----- encoding restricted restricted launch launch equalization parallel transmission longer wavelength multi- wavelength sub-rate data View Graph 7: "Encoding" @ Present 8B10B code inefficient with 20% overhead - 0.8 bits/baud, first spectral null at 1250 MHz @ Short run-length, balanced code desirable for low modal noise, baseline wander and clock recovery @ Consider three-level codes to increase link length - BNZS: 1 bit/baud, first null at 1000 MHz, 25% longer links - PST: 1 bit/baud, first null at 1000 MHz, 25% longer links - 4B3T: 1.33 bits/baud, first null at 750 MHz, 67% longer links @ 3-dB power penalty incurred @ Cost impact for new silicon in transmitter and receiver View Grahp 8: "Equalization" @ Linear and/or decision feedback equalizer in receiver - Linear equalization emphasizes attenuated high frequencies - Decision Feedback Equalization cancels ISI @ DFE advantages - Smaller power penalty than multi-level encoding - Adaptable to channel characteristics - Dramatic distance improvements possible . Double distance for 3-dB power penalty - Potentially low complexity and small cost increase . Simplest form adds one flip-flop and weighted summer . Realizable with commercial components at 1 Gb/s View Graph 9: "Longer Wavelengths" @ Use higher bandwidth wavelengths - 980 nm VCSELs (~300 MHz-km) - 1300 nm FP Lasers (500 MHz-km) @ Distance increase proportional to bandwidth increase - ~ 2x for 980 nm over 850 nm - ~ 3x for 1300 nm over 850 nm @ Cost increase less than proportional to distance increase View Graph 10: "Theoretical Bandwidth vs Wavelength 62.5 um" This view graph is a plot of the theoretical modal bandwidth across the spectrum from short to long wavelengths. The shape of the curve is a Gaussian-like bell with the peak wavelength exceeding 3000 MHz-km, but falling rapidly to either side so that at +/- 200 nm from peak the bandwidth has decreased to about 750 MHz-km. Four discrete wavelengths are highlighted: 780, 850, 980 and 1300 nm. The peak wavelength of this plot is placed at 1150 nm. In this case the bandwidths of at 980 and 1300 nm are nearly the same. The 780 nm bandwidth is about a 25% lower than at 850 nm. View Graph 11: "Theoretical Bandwidth vs Wavelength 62.5 um" This is the same curve as above, but with the peak shifted by 50 nm to 1200 nm to show the effect of common manufacturing variation. Since the peak has shifted towards the longer wavelengths, the 1300 nm bandwidth has improved, while the 980 nm bandwidth has deminished so that the bandwidth at 1300 nm is about twice that of 980 nm. The difference between the 780 and 850 nm bandwidths has deminished to about 15% as they have been moved to the flatter part of the gaussian tail. Because of the steepness of the curve near the peak, the absolute and relative bandwidths can be very sensitive to the location of the peak wavelength. Because the peak wavelength is not easy to control precisely in manufacturing, fiber bandwidth specifications are written with generous margins to allow high production yields. View Graph 12: "Multi-Wavelength" @ Divide baud rate into multiple channels @ Each channel carried on separate wavelength within the same fiber @ Distance increase inversely proportional to channel baud rate reduction @ Distance limited by lowest performance wavelength @ Cost increase proportional to number of channels View Graph 13: "Sub-Rate Data" @ Provide option to use less than full 1 Gb/s - Half-rate option @ Several implementation methods available - Switch selected rates (like 10/100BASE products) - Auto-bauding (like modems) - Discrete rate offering (like Fibre Channel) @ Distance increase inversely proportional to baud rate decrease @ Cost impact dependent on implementation View Graph 14: "Restricted Launch Conditions" @ Control transmitter emissions to under fill mode-volume of fiber - Overfilling provides repeatability and worst case value - Under filling removes higher-order modes, potentially reducing modal dispersion and raising bandwidth @ Investigations in TIA FO2.2 underway - Define restricted launch test conditions - Determine bandwidth improvements @ Cost impact depends on implementation - Tx optics, pigtail, patch cord - Possible power budget impact View Graph 15: "Parallel Transmission" @ Divide baud rate into multiple channels @ Each channel carried on separate fiber @ Distance increase inversely proportional to channel baud rate reduction @ Potentially requires multi-terminus connector @ Cost increase proportional to number of channels View Graph 16: "Conclusion" @ Current transceiver technology proposal insufficient to support installed base for building or campus @ Many options exist to improve this situation @ Options may be used separately or in combination @ Further work required to determine best solution @ In the best interest of Gigabit Ethernet to pursue longer solutions for greatest market acceptance Paul Kolesar Lucent Technologies 908 957 5077 pkolesar@lucent.com