IEEE 802 Gb/s MMF Links: 1.063 GBd vs. 1.250 GBd Line Rate Issues Del Hanson Hewlett-Packard Company Optical Communication Division 350 W. Trimble Road San Jose, CA 95131 1. Outline * Worst Case, Fully Mode Filled, MMF Link Length Limits vs. Modal Bandwidth o FC Link Length Specifications vs. Link Model o Projected 1.063 GBd vs. 1.250 GBd Limits * Modal Bandwidth Needed For 500 m Link Length * Serial Link Jitter Issues * 10-Wide Interface Jitter Limits o 1.063 GBd 10-bit Transceiver o Projected 1.250 GBd Line Rate Limits 2. Multimode Optical Fiber Link Bandwidth Limiting Conditions * Modal Dispersion o Caused by delay differences between optical modes having the same wavelength * Chromatic Dispersion o Caused by fiber wavelength differential delay o Primary limitation for broad spectrum sources * Source Optical Response Time o Ultimate rate limitation for short links 3. Worst Case, Fully Mode Filled Modal Bandwidth vs. Wavelength for 50MMF and 62MMF (Figure shown) Wavelength 50MMF 62MMF 770 nm 400 MHz*km 160 MHz*km 850 nm 500 MHz*km 160 MHz*km 1300 nm 500 MHz*km 500 MHz*km 4. 770-860 nm LD FC MMF Link Length Specification Summary & Link Model (Figure shown compares specs & analysis) Data Rate Fiber Type Spec Model 266 MBd 50MMF 2000 m 2000 m 531 MBd 50MMF 1000 m 1000 m 1063 MBd 50MMF 500 m 470 m 1063 MBd 62MMF 300 m 290 m 5. Modal Bandwidth Related Link Length & Extended Model Bandwidth Projection (Expanded figure shows link length limits at 1063 MBd and 1250 MBd vs. fully filled modal BW) Data Rate Fiber Type Model 1063 MBd 50MMF 470 m 1063 MBd 62MMF 290 m 1250 MBd 50MMF 375 m 1250 MBd 62MMF 240 m (Analysis shows that a fully filled modal bandwidth of ~800 MHz*km is needed to achieve a 500 m link length at 1250 MBd) 6. Achieving a 500 m Worst Case Link Length With 62MMF * The link mode accurately represents the existing Fibre Channel 266, 531, 1063 MBd link lengths with 50MMF and 62MMF * Increasing the line rate by ~18% (to 1250 MBd) reduces the link length by ~18% * Is necessary to increase the modal bandwidth beyond current specifications to achieve the worst case 500 m link length at 1063 MBd & 1250 MBd * Controlled source mode coupling MAY allow extending the modal bandwidth specification 7. Existing Link Optical Power Specifications For 770-860 nm Sources (MSL: Mode Selective Loss) * Source Range: -4.0 dBm <= Pc <= -10 dBm Receiver Range 0 dBm <= Pr <= -16 dBm Specified Link Optical Power Budget: 6.0 dB MSL & Link Response Penalty: -2.0 dB MSL (based on # of fiber modes) 62MMF MSL allocation = 0.5 dB 50MMF MSL allocation = 1.0 dB 300 m Link @ 4.0 dB/km @ 770 nm: -1.2 dB Allowed connector Loss: 2.8 dB 8. Extending Modal Bandwidth Through Controlled MMF Mode Launching * Present MMF Modal Bandwidth Specifications Are Based on Full Mode Filling * Issues Needing Resolution to Achieve An Industry Extended Modal Bandwidth Specification o Specified performance with installed MMF LANs o Transmitter specifications for mode launch verifiable in a production environment o Reconciled impact on the link MSL penalty * TIA FO-2.2 is beginning to explore this issue; there is no proof for installed MMF LANs at this time 9. 1.063 GBd Fibre Channel Serial Link Jitter Specifications * Individual Serial Jitter Components are Specified More Tightly Than Necessary to Achieve Interworking Performance * A Jitter Working Group Was Formed to Refine the Jitter Specifications Based on Frequency Dependent, SONET-based Jitter Tolerance & Generation Methodology * Implications for Future Serial Link Specifications o Revised specifications will impact serial channel jitter allocation 10. 10-Wide Parallel Interface Specifications vs. Line Rate * Parallel Interface Parameters are Defined by the Fibre Channel 1063 MBd Line Rate, 10-Bit Interface Specification * The 106.3 MHz TTL/CMOS Response Time & Jitter Specifications (which follow) Were Determined After Considerable Industry Debate * Vendors are now resolving test conditions & yield as the 10-bit chip volume begins to ramp for the Fibre Channel Arbitrated Loop Storage Application 11. 10-Bit FC-AL Interface Specification at 1.063 GBd Line Rate * Transmit Response Time Specification Limits o Total baud period 9.4 ns o Clock TTL/CMOS Tr & Tf -2.4 ns o Setup & hold limit -3.5 ns o Available for data Tr/Tf & Jitter 3.5 ns * Receive Response Time Specification Limits o Total baud period 9.4 ns o Clock TTL/CMOS Tr & Tf -2.4 ns o Setup & hold limit -4.5 ns o Available for data Tr/Tf & Jitter 2.5 ns 12. 10-Bit FC-AL Interface Specification at 1.250 GBd Line Rate * Transmit Response Time Specification Limits o Total baud period 8.0 ns o Clock TTL/CMOS Tr & Tf -2.4 ns o Setup & hold limit -3.5 ns o Available for data Tr/Tf & Jitter 2.1 ns * Receive Response Time Specification Limits o Total baud period 8.0 ns o Clock TTL/CMOS Tr & Tf -2.4 ns o Setup & hold limit -4.5 ns o Available for data Tr/Tf & Jitter 1.1 ns 13. Summary of 1.063 vs. 1.250 GBd Line Rate Issues * The 1.063 GBd Fibre Channel Line Rate o Leverages PHY volume over multiple applications o Has established jitter & response time margins o Yields 300 m link length with existing modal bandwidth o Achieves multi-vendor component availability now * The 1.250 GBd Line Rate o Provides "true" 1 Gb/s line rate: 10/100/1000 o Provides potential 18% extra throughput o Reduces link length by ~18% to ~250 m o Stretches 10-bit response times & jitter limits 14. Conclusions * If an ~Gb/s LAN specification with the fastest possible time to market & 300 m worst case link length with 62MMF is satisfactory o Use 1.063 GBd line rate & leverage 8b10b 10-bit PHY components with Fibre Channel o Use duplex SC transceivers having 1X9 electrical pins * If 1 Gb/s @ 500 m link length with 62MMF is critical but time to market is not as critical o Work with Fibre Channel, the CMOS industry & TIA to modify serial jitter, 10-bit interface jitter 62MMF modal bandwidth specifications to achieve the necessary link performance