Q1: In general, what was accomplished at the March IEEE Gigabit Ethernet Plenary meeting?

Q2: What happens next?

Q3: What are the minimum distance ranges in the current draft standard?

Q4: What actions did the committee have to take to allow ratification of the standard in June?

Q5: What happened to the DMD effects? Did they go away?

Q6: Why did the distance for "FDDI-grade" (160 MHz*km) fiber cable change?

Q7: For 62.5 micron multimode fiber, why does the 1000BASE-SX specification have two different distances?

Q8: How much of the 62.5 micron multimode fiber is 160MHz*km? How much is 200MHz*km?

Q9: Why do problems with multimode fiber exist? Why have these problems just been uncovered now?

Q10: In the future, can customers go longer distances on MM fiber?

Q11: What is the impact of these issues on customers?

Q12: What does MHz*km mean?

A1: The outstanding comments to Draft 4.1 of the Gigabit Ethernet specification were resolved and incorporated into a new Draft (D4.2). Based on the work accomplished at this Plenary meeting in Irvine, California, the Gigabit Ethernet draft standard is on track for formal ratification in June 1998. The issues regarding multimode fiber transmissions were resolved. For 1000BASE-SX, the solution was achieved by qualifying the launch of the laser transmitter, introducing conformance tests for stressed receiver sensitivity and stressed receiver jitter, and reallocating the jitter budget. In addition to these refined transceiver conformance tests, the link distance for the lowest bandwidth multimode fiber was shortened. A separate task force called 802.3.ab is working on the Gigabit Ethernet over Category 5 copper wiring standard or 1000BASE-T. Significant progress was made on the 1000BASE-T draft document. Several technical issues were discussed and resolved including progress in reference to the startup protocol. The 802.3ab editor has been directed to produce Draft 2.1. The 802.3ab Task Force should be ready for Working Group Ballot during the next IEEE Plenary meeting in July.

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A2: Following the March meeting, the 802.3z Task Force continues to proceed on track towards ratification of the Gigabit Ethernet standard in June 1998. All comments received on Draft 4.0 and 4.1 were formally resolved by the Task Force and the editorial staff was directed to produce Draft 4.2, which will be recirculated to the IEEE 802 LAN/MAN Standards Committee sponsor ballot pool. Comments on this draft will be resolved at the next 802.3z interim meeting in New Hampshire at the end of April. The schedule for the June ratification includes time for an additional recirculation ballot, if necessary.

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A3: See Table 1 below

Notes:
*     The TIA 568 building wiring standard specifies 160/500 MHz*km multimode fiber
**   The international ISO/IEC 11801 building wiring standard specifies 200/500 MHz*km multimode fiber
*** The ANSI Fibre Channel specification specifies 500/500 MHz*km 50 micron multimode fiber and 500/500 MHz*km fiber has been proposed for addition to ISO/IEC 11801.

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A4: The Gigabit Ethernet standards process is on target for delivery in June. The optical sub-group executed on their detailed and aggressive work plan agreed upon at the Bellevue, Washington meeting in February. The group investigated combinations of worst case components and developed conformance tests to ensure interoperability of worst case transmitters in conjunction with worst case receivers both communicating over worst case laser launch conditions at the maximum distances. The 802.3z standards document has been completed with this analysis and will now be recirculated for review.

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A5: The jitter effects caused by differential mode delay will occur in certain circumstances combining worst case multimode fiber, worst case laser transmitter and receiver, and a worst case launch. The probability of the effect occurring in a customer installation is very small. DMD effects increase over longer distances and decrease with higher bandwidth fiber. By reducing the link distances for 1000BASE-SX transceivers over 62.5 micron MM fiber with 160 MHz*km bandwidth, we are now in a range where the DMD effects are accounted for by the modified jitter budget and receiver conformance tests. 1000BASE-SX transceivers can go further on higher bandwidth multimode fiber.

With 1000BASE-LX transceivers over multimode fiber, external patch cords will be used to mitigate DMD. Existing technologies that use the combination of short wavelength lasers and multimode fiber, such as Fibre Channel (FC), have not seen DMD effects because of the short distances used in FC applications.

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A6: Ultimately the distance of any data communications link is limited by various parameters such as the bandwidth of the physical media itself, jitter, and attenuation. Table 1 clearly shows Gigabit Ethernet goes further on fibers with higher bandwidth. Because of the relatively low bandwidth of FDDI grade fiber, the contribution of jitter from DMD (which increases with increasing link lengths), and the desire not unnecessarily to increase the cost of 1000BASE-SX optical components, the distance for 160 MHz*km 62.5 micron MM fiber cable was specified at 220 meters.

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A7:There are two distances because there are two standard 62.5 micron MM fibers in the installed base. Much of the installed base of 62.5 micron MM fiber has labeled bandwidth of 160 MHz *km. This fiber bandwidth specification corresponds to the current TIA (Telecommunications Industry Association) specification 568 for building cabling and corresponds to the FDDI specifications.

A growing portion of the installed base of fiber worldwide has a labeled bandwidth of 200 MHz*km. This MM fiber is included in the current international ISO/IEC specification for building cabling. Because this ISO standard MM fiber has a higher bandwidth, it can carry the signal farther. The IEEE 802.3z standard is now harmonized with the international building cabling standard.

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A8: Based on fiber manufacturersâ data, the majority of the installed fiber especially in North America is specified at 160MHz*km. The ISO/IEC 200MHz*km fiber has been shipping since 1995 and will become more common.

As a side note, data presented by two major international manufacturers of MM fiber stated that over 99% of the fiber that is nominally rated and specified at 160MHz*km actually provides 185MHz*km of bandwidth. Based on this data, much of the installed base of 160MHz*km fiber can support Gigabit Ethernet link distances up to 250 meters.

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A9: The challenges associated with using lasers on multimode fiber have become more apparent as the operating speed has been increased. Furthermore, the IEEE 802.3z Task Force is particularly attentive to the characteristics of the installed base of network cabling, be it copper or fiber optic cabling. The group will not allow a draft standard to progress unless it is sure that the underlying signaling technology will work on the vast majority of installed cabling. Thus, the IEEE has applied far greater scrutiny to the operating characteristics of lasers on multimode fiber than has ever been applied before. This is the first time that laser launch has been extensively tested over long multimode fiber.

A10: Yes. Customers can go longer distances on MM fiber today with 1000BASE-LX transceivers, reaching distances of 550 meters. With 1000BASE-SX transceivers, customers can also go longer distances with 50 micron diameter MM fiber reaching distances of 500 meters or more.

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A11: Most of the products shipping today are equipped with 1000BASE-SX optics. It is premature to draw definitive conclusions about the impact of the additional specification work on existing 1000BASE-SX parts. These parts may already conform to the proposed additional specifications that have been written. The standard is written to cover cases involving worst case optics operating over worst case fiber at the maximum specified distance. Conditions other than these may not exhibit any problems.

Early implementers of any networking technology are sometimes faced with an element of uncertainty when dealing with pre-standard products. The industry has faced this challenge before. These issues do not necessarily impact the functionality of the majority of installed networks or the majority of pre-standard Gigabit Ethernet products that have shipped to date. The Gigabit Ethernet products shipped to date will not stop working because of recent changes in the optical specifications. Ethernet vendors have an excellent track record of taking care of their customers and of successfully migrating customers from pre-standard to standards-based equipment. Customers should discuss this issue with their equipment suppliers and work with them to understand their vendors' specific transition plans.

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A12: This unit of measurement designates the bandwidth capacity of a fiber. This value shows the limits of the capacity of the fiber that in turn determines the maximum link distances depending on the baud rate or speed of the protocol running over it.

While the actual formula is more sophisticated, the following statement illustrates the point in concept. The bandwidth value for the fiber (160 or 200) is a constant. As the data rate (measured in MHz) increases to gigabit speeds, the distance (km) decreases.

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