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Why No Auto-Negotiation for Fiber Optic Media?

Auto-Negotiation for fiber optic media segments turned out to be sufficiently difficult to achieve that most Ethernet fiber optic segments do not support Auto-Negotiation. During the development of the Auto-Negotiation standard, attempts were made to de‐ velop a system of Auto-Negotiation signaling that would work on the 10BASE-FL and 100BASE-FX fiber optic media systems.

However, these two media systems use different wavelengths of light and different signal timing, and it was not possible to come up with an Auto-Negotiation signaling standard that would work on both. That’s why there is no IEEE standard Auto-Negotiation sup‐ port for these fiber optic link segments. The same issues apply to 10 Gigabit Ethernet segments, so there is no Auto-Negotiation system for fiber optic 10 Gigabit Ethernet media segments either.

The 1000BASE-X Gigabit Ethernet standard, on the other hand, uses identical signal encoding on the three media systems defined in 1000BASE-X. This made it possible to develop an Auto-Negotiation system for the 1000BASE-X media types, as defined in Clause 37 of the IEEE 802.3 standard.

This lack of Auto-Negotiation on most fiber optic segments is not a major problem, given that Auto-Negotiation is not as useful on fiber optic segments as it is on twisted- pair desktop connections. For one thing, fiber optic segments are most often used as network backbone links, where the longer segment lengths supported by fiber optic media are most effective. Compared to the number of desktop connections, there are far fewer backbone links in most networks. Further, an installer working on the back‐ bone of the network can be expected to know which fiber optic media type is being connected and how it should be configured.

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Pretty straightforward explanation why fiber does not support auto negotiation. However, I don't think you could call auto negotiation for Gigabit fiber, since the concept means stepping down on speed to adjust to the other side of the connection. In this case, the speed remains the same, 1Gb.

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