发表于:2008-01-15 16:41:00
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It is surprising how often a question arises about determining the fiber optic port compatibility between two Industrial Ethernet devices. The issue frequently involves matching a media converter to a switching hub.
On several occasions I have been asked why existing equipment is not communicating through a newly installed media converter. The problem is usually that the fiber optic port of one device is incompatible with that of the other. It seems that installers tend to assume that because the copper port of the media converter auto-negotiates the data rate to either 10 Mbps or 100 Mbps, then the fiber optic port will also adjust automatically. But that is not so (except for seldom-used equipment that is compliant with the 100BASE-SX specification).
Industrial Ethernet hubs and switches that operate exclusively at 10 Mbps — and have at least one fiber optic port — will most likely comply with the 10BASE-FL specification for fiber communication (unless the equipment is very old). Most modern switches are capable of operating at either 10 Mbps or 100 Mbps — but although their copper ports may adjust for data rate, their fiber ports will comply only with the 100BASE-FX specification.
A fiber optic port will not negotiate its data rate because it is fixed at the rate specific to the transceiver type. A 10BASE-FL transceiver passes a 10 Mbps data stream using a fixed wavelength of 850 nm. On the other hand, a 100BASE-FX transceiver passes a 100 Mbps data stream at a wavelength of 1300 nm. If someone connects an 850 nm fiber optic port to a 1300 nm fiber optic port, communication will not occur due to this difference in wavelength.
Another, less-common, issue is the compatibility of the fiber optic cable itself.
Most multimode fiber optic cable in North America is 62.5-microns in diameter (elsewhere, 50-micron cable may be more popular). This cable is basically used for segment distances under 2 km, works efficiently at either 850 nm or 1300 nm, and uses LED transmitters.
Single-mode fiber optic cable has a tiny core diameter in the range of 5 to 10 microns, works efficently at either 1300 nm or 1550 nm, and uses laser transmitters. It&nb