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dorlow's profile

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6 Messages

Tue, Nov 9, 2021 2:21 AM

How does AT&T fiber work full duplex?

Ok, so we just had AT&T Fiber installed today.  There is only one fiber wire into the house.  Years ago, I worked for a company where we installed the fiber.  We had cable installers that would actually install it to the cabinets.  Then I would go in and configure the routers and switches to work with the fiber.  Those fiber setups had two wires.  You had to have two strands because you need one for sending and one for receiving.

I asked him if the fiber was multimode and he said no, it's single mode.  So, how in the world, if the light takes up the whole fiber, does it send a signal in both directions on the fiber at the same time?

my thoughts

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AT&T is most probably using BIDI (Bi-Directional) or WDM (Wavelength Division Multiplexing), 1000Base-BX.  Which simply means that over a single strand of single-mode fiber, the transmitter and receiver, each operate on different frequencies, Which are operated in pairs, meaning on one end of the fiber, there is a download device signified by 1000Base-BX- D, and on the other-end is the upload device, signified by 1000Base-BX-U, for example.  Considering both end transmit and receives, the U and D is mostly to ensure the devices are paired properly, considering the D send on the frequency that the U receives on, and vice versa for the other-end.

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