From the “holy crap technology is neat-o” dept #1:
How does a simplex fiber cable do TX/RX at the same time?
Full-Duplex in networking (ethernet) is simultaneous transmit (tx) and receive (rx). It’s always been easy for me to conceptualize full-duplex operation over Cat5/6 due to the presence of multiple twisted pairs of copper. So in my head it was easy to conclude one pair is used for sending data and another pair is used for receiving.
Same with fiber cables like this one. A & B right? One fiber for sending and the other for receiving:
But wait…ever been in a datacenter, or took a peak at service provider NNI, or ever look at the fibre cable that terminates into your home FTTH router? Why does it look like this:
Or like this:
That’s just…one cable…one strand of glass…how can that do full-duplex?
The answer is Wave-length Division Multiplexing, which is a fancy way of saying multiple waves (colours) of light are sent across the same optical fiber. That’s how it can send and receive at the same time using a single fiber optic cable! I’m not a fiber optics expert, but I remember finding out about this and just thinking of how darn cool it was.
