Hi,
I am currently studying computer networks and I have been reading about how data is transmitted via copper wires and fiber optics.
I understand the very basics of computers, data, logic gates and binary code.
However, currently I am struggling to wrap my head around how data can be transmitted by copper/light? It just does not make sense to me!
Can someone shed light on this?
In: Technology
In principle, it is just turning the light on and off or the voltage from 0 to a positive voltage. Compare to morse code on a telegraph where you both used wires on land and blinking light between ships. A computer can read and transmit more code.
Morse is in a way a binary signal where a gap is a 0 a dot is a 1 and a dash is 111. It is not efficient for computer-like ASCII that gives you more charachters, is but it can be used. B is ” – . . .” = “111010101” or 9 bits
On a fiber is a laser or a led that just blinks on and off to send the data. On the other side a light-sensitive part, a photodiode if I am not mistaken, is used to convert the light to electricity.
It is not just the raw bits you send but encoded in a way so you always have som bits as zero and some as one. You could, for example, send 10 bits for every 8 bits of data. Look up [8b/10b_encoding](https://en.wikipedia.org/wiki/8b/10b_encoding) You have most of the time a pair of fibers one to send data and one to receive data
You can send multiple streams of data in the same fiber by using different colors of light then multiple lasers are used to send the and the signal optically combines. You also split the signal apart optically, a prism is a simple example of how to split light by color.
The hard part to do a simple receiver is not to convert light to electricity but to know when bist start and stop so you use designs like [Phase-locked_loop](https://en.wikipedia.org/wiki/Phase-locked_loop) to get a clock from the data.
For copper wires, it is a bit more complex. You could just turn the between 0V and 5V (or what is used) like inside a circuit with the bit pattern. The problem is the signal can change because of the wire and the environment especially and high speed for long-distance.
Often you use two wires where then one is high the other is low and vise versa. So you drive one wire with the signal and one with the inverted signal. This is to reduce the effect of external interference, this is called differential signaling.
If you signal like that after you encode bits a bit like the 8b/10 format, have 3 parallel data pairs and apart for the clock you have an HDMI cable. The system only allows for communication in one direction on the wires
For connection like gigabit ethernet, you have multiple voltage levels, two negative, tow positive and a zero. You have 4 pairs of wires and there will be interference between them so you need complex filters on the receiver to interpret the signal.
It also sends and receives data on the same pairs that make it a lot more complex.
Latest Answers