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I have been learning how internet data travels in different kind of Broadband access.

In case of telephone broadband, voice signals travels through the telephone line. At the user premise, the modem coverts the voice signals into digital information. The Fiber Optic medium transfers light pulses. Now, here are few questions in my mind after learning that:

(1) If the telephone infrastructure is migrated from copper wires to the Fiber Optic cables, then how the data transmission will take place ? Because, the Fiber Optic medium transfers light pulses

(2) Will I need a different kind of MODEM if I migrate my internet connection from ADSL broadband to Fiber Optic access ?

(3) In case of Television cable internet, what kind of signals travels through the cable ? And what makes Cable internet faster than ADSL ?

Thanks in Advance !!!

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  • First, questions about home networking and/or consumer-grade equipment are explicitly off-topic here. Also, you are asking questions about something where the answers are probably too technical for your level of understanding. You should study signalling and encoding, It's all electromagnetic communication, whether on copper or optical fiber. – Ron Maupin Mar 26 '16 at 16:02
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I'll answer your heading question:

There are two ways that voice can be carried over fiber lines: analog and digital.

In an analog system, voice can be carried over a fiber line by modulating an LED (light emitting diode) with a microphone and associated circuitry. The circuitry modulates the light signal by varying the power to the LED based on the frequency and strength of the sound wave that is picked up by the microphone. So the light traveling through the the fiber cable has the same characteristics as the sound wave. Then on the other end it is converted back into an electric wave and then sound wave by a phototransistor and speaker, respectively (and associated circuitry).

In a digital system, the microphone feeds an ADC (analog to digital converter), which converts the electric signal into raw digital data numbered levels called a "bitstream" that represents the analog sound wave. The ADC (usually) then feeds an audio coder, which converts the digital bitstream into a codec format that can be packaged into "blocks" of sound data suitable for being sent as "packets" or "cells" over a network infrastructure like the Internet or a private phone company network. The audio coder puts out a coded bitstream that will then be sent to an LED that will be modulated to be "on" or "off" based on the 1's and 0's in the bitstream. This digital signal goes through the fiber line to the other end (through the voice network controlled by the phone company) where it is received and converted back into electrical pulses by a phototransistor, then fed into a audio codec decoder, then into a DAC (digital to analog converter), which feeds a speaker that converts the analog electrical wave from the DAC into a sound wave that moves the air.

This is grossly oversimplified of course, but it's basically how it works.

Pretty much any signal that you can send over a wire can be converted into light by modulation of an LED (or other light source) and then sent over a fiber line. Then it is converted back into an electrical signal on the other end by a phototransistor.

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In case of telephone broadband, voice signals travels through the telephone line. At the user premise, the modem coverts the voice signals into digital information.

A dialup modem converts between digital signals and analog signals in the voice-band hence why you couldn't use your phone at the same time as your dialup modem..

A DSL modem is generally designed to avoid the voice band. It uses higher frequency signals, filters are used to prevent these high frequency signals reaching the voice equipment allowing voice and DSL to coexist on the same line at the same time.

(1) If the telephone infrastructure is migrated from copper wires to the Fiber Optic cables, then how the data transmission will take place ? Because, the Fiber Optic medium transfers light pulses

Analog voice over fiber is possible in theory but i've never heard of any provider doing it.

If voice is sent over fiber then generaly it will be digitised first. Then the digital data streams will be merged in some way (there are MANY different ways of doing this) and sent down the fiber.

The core of the phone network has been mostly digital for many years. It's much easier to merge, split and switch digital data streams without causing quality problems than it is analog voice signals.

(2) Will I need a different kind of MODEM if I migrate my internet connection from ADSL broadband to Fiber Optic access ?

Terminology varies a bit depending on the exact type of fiber access you are talking about and what exactly you are connecting to it. Devices for GPON seem to be reffered to as "modems", while devices for dedicated fiber tend to be reffered to as "transcivers" or "media converters" but yes you will need a device to convert from the signals used on the long distance fibers and that device will be different from your DSL modem.

(3) In case of Television cable internet, what kind of signals travels through the cable ? And what makes Cable internet faster than ADSL ?

With both DSL and cable the data signals are modulated onto high frequency carriers. The exact modulation schemes are different to suit the different types of cable and to allow coexistance with other services on those cables.

The main reason cable internet is faster is because cable TV cable has better performance (that is it degrades the signals less) at high frequencies than phone pairs do. Phone pairs were designed for analog voice at up to a few kHz and their high frequency performance is pretty poor. Frankly it's amazing that DSL works as well as it does.

On the downside Cable internet has to share the cable with cable TV services which take up a lot more bandwidth than voice does. Cable TV cables are also a shared medium which can lead to congestion problems.

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