How is data transmitted through a a communication channel b destination computer c switching device d source computer?

Answer 1

Assuming that you are referring to a modem (analog dial up, or DSL , or Cable Modem - they all use one form or more of QAM or QPSK), then there a radio device that decodes an analog modulated signal (with forward error correction) into digital bits and double-checks their integrity, and then tweaks the digital stream a bit to prepare

it to be placed upon an ethernet bus. Ethernet has it's own special cable and electrical and encryption and protocol specifications also, but to keep things short, the physical uses Manchester codes to send both data and clock signals, and prevent a DC bias from appearing on the line or in the conducting transformer. And, then, after the Physical Layer, there are three more layers of topology to help separate the different stages of passing the message (packet) of data.

(Read more at Wiki's article on Ethernet or the internet Protocol Suite).

The messages are passed from your Router to your Computer over the Ethernet Cable to the receiving end (your computer) and another radio decodes the modulation and converts the signals back into a stream of bits and bytes that the computer can use (via the communications busses of PCI/PCI-e, etc. and the requesting computer normally puts the received information into RAM so the application can use it.

This is a simplified version of what really goes on. You have your question out-of-order as the switches and communications channel need to be between the source and destination computers.

If I were you, I'd study oup on Ethernet, and Docis 1,Docsis 2 standsards and once you feel comrfortable with that, then you can pick up routing and NAT and Firewalling, and that is where you can get a better functional understanding of how things work. Don't forget that there are plenty of online web resources to help teach you on IP Protocols and Packet Transmission over the internet.