For internet connection we might have used DSL modem. I am using BSNL modem in my home. Internally how modem is working?
We will connect telephone connection with DSL modem to receive/send over the network. From modem, we will connect the ethernet cable with PC to get internet connection. Initially modem was connected to RS232 serial port or USB 1.1 port. But it will have very less speed. Serialport maxspeed is at max 192 kbps. To speed up internet connection, PPPoE connection was made.
PPP protocol client is running in PC. PPP server will be running in Modem.
PC 's ethernet card communicates with modem's ethernet card. It is like connection ethernet cable between two systems as like a serial cable.
PPP client is running in PC, It will interacts with modem [PPP server] to have internet connection. Usually modem internet connection will be authenticated by username and password.
Since internet connection is made through PPP protocol. If OS supports this PPP client, then it will be able to access the modem. That's why we are able to get internet connection regardless of OS .
Wireless DSL router has antennas to access wireless access points. Wireless router will have its own page settings. By giving this from PC, http://192.168.1.1 we can change the router settings.
How data is transmitted in DSL modem:
DSL modem communicates with nearest telephone exchange's device. This device is called as Digital Subscriber Line Access Multiplexer (DSLAM). Data will be transferred over the telephone exchange's optical fiber cable. Whenever we are downloading a web page, packets of webpage travel over optical fiber internet lines directly to the DSLAM at the neighborhood telephone exchange. At the DSLAM, they are split into as many as paralllel data streams, modulated onto a separate signal and sent through cable. The modem demodulates the signal to datastream also will do error correction,put the data in proper order and sends it to the computer over ethernet line.