The Journey of a Message Through the Internet
Do you ever wonder how messages, emails, or video chats from our laptops or phones reach our friends and family in another location?
Each of our networking devices such as mobile phones, laptops, or Internet of Things (IoT) appliances has private IP addresses assigned to them. These private IP addresses cannot communicate directly with the outside world.
When we send messages from our mobile device, it first reaches the router in our home provided by our Internet Service Provider(ISP). The router creates the Local Area Network (LAN) or Wireless LAN (WLAN) that connects all our devices within the local network. In workspaces like offices, all the employees laptops have private IP addresses and are interconnected through a LAN. They communicate with the outside world via the router.
The router has a public IP address assigned by the ISP, to communicate with the internet. Why only router has the public IP address and not the individual machines? It is because there are only limited number of public IP addresses in the world. IPV4 used to denote network devices are 32 bits in length and can cover only (2³² - 4.3 billion) Ip addresses).
After router receives the message, it has to be sent to the outside world. Normally, our ISP installs a dial-up or fiber cable to our home, and the digital signals from our LAN should be converted to analog signals to be transferred through that cable. A hardware that does that is called a modem (short for "modulator-demodulator"). Usually, the ISP will provide both router and modem when they set up the internet connection to our home.
Thus the messages will leave our network through router and modem and it will travel to ISP's network via Wide Area Network (WAN). WANs connect devices over large geographical areas, such as cities or countries.
The messages then reach a peer point, also referred to as an Internet Exchange Point (IXP), where messages from different ISPs are exchanged.
Major network providers, ISPs and content delivery networks operate a collection of high-bandwidth network connections called Internet Backbone. Message we sent has to pass through multiple Internet Exchange Points (IXP) in the Internet Backbone to reach our recipient’s ISP.
From the ISP, the message travels through WAN to reach our friend's router. The router, using its public IP address, receives the message and directs it to the appropriate device within the LAN using the device's private IP address.
Communication process is now complete.