What is the Internet? What is a Network?
Introduction
The Internet is composed of a large number of interconnected networks. Data is transferred between networks through a series of "layers" -- from the "physical" layer (L1) to the "network" layer (L3), data is routed seamlessly for the end user over a series of autonomous systems (i.e. networks).
Given that the Internet is a large autonomous system (with no one single party controlling it), it is often referred to as a decentralized “network of networks.” For example, if a user was to visit “192.168.168.1” (assuming this local address was routable over the Internet), an ISP’s network will — over the Border Gateway Protocol (BGP) — find a route to your destination network. It does this by finding the shortest path*, with data often traveling through intermediary networks (through peering) until the network announcing the IP address is finally reached.
What is a Network?
A network is a series of connected devices (this can be a number of servers — even your smartphone) on a central distribution hub (router).
The illustration above shows a request from your PC (“Network A” being your ISP) to a remote server (10.0.200.2). The network 10.0.200.0/24 is being announced by network D, so your ISP will route traffic to — in this case — an intermediate network (“Network C”) before being forwarded to the destination network (“Network D”).
In essence, a network (in the simplest form) is a series of devices — whether it is a smartphone, home server, TV, or even your watch — connected together through a shared hub. This shared hub then connects to an upstream network (for example, your ISP), which then connects to other networks (networks that are also connected to other networks). This is what forms the Internet.
Conclusion
To conclude: the Internet is a series of interconnected networks. These networks connect to other networks themselves (i.e. a “network of networks”). In the simplest sense, a network consists of a number of devices connected to a routing device (i.e. a hub, your router).
In this series, you’ll learn more about BGP (the Border Gateway Protocol) and other networking related topics.
