The Internet is a large complex that includes local networks and autonomous computers interconnected by any means of communication, as well as software that ensures the interaction of all these means on the basis of a single transport protocol TCP and address protocol IP.
Internet backbone network
The Internet core network is represented by node computers and communication channels connecting them. Node computers are also called servers or hosts.
Routers
On each of the nodes there are so-called routers that are able to automatically determine by the IP address of the received TCP packet to which of the neighboring nodes the packet should be forwarded. A router can be a program, but it can also be a separate, specially dedicated computer for this purpose. The router continuously scans the space of neighboring servers, communicates with their routers and therefore knows the state of its environment. It knows when any of the neighbors is “closed” for maintenance or simply overloaded. When deciding to forward a received TCP packet, the router takes into account the state of its neighbors and dynamically redistributes the flows so that the packet goes in the direction that is most optimal at that moment.
Gateways
Local networks, working on the basis of their own protocols (not TCP/IP, but others), are connected to the node computers of the Internet with the help of so-called gateways. Again, a gateway can be a special computer, but it can also be a special program. Gateways perform data conversion from formats accepted in the local network to the format accepted on the Internet and vice versa.