ABSTRACT
This chapter describes how multiple packet switching networks can be interconnected to form an Internet that functions like a single, large network. Two basic ideas will help explain the technology the Internet uses to connect networks: the structure of network interface hardware and multiple interfaces. A specialized computer that interconnects networks has one major task to perform: when a device on one network sends packets to a device on another network, the packets must be sent from the first network to the second. A specialized computer that interconnects networks and performs the task of forwarding packets among them is known as a router. Each of a user’s Internet devices is a host, including desktops, laptops, smart phones, and devices like smart home climate control systems that can be accessed over the Internet. A key part of the Internet structure arises because a set of Internet Service Providers own and operate networks in the middle of the Internet.
