ABSTRACT
This chapter describes the basic software that makes the Internet appear to be a single, large network. A network communication protocol is an agreement that specifies a common language two devices will use to exchange messages. In the Internet, one of the key communication protocols is called, appropriately, the Internet Protocol (IP). The IP introduced an important principle: packets are not changed as they pass from the sending device to their destination. Thus, when an IP packet arrives at a device, the packet that arrives is an exact copy of the original IP packet that was sent. To communicate on the Internet, a device needs IP software. Indeed, every device that uses the Internet, including conventional computers, smart phones, and Internet of Things devices, must use IP software for Internet communication. To distinguish between Internet packets and packets for other networks, people call a packet that follows the IP specification an IP datagram.
