3. IPv4: Internet Protocol version 4

An Internet network is seen by the user as a single virtual network that interconnects all machines and through which we can communicate. The underlying architecture is both hidden and irrelevant. An Internet network is an abstraction of a physical network, because at its lowest level it provides the same functions, such as accepting packets or delivering them to the recipient.

The service provided by the IPv4 protocol is determined by an unreliable, "best-effort", connectionless packet delivery system. Service is said to be unreliable because delivery is not guaranteed. A packet can be lost, duplicated or delivered out of sequence, but the IP protocol will detect nothing and inform neither the sender nor the receiver. It is said to be connectionless because each packet is processed independently of the others. Packets of the same message, in transit from one machine...