Fig. 23.1.1 shows the typical "cloud diagram" for a network of any kind, LAN or WAN. The owners or operators of the computers which are connected to the net are less concerned with how the network works than the fact that it does work. The diaphanous blob labeled network represents whatever software and hardware that exists to deliver messages between computers attached to it. In this simple figure, computers are given unique identifying numbers, called addresses, which they use to designate who gets the information they are sending, much as we use telephone numbers or postal addresses.