If the network is small this may be trivial as knowledge may exist for the location of all files and the addresses of all systems, however on a large network such as the Internet which has a claimed 25 million users this presents problems. A PAD is a device for converting the format of the data and generally the transmission speed as well of incoming and outgoing data. One of its uses is to convert from serial information for example from a dumb terminal to packets of data. This involves collecting the data from the dumb terminal at relatively low speed, putting the data in a packet, with additional information such as source and destination address dependent on the protocol involved, and then putting the data onto the network at the correct speed for the next destination in the link between the sender and receiver.
Some PADs operate in command mode when they are first accessed.
This may involve giving commands for their mode of operation or manually setting up the next link in the network. A large interconnected network such as the Internet needs a protocol to move data from one computer to the next. To achieve this it needs the addresses of the computers and where they are on the network hierarchy. This hierarchy is divided into domains or areas of allied users of the network such as countries, education or bradford. The sequence of these numbers is in the order of local computer first, then organisation, area of activity followed by country separated by full stops.