Digital devices have the ability to communicate one with another. When two or more are connected together, the set of devices is said to be 'a system'.

The ability of one device to understand another implies that a messaging protocol exists to define common syntax and meaning of words in messages. This is usually a machine language, often in the form a predefined byte-coded symbols.

In addition, there will exist a communication protocol which enables a device to identify the source of a received message and to direct its own messages to the intended destination. This protocol will also have rules for packaging the message in such a way that the communication hardware can carry the message and transmit it efficiently.

Two frameworks are evolving:

Neither are based on the functions of a device itself with the result that products developed for either system are 'bound' to either a particular communications system or to a particular operating system. Since these technologies are still evolving, device manufacturers have held back from commitment to either framework.