Open Systems Interconnection (OS1):

As there are many different protocols for LANs and WANs, communication between two different systems can be difficult. The International Standards Organisation. (ISO) has attempted with some success to solve the problem by the introduction of Open 'Systems Interconnection (OSI). OSI defines a set of procedures and standards grouped into seven layers, for the exchange of information between terminals and computers. 

In theory all systems which conform to OSI specifications should be able to interconnect, but the definitions are vague in certain areas and incompatibilities do arise. To overcome this, some countries have developed their own more detailed standards. 

Anyone involved in the purchase of equipment which is to be linked to a network should find out whether there are any industry specific GOSIPS (Government OSI Profiles) to which they must conform.