The Air Force puts out a bid and IBM wins. The Navy bid is won by Unisys. Then the President decides to invade Grenada and the armed forces discover that their computers cannot talk to each other. However, larger networks based on long distances and phone lines are more volatile. In Europe, the national phone companies traditionally standardize on X.25.
New technologies arise and become obsolete within a few years.
With cable TV and phone companies competing to build the National Information Superhighway, no single standard can govern citywide, nationwide, or worldwide communications. Furthermore, machines connected to any of these networks can communicate to any other network through gateways supplied by the network vendor. Each technology has its own convention for transmitting messages between two machines within the same network. In an SNA network, every machine has Logical Units with their own network address. IPX all have a scheme for assigning numbers to each local network and to each workstation attached to the network.