APPC and APPN

A reasonable comparison between APPC and APPN is the difference between a person using the telephone and the services the telephone company offers.

APPC
For example, when you want to call someone, you look up the telephone number and then enter it. Both parties identify themselves and the exchange of information begins. When the conversation is finished, both parties say good bye and hang up. This protocol, although informal, is generally accepted and makes it much easier to communicate.

APPC provides the same functions and rules, only between application programs instead of people. An application program tells APPC with whom it needs a conversation. APPC starts a conversation between the programs so they can exchange data. When all the data has been exchanged, APPC provides a way for
the programs to end the conversation.

APPN
APPN provides networking functions similar to those provided by the telephone companies. After dialing a telephone number, the telephone network routes the call through trunks, switches, branches, and so on. To make the connection, the network takes into consideration what it knows about available routes and current problems. This happens without the caller understanding the details of the network. A person is able to talk on the telephone to another person no matter where they are or no matter how the call was routed.

APPN provides these functions for APPC applications and their data. It computes routes for APPC communication through the network, dynamically calculating which route is best. Like the telephone company, APPN's routing is done transparently. APPC applications cannot tell whether the communications partner in the APPN network is located in the same computer, one office away, or in another country. Similarly, if someone moves within the same city and takes their phone number, the phone network handles the change with no other user impact.