Advanced peer to peer networking, is a group of protocols that are used to set up program to program communication, within IBM’s SNA Network. In APPN, among the group of computers, one acts as the network controller, so that the peer programs on the other computers can communicate with each other using network routing.
Once of the biggest advantages of APPN is that since the network control is distributed, terminal failures can be isolated, which is something that you cannot do in a hierarchical system. The flexibility of APPN also allows it to be used within any kind of network topology.
APPN most often, works with Advanced Program-to-Program Communication (APPC) software that dictates how programs will communicate with each other through two interfaces: one that responds to requests from application programs that want to communicate and one that exchanges information with communications hardware.