In the mid-1980s, SNA subarea networking was the dominant networking protocol used for data processing. Its robustness, management tools, and predictable response time attracted many organizations to SNA, and they used SNA in their mission-critical applications. The major drawback of SNA subarea network was the requirement to provide static definitions for most SNA resources.

At the same time, intelligent workstations were proliferating. The hierarchical nature of subarea SNA was not suitable for these workstations, which required peer connections and dynamic definitions.

Another criticism users of SNA subarea networking had addressed session continuity. Although subarea networks use alternate routes, failure of hardware or software components along the route causes the sessions along the route to fail. Although sessions can be reestablished over alternate routes, the process affects the end-user's session availability.

IBM developed APPN to reduce to a minimum the task of defining SNA resources and routes. The definitions are limited to the local APPN node where one defines the name assigned to the resources, the attachment (LAN or WAN) to be used, and the node type.

APPN learns the network topology and the location of the various nodes in the local network, and searches for resources in the network and adjacent networks. When establishing a session, APPN selects the best available route between the session partners.

Some APPN nodes implement intermediate session routing. Nodes that support intermediate session routing are used along the session path to route session data between the two session endpoints.

The initial APPN implementation did not address the session continuity problem, and when organizations started to implement APPN they realized that the performance of the intermediate session routing function was poor. IBM went "back to the drawing board" and developed an extension to APPN, called high performance routing (HPR).

HPR introduced the rapid transport protocol (RTP) and automatic network routing (ANR). These two added functions address session continuity and the performance issue of intermediate session routing. With HPR, a session is switched to an available route without disrupting the session. The end user is not aware that a failure took place along the path of the session.