SNA Terms and Concepts

Basic APPN Concepts

An APPN end node can also receive (and respond to) LOCATE search requests from its network node server to search for, or confirm the continued presence of, specific LUs in the end node.

Each APPN end node registers its LUs with its network node server by sending the network node a registration message. In this way, the network node maintains current directory information for the end nodes in its domain. A LEN node cannot register LUs with its network node server. Therefore, all LUs on the LEN node must be predefined, through configuration, to the network node server.

Session Routing

APPN supports the following dynamic route selection procedures:

•For sessions with adjacent nodes, direct session routing.

•For sessions that traverse one or more intermediate nodes, one of the following:

•Intermediate session routing (ISR), which provides a route that does not change during the course of the session.

•High-Performance Routing (HPR), which includes the Rapid Transport Protocol (RTP) and automatic network routing (ANR) facilities. RTP enables you to reroute session traffic around route failures or congestion, and ANR minimizes cycles and storage requirements for routing network layer packets through intermediate nodes on a session route.

The APPN functions that provide dynamic route selection are known as topology and routing services (TRS).

Topology and Routing Services

Each APPN node includes a topology database that stores information about other APPN nodes and about transmission groups, which are sets of links between a specific pair of nodes. The contents of the database for a specific node depend on the node type:

•All network nodes share a copy of the network topology database. This shared database includes information about all other network nodes—including network IDs, CP names, and other node characteristics—and about the transmission groups between each pair of network nodes. This database provides a complete view of the

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