SNA Terms and Concepts

Basic APPN Concepts

reside on the LEN node's network node server. The LEN node establishes sessions with LUs on its network node server. The network node routes the session through the APPN network to the proper node in the network.

A LEN node can also use wildcards in a directory entry to specify multiple partner LUs that can be accessed over a specific link.

•An APPN end node maintains a directory that includes its own LUs. It can also be configured to store directory entries for partner LUs in adjacent nodes. This enables local LUs to establish peer-to-peer sessions with those LUs without using APPN functions.

If a resource is not locally defined to an end node or currently cannot be reached by the end node, the end node sends a request to its network node server asking it to search the APPN network for the resource.

•An APPN network node maintains a directory that includes its own LUs and the end node and LEN node LUs in its domain. An end node can dynamically register its LUs with its network node server. (LEN nodes cannot register LUs with a network node server, so LEN node LUs must be configured on their network node server.) A network node directory can also contain cached entries for LUs that are not in the network node's domain, but whose location has been determined through a previous search.

Network nodes provide directory services to other nodes in two ways:

•Searching for remote resources in response to session requests from end nodes or LEN nodes

•Responding positively to directory search requests from other network nodes when a named resource is found in the local directory

LEN Node Directories. An example of a LEN node directory is shown in Figure 1-5, “LEN Node Directory.” Since LEN nodes do not support CP-CP sessions, the directory for Node LEN1 must contain all the LUs with which it communicates. The directory for Node LEN1 identifies its network node server (NNA) as the location for any LUs that are not on an adjacent peer end node. Since Node LEN1 can access the LUs only through Node NNA, it defines the CP on the network node as the “owning CP” of all the LUs, including LUs located on the end nodes.

Chapter 1

49