HP-UX SNAplus2 R7 Administration Guide

SNA Terms and Concepts
Basic APPN Concepts
2. If the destination LU is not located in the network node—but appears in its directory—the network node sends
a directed search request to the destination network node server to verify the location of the LU.
If the LU is not in the network node directory, the node initiates a search of the network by sending a broadcast
search to every adjacent network node.
3. Each node in turn propagates the broadcast and returns replies indicating success or failure.
For its future needs, a network node caches information obtained from successful broadcast searches.
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.
1.3.4 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 minimizes cycles and storage requirements for routing network layer packets
through intermediate nodes on a session route, and ANR enables you to reroute session traffic around route
failures or congestion.
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
network backbone topology—the nodes and transmission groups that can be used for routing sessions between
any pair of nodes in the network.
In addition, the topology database on each network node contains local information about transmission groups
from that network node to adjacent end nodes or LEN nodes.
The network node uses the topology database to calculate routes for sessions between LUs in its domain and
remote LUs, or to provide information to other network nodes to enable them to calculate session routes.
• Each end node has a local topology database with information about transmission groups from that end node to
adjacent nodes.
The end node provides this information to its network node server as part of the request to locate an LU and
calculate a session route to that LU. The network node server uses the end node topology information when
calculating the session route for the end node. The end node uses this information when establishing sessions
with predefined LUs on adjacent nodes. The end node topology database supports communication only with
adjacent nodes.
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