HP-UX SNAplus2 General Information (October 1998)

28 Chapter 2
Introducing SNAplus2
SNAplus2 Resources
Such a network is referred to as a shared-access
transport facility (SATF). However, to enable direct
communications between two nodes, you need to define
link stations between every pair of nodes; this results
in a very large number of link station definitions if you
want to enable any two nodes on the SATF to
communicate directly.
APPN enables you to set up this type of configuration
without having to define each link station explicitly, by
defining a connection network that represents the
SATF. For each node on the SATF, you define one or
more ports used to access the connection network.
Instead of defining a link station to each remote node,
you specify the name of a virtual routing node (VRN) as
part of the port definition. You can think of the VRN as
an imaginary node that represents all the other nodes
on the SATF. All nodes on the connection network use
the same VRN name.
When two nodes on the SATF need to communicate,
and both have a port defined with the same VRN name,
APPN can dynamically establish a direct connection
between them; no additional configuration is necessary.
Because the connection is direct and does not need to
go through any intermediate nodes, using a connection
network reduces traffic on the LAN and improves
performance.
Logical units
An LU is the node's point of contact with a user
program (3270 emulation program, RJE workstation,
APPC TP, CPI-C, or LUA application). LUs are divided
into the following categories:
• LU types 0–3 (sometimes referred to as “old LUs”)
are used to communicate with hosts using 3270
emulation, RJE, or LUA.
• LU type 6.2 is used to communicate with either
hosts or peer computers using APPC or CPI-C.
Type 0–3 LUs are referred to as “dependent LUs.” They
can support only one user session at a time. The user
session is controlled by the host program. Type 6.2 LUs