HP-UX SNAplus2 R7 General Information

SNA Networking
SNA and APPN
Physical Units (PUs)
The PU type 2 manages the data link to the host.
Logical Units
The node contains LUs that provide access points to the network for end users and terminal applications.
Communication sessions are maintained between these LUs and the LUs on the host.
LUs in subarea networks are dependent LUs; they depend on the support of the SSCP on the host. Before two
dependent LUs can establish and use a session, the SSCP must establish a session with the PU on the remote node
(the SSCP-PU session). The SSCP uses this session to control and monitor resources on the remote node.
Additionally, the SSCP establishes a session to the remote LU (the SSCP-LU session). The SSCP-LU session is
used to control and manage both the LU itself and the session between the host and remote LUs. The remote LU
uses the SSCP-LU session to request the SSCP to establish a session between the host and remote LUs (the LU-LU
session).
When a session is requested, the SSCP manages the host LU to establish the LU-LU session with the remote LU.
The LU on the host is called the “primary LU” (PLU); it initiates the LU-LU session and is also able to terminate
the session. The LU on the remote node is called the “secondary LU” (SLU); it responds to the session initiation
but is unable to initiate sessions in its own right.
1.1.2 Peer-to-Peer Connections
The description of the remote node in a subarea network assumes that the remote node is a type 2 node, which can
communicate only with a host system. In more modern subarea networks, however, pairs of type 2.1 nodes (such as
SNAplus2) can communicate without needing to send information through the host. Each node is configured with
information about the other node’s LUs; the nodes can then use a direct communications link to establish LU-LU
sessions.
1.2 SNA and APPN
As well as including subarea networks, many networks today also use APPN. A purely APPN network is
decentralized. It is made up of interconnected nodes that communicate as peers across local and wide-area networks.
A sample APPN network is shown in Figure 1–2,
Portion of a Sample APPN Network. This example includes a
network node in the APPN network that also belongs to a subarea network; that node can provide the APPN nodes
with access to host resources (alternatively, the host could be part of the APPN network).
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