HP-UX SNAplus2 R7 Administration Guide

SNA Terms and Concepts
Basic APPN Concepts
the network node provides services. Because an APPN network node acts as the network entry point for end and
LEN nodes in its domain, the network node is also referred to as the network node server for those nodes.
A network node provides the following services:
• LU-LU session services for its local LUs
• Directory searches and route selection for all LUs in its domain
• Intermediate session routing (see Figure 1–8,
Network Topology Database in Network Nodes)
• Routing for management services (MS) data, such as alerts, between a served end node and an MS focal point
APPN End Nodes
An APPN end node is a type 2.1 node that serves as an end point in an APPN network. It maintains directory
information only for local resources. An APPN end node can independently establish sessions between local LUs
and LUs on adjacent nodes. For sessions with LUs on nodes not directly connected to the end node, an end node
requests routing and directory information from its network node server using CP-CP sessions.
APPN end nodes can register their local LUs with their network node server. This capability means the network
operator at the network node server does not have to predefine the names of all LUs on the attached end nodes to
which the network node provides services.
An APPN end node can be attached to multiple network nodes (see EN3 in Figure 1–4, Portion of a Sample APPN
Network), but it can have CP-CP sessions active with only one network node at a time—its network node server.
The other network nodes can be used only to provide intermediate routing for the end node or as substitute network
node servers if the main network node server becomes unavailable.
An APPN end node can also have a direct link to another APPN end node or a LEN node, but CP-CP sessions are
never established between two end nodes.
LEN Nodes
A low-entry networking node (LEN node) is a type 2.1 node that uses independent LU 6.2 protocols, but does not
support CP-CP sessions. It can be connected to an APPN network node or end node, but does not support APPN
functions.
An APPN network node can provide routing services for an attached LEN node, enabling the LEN node to partici-
pate in an APPN network without requiring link stations to be defined between the LEN node and all of the nodes
in the APPN network.
LUs in the APPN network with which the LEN node may want to establish sessions must be defined to the LEN
node as if they 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 node in the network
where the LU actually resides. LUs on the LEN node must be predefined to the network node that serves the LEN
node. LU resources on LEN nodes (unlike those on end nodes) cannot be registered on the network node server.
An APPN end node cannot provide intermediate routing. When a LEN node’s only link is to an APPN end node,
the LEN node can communicate only with LUs on the end node through the direct link between the two nodes.
1.3.2 APPN Control Point
An APPN control point is a set of functions that manages node resources and supports both physical unit and
logical unit functions on a type 2.1 node. An APPN CP directs local node functions (such as activating and
deactivating adapters and links), provides directory and topology information, and assists LUs in session initiation
and termination.
Adjacent nodes in an APPN network use a pair of parallel CP-CP sessions to exchange network information and to
provide directory and route selection services. Both sessions of a given pair must be active in order for the partner
CPs to begin and sustain their interactions. Different node types use these sessions differently, as follows:
• Two parallel CP-CP sessions are established between an APPN network node and each adjacent network node.
These CP-CP sessions are used to exchange directory, topology, and management services data.
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