HP HP-UX SNAplus2, Руководство администратора

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46 Chapter 1
SNA Terms and Concepts
Basic APPN Concepts
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 participate 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.