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62 Chapter 1
SNA Terms and Concepts
Basic APPN Concepts
Figure 1-11 Definitions Needed for Direct Links Using a Virtual Node
To support direct links between any two end nodes in the APPN network,
a total of ten link definitions is required. (Each end node needs two link
definitions: one to a network node server and one to the virtual node.)
Compared to the direct connectivity requirements for an APPN network
that does not use a connection network (see Figure 1-10), you can have a
much smaller number of link definitions (10 instead of 30 in this
example). In a larger network, the difference in definition requirements
becomes even more substantial.
A session between LUs on two nodes in the connection network is
established as follows:
1. Each end node first establishes CP-CP sessions with its network node
server. (If two end nodes have different network node servers, those
network nodes must have a link that supports CP-CP sessions.)
2. End nodes also report their VRN links and local address information
to the network node server. The local address information can be a
service access point (SAP) address and a medium access control
(MAC) address.