HP-UX SNAplus2 R7 Administration Guide

SNA Terms and Concepts
Basic APPN Concepts
Figure 1–11 Definitions Needed for Direct Links Using a Virtual Node
End Node 1 (EN1)
Virtual Node 1 (VN)
Link Definitions Needed for Node 1 EN1:
EN1 to NNA
EN1 to VN
End Node 5 (EN5)
End Node 4 (EN4)
End Node 3 (EN3)
End Node 2 (EN2)
Network Node A (NNA)
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,
Definitions Needed for Direct Links from Node EN1 to Every Node in an APPN Network), 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.
3. The server normally selects the direct link between two end nodes as the optimal route for the LU-LU session.
It provides the node with the primary LU the information it needs to establish a dynamic link to the node with
the partner LU.
4. The end nodes can then establish an LU-LU session without the need for intermediate session routing.
1.3.5 Branch Extender
As described in the previous sections, network nodes in an APPN network need to maintain topology information
(about the location of other nodes in the network and the communications links between them), and to forward this
information around the network when the topology changes. As the network grows in size, the amount of stored
information and topology-related network traffic can become large and difficult to manage.
It is possible to avoid these problems by separating the network into subnetworks, so that each node only needs to
maintain topology information about the nodes in its own subnetwork. However, this results in increased network
traffic when trying to locate resources in other subnetworks.
The Branch Extender feature of APPN, illustrated in Figure 1–12, Branch Extender, provides a solution to these
problems.
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