Direct connectivity

Direct connectivity enables session traffic to travel directly between two nodes without the need for an APPN network node to route the session. In general, sessions between directly connected nodes can exchange data more quickly than sessions for which data is routed through a network node. For nodes on a shared-access transport facility (SATF) - for example, for nodes on a LAN segment or IP network using Enterprise Extender as shown in Figure 1 - efficiency would be increased by defining links between every pair of nodes in your network. However, this can be a difficult task - the number of link stations is n x (n-1), where n is the number of nodes in the network.

An APPN network on a LAN segment or IP network using Enterprise Extender is shown in Figure 1.

Figure 1. APPN Network Using a Shared-Access Transport Facility

If Node EN1 has a link definition for each of the links in the network, it can establish a direct link to any node. The link definitions needed to support direct links between Node EN1 and every other node in the APPN network are shown in Figure 2. For a network that includes five other nodes, Node EN1 needs five link definitions:

  • EN1 to NNA
  • EN1 to EN2
  • EN1 to EN3
  • EN1 to EN4
  • EN1 to EN5
Figure 2. Definitions Needed for Direct Links from Node EN1 to Every Node in an APPN Network

If all of the nodes in the network are to support direct links to every other node, a total of 30 link definitions are needed on the six nodes in this example. In general, the number of link definitions can be calculated as n x (n-1), where n is the number of nodes in the network. In a larger network, the number of link definitions quickly becomes unwieldy. Increasing the number of link definitions between network nodes also increases the number of TDUs flowing through the network, which can degrade network performance.

APPN connection networks provide a solution to this problem.