SNA Terms and Concepts
Accessing Subarea Networks from APPN NetworksAccessing Subarea Networks from APPN Networks
Although APPN networks do not require a host to control resources in the network, hosts often participate in APPN networks. APPN has been implemented on many host platforms, and allows the hosts to perform as network nodes in the APPN network while still providing an SSCP to control any old subarea SNA function.
Many SNA networks contain elements of both subarea SNA and APPN. The backbone of the network is built from network nodes that must bridge the gap between a dependent LU and the facilities on the host. Two additional services are required to achieve this:
•Dependent LU server (DLUS) on the host provides access to the old SSCP functions and interfaces to the APPN network.
•Dependent LU requester (DLUR) on a network node or end node provides a means of transporting session traffic from dependent LUs to a host through an APPN network. This function enables dependent LU sessions to take advantage of the more versatile routing functions provided by APPN.
This combination of DLUR and DLUS (generally known simply as DLUR) allows dependent LU traffic to be transported over the APPN backbone. Existing SNA applications that use dependent LUs can be retained without modification, while taking advantage of APPN's network management, dynamic resource location, and route selection capabilities. In this way, DLUR provides a useful migration path from subarea SNA to APPN.
The dependent LU does not need to reside on the node that provides the DLUR function. If the DLUR function is provided by a network node, the dependent LU can be on an adjacent network node, end node, or LEN node. If the DLUR function is provided by an end node, the dependent LU must be on the end node itself.
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