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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, enabling the hosts to perform as network nodes in the APPN network; at the same time, the host provides an SSCP to control subarea SNA functions.
Many SNA networks reflect their history, containing 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.
The following additional services are required to achieve this:
On the host, DLUS provides access to the old SSCP functions and acts as an interface to the APPN network.
On a network node or end node, DLUR provides passthrough function to the host for dependent LUs.
This combination of DLUR and DLUS (generally known simply as DLUR) enables 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.
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