Downstream Connections

In hierarchical SNA environments, 3270 communications between SNA nodes is configured using SNA protocols. Usually those nodes are SNA Server computers and mainframes. A downstream system, however, is an SNA node that uses SNA Server as a PU gateway. To the downstream system, the SNA Server computer appears to be the actual mainframe providing the PUs and 3270 LUs (Figure 5.5).

Figure 5.5 Downstream connections using SNA Server.

A downstream system in this type of environment must be a PU 2 device—for instance, a cluster controller like an IBM 3745, or a client PC running a terminal emulator that emulates a PU 2 and acquires LU sessions from the SNA Server computer.

On the SNA Server computer, two connections are required to support downstream systems:

• A host connection between the server and the mainframe. This can be any standard physical connection method supported by the mainframe.

• A downstream connection between the server and the downstream system. This physical connection can be an 802.2/DLC, SDLC, or X.25 connection.

Once configured, SNA Server can manage the downstream LUs in a manner similar to other LUs, including assigning them to LU pools.