Dynamic Port Allocation

The spool manager task, and the AST task, post the dynamic port allocation ECB when a request element is placed on the DMTASTSQ queue anchor. This queue contains start request elements for dial-out links that have not been assigned a dial-out port. These links may be started because a file has been enqueued on the link or they are eligible for an auto-start. They may also be started if their RETRY interval has expired.

In each case, the AST task obtains exclusive use of the PORT table and searches for an available dial-out port to assign to the link. If no dial-out ports are available, AST marks the link in the dial-queue state until a dial-out port is freed.

If an operator or an exec issues a START command for an auto-dial link that requires a dynamically-allocated port, the AST task does not process the request. Rather, DMTLAXEP attempts to allocate a port. If no ports are available, the START command fails and the command originator is notified. The link is not placed in the dial-queue state and the AST task does not attempt to start the link when a port is freed.