When an alert is generated (by either SNA Transport or an HP 3000 operator), it is stored in an MPE message file named nodename.PUB.SYS (where nodename is the name of the configured SNA node the alert is to be sent to).
SNA Transport continually checks the message files for alerts. When it finds an alert in a message file, it sends the alert to the remote system and waits for an acknowledgement that the remote system received it. When it receives the acknowledgement, SNA Transport purges the alert from the message file (but not before then). This method ensures that all alerts are sent to the remote system. Note that this method also might cause an alert to be sent to the remote system twice. That could happen if an alert is sent but a link failure occurs before the acknowledgement is received from the remote system. Since the acknowledgement was not received, the alert was not purged from the message file. So, when SNA Transport comes back up, it will find the alert still in the message file, and send it again.
