PMDF System Manager's Guide

If a channel is capable of master-mode operations (as specified with the master keyword), such operations may be initiated either by a periodic service job or on demand as delivery is needed. The keyword periodic inhibits initiation of delivery jobs on demand for the channel it is associated with regardless of priority. The immediate keyword, which is the default, specifies that jobs should run on demand for messages of appropriate urgency; what appropriate urgency means is controlled via the keywords described below.

• immurgent enables immediate delivery processing on messages with a priority setting of urgent. Messages with a lower priority will wait for periodic processing.
• immnormal enables immediate delivery for messages with normal or urgent priority. immnormal is the default.
• immnonurgent enables immediate delivery for urgent, normal, and non-urgent messages.

Thus the default behavior (immediate immnormal) enables immediate processing for all but nonurgent or lower priority messages.

Delivery via periodic service jobs is always possible unless the channel is marked with the slave keyword. Channels capable of master-mode operation are periodically checked for pending messages by periodic service jobs. These jobs runs at fixed intervals --- usually every four hours, though you may change this interval, if desired. On OpenVMS systems, the interval is changed by setting the system logical PMDF_POST_INTERVAL; if used, PMDF_POST_INTERVAL should be set to a string of the form DD HH:MM:SS (e.g., "0 00:30:00"). On UNIX systems, the interval is determined in the crontab entry for the post job; see the appropriate edition of the PMDF Installation Guide.

Not all channels may need service at the same intervals. For example, a channel may see little traffic and be expensive to service (i.e., it costs money to place a connecting phone call on a master-only periodic PhoneNet channel). Servicing such a channel at longer intervals than that of a single period between periodic jobs may lower the cost of operation without significantly affecting the quality of service. In another case, one particular channel may see very heavy traffic and may require frequent service, while other channels need servicing much less often. In this situation it may be appropriate to service the heavily used channel more often than any other.

The period keyword can be used to control how often a channel is serviced. This keyword must be followed by an integer value N. The channel is then serviced by every Nth service job. The default value of the period keyword is 1, which means that every periodic service job will check the channel for pending messages.