Explanation of "WaitOnPrinter"

NDPSGW.NLM dated 27JUL2007 and later includes a feature named WaitOnPrinter.
This feature is known to resolve the LPR Communication Failed issue when the Printer Agent is able to send print jobs to a printer, but fails on large jobs (either large in disk size or large number of pages).

The"WaitOnPrinter" setting affects the way NDPSGW (the gateway) communicates with the printer. The LPR Communication problem addressed by this feature is a condition where the printer's buffer is full. When the printer's buffer is full, it replies to the Gateway that its TCP Windows size is 0 (or "I'm full"). When the gateway receives the packet with window size of zero, it retries for 5 minutes. If the printer is full for 5 minutes, then the connection is reset by the gateway and the job is sent again. From the end user perspective, the job is repeatedly partially printed.

The wait on printer feature allows the administrator to specify the number of minutes the gateway should wait on the printer before resetting the connection. During this period of time the gateway will periodically send a very small packet to the printer requesting status.  If the printer does not respond positively within the specified period the gateway will rest the connection.  Setting this number to 20 minutes is usually sufficient for slow, lower-end printers.