Xerox 6180N FreeFlow® Print Server IBM® IPDS User Guide - Page 42

Using Xerox FreeFlow® Print Server IPS Manager host reflect only the pages printed. Therefore, if there is a failure, and the host retransmits pages that were not yet stacked, some of the pages saved during recovery may duplicate pages saved before the failure. Canceling IPDS Jobs Xerox FreeFlow® Print Server integrates the standard IPDS Cancel behavior with its own Cancel mechanism. To cancel a job, open Job Manager and select [Cancel] from the job menu. The print server generally assumes that all print job management functions are controlled from the printer. When a user invokes Cancel from the Job Manager dialog for PDLs other than IPDS, the print server simply terminates the selected job without informing the host. However, the IPDS protocol assumes that all print job management functions are controlled from the host. Consequently, when the user cancels a print job on a typical IPDS printer, the printer itself is not actually responsible for canceling the job. Instead, the printer requests the host to cancel the job. In response, the host stops sending additional data for the job, and instructs the printer to discard any pages that are not yet committed for printing. Once the printer reports that a page is committed, the host assumes that it cannot be discarded during a cancel operation. The IPDS host uses page counts returned by the printer to determine when uncommitted pages have been discarded, and when committed pages have completed printing. If the cancel request is honored by the host, most hosts transmit a page with an information message indicating the cancel key on the printer was pressed. The host then sends the end banner. The printer processes these final pages just as it would any other print data. The Xerox FreeFlow® Print Server job status indicates that the job ends normally after these final trailer pages are printed. Since the protocol and the PDL are independent for most data streams, Xerox FreeFlow® Print Server Cancel behavior does not cause a problem for most PDLs, other than IPDS. However, this operability is not suitable for IPDS. When an IPDS host detects that a job has stopped processing without completing, it assumes that the printer has failed. The host then tries to recover, by retransmitting data from the most recent checkpoint before the failure. If this were allowed to occur on the print server, it would defeat the attempt to end the job. The Xerox FreeFlow® Print Server reconciles the standard IPDS Cancel behavior with its own Cancel mechanism by recognizing when Cancel is invoked for an IPDS job, and ensuring that the 3-20 IPDS User Guide