Besides providing information from the LP print queue, the lpd also provides information about the printer’s spool queue which contains all jobs that are processed (spooling, spooled or ripping). When a job is fully ripped, it will not be accessible and visible anymore via the LP interface. The print jobs are visible and can be managed in the list of scheduled jobs or the list of waiting jobs. These print jobs may also originate from other network interfaces than the LP interface, for example: socket.
LPD workflowThe printer only provides LP server functionality; no LP client functionality. The printer acts as a passive station that waits for requests from remote users or systems.
The use of lpd is bound to the use of the TCP/IP networking protocol stack, or, more specifically to the use of the TCP protocol. The printer-specific LPD server uses TCP port 515 for communication with the client system.