Now, in addition to the LPR/LPD protocol, some of the printer vendors' products, like HP JetDirect, Lexmark Marknet, IBM NP Series, and AXIS also support bi-directional TCP/IP application protocols. HP calls this protocol for TCP/IP Direct Mode printing. Other vendors call this protocol Reverse Telnet, Direct Sockets Interface or TCP/IP Stream protocol. We are using the term PrintDirect protocol.
Hewlett-Packard has developed a special Job Control Language for printing called Printer Job Language (PJL). Using PJL, it is possible to switch printer language, monitor printer status, request printer model and configuration, change default or job printer configuration parameters, and obtain control panel messages.
As most printer vendors support PCL nowadays, they also support PJL to some extent. PJL has become a de facto standard for printer job control. The PrintDirect support is based on PJL. Using the PJL protocol, it has been possible to implement the same kind of recovery and end-user control for TCP/IP-attached printers that we have for VTAM- and PSF-attached printers.
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