The Network Printing Alliance has unveiled a software specification intended to define a standard protocol for communications between distributed printers and personal computer users on a local network. Called the Network Printing Alliance Protocol, NPAP, it is claimed to provide a base set of printer-to-host specification commands to exchange status, control and configuration information. It also establishes implementation guidelines for software developers and printer manufacturers intending to support it. The group claims that the Protocol is independent of page description language, printer technology and the device’s communication interface. It further says it can be incorporated in phases, ranging from basic to extended functionality. The final specification was made available at the NetWorld trade show in Boston but Alliance members say that work will continue on refining it and developing future specifications. Conforming products are expected on the market this year. The Alliance is claiming that its new specification is more effective than others currently available, notably Hewlett-Packard Co’s Printer Job Language. Indeed, in the white paper that accompanies the specification’s publication, the Alliance draws a direct comparison between its Printing Alliance Protocol and the Hewlett-Packard language. It contends that while Hewlett-Packard’s protocol is designed to deal only with print jobs, NPAP can also handle all of the capabilities of an imaging device in a way that enables multi-tasking and assumes – but does not require – a complex networking environment. Hewlett-Packard seems to have been caught on the hop by the announcement; a spokeswoman for the company would not say whether the it would eventually adopt the NPAP, but did comment that Hewlett-Packard’s protocol is currently the only de facto standard for networked printing. She would also not comment on whether Hewlett-Packard would widen the scope of its protocol to counter the criticisms of it put forward in the Alliance white paper.
Coalition
The Network Printing Alliance is a coalition of printing companies founded in April 1991 by Insight Development, Intel Corp, Lexmark International Inc and Texas Instruments Inc. In addition to these, it now has more than 50 participating members – including Eastman Kodak Co, Unisys Corp, NEC Corp and IBM Corp – and says that participation is open to all. Network Printing Alliance Protocol basic packet types are:
Request Device Characteristics: provides basic printer information such as Page Description Languages, printer speed, colour capabilities and printing resolution.
Request Interpreter Characteristics: gives information about the available page description languages, their features (for example the available fonts). It can also show if a page description interpreter can fully use the printer’s capabilities.
Job Control: indicates start and end of a job; also used to query job information.
Request Device Status: used by the host computer to determine printer status (such as whether paper trays are full or empty); other Printer statistics are also given.
Printer Configuration Control: sets or reads printer configuration such as error checking, alert status and packet size.
Device Status Alert: sent by the printer to the host. Contains unsolicited data on changes in printer status (such as input jams, job complete or service required).
Interpreter Message Alerts: Packets containing unsolicited messages from a printer’s page description language interpreter sent back to the host. Enabled or disabled via Printer Configuration Control command.
