AirPrint is a brand-name owned by Apple which describes a proprietary technology to make printers easily discoverable and useable by iPhone and iPad (iOS) clients. Printer vendors can go through a certification process with Apple to get their devices tagged as AirPrint-compatible. AirPrint technology bases itself on 4 major corner stones: mDNS, DNS-SD, IPP and an Apple-specific PDL (Page Description Language) called URF:
The clients send their print job data (and get feedback from the devices about job progress) via
IPP(Internet Printing Protocol). IPP is an IETF standard created by the PWG (Printer Working Group) and described in a series of RFCs, starting with RFC2910 and RFC2911.
There is no known, publicly and officially available information about the specifics of URF. It is a proprietary Apple file format. However, it seems to be very similar to the PWG-Raster format defined by the PWG with some Apple-specific extensions added. Unless a devices includes in its mDNS announcements the following two TXT keys:
iOS clients will not show it as AirPrint-capable.
AirPrint clients show a very limited set of print options, however, and only then, if the target printer supports them. Users can select:
- Number of copies to be printed.
- Page ranges to be printed.
- Color or black+white output (for color printers only).
- Two- or one-sided printing (for printers supporting two-sided).
- Paper size (for printers who have different sizes loaded in different trays).
Whereas very early AirPrint-capable apps had as the only PDL they could generate for print jobs, more recently most of them can also generate PDF. Whenever an AirPrint service announcement includes in its TXT entry
pdl="application/pdf,image/urf,..." the clients do indeed sent PDF as the print job format. However, if the
image/urf part is skipped, the clients will no longer recognize the device as an AirPrint-capable one.