Reasons to use IPP-over-USB.
Removed wiki tip contrasting ipp-usb and ippusbxd.
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|The previous methods to set up driverless printing with CUPS are presented in the context of a network-only connection (wireless or ethernet). They require IPP for querying the capabilities of the printer so that the [[#generator1|PPD can be generated]]. They also need IPP to send option settings to the printer (as IPP attributes).
Fortunately, driverless printing is not confined to the network only, but also works in exactly the same way via USB using the IPP-over-USB daemon, DebianMan:ippusbxd. A recent AirPrint printer [[https://lists.cups.org/pipermail/cups/2018-September/074272.html|should support]] IPP-over-USB. The support situation regarding USB-only printers has yet to be clarified.
An [[DebianBug:961218|alternative IPP-over-USB daemon]] to ''ippusbxd'' is [[https://github.com/OpenPrinting/ipp-usb|ipp-usb]]. It is [[https://ftp.pwg.org/pub/pwg/liaison/openprinting/presentations/cups-filters-ippusbxd-2020.pdf|acknowledged]] as being more capable than ''ippusbxd''. [[https://download.opensuse.org/repositories/home:/pzz/Debian_10/|Debian packages]] are provided by the ''ipp-usb'' author.
|The previous methods to set up driverless printing with CUPS are presented in the context of a network-only connection (wireless or ethernet). They require the Internet Printing Protocol ([[PrintingGlossaryandIndex#ipp|IPP]]) for querying the capabilities of the printer so that the [[#generator1|PPD can be generated]]. They also need IPP to send option settings to the printer (as IPP attributes).
Fortunately, driverless printing is not confined to the network only, but also works in exactly the same way via USB using the IPP-over-USB daemon, DebianMan:ippusbxd. A recent AirPrint printer [[https://lists.cups.org/pipermail/cups/2018-September/074272.html|should support]] IPP-over-USB. The support situation regarding USB-only IPP printers has yet to be completely clarified.
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=== IPP-over-USB on buster using ippusbxd ===
The ''readme.md'' in ''/usr/share/doc/ippusbxd'' and the [[https://github.com/tillkamppeter/ippusbxd|ippusbxd website]] lay out the principles underlying the program's operation. We will look at implementing these principles in the context of exposing a printer on a dummy0 interface on a Debian 10 (buster) installation with [[#cupsbrowsed|cups-browsed]] running.
Set up the dummy0 interface:
ip link add dummy0 type dummy # Load the dummy module and create a dummy interface.
ip link set dummy0 up multicast on # Bring the interface up.
ip addr add 192.168.7.80/24 dev dummy0 # Give the interface an unused address.
Check the existence of the interface with
It is tedious to have to do this every time the computer is switched on, so a [[https://www.freedesktop.org/software/systemd/man/systemd.service.html|systemd service]] is indicated.
Create the file ''/usr/local/sbin/create-dummy0'':
IP=$(ip a | grep dummy0)
if [ -z "$IP" ]
ip link add dummy0 type dummy
ip link set dummy0 up multicast on
ip addr add 192.168.7.222/24 dev dummy0
else rmmod dummy
Now create ''/lib/systemd/system/dummy0.service'':
Description=Create a dummy interface for ippusbxd
The dummy0 service will be started when the machine is booted.
Thereafter, control whether it is operative with
systemctl stop dummy0.service
systemctl start dummy0.service
Having exposed the printer on the dummy0 interface it should be sufficient to connect a suitable printer to a computer, switch it on and issue the command
ippusbxd -i dummy0
to have a PPD generated by cups-browsed and a [[#tempq|permanent queue]] for the printer created.
ls -l /etc/cups/ppd
ipstat -l -e
The ippusbxd daemon is stopped and the print queue removed when the printer is turned off or disconnected from its USB cable.
Versions of cups-browsed greater than 1.14.0 have ''!LocalOnly'' as the default value of ''CreateIPPPrinterQueues''.
Consequently, no adjustments are needed to ''/etc/cups/cups-browsed.conf'' to have the printer visible locally.
See the cups-browsed [[https://github.com/OpenPrinting/cups-filters/blob/master/NEWS|changelog]] for the rationale.
Starting and stopping ippusbxd automatically to create and delete a print queue (rather than using the command line) becomes possible using the ippusbxd-provided systemd service file:
cp /usr/share/doc/ippusbxd/examples/ippusbxd@.service.dummy0 /etc/systemd/system/ippusbxd@.service
Power-on and power-off the printer (or attach or detach its USB cable) to have this auto-creation of a queue.
Share the queue on the local network using the [[PrintQueuesCUPS#webinterface|CUPS web interface]] or do
lpadmin <queue_name> -o printer-is-shared=true
You are free, of course, to [[https://lists.debian.org/debian-printing/2018/09/msg00129.html|follow upstream's advice]] and expose the printer on the localhost interface.
But, until [[DebianBug:909564|bug #909564]] is resolved, you will have to patch avahi yourself.
Note also that the scanning function of an [[PrintingGlossaryandIndex#mfd|MFD]] becomes [[https://lists.debian.org/debian-printing/2019/02/msg00014.html|unavailable]] when IPP-over-USB is used.
=== CUPS 2.2.4 and Driverless Printing (Short Version) ===
Without cups-browsed running.
Display local and remote queues and remote IPP printers:
lpstat -l -e
Query printer options:
lpoptions -p <destination>
lpoptions -p <destination> -l
lp -d <queue_or_printer> -o [option] <file>
Driverless printing with CUPS. Requires at least CUPS 2.2.2 and version 1.13.0 of cups-filters. Debian 10 (buster) and later installations meet both these conditions. The advice here could get your modern IPP printer going with little effort.
- The Concept of Driverless Printing
- Driverless Printing and Printers
- PDLs for Driverless Printing
- CUPS: PWG and Apple Raster
- The CUPS PPD Generator
- The cups-filters PPD Generator
- Creating a Driverless Print Queue with lpadmin (Short Version)
- Creating a Driverless Print Queue with lpadmin
- Creating a Driverless Print Queue with the CUPS Web Interface
- Creating a Driverless Print Queue with system-config-printer
- Creating a Driverless Print Queue with cups-browsed (Short Version)
- Creating a Driverless Print Queue with cups-browsed
- IPP-over-USB and avahi-daemon
- CUPS 2.2.4 and Driverless Printing
- CUPS 2.2.4 and the GTK Print Dialog
- CUPS and Driverless Printing: Miscellaneous
- See Also
The Concept of Driverless Printing
Driverless printing is targeted at the client side of printing and refers to the ability of the client device (computer, smartphone, tablet, laptop etc) to print without having to install any static capability files or drivers (manufacturer-specific or otherwise) on the client.
There exist a variety of methods for a client to submit a job to a printing system and print driverlessly:
Print directly from an application on the client.
Use a cloud service such as ?Google Cloud Print (GCP).
- Send the job as an email attachment to a special address.
- Web print. The document is uploaded from a web browser via a web form style interface.
This page is intended to highlight and explain driverless printing in the context of directly communicating with a printer using packages provided by Debian, so not all these methods will receive attention here. Furthermore, details for using iOS and Android mobile clients are not treated.
Remember that CUPS can act as a client or server. In its server capacity it can emulate an IPP Everywhere or Apple AirPrint printer. However, the focus here is on CUPS as a client connecting to a printer that offers driverless printing functions.
Driverless Printing and Printers
A traditional printing system based on CUPS, cups-filters and cups-browsed generally obtains information about printer features and capabilities from what is stored in a static capability file such as a PostScript Printer Description (PPD) file. This static file is stored on the client device (desktop computer, laptop, tablet etc) itself. If the PPD on the client requires the sending of a job using a non-standardised Page Description Language (PDL), a driver would be required for converting to the printer-specific PDL and that driver too would have to be on the client. A client that regularly connected to different printers would have to maintain static capability files and drivers for each printer.
This is not seen as an acceptable situation, especially for mobile clients, which may have limited storage for PPDs and drivers and that may lack resources, such as battery power. Neither is it deemed particularly realistic for a user to have to set up or reconfigure a laptop computer or mobile device for each printer that is encountered. This requires a level of expertise and a time and effort commitment that cannot be assumed to be possessed.
Then contrast the printer situation with the behaviour of other peripherals like keyboards, mice, cameras and USB mass storage. Plug such devices in and they are immediately and reliably there to be used. The objective is to have printing no less available when a printer is detected.
The response of printer manufacturers to the desire for driverless printing has been to enhance their printers in the following way:
The printer advertises its presence and capabilities with mDNS/DNS-SD (Bonjour). This is the discovery protocol; accessible printers can be identified and selected from the Bonjour broadcasts of the printer. The discovery protocol is also configured to obtain capability information from accessible printers to include in its broadcasts.
The client and printer communicate using the IPP protocol. This is the transport protocol; it can obtain capability information from the selected printer and transport data to it.
There is a common PDL that the client can send and that the printer will accept. The common PDL is based on what is obtained from the capability information for the selected printer. A driverless-enabled printer will offer at least one of Apple raster, PWG raster, PDF or PCLm as a PDL.
Note again that we are talking here about sending a job directly to a printer, not to a print queue being advertised by CUPS.
PDLs for Driverless Printing
Two raster formats, Apple raster and PWG raster, have been developed to implement driverless printing.
In the case of PWG raster the raster format was chosen because it is a simpler format than that of the high-level languages, which also require significant resources on the printer. Printer-embedded PostScript interpreters can be buggy and/or slow and PostScript also has the disadvantage that it makes interoperability between client and printer difficult because PostScript does not fit cleanly with the IPP and PWG models. Streaming was chosen to send a job to a printer rather than generating a file that is downloaded and then printed. This way large jobs don't take up too much memory or storage space on the printer and printing commences with minimum delay.
Apple raster has existed for a number of years and is used with Apple's AirPrint. Unfortunately, it is not officially documented but it is known that it and PWG raster are very similar. The MIME media type is image/urf.
CUPS: PWG and Apple Raster
The abilitity to create Apple raster files has been added to the existing PWG raster support in CUPS and made its appearence in CUPS 2.2.2; this enhancement was soon applied in version 1.13.0 of cups-filters and cups-browsed. Complete support for IPP Everywhere printers was already in Debian, so, with CUPS 2.2.2, AirPrint printers joined the class of printers that will work driverless with Debian.
With the incorporation of the two raster formats as a PDL in CUPS, IPP 2.0 to allow for querying the capabilities information from the printer and Bonjour/DNS-SD to find the printers in the network, Debian has everything needed for driverless printing to an IPP printer.
The processing of a job to create an Apple raster file is taken care of by CUPS' rastertopwg filter. The file produced by the filter is sent directly to the printer with IPP so no vendor-specific filters are involved. This opens up the possibility of avoiding the use of non-free drivers on the CUPS client or server used for printing.
The CUPS PPD Generator
To support driverless printing fully, CUPS has a PPD generator that will drive a traditional CUPS print queue. The generator queries the printer and creates the necessary PPD options and values needed to support Apple Raster, PWG Raster, JPEG, and PDF printing. A CUPS generated PPD uses the everywhere model and can be identified from the *PCFileName "ippeve.ppd" line in the PPD.
- The auto-generated PPD is consulted and a printer-ready file in the required PDL is produced.
- The print job is submitted to the printer with the data produced from the filters.
- If a PDF or JPEG file is being printed, it can be sent to the printer without any filtering; this is accounted for in the *cupsFilter2 lines that are added to the generated PPD.
A text file sent to an AirPrint or IPP Everywhere printer would often be filtered by CUPS and cups-filters to output an Apple or PWG raster file. If the printer has PDL support for MIME media type application/pdf, a PDF would be sent instead because a PDF is given the highest priority. Typical possibilities for the filter chain are:
->|--------------------------------------------> Printer text -> texttopdf -> pdftopdf -> PDF ->| gstoraster -> rastertopwg -> PWG raster ---> Printer ->| gstoraster -> rastertopwg -> Apple raster -> Printer
The GTK print dialog does not use CUPS to communicate directly with IPP printers. In addition, applications using the dialog always produce a PDF to send to the printer. If this is not an acceptable PDL for the printer, printing will not take place.
The cups-filters PPD Generator
This generator uses the driverless utility and is basically a copy of the PPD generator from CUPS that has been put into the libcupsfilters library. It is kept in sync with the original by incorporating any changes to the original. A libcupsfilters generated PPD can be identified from the *PCFileName "drvless.ppd" line in the PPD.
The cups-filters PPD generator is used by default with cups-browsed when a local print queue is auto-created for an IPP network printer.
Although the cups-filters PPD generator is kept closely in step with the CUPS one, the two are not identical:
The original PPD generator only supports PWG Raster, Apple Raster, PDF, and JPEG as printer PDLs. The cups-filters PPD generator also accepts (with lower priority) PostScript, PCL-XL, and PCL 5c/e for legacy printers.
The original PPD generator requires all printer capability, option, and choice information from the printer attributes IPP request. The cups-filters generator can, in some cases, fall back to using information from the Bonjour record or even hard-coded default values. This adds support for some legacy printers.
The cups-filters PPD generator is more flexible when it comes to adding support for PDLs. For example, consider PCLm: PCLm has nothing to do with PCL 5c/e and PCL-XL but is a streaming PDF-based, raster protocol (Printer Control Lanaguage-Mobile). It is mandated by the Wi-Fi Direct standard. Since version 1.17.0 of cups-filters, application/PCLm has been a supported MIME media type via the rastertopclm filter. CUPS itself will never support PCLm.
text -> texttopdf -> pdftopdf -> PDF -> gstoraster -> rastertopclm -> PCLm ---> Printer
- cups-filters has a policy of supporting new driverless printing technologies (see above), so its PPD generator is quite likely to accomodate developments.
Printers have bugs in their implementation of IPP. It is more likely that the cups-filters PPD generator will produce a fix than the CUPS version of the generator.
Creating a Driverless Print Queue with lpadmin (Short Version)
Obtain the URI of a printer:
Set up the print queue (uses the CUPS PPD generator):
lpadmin -p <print_queue_name> -v <URI> -E -m everywhere or lpadmin -p <print_queue_name> -v $(driverless) -E -m everywhere
Set up the print queue (uses the cups-filters PPD generator):
lpadmin -p <print_queue_name> -v <URI> -E -m driverless:<URI> or lpadmin -p <print_queue_name> -v $(driverless) -m driverless:$(driverless)
Creating a Driverless Print Queue with lpadmin
Some familiarity with a device-uri is assumed in this section.
With a single AirPrint printer on the network a partial output from /usr/sbin/lpinfo -v could be:
network dnssd://HP%20ENVY%204500%20series%20%5BFAFAC2%5D._ipp._tcp.local/?uuid=1c852a4d-b800-1f08-abcd-308d99fafac2 network socket://192.168.7.235:9100 network ipp://envy4500.local:631/ipp/print
The ENVY 4500 has also been discovered from the printer's Bonjour broadcasts using the dnssd and ipp backends. Both these URIs are equally stable and can be used for driverless printing, with a dnssd URI being preferred if the ipp URI is using a numeric IP address.
The device-uri for the printer can also be found with the ippfind or driverless utilities. ippfind locates DNS-SD advertised printers and queues. driverless (a cups-filters utility) lists IPP printers only.
ippfind (Shows IPP printers and print queues). ippfind -T 5 (Possibly more reliable). ippfind ! --txt printer-type (Show IPP printers only). driverless (To get the device-uri). driverless list (For the device-uri and printer metadata). driverless <device-uri> (Generate a PPD for the printer at <device-uri>).
A queue for driverless printing from a client is now set up with
lpadmin -p <print_queue_name> -v <device-uri> -E -m everywhere
The everywhere model causes the printer referred to by the -v option to be queried. A list of printer capabilities is returned and a PPD is automatically generated by CUPS for use by command line programs and applications.
It might be preferred to have the PPD generated by cups-filters, so first find the driver URI (driverless:ipp://...) with
and create the queue with
lpadmin -p <print_queue_name> -v <device-uri> -E -m <driver URI>
If the -v option is the URI of a queue on a remote CUPS server, this technique can create a driverless queue on the client for a remote non-raw queue. This is the method employed when CUPS sets up a temporary queue on a client.
Creating a Driverless Print Queue with the CUPS Web Interface
Some familiarity with the CUPS web interface is assumed in this section.
Open the web interface and choose Administration. Select Add Printer.
Your printer will be under the Discovered network Printers:, probably with more than one entry. Choose the entry that contains the word driverless and move on to Continue.
Check that Connection is ipp://... and continue to the next page.
Under Model there should be an option of driverless, cups-filters. This option uses the cups-filters PPD generator. Select and activate Add Printer.
Users who prefer to use the cups-filters PPD generator could be better off starting the above procedure by choosing Find New Printers from Administration.
Creating a Driverless Print Queue with system-config-printer
Some familiarity with system-config-printer is assumed in this section.
Start system-config-printer and choose Add followed by Network Printer.
Highlight the printer entry and choose the Driverless IPP entry.
Moving on has system-config-printer searching for a driver, auto-generating a PPD with the cups-filters generator and offering a screen to describe the printer. Choose Apply when done.
Creating a Driverless Print Queue with cups-browsed (Short Version)
Edit /etc/cups/cups-browsed.conf to uncomment the directive below:
systemctl restart cups-browsed
cups-browsed version 1.27.1 changed the default for CreateIPPPrinterQueues to All. Considering that cups-browsed is a recommended package for cups-daemon, this change should lead to making IPP printers immediately visible and available.
Creating a Driverless Print Queue with cups-browsed
This method leads to discovery of an AirPrint or IPP Everywhere printer and the automatic set up of a print queue with lpadmin. A PPD for the queue is created using the cups-filters PPD generator. The CUPS PPD generator may be used instead; see the UseCUPSGeneratedPPDs directive in the cups-browsed.conf manual. The PPD is used to display printer options for command line programs and in applications. There are just two operations a user has to carry out:
Edit /etc/cups/cups-browsed.conf to set the CreateIPPPrinterQueues to All or Driverless and restart cups-browsed.
CreateIPPPrinterQueues All CreateIPPPrinterQueues Driverless systemctl restart cups-browsed
cups-browsed version 1.27.1 changed the default for CreateIPPPrinterQueues to All. Considering that cups-browsed is a recommended package for cups-daemon, this change should lead to making IPP printers immediately visible and available.
- Check the existence of the queue and its options with
lpstat -t lpoptions -p <queue_name> -l
The device-uri should begin ipp://.... The queue name is got from lpstat -t.
- The queue persists provided the printer is switched on and cups-browsed is running.
With the CreateIPPPrinterQueues directive cups-browsed sets up a queue for a remote printer. With NewIPPPrinterQueuesShared Yes in /etc/cups/cups-browsed uncommented the printer is shared with other machines on the local network.
cups-browsed supports also a kind of legacy driverless printing. This means that some other common PDLs such as PostScript, PCL-XL, and PCL 5c/e are supported and also older IPP versions (1.x). Note that missing capability information can be replaced with default values and that implementations of these languages in the printers are often not reliable, so that, in contrast to official driverless printing, printing often does not work perfectly. Note that the PCL of HP inkjets does not work and therefore cups-browsed does not auto-create queues for this PDL.
The previous methods to set up driverless printing with CUPS are presented in the context of a network-only connection (wireless or ethernet). They require the Internet Printing Protocol (IPP) for querying the capabilities of the printer so that the PPD can be generated. They also need IPP to send option settings to the printer (as IPP attributes).
Fortunately, driverless printing is not confined to the network only, but also works in exactly the same way via USB using the IPP-over-USB daemon, ippusbxd. A recent AirPrint printer should support IPP-over-USB. The support situation regarding USB-only IPP printers has yet to be completely clarified.
The IPP USB specification describes an extension to USB that defines a standard for making IPP available over a USB Print class interface, and is intended to allow USB connected devices to achieve functional parity with network connected devices using IPP. In other words, whatever can be done over a network connection may also be done over a USB connection. A USB connected printer is therefore seen as a network printer when IPP-over-USB is used.
- A local network does not exist.
- The local network is regarded as operating unreliably.
- The computer is USB-only.
- The MFD or printer is USB-only.
- The user sees setting up a network connection as an extra complication to avoid.
- The MFD or printer is rarely used. When it is, it is simpler and easier just to plug it into a USB port.
- Sending confidential documents via USB is mandated as being more secure than sending them over a network.
Whether a printer can use IPP-over-USB may be determined by executing lsusb -v|less and searching for the line containing bInterfaceClass.*7. A bInterfaceProtocol line should be found a few lines below this one.
A value of 4 for bInterfaceProtocol indicates a USB IPP device.
IPP-over-USB and avahi-daemon
An important idea underlying IPP-over-USB is to expose the local USB-connected printer only to localhost and not to the entire local network. This condition is fulfilled by using at least version 0.8-1 of avahi-daemon. For printing, it is sufficient to follow these steps:
- Plug a switched-on IPP-over-USB printer into a USB port.
Start the daemon as root with the ippusbxd command.
An alternative to the third step is to employ the provided systemd service file to get automatic starting and stopping of the daemon when the printer is plugged in and out:
cp /usr/share/doc/ippusbxd/examples/ippusbxd@.service /etc/systemd/system/ systemctl daemon-reload
CUPS 2.2.4 and Driverless Printing
CUPS' ability directly to browse the DNS-SD (Bonjour) broadcasts of remote print queues and printers, previously absent, was introduced in CUPS 2.2.4. This means that a system with CUPS 2.2.4 or later, such as Debian 10 (Buster), will display remote queues and IPP printers with lpstat -e and in the print dialogs of some applications without cups-browsed (needed on Debian 8 (Jessie) and Debian 9 (stretch) for remote queue management being on the system. No action on the part of the user is required.
Essentially, CUPS uses its CupsGetDests and CupsEnumDests functions to discover shared queues and IPP printers that can be printed to on the local network and makes them available for display in an application. Whether or not the application displays them depends on the chosen application. Printing to an enumerated entry leads to the formation of a temporary queue.
lpstat -a shows only queues of the local CUPS daemon and not DNS-SD advertised queues or printers. lpstat -e and lpstat -l -e additionally enumerate queues and printers that can be accessed on the network.
The libreoffice print dialog behaves the same way as the Qt dialog.
the GTK print dialog has its own way of dealing with a network printer.
CUPS 2.2.4 and the GTK Print Dialog
The print dialog of GTK applications such as firefox and evince does not function in the same way as the Qt and Libreoffice dialogs. It obtains queue and printer information directly from DNS-SD broadcasts and not through CUPS, so it has no knowledge of what CUPS 2.2.4 and later are capable of doing.
In addition, using the GTK print dialog always results in the production of a PDF. Printers that that do not have PDF as an acceptable PDL will not process such a print job.
This leads to the following problem.
Although the GTK dialog is aware of IPP printers on the local network via DNS-SD, it does not support printing to them and will possibly display a destination print and Rejecting Jobs for an IPP printer.
One solution is to check that cups-browsed is on the system and, in cups-browsed.conf, have cups-browsed create permanent, local queues for remote queues and printers (rather than the CUPS temporary queues that Qt applications and LibreOffice use). This technique is described above.
Because the GTK dialog might already show local queues and remote queues on CUPS servers it is likely that, with this first solution, only the additional entry for the remote printer is wanted. So alter cups-browsed.conf to have
Managing queues and printers in the GTK dialog with the first solution also leads to the other dialogs adopting cups-browsed as the queue and printer management application.
CUPS and Driverless Printing: Miscellaneous
AirPrint and IPP Everywhere printers generally have a web interface for administration. It is accessed in a web browser with
http://<IP_address or host name of the printer>
The hostname can be obtained from the output of avahi-browse (see below). Make sure that IPP support and Bonjour broadcasting on the printer are enabled. The configuration options will probably be accessed under a Networking link and it could be that activating AirPrint is sufficient to activate both services.
avahi-browse -rt _ipp._tcp
Bonjour-advertised IPP printers are now identified. Look for entries beginning URF=... and pdl=... . If URF=... exists and pdl=... contains image/urf you have an AirPrint printer.
For an HP Envy 4502:
For a Brother MFC-J650DW:
URF = SRGB24,W8,CP1,IS1,MT1-8-11,OB9,PQ4-5,RS300,OFU0,V1.2,DM3 pdl = application/octet-stream,application/vnd.brother-hbp,image/pwg-raster,image/urf,image/jpeg
The pdl entry for the MFC-J650DW contains an additional image/pwg-raster. This printer will accept and print PWG raster files. It could be an IPP Everywhere printer, but that all depends on whether it fulfills all the criteria necessary for the manufacturer to self-certify it with the Printer Working Group (PWG). However, the presence of image/urf indicates the printer IPP implementation is sufficient for driverless printing to be used with CUPS.
Driverless printing usually allows only adjustments on printing as they are thought out by the printer manufacturers. A printer driver like Gutenprint allows a lot fine tuning that goes far beyond a manufacturer's possibilities. This driver may suit photo enthusiasts more than a driverless solution. Having said that, the quality of text or images printed with rastertopwg is yet to be challenged.
Purchasing a printer with Apple raster and/or PWG raster capability means looking at the box containing the printer and printer brochures and manuals. AirPrint has been going for some time so it is usually fairly prominent as a feature in the literature. IPP Everywhere is much newer and may not be advertised. However, PWG raster could be on a ?GCP-enabled (GCP Ready) printer. If PDF is not a PDL for the printer it is obliged to have PWG raster. With PDF as a language it might have PWG raster as a fallback PDL.
Didier 'OdyX' Raboud <email@example.com> for guiding and supporting CUPS 2.2.2, cups-filters and cups-browsed through the experimental archive and into unstable. Till Kamppeter <firstname.lastname@example.org> for his integration of cups-filters and cups-browsed with CUPS 2.2.2. Michael R. Sweet <email@example.com> for developing the rastertopwg filter to support Apple raster.