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	<title>An Overview of the Common UNIX Printing System</title>
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	<td><img src='images/cups-large.gif' width='103'
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	<td><h1 align='right'>An Overview of the<br />
	Common UNIX Printing System,<br />
	Version 1.2</h1>

	<p align='right'>July 3, 2004<br />
	Michael Sweet, Easy Software Products<br />
	Copyright 1998-2004, All Rights Reserved.</p>
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<pre>
New Outline:

New Features:

1. Networking
   a. IPv6
        i. Next-generation Internet support
       ii. ????
   b. Domain sockets
        i. Enhanced performance under load for local clients.
       ii. Authentication without passwords on platforms that support it.
   c. CUPS browsing updates
        i. "Delete" bit for printers
       ii. "lease-time" for printers so that clients and servers don't need
          the same browse timeout/interval settings
      iii. Additional attributes/default options for network-wide defaults
       iv. Network default printer
        v. Ability to control send and receive protocols independently
   d. Rendevous support
   e. LDAP support
   f. Per-printer sharing

2. IPP Support
   a. Notifications
   b. Document object
   c. Send-URI, Print-URI
   d. Other stuff?
   e. Add/delete device operations

3. Scheduler
   a. Backchannel support
   b. Port monitor support
   c. Device monitor
      i. Dynamic device discovery/management
   d. All errors include a localized message.
   e. Fine-grain policies, server default + per-printer
   f. UTF-8 throughout

4. Web Interface
   a. cupsd.conf interface
   b. Move-Job
   c. Export printers to windows
   d. Per-printer sharing controls
   e. Per-printer access control lists 
   f. Policy stuff

5. I18N
   a. Support for ... character sets
   b. All commands and messages are localized
   c. Character set transcoding
   d. ... , and Japanese localizations

6. Drivers
   a. New HP-RTL driver.

</pre>

<p>This whitepaper describes the Common UNIX Printing
System<sup>TM</sup> (CUPS<sup>TM</sup>), a portable and
extensible printing system for Linux<sup>&reg;</sup>,
MacOS<sup>&reg;</sup> X, UNIX<sup>&reg;</sup>. CUPS is developed
by <a href='http://www.easysw.com'>Easy Software Products</a>, a
software firm located in Hollywood, Maryland that has been
selling commercial software for UNIX since 1993 through more
than 40 distributors serving over 80 countries worldwide.</p>

<p>CUPS is used by Apple to provide printing on MacOS X and is
the defacto-standard for Linux. Additional information on CUPS
is available on the World Wide Web at the following URL:</p>

<pre>
    <a href='http://www.cups.org/'>http://www.cups.org/</a>
</pre>


<h2>Background</h2>

<p>Printing within UNIX has historically been done using one of
two printing systems - the Berkeley Line Printer Daemon (LPD)
[RFC1179] and the AT&amp;T Line Printer system. These printing
systems were designed in the 70's for printing text to line
printers; vendors have since added varying levels of support for
other types of printers.</p>

<p>Replacements for these printing systems have emerged [LPRng,
Palladin, PLP], however none of the replacements change the
fundamental capabilities of these systems.</p>

<p>Over the years several attempts at developing a standard
printing interface have been made, including the draft POSIX
Printing standard developed by the Institute of Electrical and
Electronics Engineers, Inc. (IEEE) [IEEE-1387.4] and Internet
Printing Protocol (IPP) developed by the Internet Engineering
Task Force (IETF) through the Printer Working Group (PWG)
[IETF-IPP]. The POSIX printing standard defines a common set of
command-line tools as well as a C interface for printer
administration and print jobs, but has been shelved by the
IEEE.</p>

<p>The Internet Printing Protocol defines extensions to the
HyperText Transport Protocol 1.1 [RFC2616] to provide support
for remote printing services. IPP/1.1 was accepted by the IETF
as a proposed standard in ??? of ???. Unlike POSIX Printing, IPP
enjoys widespread industry support and has become the standard
network printing solution for all operating systems.</p>

<p>CUPS uses IPP/1.1 to provide a complete, modern printing
system for UNIX that can be extended to support new printers,
devices, and protocols while providing compatibility with
existing UNIX applications. CUPS is free software provided under
the terms of the GNU General Public License and GNU Library
General Public License.</p>

<h2>History</h2>

<p>The first production release of CUPS (based on IPP/1.0) was
released in October of 1999. Version 1.1 of CUPS was released in
August of 2002 ???? and added support for IPP/1.1.</p>

<p>CUPS 1.2 is based on IPP/1.1 and adds many of the functional
enhancements that have been requested by our users. As with CUPS
1.1, CUPS 1.2 will be followed by patch releases that address
any problems found with the software. New features will be put
in the 1.3 release to follow.</p>

<h2>Design Overview</h2>

<p>Like most printing systems, CUPS is designed around a central
print scheduling process that dispatches print jobs, processes
administrative commands, provides printer status information to
local and remote programs, and informs users as needed. Figure 1
shows the basic organization of CUPS.</p>

<p align='center'><img src='images/cups-block-diagram.gif'
width='470' height='170' alt='CUPS Block Diagram'/><br />
<i>Figure 1 - CUPS Block Diagram</i></p>

<h3>Scheduler</h3>

<p>The scheduler is a HTTP/1.1 server application that handles
HTTP requests. Besides handling printer requests via IPP POST
requests, the scheduler also acts as a full-featured web server
for documentation, status monitoring, and administration.</p>

<p>The scheduler also manages a list of available printers on
the LAN and dispatches print jobs as needed using the
appropriate filters and backends.</p>

<h3>Configuration Files</h3>

<p>The configuration files consist of:</p>

<ul>

	<li>The HTTP server configuration file.</li>

	<li>Printer and class definition files.</li>

	<li>MIME type and conversion rule files.</li>

	<li>PostScript Printer Description (PPD) files.</li>

</ul>

<p>The HTTP server configuration file is purposely similar to
the Apache server configuration file and defines all of the
access control properties for the server.</p>

<p>The printer and class definition files list the available
printer queues and classes. Printer classes are collections of
printers. Jobs sent to a class are forwarded to the first
available printer in the class, round-robin fashion.</p>

<p>The MIME type files list the supported MIME types
(text/plain, application/postscript, etc.) and "magic' rules for
automatically detecting the format of a file.  These are used by
the HTTP server to determine the <tt>Content-Type</tt> field for
<tt>GET</tt> and <tt>HEAD</tt> requests and by the IPP request
handler to determine the file type when a <tt>Print-Job</tt> or
<tt>Send-File</tt> request is received with a
<tt>document-format</tt> of
<tt>application/octet-stream</tt>.</p>

<p>The MIME conversion rule files list the available filters.
The filters are used when a job is dispatched so that an
application can send a convenient file format to the printing
system which then converts the document into a printable format
as needed. Each filter has a relative cost associated with it,
and the filtering algorithm chooses the set of filters that will
convert the file to the needed format with the lowest total
"cost".</p>

<p>The PPD files describe the capabilities of all printers, not
just PostScript printers. There is one PPD file for each
printer. PPD files for non-PostScript printers define additional
filters through <tt>cupsFilter</tt> attributes to support
printer drivers.</p>

<h3>CUPS API</h3>

<p>The CUPS API contains CUPS-specific convenience functions for
queuing print jobs, getting printer information, accessing
resources via HTTP and IPP, and manipulating PPD files. Unlike
the rest of CUPS, the CUPS API is provided under the terms of
the GNU LGPL so it may be used by non-GPL applications.</p>

<h3>Berkeley and System V Commands</h3>

<p>CUPS provides the System V and Berkeley command-line
interfaces for submitting jobs and checking the printer status.
The <tt>lpstat</tt> and <tt>lpc status</tt> commands
also show network printers ("printer@server") when printer
browsing is enabled.</p>

<p>The System V administation commands are supplied for managing
printers and classes. The Berkeley printer administration tool
(<tt>lpc</tt>) is only supported in a "read-only' mode to
check the current status of the printer queues and
scheduler.</p>

<h3>Filters</h3>

<p>A filter program reads from the standard input or from a file
if a filename is supplied. All filters must support a common set
of options including printer name, job ID, username, job title,
number of copies, and job options. All output is sent to the
standard output.</p>

<p>Filters are provided for many file formats and include image
file and PostScript raster filters that support non-PostScript
printers. Multiple filters are run in parallel to produce the
required output format.</p>

<p>The PostScript raster filter is based on the ESP Ghostscript
core. Instead of using the Ghostscript printer drivers, the CUPS
filter uses a generic CUPS raster printer driver and
CUPS-compliant front-end to support any kind of raster printer.
This allows the same printer driver filter to be used for
printing raster data from any filter.</p>

<pre>Talk about Apple's use of CUPS...</pre>

<h3>CUPS Imaging</h3>

<p>The CUPS Imaging library provides functions for managing
large images, doing colorspace conversion and color management,
scaling images for printing, and managing raster page streams.
It is used by the CUPS image file filters, the PostScript RIP,
and all raster printers drivers.</p>

<h3>Backends</h3>

<p>A backend program is a special filter that sends print data
to a device or network connection. Backends for parallel,
serial, USB, LPD, IPP, and AppSocket (JetDirect) connections are
provided in CUPS 1.2.</p>

<p>SAMBA version 2.0.6 and higher includes a SMB backend
(<tt>smbspool(1)</tt>) that can be used for printing to
Windows.</p>

<h2>Network Printing</h2>

<p>Traditionally, network printing has been one of the hardest
things to get working under UNIX. One reason is because each
vendor added their own extensions to the LPD protocol (the
previous standard for network printing), making cross-platform
printing difficult if not impossible.</p>

<p>Another reason is that you have to administer every network
printer on every client machine. In some cases you can "clone'
the printer configuration from a "master' client to each of the
others, but even that can be time-consuming and error-prone.
Something better is needed.</p>

<p>CUPS provides "printer browsing", which allows clients to
automatically see and use printers from any server on a LAN.
This means that you only need to configure the server and the
clients will automatically see the printers and classes on
it.</p>

<p>In addition, CUPS can automatically merge multiple identical
network printers into "implicit classes". This allows clients to
send jobs to the implicit class and have them print on the first
available printer or server. In addition, failsafe and
load-balancing functions are enabled simply by defining the same
printer on multiple servers!</p>

<h2>New Features in CUPS 1.2</h2>

<p>CUPS 1.2 includes many new features and capabilities:

<ol>

	<li><a href='#BACKENDS'>Backends</a>

	<li><a href='#BANNERS'>Banner Page Support</a>

	<li><a href='#DIGEST'>Digest Authentication</a>

	<li><a href='#DIRSVC'>Directory Services</a>

	<li><a href='#FHS2'>Directory Structure Changes</a>

	<li><a href='#DOCOS'>Documentation</a>

	<li><a href='#DRIVERS'>Drivers</a>

	<li><a href='#FILTERS'>Filters</a>

	<li><a href='#IPP'>IPP Support</a>

	<li><a href='#PERSISTENCE'>Job Persistence</a>

	<li><a href='#LPD'>LPD Client Support</a>

	<li><a href='#USEROPTS'>User-Defined Printers and Options</a>

	<li><a href='#WEB'>Web Administration Interface</a>

</ol>

<h3><a name='BACKENDS'>1. Backends</a></h3>

<p>CUPS 1.2 implements a new backend interface for retrieving a
list of available devices for CUPS clients. This allows
administration interfaces to query the CUPS scheduler for a list
of available devices, automatically configure printers if the
device identification information is available, and present the
user with a list of available devices rather than relying on the
user to know what devices are configured on the system.</p>

<p>The new release also includes a backend for USB printers
under *BSD and Linux. Support for USB under Solaris 8 will be
provided in a subsequent patch release.</p>

<h3><a name='BANNERS'>2. Banner Page Support</a></h3>

<p>CUPS 1.2 includes support for banner pages at the beginning
and end of a job. Banner pages may be of any file format and
support variable substitution for job titles, usernames, etc.
Default banner pages are associated with each printer and can be
overridden with command-line options by the user.</p>

<h3><a name='DIGEST'>3. Digest Authentication</a></h3>

<p>Digest authentication provides a more secure method of
authenticating access to the printing system. Unlike Basic
authentication, Digest authentication does not send passwords
"in the clear' so it is more difficult to gain unauthorized
access to your system.</p>

<p>CUPS 1.2 implements Digest authentication using a special MD5
password file instead of the UNIX password file. This file is
managed using the new <tt>lppasswd</tt> command.</p>

<h3><a name='DIRSVC'>4. Directory Services</a></h3>

<p>CUPS 1.2 adds new directory service ("printer browsing")
features to make using CUPS on large LANs and WANs easier. You
can now poll a remote server for printer information and relay
it to the LAN as well as restrict what printer information is
processed (e.g. to "hide" servers, domains, or networks that you
don't want to see.)</p>

<h3><a name='FHS2'>5. Directory Structure Changes</a></h3>

<p>CUPS 1.2 now uses a directory structure that complies with
the Filesystem Hierarchy Standard (FHS), version 2.0. This
should make integration into existing Linux and *BSD
distributions a lot easier.</p>

<h3><a name='DOCOS'>6. Documentation</a></h3>

<p>The CUPS 1.2 documentation has gone through many revisions,
including a completely rewritten administrators manual, a new
programmers manual, and an IPP implementation reference
manual.</p>

<h3><a name='DRIVERS'>7. Drivers</a></h3>

<p>CUPS 1.2 includes drivers for EPSON dot-matrix and inkjet
printers. As with the HP PCL drivers, the EPSON drivers don't
necessarily provide the best possible output for each printer
but should provide adequate printing quality for general
day-to-day printing.</p>

<h3><a name='FILTERS'>8. Filters</a></h3>

<p>CUPS 1.2 includes new image, PostScript, PDF, and text
filters. The image filters have been upgraded to support Windows
BMP and Alias PIX files.</p>

<p>The PostScript filter is now based off ESP Ghostscript. The
new filter provides much better performance with
higher-resolution printers and supports all Level 3 PostScript
language features.</p>

<p>The new PDF filter is based off the excellent Xpdf software
from Derek Noonburg and supports automatic page scaling. The new
filter is a faster, smaller, more reliable replacement for the
GNU Ghostscript PDF filtering that was used in CUPS 1.0.</p>

<p>The new text filter now supports bidirectional text and can
embed fonts as needed.</p>

<h3><a name='IPP'>9. IPP Support</a></h3>

<p>Probably the least visible portion of CUPS is the IPP
support. CUPS 1.1 implements all of the required IPP/1.1
operations and attributes and most of the optional ones. The
optional Create-Job and Send-File operations are now
implemented, allowing for better System V printing system
compatibility (one job ID per <tt>lp</tt> command) and support
for banner pages.</p>

<h3><a name='PERSISTENCE'>10. Job Persistence</a></h3>

<p>CUPS 1.2 supports job persistence. This means that jobs are
preserved even after a reboot, a feature that was sorely missing
from CUPS 1.0.</p>

<p>In addition, CUPS 1.2 allows you to keep job information
after the job has printed. The basic post-job persistence mode
provides a job history (number of pages printed, time job was
printed, etc.) but does not preserve the actual job files. This
can be changed to discard all information after a job is printed
or keep the job files after printing so you can reprint a job at
some later time.</p>

<h3><a name='LPD'>11. LPD Client Support</a></h3>

<p>By popular request, CUPS 1.2 supports LPD-based clients using
a new mini-daemon that handles LPD requests and passes them on
to the main server.</p>

<h3><a name='USEROPTS'>12. User-Defined Printers and Options</a></h3>

<p>CUPS 1.2 includes support for user-defined printers and
options via a new <tt>lpoptions</tt> command. User-defined
printers are special instances of the available printers (e.g.
"printer/instance" or "printer@server/instance") that can have
their own default options such as media size, resolution, and so
forth. The <tt>lpoptions</tt> command can also be used to set a
different default printer queue.</p>

<h3><a name='WEB'>13. Web Administration Interface</a></h3>

<p>CUPS 1.0 provided a simple class, job, and printer monitoring
interface for web browsers. CUPS 1.2 replaces this interface
with an enhanced administration interface that allows you to
add, modify, delete, configure, and control classes, jobs, and
printers.</p>

<h2>Software Using CUPS</h2>

<p>A lot has happened since CUPS 1.0 came out, and many software
packages are supporting CUPS. We have contributed code to the
SAMBA team to support CUPS, and parts of that are already
available in SAMBA 2.0.6 and 2.0.7. With any luck the final
pieces that provide a complete integration with SAMBA will be
available in the next release of SAMBA.</p>

<p>Two graphical interfaces have appeared on the scene that use
CUPS as well. The KUPS project provides a KDE-based interface
for CUPS and can be found at:</p>

<pre>
    <a href='http://kups.sourceforge.net'>http://kups.sourceforge.net</a>
</pre>

<p>The X Printing Panel (XPP) project provides a graphical
printing panel for CUPS and can be found at:</p>

<pre>
    <a href='http://www.phy.uni-bayreuth.de/till/xpp'>http://www.phy.uni-bayreuth.de/till/xpp/</a>
</pre>

<p>Numerous other filters, drivers, tutorials, etc. have been
made available on the CUPS Links web page, available at:</p>

<pre>
    <a href='http://www.cups.org/links.php'>http://www.cups.org/links.php</a>
</pre>

<p>Finally, our own ESP Print Pro software uses CUPS to provide
drivers for thousands of printers and can be found at:</p>

<pre>
    <a href='http://www.easysw.com/printpro'>http://www.easysw.com/printpro</a>
</pre>

<h2>Operating Systems Using CUPS</h2>

<p>One of our goals has always been to get as many UNIX/Linux
distributions using CUPS as possible. Debian is currently
providing CUPS as part of its stable distribution, and many
other distributions are considering it in their next
releases.</p>

<h2>Summary</h2>

<p>The Common UNIX Printing System provides a modern printing
interface for UNIX applications that is both flexible and
user-friendly. The software provides System V and Berkeley
compatible command-line interfaces to ensure compatibility with
existing applications. CUPS 1.2 adds many new features that make
it an even better choice for printing under UNIX.</p>

<h2>Who to Contact</h2>

<p>For more information on CUPS please contact us at:

<pre>
    Attn: CUPS Information
    Easy Software Products
    44141 Airport View Drive Suite 204
    Hollywood, Maryland 20636-3142 USA

    +1.301.373.9600

    <a href='mailto:cups-info@cups.org'>cups-info@cups.org</a>
</pre>

<h2>References</h2>

<dl>

	<dt>IEEE-1387.4</dt>

	<dd>System Administration - Part 4: Printing Interfaces
	(draft)</dd>

	<dt><a href='http://www.pwg.org/ipp/index.html'>IETF-IPP</a></dt>

	<dd>Internet Printing Protocol/1.1</dd>

	<dt><a href='http://www.astart.com/lprng.html'>LPRng</a></dt>

	<dd>An enhanced, extended, and portable implementation
	of the Berkeley LPR print spooler functionality</dd>

	<dt>Palladin</dt>

	<dd>A printing system developed at the Massachussetts
	Institute of Technology</dd>

	<dt><a href='http://www-usa.iona.com//hyplan/jmason/plp.html'>PLP</a></dt>

	<dd>The Portable Line Printer spooler system</dd>

	<dt><a href='http://www.ietf.org/rfc/rfc1179.txt'>RFC1179</a></dt>

	<dd>Line Printer Daemon Protocol</dd>

	<dt><a href='http://www.ietf.org/rfc/rfc2046.txt'>RFC2046</a></dt>

	<dd>Multipurpose Internet Mail Extensions (MIME) Part
	Two: Media Types</dd>

	<dt><a href='http://www.ietf.org/rfc/rfc2616.txt'>RFC2616</a></dt>

	<dd>Hypertext Transfer Protocol -- HTTP/1.1</dd>

</dl>

<h2>Trademarks</h2>

<p>The Common UNIX Printing System, CUPS, and the CUPS logo are
the trademark property of Easy Software Products. All other
trademarks are the property of their respective owners.</p>

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