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  11         <TD><H1 ALIGN="RIGHT">An Overview of the<BR>
  12         Common UNIX Printing System,<BR>
  13         Version 1.1</H1>
  14
  15         <P ALIGN="RIGHT">July 10, 2000<BR>
  16         Michael Sweet, Easy Software Products<BR>
  17         Copyright 1998-2001, All Rights Reserved.</P>
  18         </TD>
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  21
  22 <P>This whitepaper describes the Common UNIX Printing
  23 System<SUP>TM</SUP> ("CUPS<SUP>TM</SUP>"), a portable and extensible
  24 printing system for UNIX<SUP>&reg;</SUP>. CUPS is being developed by
  25 <A HREF="http://www.easysw.com">Easy Software Products</A>, a software
  26 firm located in Hollywood, Maryland that has been selling commercial
  27 software for UNIX since 1993 through more than 40 distributors serving
  28 over 80 countries worldwide.
  29
  30 <P>Additional information on CUPS is available on the World Wide Web at
  31 "<A HREF="http://www.cups.org">http://www.cups.org</A>".
  32
  33 <H2>Background</H2>
  34
  35 <P>Printing within UNIX has historically been done using one of two
  36 printing systems - the Berkeley Line Printer Daemon ("LPD") [RFC1179]
  37 and the AT&amp;T Line Printer system. These printing systems were
  38 designed in the 70's for printing text to line printers; vendors have
  39 since added varying levels of support for other types of printers.
  40
  41 <P>Replacements for these printing systems have emerged [LPRng,
  42 Palladin, PLP], however none of the replacements change the fundamental
  43 capabilities of these systems.
  44
  45 <P>Over the last few years several attempts at developing a standard
  46 printing interface have been made, including the draft POSIX Printing
  47 standard developed by the Institute of Electrical and Electronics
  48 Engineers, Inc. ("IEEE") [IEEE-1387.4] and Internet Printing Protocol
  49 ("IPP") developed by the Internet Engineering Task Force ("IETF")
  50 through the Printer Working Group ("PWG") [IETF-IPP]. The POSIX
  51 printing standard defines a common set of command-line tools as well as
  52 a C interface for printer administration and print jobs, but has been
  53 shelved by the IEEE.
  54
  55 <P>The Internet Printing Protocol defines extensions to the HyperText
  56 Transport Protocol 1.1 [RFC2616] to provide support for remote printing
  57 services. IPP/1.0 was accepted by the IETF as an experimental Request
  58 For Comments [RFC] document in October of 1999. Since then the Printer
  59 Working Group has developed an updated set of specifications for
  60 IPP/1.1 which have been accepted by the IETF and are awaiting
  61 publication as proposed standards. Unlike POSIX Printing, IPP enjoys
  62 widespread industry support and is poised to become the standard
  63 network printing solution for all operating systems.
  64
  65 <P>CUPS uses IPP/1.1 to provide a complete, modern printing system for
  66 UNIX that can be extended to support new printers, devices, and
  67 protocols while providing compatibility with existing UNIX
  68 applications. CUPS is free software provided under the terms of the
  69 GNU General Public License and GNU Library General Public License.
  70
  71 <H2>History</H2>
  72
  73 <P>The first production release of CUPS (based on IPP/1.0) was released
  74 in October of 1999. Since then, we have released several patch updates
  75 to the original CUPS 1.0 release that addressed security, portability,
  76 and bugs found, but no new functionality was added to improve the
  77 stability of the CUPS code.
  78
  79 <P>CUPS 1.1 is based on IPP/1.1 and adds many of the functional
  80 enhancements that have been requested by our users. As with 1.0, CUPS
  81 1.1 will be followed by patch releases that address any problems found
  82 with the software but add no new features.
  83
  84 <H2>Design Overview</H2>
  85
  86 <P>Like most printing systems, CUPS is designed around a central print
  87 scheduling process that dispatches print jobs, processes administrative
  88 commands, provides printer status information to local and remote
  89 programs, and informs users as needed. Figure 1 shows the basic
  90 organization of CUPS.
  91
  92 <CENTER><IMG SRC="images/cups-block-diagram.gif" WIDTH="470" HEIGHT="170"></CENTER>
  93 <P ALIGN="CENTER">Figure 1 - CUPS Block Diagram</P>
  94
  95 <H3>Scheduler</H3>
  96
  97 <P>The scheduler is a HTTP/1.1 server application that handles HTTP
  98 requests. Besides handling printer requests via IPP POST requests, the
  99 scheduler also acts as a full-featured web server for documentation,
 100 status monitoring, and administration.
 101
 102 <P>The scheduler also manages a list of available printers on the LAN
 103 and dispatches print jobs as needed using the appropriate filters and
 104 backends.
 105
 106 <H3>Configuration Files</H3>
 107
 108 The configuration files consist of:
 109
 110 <UL>
 111
 112         <LI>The HTTP server configuration file.
 113
 114         <LI>Printer and class definition files.
 115
 116         <LI>MIME type and conversion rule files.
 117
 118         <LI>PostScript Printer Description ("PPD") files.
 119
 120 </UL>
 121
 122 <P>The HTTP server configuration file is purposely similar to the
 123 Apache server configuration file and defines all of the access control
 124 properties for the server.
 125
 126 <P>The printer and class definition files list the available printer
 127 queues and classes. Printer classes are collections of printers. Jobs
 128 sent to a class are forwarded to the first available printer in the
 129 class, round-robin fashion.
 130
 131 <P>The MIME type files list the supported MIME types (text/plain,
 132 application/postscript, etc.) and "magic" rules for automatically
 133 detecting the format of a file.  These are used by the HTTP server to
 134 determine the <I>Content-Type</I> field for <I>GET</I> and <I>HEAD</I>
 135 requests and by the IPP request handler to determine the file type
 136 when a <I>Print-Job</I> or <I>Send-File</I> request is received with a
 137 <I>document-format</I> of <I>application/octet-stream</I>.
 138
 139 <P>The MIME conversion rule files list the available filters. The
 140 filters are used when a job is dispatched so that an application can
 141 send a convenient file format to the printing system which then
 142 converts the document into a printable format as needed. Each filter
 143 has a relative cost associated with it, and the filtering algorithm
 144 chooses the set of filters that will convert the file to the needed
 145 format with the lowest total "cost".
 146
 147 <P>The PPD files describe the capabilities of all printers, not just
 148 PostScript printers. There is one PPD file for each printer. PPD files
 149 for non-PostScript printers define additional filters through
 150 <I>cupsFilter</I> attributes to support printer drivers.
 151
 152 <H3>CUPS API</H3>
 153
 154 <P>The CUPS API contains CUPS-specific convenience functions for queuing
 155 print jobs, getting printer information, accessing resources via HTTP
 156 and IPP, and manipulating PPD files. Unlike the rest of CUPS, the CUPS
 157 API is provided under the terms of the GNU LGPL so it may be used by
 158 non-GPL applications.
 159
 160 <H3>Berkeley and System V Commands</H3>
 161
 162 <P>CUPS provides the System V and Berkeley command-line interfaces for
 163 submitting jobs and checking the printer status. The
 164 <CODE>lpstat</CODE> and <CODE>lpc status</CODE> commands also show
 165 network printers ("printer@server") when printer browsing is enabled.
 166
 167 <P>The System V administation commands are supplied for managing
 168 printers and classes. The Berkeley printer administration tool
 169 (<CODE>lpc</CODE>) is only supported in a "read-only" mode to check the
 170 current status of the printer queues and scheduler.
 171
 172 <H3>Filters</H3>
 173
 174 <P>A filter program reads from the standard input or from a file if a
 175 filename is supplied. All filters must support a common set of options
 176 including printer name, job ID, username, job title, number of copies,
 177 and job options. All output is sent to the standard output.
 178
 179 <P>Filters are provided for many file formats and include image file
 180 and PostScript raster filters that support non-PostScript printers. Multiple
 181 filters are run in parallel to produce the required output format.
 182
 183 <P>The PostScript raster filter is based on the GNU Ghostscript 5.50
 184 core. Instead of using the Ghostscript printer drivers and front-end,
 185 the CUPS filter uses a generic raster printer driver and CUPS-compliant
 186 front-end to support any kind of raster printer. This allows the same
 187 printer driver filter to be used for printing raster data from any
 188 filter.
 189
 190 <H3>CUPS Imaging</H3>
 191
 192 <P>The CUPS Imaging library provides functions for managing large
 193 images, doing colorspace conversion and color management, scaling
 194 images for printing, and managing raster page streams. It is used by
 195 the CUPS image file filters, the PostScript RIP, and all raster
 196 printers drivers.
 197
 198 <H3>Backends</H3>
 199
 200 <P>A backend program is a special filter that sends print data to a
 201 device or network connection. Backends for parallel, serial, USB, LPD, IPP,
 202 and AppSocket (JetDirect) connections are provided in CUPS 1.1.
 203
 204 <P>SAMBA version 2.0.6 and higher includes a SMB backend
 205 (<CODE>smbspool(1)</CODE>) that can be used with CUPS 1.0 or 1.1 for
 206 printing to Windows.
 207
 208 <H2>Network Printing</H2>
 209
 210 <P>Traditionally, network printing has been one of the hardest things to
 211 get working under UNIX. One reason is because each vendor added their
 212 own extensions to the LPD protocol (the previous standard for network
 213 printing), making cross-platform printing difficult if not impossible.
 214
 215 <P>Another reason is that you have to administer every network printer
 216 on every client machine. In some cases you can "clone" the printer
 217 configuration from a "master" client to each of the others, but even
 218 that can be time-consuming and error-prone. Something better is needed.
 219
 220 <P>CUPS provides "printer browsing", which allows clients to
 221 automatically see and use printers from any server on a LAN. This means
 222 that you only need to configure the server and the clients will
 223 automatically see the printers and classes on it.
 224
 225 <P>In addition, CUPS can automatically merge multiple identical network
 226 printers into "implicit classes". This allows clients to send jobs to
 227 the implicit class and have them print on the first available printer
 228 or server. In addition, failsafe and load-balancing functions are
 229 enabled simply by defining the same printer on multiple servers!
 230
 231 <H2>New Features in CUPS 1.1</H2>
 232
 233 <P>CUPS 1.1 includes many new features and capabilities:
 234
 235 <OL>
 236
 237         <LI><A HREF="#BACKENDS">Backends</A>
 238
 239         <LI><A HREF="#BANNERS">Banner Page Support</A>
 240
 241         <LI><A HREF="#DIGEST">Digest Authentication</A>
 242
 243         <LI><A HREF="#DIRSVC">Directory Services</A>
 244
 245         <LI><A HREF="#FHS2">Directory Structure Changes</A>
 246
 247         <LI><A HREF="#DOCOS">Documentation</A>
 248
 249         <LI><A HREF="#DRIVERS">Drivers</A>
 250
 251         <LI><A HREF="#FILTERS">Filters</A>
 252
 253         <LI><A HREF="#IPP">IPP Support</A>
 254
 255         <LI><A HREF="#PERSISTENCE">Job Persistence</A>
 256
 257         <LI><A HREF="#LPD">LPD Client Support</A>
 258
 259         <LI><A HREF="#USEROPTS">User-Defined Printers and Options</A>
 260
 261         <LI><A HREF="#WEB">Web Administration Interface</A>
 262
 263 </OL>
 264
 265 <H3><A NAME="BACKENDS">1. Backends</A></H3>
 266
 267 <P>CUPS 1.1 implements a new backend interface for retrieving a list of
 268 available devices for CUPS clients. This allows administration
 269 interfaces to query the CUPS scheduler for a list of available devices,
 270 automatically configure printers if the device identification
 271 information is available, and present the user with a list of available
 272 devices rather than relying on the user to know what devices are
 273 configured on the system.
 274
 275 <P>The new release also includes a backend for USB printers under
 276 *BSD and Linux. Support for USB under Solaris 8 will be provided in
 277 a subsequent patch release.
 278
 279 <H3><A NAME="BANNERS">2. Banner Page Support</A></H3>
 280
 281 <P>CUPS 1.1 includes support for banner pages at the beginning and end
 282 of a job. Banner pages may be of any file format and support variable
 283 substitution for job titles, usernames, etc. Default banner pages are
 284 associated with each printer and can be overridden with command-line
 285 options by the user.
 286
 287 <H3><A NAME="DIGEST">3. Digest Authentication</A></H3>
 288
 289 <P>Digest authentication provides a more secure method of authenticating
 290 access to the printing system. Unlike Basic authentication, Digest
 291 authentication does not send passwords "in the clear" so it is more
 292 difficult to gain unauthorized access to your system.
 293
 294 <P>CUPS 1.1 implements Digest authentication using a special MD5
 295 password file instead of the UNIX password file. This file is managed
 296 using the new <CODE>lppasswd</CODE> command.
 297
 298 <H3><A NAME="DIRSVC">4. Directory Services</A></H3>
 299
 300 <P>CUPS 1.1 adds new directory service ("printer browsing") features to
 301 make using CUPS on large LANs and WANs easier. You can now poll a
 302 remote server for printer information and relay it to the LAN as well
 303 as restrict what printer information is processed (e.g. to "hide"
 304 servers, domains, or networks that you don't want to see.)
 305
 306 <H3><A NAME="FHS2">5. Directory Structure Changes</A></H3>
 307
 308 <P>CUPS 1.1 now uses a directory structure that complies with the
 309 Filesystem Hierarchy Standard ("FHS"), version 2.0. This should make
 310 integration into existing Linux and *BSD distributions a lot easier.
 311
 312 <H3><A NAME="DOCOS">6. Documentation</A></H3>
 313
 314 <P>The CUPS 1.1 documentation has gone through many revisions,
 315 including a completely rewritten administrators manual, a new
 316 programmers manual, and an IPP implementation reference manual.
 317
 318 <H3><A NAME="DRIVERS">7. Drivers</A></H3>
 319
 320 <P>CUPS 1.1 includes drivers for EPSON dot-matrix and inkjet printers.
 321 As with the HP PCL drivers, the EPSON drivers don't necessarily provide
 322 the best possible output for each printer but should provide adequate
 323 printing quality for general day-to-day printing.
 324
 325 <H3><A NAME="FILTERS">8. Filters</A></H3>
 326
 327 <P>CUPS 1.1 includes new image, PostScript, PDF, and text filters. The image
 328 filters have been upgraded to support Windows BMP and Alias PIX files.
 329
 330 <P>The PostScript filter is now based off GNU Ghostscript 5.50. The new
 331 filter provides much better performance with higher-resolution printers
 332 and supports most Level 3 PostScript language features.
 333
 334 <P>The new PDF filter is based off the excellent Xpdf software from
 335 Derek Noonburg and supports automatic page scaling. The new filter is a
 336 faster, smaller, more reliable replacement for the GNU Ghostscript PDF
 337 filtering that was used in CUPS 1.0.
 338
 339 <P>The new text filter now supports bidirectional text and can embed
 340 fonts as needed.
 341
 342 <H3><A NAME="IPP">9. IPP Support</A></H3>
 343
 344 <P>Probably the least visible portion of CUPS is the IPP support. CUPS
 345 1.1 implements all of the required IPP/1.1 operations and attributes
 346 and most of the optional ones. The optional Create-Job and Send-File
 347 operations are now implemented, allowing for better System V printing
 348 system compatibility (one job ID per <CODE>lp</CODE> command) and
 349 support for banner pages.
 350
 351 <H3><A NAME="PERSISTENCE">10. Job Persistence</A></H3>
 352
 353 <P>CUPS 1.1 supports job persistence. This means that jobs are preserved
 354 even after a reboot, a feature that was sorely missing from CUPS 1.0.
 355
 356 <P>In addition, CUPS 1.1 allows you to keep job information after the
 357 job has printed. The basic post-job persistence mode provides a job
 358 history (number of pages printed, time job was printed, etc.) but does
 359 not preserve the actual job files. This can be changed to discard all
 360 information after a job is printed or keep the job files after printing
 361 so you can reprint a job at some later time.
 362
 363 <H3><A NAME="LPD">11. LPD Client Support</A></H3>
 364
 365 <P>By popular request, CUPS 1.1 supports LPD-based clients using a new
 366 mini-daemon that handles LPD requests and passes them on to the main
 367 server.
 368
 369 <H3><A NAME="USEROPTS">12. User-Defined Printers and Options</A></H3>
 370
 371 <P>CUPS 1.1 includes support for user-defined printers and options via
 372 a new <CODE>lpoptions</CODE> command. User-defined printers are special
 373 instances of the available printers (e.g. "printer/instance" or
 374 "printer@server/instance") that can have their own default options such
 375 as media size, resolution, and so forth. The <CODE>lpoptions</CODE>
 376 command can also be used to set a different default printer queue.
 377
 378 <H3><A NAME="WEB">13. Web Administration Interface</A></H3>
 379
 380 <P>CUPS 1.0 provided a simple class, job, and printer monitoring
 381 interface for web browsers. CUPS 1.1 replaces this interface with an
 382 enhanced administration interface that allows you to add, modify,
 383 delete, configure, and control classes, jobs, and printers.
 384
 385 <H2>Software Using CUPS</H2>
 386
 387 <P>A lot has happened since CUPS 1.0 came out, and many software packages
 388 are supporting CUPS. We have contributed code to the SAMBA team to support
 389 CUPS, and parts of that are already available in SAMBA 2.0.6 and 2.0.7.
 390 With any luck the final pieces that provide a complete integration with
 391 SAMBA will be available in the next release of SAMBA.
 392
 393 <P>Two graphical interfaces have appeared on the scene that use CUPS as
 394 well. The KUPS project provides a KDE-based interface for CUPS and can be
 395 found at:
 396
 397 <UL><PRE>
 398 <A HREF="http://kups.sourceforge.net">http://kups.sourceforge.net</A>
 399 </PRE></UL>
 400
 401 <P>The X Printing Panel ("XPP") project provides a graphical printing
 402 panel for CUPS and can be found at:
 403
 404 <UL><PRE>
 405 <A HREF="http://www.phy.uni-bayreuth.de/till/xpp">http://www.phy.uni-bayreuth.de/till/xpp/</A>
 406 </PRE></UL>
 407
 408 <P>Numerous other filters, drivers, tutorials, etc. have been made available
 409 on the CUPS bazaar, available at:
 410
 411 <UL><PRE>
 412 <A HREF="http://www.cups.org/bazaar.cgi">http://www.cups.org/bazaar.cgi</A>
 413 </PRE></UL>
 414
 415 <P>Finally, our own ESP Print Pro software uses CUPS to provide drivers
 416 for over 2300 printers and can be found at:
 417
 418 <UL><PRE>
 419 <A HREF="http://www.easysw.com/printpro">http://www.easysw.com/printpro</A>
 420 </PRE></UL>
 421
 422 <H2>Operating Systems Using CUPS</H2>
 423
 424 <P>One of our goals has always been to get as many UNIX/Linux
 425 distributions using CUPS as possible. Debian is currently providing
 426 CUPS as part of its stable distribution, and many other distributions
 427 are considering it in their next releases.
 428
 429 <H2>Summary</H2>
 430
 431 <P>The Common UNIX Printing System provides a modern printing interface
 432 for UNIX applications that is both flexible and user-friendly. The
 433 software provides System V and Berkeley compatible command-line
 434 interfaces to ensure compatibility with existing applications. CUPS 1.1
 435 adds many new features that make it an even better choice for printing
 436 under UNIX.
 437
 438 <H2>Who to Contact</H2>
 439
 440 <P>For more information on CUPS please contact us at:
 441
 442 <UL><PRE>
 443 Attn: CUPS Information
 444 Easy Software Products
 445 44141 Airport View Drive Suite 204
 446 Hollywood, Maryland 20636-3111 USA
 447
 448 +1.301.373.9600
 449
 450 <A HREF="mailto:cups-info@cups.org">cups-info@cups.org</A>
 451 </PRE></UL>
 452
 453 <H2>References</H2>
 454
 455 <DL>
 456
 457         <DT>IEEE-1387.4</DT>
 458
 459         <DD>System Administration - Part 4: Printing Interfaces (draft)</DD>
 460
 461         <DT><A HREF="http://www.pwg.org/ipp/index.html">IETF-IPP</A></DT>
 462
 463         <DD>Internet Printing Protocol/1.1</DD>
 464
 465         <DT><A HREF="http://www.astart.com/lprng.html">LPRng</A></DT>
 466
 467         <DD>An enhanced, extended, and portable implementation of the
 468         Berkeley LPR print spooler functionality</DD>
 469
 470         <DT>Palladin</DT>
 471
 472         <DD>A printing system developed at the Massachussetts Institute
 473         of Technology</DD>
 474
 475         <DT><A HREF="http://www-usa.iona.com//hyplan/jmason/plp.html">PLP</A></DT>
 476
 477         <DD>The Portable Line Printer spooler system</DD>
 478
 479         <DT><A HREF="http://www.ietf.org/rfc/rfc1179.txt">RFC1179</A></DT>
 480
 481         <DD>Line Printer Daemon Protocol</DD>
 482
 483         <DT><A HREF="http://www.ietf.org/rfc/rfc2046.txt">RFC2046</A></DT>
 484
 485         <DD>Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</DD>
 486
 487         <DT><A HREF="http://www.ietf.org/rfc/rfc2616.txt">RFC2616</A></DT>
 488
 489         <DD>Hypertext Transfer Protocol -- HTTP/1.1</DD>
 490
 491 </DL>
 492
 493 <H2>Trademarks</H2>
 494
 495 <P>The Common UNIX Printing System, CUPS, and the CUPS logo are the
 496 trademark property of Easy Software Products. All other trademarks are
 497 the property of their respective owners.
 498
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