set of possible attributes that may be supported by instances of that
   object type.  For each object (instance), the actual set of supported
   attributes and values describe a specific implementation.  The
   object's attributes and values describe its state, capabilities,
   realizable features, job processing functions, and default behaviors
   and characteristics.  For example, the Printer object type is defined
   as a set of attributes that each Printer object potentially supports.
   In the same manner, the Job object type is defined as a set of
   attributes that are potentially supported by each Job object.

   Each attribute included in the set of attributes defining an object
   type is labeled as:






 
RFC 2566              IPP/1.0: Model and Semantics            April 1999


     - "REQUIRED": each object MUST support the attribute.
     - "OPTIONAL": each object MAY support the attribute.

   There is no such similar labeling of attribute values.  However, if
   an implementation supports an attribute, it MUST support at least one
   of the possible values for that attribute.

2.1 Printer Object

   The major component of the IPP/1.0 model is the Printer object.  A
   Printer object implements the server-side of the IPP/1.0 protocol.
   Using the protocol, end users may query the attributes of the Printer
   object and submit print jobs to the Printer object.  The actual
   implementation components behind the Printer abstraction may take on
   different forms and different configurations.  However, the model
   abstraction allows the details of the configuration of real
   components to remain opaque to the end user.  Section 3 describes
   each of the Printer operations in detail.

   The capabilities and state of a Printer object are described by its
   attributes.  Printer attributes are divided into two groups:

     - "job-template" attributes: These attributes describe supported
       job processing capabilities and defaults for the Printer object.
       (See section 4.2)
     - "printer-description" attributes: These attributes describe the
       Printer object's identification, state, location, references to
       other sources of information about the Printer object, etc. (see
       section 4.4)

   Since a Printer object is an abstraction of a generic document output
   device and print service provider, a Printer object could be used to
   represent any real or virtual device with semantics consistent with
   the Printer object, such as a fax device, an imager, or even a CD
   writer.

   Some examples of configurations supporting a Printer object include:

     1) An output device with no spooling capabilities
     2) An output device with a built-in spooler
     3) A print server supporting IPP with one or more associated output
        devices
        3a) The associated output devices may or may not be capable of
          spooling jobs
        3b) The associated output devices may or may not support IPP







 
RFC 2566              IPP/1.0: Model and Semantics            April 1999


   The following figures show some examples of how Printer objects can
   be realized on top of various distributed printing configurations.
   The embedded case below represents configurations 1 and 2. The hosted
   and fan-out figures below represent configurations 3a and 3b.

   Legend:

   ##### indicates a Printer object which is
         either embedded in an output device or is
         hosted in a server.  The Printer object
         might or might not be capable of queuing/spooling.

   any   indicates any network protocol or direct
         connect, including IPP


   embedded printer:
                                             output device
                                           +---------------+
    O   +--------+                         |  ###########  |
   /|\  | client |------------IPP------------># Printer #  |
   / \  +--------+                         |  # Object  #  |