document.  However, there can be identical copies of the stream in
   other documents in the same or different Job objects.  If the
   contained document is just a reference to a stream of document data,
   other documents (in the same or different Job object(s)) may contain
   the same reference.

2.4 Object Identity

   All Printer and Job objects are identified by a Uniform Resource
   Identifier (URI) [RFC2396] so that they can be persistently and
   unambiguously referenced.  The notion of a URI is a useful concept,
   however, until the notion of URI is more stable (i.e., defined more
   completely and deployed more widely), it is expected that the URIs
   used for IPP objects will actually be URLs [RFC2396].  Since every
   URL is a specialized form of a URI, even though the more generic term
   URI is used throughout the rest of this document, its usage is
   intended to cover the more specific notion of URL as well.

   An administrator configures Printer objects to either support or not
   support authentication and/or message privacy using SSL3 [SSL] (the
   mechanism for security configuration is outside the scope of
   IPP/1.0).  In some situations, both types of connections (both
   authenticated and unauthenticated) can be established using a single
   communication channel that has some sort of negotiation mechanism.
   In other situations, multiple communication channels are used, one
   for each type of security configuration.  Section 8 provides a full
   description of all security considerations and configurations.

   If a Printer object supports more than one communication channel,
   some or all of those channels might support and/or require different
   security mechanisms.  In such cases, an administrator could expose
   the simultaneous support for these multiple communication channels as
   multiple URIs for a single Printer object where each URI represents
   one of the communication channels to the Printer object. To support
   this flexibility, the IPP Printer object type defines a multi-valued
   identification attribute called the "printer-uri-supported"
   attribute.  It MUST contain at least one URI.  It MAY contain more
   than one URI.  That is, every Printer object will have at least one




 
RFC 2566              IPP/1.0: Model and Semantics            April 1999


   URI that identifies at least one communication channel to the Printer
   object, but it may have more than one URI where each URI identifies a
   different communication channel to the Printer object.  The
   "printer-uri-supported" attribute has a companion attribute, the
   "uri-security-supported" attribute, that has the same cardinality as
   "printer-uri-supported".  The purpose of the "uri-security-supported"
   attribute is to indicate the security mechanisms (if any) used for
   each URI listed in "printer-uri-supported".  These two attributes are
   fully described in sections 4.4.1 and 4.4.2.

   When a job is submitted to the Printer object via a create request,
   the client supplies only a single Printer object URI.  The client
   supplied Printer object URI MUST be one of the values in the
   "printer-uri-supported" Printer attribute.

   Note:  IPP/1.0 does not specify how the client obtains the client
   supplied URI, but it is RECOMMENDED that a Printer object be
   registered as an entry in a directory service.  End-users and
   programs can then interrogate the directory searching for Printers.
   Section 16 defines a generic schema for Printer object entries in the
   directory service and describes how the entry acts as a bridge to the
   actual IPP Printer object.  The entry in the directory that
   represents the IPP Printer object includes the possibly many URIs for
   that Printer object as values in one its attributes.

   When a client submits a create request to the Printer object, the
   Printer object validates the request and creates a new Job object.
   The Printer object assigns the new Job object a URI which is stored
   in the "job-uri" Job attribute.  This URI is then used by clients as
   the target for subsequent Job operations.  The Printer object
   generates a Job URI based on its configured security policy and the
   URI used by the client in the create request.

   For example, consider a Printer object that supports both a
   communication channel secured by the use of SSL3 (using HTTP over
   SSL3 with an "https" schemed URI) and another open communication
   channel that is not secured with SSL3 (using a simple "http" schemed
   URI).  If a client were to submit a job using the secure URI, the
   Printer object would assign the new Job object a secure URI as well.
   If a client were to submit a job using the open-channel URI, the
   Printer would assign the new Job object an open-channel URI.

   In addition, the Printer object also populates the Job object's
   "job-printer-uri" attribute.  This is a reference back to the Printer
   object that created the Job object.  If a client only has access to a
   Job object's "job-uri" identifier, the client can query the Job's
   "job-printer-uri" attribute in order to determine which Printer
   object created the Job object.  If the Printer object supports more




 
RFC 2566              IPP/1.0: Model and Semantics            April 1999