RFC2566 - Internet Printing Protocol/1.0: Model and Semantics

Network Working Group R. deBry
Request for Comments: 2566 Utah Valley State College
Category: EXPerimental T. Hastings
Xerox Corporation
R. Herriot
Xerox Corporation
S. Isaacson
Novell, Inc.
P. Powell
Astart Technologies
April 1999
Internet Printing Protocol/1.0: Model and Semantics
Status of this Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
IESG Note
This document defines an Experimental protocol for the Internet
community. The IESG expects that a revised version of this protocol
will be published as Proposed Standard protocol. The Proposed
Standard, when published, is expected to change from the protocol
defined in this memo. In particular, it is expected that the
standards-track version of the protocol will incorporate strong
authentication and privacy features, and that an "ipp:" URL type will
be defined which supports those security measures. Other changes to
the protocol are also possible. Implementors are warned that future
versions of this protocol may not interoperate with the version of
IPP defined in this document, or if they do interoperate, that some
protocol features may not be available.
The IESG encourages experimentation with this protocol, especially in
combination with Transport Layer Security (TLS) [RFC2246], to help
determine how TLS may effectively be used as a security layer for
IPP.
Abstract
This document is one of a set of documents, which together describe
all ASPects of a new Internet Printing Protocol (IPP). IPP is an
application level protocol that can be used for distributed printing
using Internet tools and technologies. This document describes a
simplified model consisting of abstract objects, their attributes,
and their operations that is independent of encoding and transport.
The model consists of a Printer and a Job object. A Job optionally
supports multiple documents. IPP 1.0 semantics allow end-users and
operators to query printer capabilities, submit print jobs, inquire
about the status of print jobs and printers, and cancel print jobs.
This document also addresses security, internationalization, and
Directory issues.
The full set of IPP documents includes:
Design Goals for an Internet Printing Protocol [RFC2567]
Rationale for the StrUCture and Model and Protocol for the Internet
Printing Protocol [RFC2568]
Internet Printing Protocol/1.0: Model and Semantics (this document)
Internet Printing Protocol/1.0: Encoding and Transport [RFC2565]
Internet Printing Protocol/1.0: Implementer"s Guide [ipp-iig]
Mapping between LPD and IPP Protocols [RFC2569]
The "Design Goals for an Internet Printing Protocol" document takes a
broad look at distributed printing functionality, and it enumerates
real-life scenarios that help to clarify the features that need to be
included in a printing protocol for the Internet. It identifies
requirements for three types of users: end users, operators, and
administrators. It calls out a subset of end user requirements that
are satisfied in IPP/1.0. Operator and administrator requirements
are out of scope for version 1.0.
The "Rationale for the Structure and Model and Protocol for the
Internet Printing Protocol" document describes IPP from a high level
view, defines a roadmap for the various documents that form the suite
of IPP specifications, and gives background and rationale for the
IETF working group"s major decisions.
The "Internet Printing Protocol/1.0: Encoding and Transport" document
is a formal mapping of the abstract operations and attributes defined
in the model document onto HTTP/1.1. It defines the encoding rules
for a new Internet media type called "application/ipp".
The "Internet Printing Protocol/1.0: Implementer"s Guide" document
gives insight and advice to implementers of IPP clients and IPP
objects. It is intended to help them understand IPP/1.0 and some of
the considerations that may assist them in the design of their client
and/or IPP object implementations. For example, a typical order of
processing requests is given, including error checking. Motivation
for some of the specification decisions is also included.
The "Mapping between LPD and IPP Protocols" document gives some
advice to implementers of gateways between IPP and LPD (Line Printer
Daemon) implementations.
Table of Contents
1. Introduction 8
1.1 Simplified Printing Model 9
2. IPP Objects 11
2.1 Printer Object 12
2.2 Job Object 14
2.3 Object Relationships 14
2.4 Object Identity 15
3. IPP Operations 18
3.1 Common Semantics 19
3.1.1 Required Parameters 19
3.1.2 Operation IDs and Request IDs 20
3.1.3 Attributes 20
3.1.4 Character Set and Natural Language Operation Attributes 22
3.1.4.1 Request Operation Attributes 22
3.1.4.2 Response Operation Attributes 26
3.1.5 Operation Targets 28
3.1.6 Operation Status Codes and Messages 29
3.1.7 Versions 30
3.1.8 Job Creation Operations 32
3.2 Printer Operations 34
3.2.1 Print-Job Operation 34
3.2.1.1 Print-Job Request 34
3.2.1.2 Print-Job Response 38
3.2.2 Print-URI Operation 41
3.2.3 Validate-Job Operation 42
3.2.4 Create-Job Operation 42
3.2.5 Get-Printer-Attributes Operation 43
3.2.5.1 Get-Printer-Attributes Request 44
3.2.5.2 Get-Printer-Attributes Response 46
3.2.6 Get-Jobs Operation 47
3.2.6.1 Get-Jobs Request 47
3.2.6.2 Get-Jobs Response 49
3.3 Job Operations 50
3.3.1 Send-Document Operation 50
3.3.1.1 Send-Document Request 51
3.3.1.2 Send-Document Response 53
3.3.2 Send-URI Operation 54
3.3.3 Cancel-Job Operation 54
3.3.3.1 Cancel-Job Request 54
3.3.3.2 Cancel-Job Response 55
3.3.4 Get-Job-Attributes Operation 56
3.3.4.1 Get-Job-Attributes Request 57
3.3.4.2 Get-Job-Attributes Response 57
4. Object Attributes 58
4.1 Attribute Syntaxes 59
4.1.1 "text" 60
4.1.1.1 "textWithoutLanguage" 61
4.1.1.2 "textWithLanguage" 61
4.1.2 "name" 62
4.1.2.1 "nameWithoutLanguage" 62
4.1.2.2 "nameWithLanguage" 63
4.1.2.3 Matching "name" attribute values 63
4.1.3 "keyWord" 64
4.1.4 "enum" 65
4.1.5 "uri" 65
4.1.6 "uriScheme" 65
4.1.7 "charset" 66
4.1.8 "naturalLanguage" 67
4.1.9 "mimeMediaType" 67
4.1.10 "octetString" 69
4.1.11 "boolean" 69
4.1.12 "integer" 69
4.1.13 "rangeOfInteger" 69
4.1.14 "dateTime" 69
4.1.15 "resolution" 69
4.1.16 "1setOf X" 70
4.2 Job Template Attributes 70
4.2.1 job-priority (integer(1:100)) 74
4.2.2 job-hold-until (type3 keyword name (MAX)) 75
4.2.3 job-sheets (type3 keyword name(MAX)) 75
4.2.4 multiple-document-handling (type2 keyword) 76
4.2.5 copies (integer(1:MAX)) 77
4.2.6 finishings (1setOf type2 enum) 78
4.2.7 page-ranges (1setOf rangeOfInteger (1:MAX)) 79
4.2.8 sides (type2 keyword) 80
4.2.9 number-up (integer(1:MAX)) 80
4.2.10 orientation-requested (type2 enum) 81
4.2.11 media (type3 keyword name(MAX)) 82
4.2.12 printer-resolution (resolution) 83
4.2.13 print-quality (type2 enum) 83
4.3 Job Description Attributes 84
4.3.1 job-uri (uri) 85
4.3.2 job-id (integer(1:MAX)) 85
4.3.3 job-printer-uri (uri) 86
4.3.4 job-more-info (uri) 86
4.3.5 job-name (name(MAX)) 86
4.3.6 job-originating-user-name (name(MAX)) 86
4.3.7 job-state (type1 enum) 87
4.3.8 job-state-reasons (1setOf type2 keyword) 90
4.3.9 job-state-message (text(MAX)) 92
4.3.10 number-of-documents (integer(0:MAX)) 93
4.3.11 output-device-assigned (name(127)) 93
4.3.12 time-at-creation (integer(0:MAX)) 93
4.3.13 time-at-processing (integer(0:MAX)) 93
4.3.14 time-at-completed (integer(0:MAX)) 94
4.3.15 number-of-intervening-jobs (integer(0:MAX)) 94
4.3.16 job-message-from-operator (text(127)) 94
4.3.17 job-k-octets (integer(0:MAX)) 94
4.3.18 job-impressions (integer(0:MAX)) 95
4.3.19 job-media-sheets (integer(0:MAX)) 95
4.3.20 job-k-octets-processed (integer(0:MAX)) 96
4.3.21 job-impressions-completed (integer(0:MAX)) 96
4.3.22 job-media-sheets-completed (integer(0:MAX)) 96
4.3.23 attributes-charset (charset) 97
4.3.24 attributes-natural-language (naturalLanguage) 97
4.4 Printer Description Attributes 97
4.4.1 printer-uri-supported (1setOf uri) 99
4.4.2 uri-security-supported (1setOf type2 keyword) 100
4.4.3 printer-name (name(127)) 101
4.4.4 printer-location (text(127)) 101
4.4.5 printer-info (text(127)) 101
4.4.6 printer-more-info (uri) 101
4.4.7 printer-driver-installer (uri) 102
4.4.8 printer-make-and-model (text(127)) 102
4.4.9 printer-more-info-manufacturer (uri) 102
4.4.10 printer-state (type1 enum) 102
4.4.11 printer-state-reasons (1setOf type2 keyword) 103
4.4.12 printer-state-message (text(MAX)) 106
4.4.13 operations-supported (1setOf type2 enum) 106
4.4.14 charset-configured (charset) 107
4.4.15 charset-supported (1setOf charset) 107
4.4.16 natural-language-configured (naturalLanguage) 107
4.4.17 generated-natural-language-supported(1setOf naturalLanguage108
4.4.18 document-format-default (mimeMediaType) 108
4.4.19 document-format-supported (1setOf mimeMediaType) 108
4.4.20 printer-is-accepting-jobs (boolean) 109
4.4.21 queued-job-count (integer(0:MAX)) 109
4.4.22 printer-message-from-operator (text(127)) 109
4.4.23 color-supported (boolean) 109
4.4.24 reference-uri-schemes-supported (1setOf uriScheme) 109
4.4.25 pdl-override-supported (type2 keyword) 110
4.4.26 printer-up-time (integer(1:MAX)) 110
4.4.27 printer-current-time (dateTime) 111
4.4.28 multiple-operation-time-out (integer(1:MAX)) 111
4.4.29 compression-supported (1setOf type3 keyword) 111
4.4.30 job-k-octets-supported (rangeOfInteger(0:MAX)) 112
4.4.31 job-impressions-supported (rangeOfInteger(0:MAX)) 112
4.4.32 job-media-sheets-supported (rangeOfInteger(0:MAX)) 112
5. Conformance 112
5.1 Client Conformance Requirements 112
5.2 IPP Object Conformance Requirements 113
5.2.1 Objects 113
5.2.2 Operations 113
5.2.3 IPP Object Attributes 114
5.2.4 Extensions 114
5.2.5 Attribute Syntaxes 115
5.3 Charset and Natural Language Requirements 115
5.4 Security Conformance Requirements 115
6. IANA Considerations (registered and private extensions) 116
6.1 Typed "keyword" and "enum" Extensions 116
6.2 Attribute Extensibility 119
6.3 Attribute Syntax Extensibility 119
6.4 Operation Extensibility 120
6.5 Attribute Groups 120
6.6 Status Code Extensibility 120
6.7 Registration of MIME types/sub-types for document-formats 121
6.8 Registration of charsets for use in "charset" attribute values121
7. Internationalization Considerations 121
8. Security Considerations 125
8.1 Security Scenarios 126
8.1.1 Client and Server in the Same Security Domain 126
8.1.2 Client and Server in Different Security Domains 126
8.1.3 Print by Reference 127
8.2 URIs for SSL3 and non-SSL3 Access 127
8.3 The "requesting-user-name" (name(MAX)) Operation Attribute 127
8.4 Restricted Queries 129
8.5 Queries on jobs submitted using non-IPP protocols 129
8.6 IPP Security Application Profile for SSL3 130
9. References 131
10. Authors" Addresses 134
11. Formats for IPP Registration Proposals 136
11.1 Type2 keyword attribute values registration 136
11.2 Type3 keyword attribute values registration 137
11.3 Type2 enum attribute values registration 137
11.4 Type3 enum attribute values registration 137
11.5 Attribute registration 138
11.6 Attribute Syntax registration 138
11.7 Operation registration 139
11.8 Attribute Group registration 139
11.9 Status code registration 139
12.APPENDIX A: Terminology 141
12.1 Conformance Terminology 141
12.1.1 NEED NOT 141
12.2 Model Terminology 141
12.2.1 Keyword 141
12.2.2 Attributes 141
12.2.2.1 Attribute Name 141
12.2.2.2 Attribute Group Name 142
12.2.2.3 Attribute Value 142
12.2.2.4 Attribute Syntax 142
12.2.3 Supports 142
12.2.4 print-stream page 144
12.2.5 impression 144
13.APPENDIX B: Status Codes and Suggested Status Code Messages 145
13.1 Status Codes 146
13.1.1 Informational 146
13.1.2 Successful Status Codes 146
13.1.2.1 successful-ok (0x0000) 146
13.1.2.2 successful-ok-ignored-or-substituted-attributes (0x0001) 146
13.1.2.3 successful-ok-conflicting-attributes (0x0002) 147
13.1.3 Redirection Status Codes 147
13.1.4 Client Error Status Codes 147
13.1.4.1 client-error-bad-request (0x0400) 147
13.1.4.2 client-error-forbidden (0x0401) 147
13.1.4.3 client-error-not-authenticated (0x0402) 148
13.1.4.4 client-error-not-authorized (0x0403) 148
13.1.4.5 client-error-not-possible (0x0404) 148
13.1.4.6 client-error-timeout (0x0405) 148
13.1.4.7 client-error-not-found (0x0406) 149
13.1.4.8 client-error-gone (0x0407) 149
13.1.4.9 client-error-request-entity-too-large (0x0408) 149
13.1.4.10client-error-request-value-too-long (0x0409) 150
13.1.4.11client-error-document-format-not-supported (0x040A) 150
13.1.4.12client-error-attributes-or-values-not-supported (0x040B) 150
13.1.4.13client-error-uri-scheme-not-supported (0x040C) 151
13.1.4.14client-error-charset-not-supported (0x040D) 151
13.1.4.15client-error-conflicting-attributes (0x040E) 151
13.1.5 Server Error Status Codes 151
13.1.5.1 server-error-internal-error (0x0500) 151
13.1.5.2 server-error-operation-not-supported (0x0501) 152
13.1.5.3 server-error-service-unavailable (0x0502) 152
13.1.5.4 server-error-version-not-supported (0x0503) 152
13.1.5.5 server-error-device-error (0x0504) 152
13.1.5.6 server-error-temporary-error (0x0505) 153
13.1.5.7 server-error-not-accepting-jobs (0x0506) 153
13.1.5.8 server-error-busy (0x0507) 153
13.1.5.9 server-error-job-canceled (0x0508) 153
13.2 Status Codes for IPP Operations 153
14.APPENDIX C: "media" keyword values 155
15.APPENDIX D: Processing IPP Attributes 160
15.1 Fidelity 160
15.2 Page Description Language (PDL) Override 161
15.3 Using Job Template Attributes During Document Processing. 163
16.APPENDIX E: Generic Directory Schema 166
17.APPENDIX F: Change History for the Model and Semantics document 168
18.FULL COPYRIGHT STATEMENT 173
1. Introduction
The Internet Printing Protocol (IPP) is an application level protocol
that can be used for distributed printing using Internet tools and
technologies. IPP version 1.0 (IPP/1.0) focuses only on end user
functionality. This document is just one of a suite of documents
that fully define IPP. The full set of IPP documents includes:
Design Goals for an Internet Printing Protocol [RFC2567]
Rationale for the Structure and Model and Protocol for the Internet
Printing Protocol [RFC2568]
Internet Printing Protocol/1.0: Model and Semantics (this document)
Internet Printing Protocol/1.0: Encoding and Transport [RFC2565]
Internet Printing Protocol/1.0: Implementer"s Guide [ipp-iig]
Mapping between LPD and IPP Protocols [RFC2569]
Anyone reading these documents for the first time is strongly
encouraged to read the IPP documents in the above order.
This document is laid out as follows:
- The rest of Section 1 is an introduction to the IPP simplified
model for distributed printing.
- Section 2 introduces the object types covered in the model with
their basic behaviors, attributes, and interactions.
- Section 3 defines the operations included in IPP/1.0. IPP
operations are synchronous, therefore, for each operation, there
is a both request and a response.
- Section 4 defines the attributes (and their syntaxes) that are
used in the model.
- Sections 5 - 6 summarizes the implementation conformance
requirements for objects that support the protocol and IANA
considerations, respectively.
- Sections 7 - 11 cover the Internationalization and Security
considerations as well as References, Author contact information,
and Formats for Registration Proposals.
- Sections 12 - 14 are appendices that cover Terminology, Status
Codes and Messages, and "media" keyword values.
Note: This document uses terms such as "attributes",
"keywords", and "support". These terms have special
meaning and are defined in the model terminology section
12.2. Capitalized terms, such as MUST, MUST NOT, REQUIRED,
SHOULD, SHOULD NOT, MAY, NEED NOT, and OPTIONAL, have
special meaning relating to conformance. These terms are
defined in section 12.1 on conformance terminology, most of
which is taken from RFC2119 [RFC2119].
- Section 15 is an appendix that helps to clarify the effects of
interactions between related attributes and their values.
- Section 16 is an appendix that enumerates the subset of Printer
attributes that form a generic directory schema. These
attributes are useful when registering a Printer so that a
client can find the Printer not just by name, but by filtered
searches as well.
- Section 17 is an appendix that provides a Change History
summarizing the clarification and changes that might affect an
implementation since the June 30, 1998 draft.
1.1 Simplified Printing Model
In order to achieve its goal of realizing a workable printing
protocol for the Internet, the Internet Printing Protocol (IPP) is
based on a simplified printing model that abstracts the many
components of real world printing solutions. The Internet is a
distributed computing environment where requesters of print services
(clients, applications, printer drivers, etc.) cooperate and interact
with print service providers. This model and semantics document
describes a simple, abstract model for IPP even though the underlying
configurations may be complex "n-tier" client/server systems. An
important simplifying step in the IPP model is to expose only the key
objects and interfaces required for printing. The model described in
this model document does not include features, interfaces, and
relationships that are beyond the scope of the first version of IPP
(IPP/1.0). IPP/1.0 incorporates many of the relevant ideas and
lessons learned from other specification and development efforts
[HTPP] [ISO10175] [LDPA] [P1387.4] [PSIS] [RFC1179] [SWP]. IPP is
heavily influenced by the printing model introduced in the Document
Printing Application (DPA) [ISO10175] standard. Although DPA
specifies both end user and administrative features, IPP version 1.0
(IPP/1.0) focuses only on end user functionality.
The IPP/1.0 model encapsulates the important components of
distributed printing into two object types:
- Printer (Section 2.1)
- Job (Section 2.2)
Each object type has an associated set of operations (see section 3)
and attributes (see section 4).
It is important, however, to understand that in real system
implementations (which lie underneath the abstracted IPP/1.0 model),
there are other components of a print service which are not
explicitly defined in the IPP/1.0 model. The following figure
illustrates where IPP/1.0 fits with respect to these other
components.
+--------------+
Application
o +. . . . . . .
/ Spooler
/ +. . . . . . . +---------+
End-User Print Driver --- File
+-----------+ +-----+ +------+-------+ +----+----+
Browser GUI
+-----+-----+ +--+--+

+---+------------+---+
N D S IPP Client ------------+
O I E +---------+----------+
T R C
I E U
F C R -------------- Transport ------------------
I T I
C O T --+
A R Y +--------+--------+
T Y IPP Server
I +--------+--------+
O
N +-----------------+ IPP Printer
Print Service
+-----------------+
--+
+-----------------+
Output Device(s)
+-----------------+
An IPP Printer object encapsulates the functions normally associated
with physical output devices along with the spooling, scheduling and
multiple device management functions often associated with a print
server. Printer objects are optionally registered as entries in a
directory where end users find and select them based on some sort of
filtered and context based searching mechanism (see section 16). The
directory is used to store relatively static information about the
Printer, allowing end users to search for and find Printers that
match their search criteria, for example: name, context, printer
capabilities, etc. The more dynamic information, such as state,
currently loaded and ready media, number of jobs at the Printer,
errors, warnings, and so forth, is directly associated with the
Printer object itself rather than with the entry in the directory
which only represents the Printer object.
IPP clients implement the IPP protocol on the client side and give
end users (or programs running on behalf of end users) the ability to
query Printer objects and submit and manage print jobs. An IPP
server is just that part of the Printer object that implements the
server-side protocol. The rest of the Printer object implements (or
gateways into) the application semantics of the print service itself.
The Printer objects may be embedded in an output device or may be
implemented on a host on the network that communicates with an output
device.
When a job is submitted to the Printer object and the Printer object
validates the attributes in the submission request, the Printer
object creates a new Job object. The end user then interacts with
this new Job object to query its status and monitor the progress of
the job. End users may also cancel the print job by using the Job
object"s Cancel-Job operation. The notification service is out of
scope for IPP/1.0, but using such a notification service, the end
user is able to register for and receive Printer specific and Job
specific events. An end user can query the status of Printer objects
and can follow the progress of Job objects by polling using the Get-
Printer-Attributes, Get-Jobs, and Get-Job-Attributes operations.
2. IPP Objects
The IPP/1.0 model introduces objects of type Printer and Job. Each
type of object models relevant aspects of a real-world entity such as
a real printer or real print job. Each object type is defined as a
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:
- "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
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 #
###########
+---------------+
hosted printer:
+---------------+
O +--------+ ###########
/ client --IPP--># Printer #-any-> output device
/ +--------+ # Object #
########### +---------------+
+---------------+
fan out:
+--> output device
any/
O +--------+ ########### / +---------------+
/ client -IPP-># Printer #--*
/ +--------+ # Object # +---------------+
########### any
+--> output device

+---------------+
2.2 Job Object
A Job object is used to model a print job. A Job object contains
documents. The information required to create a Job object is sent
in a create request from the end user via an IPP Client to the
Printer object. The Printer object validates the create request, and
if the Printer object accepts the request, the Printer object creates
the new Job object. Section 3 describes each of the Job operations
in detail.
The characteristics and state of a Job object are described by its
attributes. Job attributes are grouped into two groups as follows:
- "job-template" attributes: These attributes can be supplied by
the client or end user and include job processing instructions
which are intended to override any Printer object defaults and/or
instructions embedded within the document data. (See section 4.2)
- "job-description" attributes: These attributes describe the Job
object"s identification, state, size, etc. The client supplies
some of these attributes, and the Printer object generates others.
(See section 4.3)
An implementation MUST support at least one document per Job object.
An implementation MAY support multiple documents per Job object. A
document is either:
- a stream of document data in a format supported by the Printer
object (typically a Page Description Language - PDL), or
- a reference to such a stream of document data
In IPP/1.0, a document is not modeled as an IPP object, therefore it
has no object identifier or associated attributes. All job
processing instructions are modeled as Job object attributes. These
attributes are called Job Template attributes and they apply equally
to all documents within a Job object.
2.3 Object Relationships
IPP objects have relationships that are maintained persistently along
with the persistent storage of the object attributes.
A Printer object can represent either one or more physical output
devices or a logical device which "processes" jobs but never actually
uses a physical output device to put marks on paper. Examples of
logical devices include a Web page publisher or a gateway into an
online document archive or repository. A Printer object contains
zero or more Job objects.
A Job object is contained by exactly one Printer object, however the
identical document data associated with a Job object could be sent to
either the same or a different Printer object. In this case, a
second Job object would be created which would be almost identical to
the first Job object, however it would have new (different) Job
object identifiers (see section 2.4).
A Job object is either empty (before any documents have been added)
or contains one or more documents. If the contained document is a
stream of document data, that stream can be contained in only one
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
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
than one URI, the Printer object picks the one URI supplied by the
client when creating the job to build the value for and to populate
the Job"s "job-printer-uri" attribute.
Allowing Job objects to have URIs allows for flexibility and
scalability. For example, in some implementations, the Printer
object might create Jobs that are processed in the same local
environment as the Printer object itself. In this case, the Job URI
might just be a composition of the Printer"s URI and some unique
component for the Job object, such as the unique 32-bit positive
integer mentioned later in this paragraph. In other implementations,
the Printer object might be a central clearing-house for validating
all Job object creation requests, but the Job object itself might be
created in some environment that is remote from the Printer object.
In this case, the Job object"s URI may have no physical-location
relationship at all to the Printer object"s URI. Again, the fact
that Job objects have URIs allows for flexibility and scalability,
however, many existing printing systems have local models or
interface constraints that force print jobs to be identified using
only a 32-bit positive integer rather than an independent URI. This
numeric Job ID is only unique within the context of the Printer
object to which the create request was originally submitted.
Therefore, in order to allow both types of client access to IPP Job
objects (either by Job URI or by numeric Job ID), when the Printer
object successfully processes a create request and creates a new Job
object, the Printer object MUST generate both a Job URI and a Job ID.
The Job ID (stored in the "job-id" attribute) only has meaning in the
context of the Printer object to which the create request was
originally submitted. This requirement to support both Job URIs and
Job IDs allows all types of clients to access Printer objects and Job
objects no matter the local constraints imposed on the client
implementation.
In addition to identifiers, Printer objects and Job objects have
names ("printer-name" and "job-name"). An object name NEED NOT be
unique across all instances of all objects. A Printer object"s name
is chosen and set by an administrator through some mechanism outside
the scope of IPP/1.0. A Job object"s name is optionally chosen and
supplied by the IPP client submitting the job. If the client does
not supply a Job object name, the Printer object generates a name for
the new Job object. In all cases, the name only has local meaning.
To summarize:
- Each Printer object is identified with one or more URIs. The
Printer"s "printer-uri-supported" attribute contains the URI(s).
- The Printer object"s "uri-security-supported" attribute
identifies the communication channel security protocols that may
or may not have been configured for the various Printer object
URIs (e.g., "ssl3" or "none").
- Each Job object is identified with a Job URI. The Job"s "job-uri"
attribute contains the URI.
- Each Job object is also identified with Job ID which is a 32-bit,
positive integer. The Job"s "job-id" attribute contains the Job
ID. The Job ID is only unique within the context of the Printer
object which created the Job object.
- Each Job object has a "job-printer-uri" attribute which contains
the URI of the Printer object that was used to create the Job
object. This attribute is used to determine the Printer object
that created a Job object when given only the URI for the Job
object. This linkage is necessary to determine the languages,
charsets, and operations which are supported on that Job (the
basis for such support comes from the creating Printer object).
- Each Printer object has a name (which is not necessarily unique).
The administrator chooses and sets this name through some
mechanism outside the scope of IPP/1.0 itself. The Printer
object"s "printer-name" attribute contains the name.
- Each Job object has a name (which is not necessarily unique). The
client optionally supplies this name in the create request. If
the client does not supply this name, the Printer object generates
a name for the Job object. The Job object"s "job-name" attribute
contains the name.
3. IPP Operations
IPP objects support operations. An operation consists of a request
and a response. When a client communicates with an IPP object, the
client issues an operation request to the URI for that object.
Operation requests and responses have parameters that identify the
operation. Operations also have attributes that affect the run-time
characteristics of the operation (the intended target, localization
information, etc.). These operation-specific attributes are called
operation attributes (as compared to object attributes such as
Printer object attributes or Job object attributes). Each request
carries along with it any operation attributes, object attributes,
and/or document data required to perform the operation. Each request
requires a response from the object. Each response indicates success
or failure of the operation with a status code as a response
parameter. The response contains any operation attributes, object
attributes, and/or status messages generated during the execution of
the operation request.
This section describes the semantics of the IPP operations, both
requests and responses, in terms of the parameters, attributes, and
other data associated with each operation.
The IPP/1.0 Printer operations are:
Print-Job (section 3.2.1)
Print-URI (section 3.2.2)
Validate-Job (section 3.2.3)
Create-Job (section 3.2.4)
Get-Printer-Attributes (section 3.2.5)
Get-Jobs (section 3.2.6)
The Job operations are:
Send-Document (section 3.3.1)
Send-URI (section 3.3.2)
Cancel-Job (section 3.3.3)
Get-Job-Attributes (section 3.3.4)
The Send-Document and Send-URI Job operations are used to add a new
document to an existing multi-document Job object created using the
Create-Job operation.
3.1 Common Semantics
All IPP operations require some common parameters and operation
attributes. These common elements and their semantic characteristics
are defined and described in more detail in the following sections.
3.1.1 Required Parameters
Every operation request contains the following REQUIRED parameters:
- a "version-number",
- an "operation-id",
- a "request-id", and
- the attributes that are REQUIRED for that type of request.
Every operation response contains the following REQUIRED parameters:
- a "version-number",
- a "status-code",
- the "request-id" that was supplied in the corresponding request,
and
- the attributes that are REQUIRED for that type of response.
The encoding and transport document [RFC2565] defines special rules
for the encoding of these parameters. All other operation elements
are represented using the more generic encoding rules for attributes
and groups of attributes.
3.1.2 Operation IDs and Request IDs
Each IPP operation request includes an identifying "operation-id"
value. Valid values are defined in the "operations-supported"
Printer attribute section (see section 4.4.13). The client specifies
which operation is being requested by supplying the correct
"operation-id" value.
In addition, every invocation of an operation is identified by a
"request-id" value. For each request, the client chooses the
"request-id" which MUST be an integer (possibly unique depending on
client requirements) in the range from 1 to 2**31 - 1 (inclusive).
This "request-id" allows clients to manage multiple outstanding
requests. The receiving IPP object copies all 32-bits of the client-
supplied "request-id" attribute into the response so that the client
can match the response with the correct outstanding request, even if
the "request-id" is out of range. If the request is terminated
before the complete "request-id" is received, the IPP object rejects
the request and returns a response with a "request-id" of 0.
Note: In some cases, the transport protocol underneath IPP might be a
connection oriented protocol that would make it impossible for a
client to receive responses in any order other than the order in
which the corresponding requests were sent. In such cases, the
"request-id" attribute would not be essential for correct protocol
operation. However, in other mappings, the operation responses can
come back in any order. In these cases, the "request-id" would be
essential.
3.1.3 Attributes
Operation requests and responses are both composed of groups of
attributes and/or document data. The attributes groups are:
- Operation Attributes: These attributes are passed in the
operation and affect the IPP object"s behavior while processing
the operation request and may affect other attributes or groups
of attributes. Some operation attributes describe the document
data associated with the print job and are associated with new
Job objects, however most operation attributes do not persist
beyond the life of the operation. The description of each
operation attribute includes conformance statements indicating
which operation attributes are REQUIRED and which are OPTIONAL
for an IPP object to support and which attributes a client MUST
supply in a request and an IPP object MUST supply in a response.
- Job Template Attributes: These attributes affect the processing
of a job. A client OPTIONALLY supplies Job Template Attributes
in a create request, and the receiving object MUST be prepared to
receive all supported attributes. The Job object can later be
queried to find out what Job Template attributes were originally
requested in the create request, and such attributes are returned
in the response as Job Object Attributes. The Printer object can
be queried about its Job Template attributes to find out what
type of job processing capabilities are supported and/or what the
default job processing behaviors are, though such attributes are
returned in the response as Printer Object Attributes. The
"ipp-attribute-fidelity" operation attribute affects processing
of all client-supplied Job Template attributes (see section 15
for a full description of "ipp-attribute-fidelity" and its
relationship to other attributes).
- Job Object Attributes: These attributes are returned in response
to a query operation directed at a Job object.
- Printer Object Attributes: These attributes are returned in
response to a query operation directed at a Printer object.
- Unsupported Attributes: In a create request, the client supplies
a set of Operation and Job Template attributes. If any of these
attributes or their values is unsupported by the Printer object,
the Printer object returns the set of unsupported attributes in
the response. Section 15 gives a full description of how Job
Template attributes supplied by the client in a create request
are processed by the Printer object and how unsupported
attributes are returned to the client. Because of extensibility,
any IPP object might receive a request that contains new or
unknown attributes or values for which it has no support. In such
cases, the IPP object processes what it can and returns the
unsupported attributes in the response.
Later in this section, each operation is formally defined by
identifying the allowed and expected groups of attributes for each
request and response. The model identifies a specific order for each
group in each request or response, but the attributes within each
group may be in any order, unless specified otherwise.
Each attribute specification includes the attribute"s name followed
by the name of its attribute syntax(es) in parenthesizes. In
addition, each "integer" attribute is followed by the allowed range
in parentheses, (m:n), for values of that attribute. Each "text" or
"name" attribute is followed by the maximum size in octets in
parentheses, (size), for values of that attribute. For more details
on attribute syntax notation, see the descriptions of these
attributes syntaxes in section 4.1.
Note: Document data included in the operation is not strictly an
attribute, but it is treated as a special attribute group for
ordering purposes. The only operations that support supplying the
document data within an operation request are Print-Job and Send-
Document. There are no operation responses that include document
data.
Note: Some operations are REQUIRED for IPP objects to support; the
others are OPTIONAL (see section 5.2.2). Therefore, before using an
OPTIONAL operation, a client SHOULD first use the REQUIRED Get-
Printer-Attributes operation to query the Printer"s "operations-
supported" attribute in order to determine which OPTIONAL Printer and
Job operations are actually supported. The client SHOULD NOT use an
OPTIONAL operation that is not supported. When an IPP object
receives a request to perform an operation it does not support, it
returns the "server-error-operation-not-supported" status code (see
section 13.1.5.2). An IPP object is non-conformant if it does not
support a REQUIRED operation.
3.1.4 Character Set and Natural Language Operation Attributes
Some Job and Printer attributes have values that are text strings and
names intended for human understanding rather than machine
understanding (see the "text" and "name" attribute syntax
descriptions in section 4.1). The following sections describe two
special Operation Attributes called "attributes-charset" and
"attributes-natural-language". These attributes are always part of
the Operation Attributes group. For most attribute groups, the order
of the attributes within the group is not important. However, for
these two attributes within the Operation Attributes group, the order
is critical. The "attributes-charset" attribute MUST be the first
attribute in the group and the "attributes-natural-language"
attribute MUST be the second attribute in the group. In other words,
these attributes MUST be supplied in every IPP request and response,
they MUST come first in the group, and MUST come in the specified
order. For job creation operations, the IPP Printer implementation
saves these two attributes with the new Job object as Job Description
attributes. For the sake of brevity in this document, these
operation attribute descriptions are not repeated with every
operation request and response, but have a reference back to this
section instead.
3.1.4.1 Request Operation Attributes
The client MUST supply and the Printer object MUST support the
following REQUIRED operation attributes in every IPP/1.0 operation
request:
"attributes-charset" (charset):
This operation attribute identifies the charset (coded character
set and encoding method) used by any "text" and "name"
attributes that the client is supplying in this request. It
also identifies the charset that the Printer object MUST use (if
supported) for all "text" and "name" attributes and status
messages that the Printer object returns in the response to this
request. See Sections 4.1.1 and 4.1.2 for the specification of
the "text" and "name" attribute syntaxes.
All clients and IPP objects MUST support the "utf-8" charset
[RFC2279] and MAY support additional charsets provided that they
are registered with IANA [IANA-CS]. If the Printer object does
not support the client supplied charset value, the Printer
object MUST reject the request, set the "attributes-charset" to
"utf-8" in the response, and return the "client-error-charset-
not-supported" status code and any "text" or "name" attributes
using the "utf-8" charset. The Printer object MUST indicate the
charset(s) supported as the values of the "charset-supported"
Printer attribute (see Section 4.4.15), so that the client can
query to determine which charset(s) are supported.
Note to client implementers: Since IPP objects are only required
to support the "utf-8" charset, in order to maximize
interoperability with multiple IPP object implementations, a
client may want to supply "utf-8" in the "attributes-charset"
operation attribute, even though the client is only passing and
able to present a simpler charset, such as US-ASCII or ISO-
8859-1. Then the client will have to filter out (or charset
convert) those characters that are returned in the response that
it cannot present to its user. On the other hand, if both the
client and the IPP objects also support a charset in common
besides utf-8, the client may want to use that charset in order
to avoid charset conversion or data loss.
See the "charset" attribute syntax description in Section 4.1.7
for the syntax and semantic interpretation of the values of this
attribute and for example values.
"attributes-natural-language" (naturalLanguage):
This operation attribute identifies the natural language used by
any "text" and "name" attributes that the client is supplying in
this request. This attribute also identifies the natural
language that the Printer object SHOULD use for all "text" and "
name" attributes and status messages that the Printer object
returns in the response to this request.
There are no REQUIRED natural languages required for the Printer
object to support. However, the Printer object"s "generated-
natural-language-supported" attribute identifies the natural
languages supported by the Printer object and any contained Job
objects for all text strings generated by the IPP object. A
client MAY query this attribute to determine which natural
language(s) are supported for generated messages.
For any of the attributes for which the Printer object generates
text, i.e., for the "job-state-message", "printer-state-
message", and status messages (see Section 3.1.6), the Printer
object MUST be able to generate these text strings in any of its
supported natural languages. If the client requests a natural
language that is not supported, the Printer object MUST return
these generated messages in the Printer"s configured natural
language as specified by the Printer"s "natural-language-
configured" attribute" (see Section 4.4.16).
For other "text" and "name" attributes supplied by the client,
authentication system, operator, system administrator, or
manufacturer (i.e., for "job-originating-user-name", "printer-
name" (name), "printer-location" (text), "printer-info" (text),
and "printer-make-and-model" (text)), the Printer object is only
required to support the configured natural language of the
Printer identified by the Printer object"s "natural-language-
configured" attribute, though support of additional natural
languages for these attributes is permitted.
For any "text" or "name" attribute in the request that is in a
different natural language than the value supplied in the
"attributes-natural-language" operation attribute, the client
MUST use the Natural Language Override mechanism (see sections
4.1.1.2 and 4.1.2.2) for each such attribute value supplied.
The client MAY use the Natural Language Override mechanism
redundantly, i.e., use it even when the value is in the same
natural language as the value supplied in the "attributes-
natural-language" operation attribute of the request.
The IPP object MUST accept any natural language and any Natural
Language Override, whether the IPP object supports that natural
language or not (and independent of the value of the "ipp-
attribute-fidelity" Operation attribute). That is the IPP
object accepts all client supplied values no matter what the
values are in the Printer object"s "generated-natural-language-
supported" attribute. That attribute, "generated-natural-
language-supported", only applies to generated messages,
not client supplied messages. The IPP object MUST remember that
natural language for all client-supplied attributes, and when
returning those attributes in response to a query, the IPP
object MUST indicate that natural language.
Each value whose attribute syntax type is "text" or "name" (see
sections 4.1.1 and 4.1.2) has an Associated Natural-Language.
This document does not specify how this association is stored in
a Printer or Job object. When such a value is encoded in a
request or response, the natural language is either implicit or
explicit:
- In the implicit case, the value contains only the
text/name value, and the language is specified by the
"attributes-natural-language" operation attribute in the
request or response (see sections 4.1.1.1
textWithoutLanguage and 4.1.2.1 nameWithoutLanguage).
- In the explicit case (also known as the Natural-Language
Override case), the value contains both the language and
the text/name value (see sections 4.1.1.2
textWithLanguage and 4.1.2.2 nameWithLanguage).
For example, the "job-name" attribute MAY be supplied by the
client in a create request. The text value for this attribute
will be in the natural language identified by the "attribute-
natural-language" attribute, or if different, as identified by
the Natural Language Override mechanism. If supplied, the IPP
object will use the value of the "job-name" attribute to
populate the Job object"s "job-name" attribute. Whenever any
client queries the Job object"s "job-name" attribute, the IPP
object returns the attribute as stored and uses the Natural
Language Override mechanism to specify the natural language, if
it is different from that reported in the "attributes-natural-
language" operation attribute of the response. The IPP object
MAY use the Natural Language Override mechanism redundantly,
i.e., use it even when the value is in the same natural language
as the value supplied in the "attributes-natural-language"
operation attribute of the response.
An IPP object MUST NOT reject a request based on a supplied
natural language in an "attributes-natural-language" Operation
attribute or in any attribute that uses the Natural Language
Override.
See the "naturalLanguage" attribute syntax description in
section 4.1.8 for the syntax and semantic interpretation of the
values of this attribute and for example values.
Clients SHOULD NOT supply "text" or "name" attributes that use an
illegal combination of natural language and charset. For example,
suppose a Printer object supports charsets "utf-8", "iso-8859-1", and
"iso-8859-7". Suppose also, that it supports natural languages "en"
(English), "fr" (French), and "el" (Greek). Although the Printer
object supports the charset "iso-8859-1" and natural language "el",
it probably does not support the combination of Greek text strings
using the "iso-8859-1" charset. The Printer object handles this
apparent incompatibility differently depending on the context in
which it occurs:
- In a create request: If the client supplies a text or name
attribute (for example, the "job-name" operation attribute) that
uses an apparently incompatible combination, it is a client
choice that does not affect the Printer object or its correct
operation. Therefore, the Printer object simply accepts the
client supplied value, stores it with the Job object, and
responds back with the same combination whenever the client (or
any client) queries for that attribute.
- In a query-type operation, like Get-Printer-Attributes: If the
client requests an apparently incompatible combination, the
Printer object responds (as described in section 3.1.4.2) using
the Printer"s configured natural language rather than the natural
language requested by the client.
In either case, the Printer object does not reject the request
because of the apparent incompatibility. The potential incompatible
combination of charset and natural language can occur either at the
global operation level or at the Natural Language Override
attribute-by-attribute level. In addition, since the response always
includes explicit charset and natural language information, there is
never any question or ambiguity in how the client interprets the
response.
3.1.4.2 Response Operation Attributes
The Printer object MUST supply and the client MUST support the
following REQUIRED operation attributes in every IPP/1.0 operation
response:
"attributes-charset" (charset):
This operation attribute identifies the charset used by any "
text" and "name" attributes that the Printer object is returning
in this response. The value in this response MUST be the same
value as the "attributes-charset" operation attribute supplied
by the client in the request. If this is not possible
(i.e., the charset requested is not supported), the request
would have been rejected. See "attributes-charset" described in
Section 3.1.4.1 above.
If the Printer object supports more than just the "utf-8"
charset, the Printer object MUST be able to code convert between
each of the charsets supported on a highest fidelity possible
basis in order to return the "text" and "name" attributes in the
charset requested by the client. However, some information loss
MAY occur during the charset conversion depending on the
charsets involved. For example, the Printer object may convert
from a UTF-8 "a" to a US-ASCII "a" (with no loss of
information), from an ISO Latin 1 CAPITAL LETTER A WITH ACUTE
ACCENT to US-ASCII "A" (losing the accent), or from a UTF-8
Japanese Kanji character to some ISO Latin 1 error character
indication such as "?", decimal code equivalent, or to the
absence of a character, depending on implementation.
Note: Whether an implementation that supports more than one
charset stores the data in the charset supplied by the client or
code converts to one of the other supported charsets, depends on
implementation. The strategy should try to minimize loss of
information during code conversion. On each response, such an
implementation converts from its internal charset to that
requested.
"attributes-natural-language" (naturalLanguage):
This operation attribute identifies the natural language used by
any "text" and "name" attributes that the IPP object is
returning in this response. Unlike the "attributes-charset"
operation attribute, the IPP object NEED NOT return the same
value as that supplied by the client in the request. The IPP
object MAY return the natural language of the Job object or the
Printer"s configured natural language as identified by the
Printer object"s "natural-language-configured" attr