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Network Working Group
Request for Comments: 3382
Updates: 2910, 2911
Category: Standards Track
R. deBry
Utah Valley State College
R. Herriot
Consultant
T. Hastings
K. Ocke
P. Zehler
Xerox Corporation
September 2002

Internet Printing Protocol (IPP):

The 'collection' attribute syntax

Status of this Memo

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

Copyright Notice

Copyright © The Internet Society (2002). All Rights Reserved.

Abstract

This document specifies an OPTIONAL attribute syntax called 'collection' for use with the Internet Printing Protocol (IPP/1.0 and IPP/1.1). A 'collection' is a container holding one or more named values, which are called "member" attributes. A collection allows data to be grouped like a PostScript dictionary or a Java Map. This document also specifies the conformance requirements for a definition document that defines a collection attribute. Finally, this document gives some illustrative example collection attribute definitions that are not intended as actual attribute specifications.

Table of Contents

   1 Introduction.....................................................3
   1.1 Problem Statement..............................................3
   1.2 Solution.......................................................3
   2 Terminology......................................................4
   2.1 Conformance Terminology........................................4
   2.2 Other terminology..............................................5
   3 Definition of a Collection Attribute.............................5
   3.1 Information to Include.........................................5
   
   3.2 Nested Collections.............................................9
   4 Collection Attributes as Attributes in Operations................9
   4.1 General Rules..................................................9
   4.2 Unsupported Values.............................................9
   5 Example definition of a collection attribute.....................9
   5.1 media-col (collection)........................................10
   5.1.1 media-color (type3 keyword | name(MAX)......................10
   5.1.2 media-size (collection).....................................11
   5.2 media-col-default (collection)................................11
   5.3 media-col-ready (1setOf collection)...........................12
   5.4 media-col-supported (1setOf type2 keyword)....................12
   6 A Second Example Definition Of A Collection Attribute...........12
   7 Encoding........................................................13
   7.1 Additional tags defined for representing a collection
       attribute value...............................................13
   7.2 Example encoding: "media-col" (collection)....................14
   8 Legacy issues...................................................20
   9 IANA Considerations.............................................20
   10 Internationalization Considerations............................20
   11 Security Considerations........................................21
   12 References.....................................................21
   Appendix A: Encoding Example of a Simple Collection (Informative).22
   Appendix B: Encoding Example of 1setOf Collection (Informative)...25
   Appendix C: Encoding Example of Collection containing 1setOf XXX
               attribute (Informative)...............................31
   Appendix D: Description of the Base IPP Documents (Informative)...35
   Authors' Addresses................................................36
   Full Copyright Statement..........................................38

Table of Tables

   Table 1 - "media-col" member attributes...........................10
   Table 2 - "media-size" collection member attributes...............11
   Table 3 - Tags defined for encoding the 'collection' attribute
             syntax .................................................13
   Table 4 - Overview Encoding of "media-col" collection.............15
   Table 5 - Example Encoding of "media-col" collection..............16
   Table 6 - Overview Encoding of simple collection..................22
   Table 7 - Example Encoding of simple collection...................22
   Table 8 - Overview Encoding of 1setOf collection..................25
   Table 9 - Example Encoding of 1setOf collection...................26
   Table 10 - Overview Encoding of collection with 1setOf value......31
   Table 11 - Example Encoding of collection with 1setOf value.......32

1 Introduction

This document is an OPTIONAL extension to IPP/1.0 [RFC2565, RFC2566] and IPP/1.1 [RFC2911, RFC2910]. For a description of the base IPP documents see Appendix D.

1.1 Problem Statement

The IPP Model and Semantics [RFC2911] supports most of the common data structures that are available in programming languages. It lacks a mechanism for grouping several attributes of different types. The Java language uses the Map to solve this problem and PostScript has a dictionary. The new mechanism for grouping attributes together (called 'collection' mechanism) must allow for optional members and the subsequent addition of new members.

The 'collection' mechanism must be encoded in a manner consistent with existing 1.0 and 1.1 parsing rules (see [RFC2910]). Current 1.0 and 1.1 parsers that don't support the 'collection' mechanism must not confuse collections or parts of a collection they receive with other attributes.

1.2 Solution

The new mechanism is a new IPP attribute syntax called a 'collection'. As such, each collection value is a value of an attribute whose attribute syntax type is defined to be a 'collection'. Such an attribute is called a collection attribute. The name of the collection attribute serves to identify the collection value in an operation request or response, as with any attribute value.

The 'collection' attribute syntax is a container holding one or more named values (i.e., attributes), which are called member attributes. Each collection attribute definition document lists the mandatory and optional member attributes of each collection value. A collection value is similar to an IPP attribute group in a request or a response, such as the operation attributes group. They both consist of a set of attributes.

As with any attribute syntax, the document that defines a collection attribute specifies whether the attribute is single-valued (collection) or multi-valued (1setOf collection). If the attribute is multi-valued (1setOf collection), each collection value MUST be a separate instance of a single definition of a collection, i.e., it MUST have the same member attributes except for OPTIONAL member attributes. If we view each collection definition as a separate syntax type, this rule continues the IPP/1.1 notion that each attribute has a single type or pattern (e.g., "keyword | name" is a pattern). Without this rule, the supported values would be more difficult to describe and the mechanism defined in item 4 of section 3.1 would not be sufficient.

The name of each member attribute MUST be unique for a collection attribute, but MAY be the same as the name of a member attribute in another collection attribute and/or MAY be the same as the name of an attribute that is not a member of a collection. The rules for naming member attributes are given in section 3.1.

Each member attribute can have any attribute syntax type, including 'collection', and can be either single-valued or multi-valued. The length of a collection value is not limited. However, the length of each member attribute MUST NOT exceed the limit of its attribute syntax.

The member attributes in a collection MAY be in any order in a request or response. When a client sends a collection attribute to the Printer, the order that the Printer stores the member attributes of the collection value and the order returned in a response MAY be different from the order sent by the client.

A collection value MUST NOT contain two or more member attributes with the same attribute name. Such a collection is mal-formed. Clients MUST NOT submit such malformed requests and Printers MUST NOT return such malformed responses. If such a malformed request is submitted to a Printer, the Printer MUST (depending on implementation) either (1) reject the request with the 'client- error-bad-request' status code (see [RFC2911] section 13.1.4.1), or (2) accept the request and use only one of each duplicate member attributes.

2 Terminology

This section defines terminology used throughout this document.

2.1 Conformance Terminology

Capitalized terms, such as MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, MAY, NEED NOT, and OPTIONAL, have special meaning relating to conformance as defined in BCP 14, RFC 2119 [RFC2119] and [RFC2911], section 12.1. If an implementation supports the extension defined in this document, then these terms apply; otherwise, they do not. These terms define conformance to this document only; they do not affect conformance to other documents, unless explicitly stated otherwise.

2.2 Other terminology

This document uses terms such as Job object (or Job), IPP Printer object (or Printer), "operation", "request", response", "attributes", "keywords", and "support". These terms have special meaning and are defined in the model terminology [RFC2911] section 12.2. The following additional terms are introduced in this document:

collection: an attribute syntax in which each attribute value is a

set of attributes, called member attributes.

member attribute: an attribute that is defined to be used as one

of the attributes in a collection.

collection attribute: an attribute whose definition specifies the

'collection' attribute syntax and each of the member attributes that MAY occur in a collection attribute value.

3 Definition of a Collection Attribute

This section describes the requirements for any collection attribute definition.

3.1 Information to Include

   When a specification document defines an "xxx" collection attribute,
   i.e., an attribute whose attribute syntax type is 'collection' or
   '1setOf collection'; the definition document MUST include the
   following aspects of the attribute semantics.  Suppose the "xxx"
   collection attribute contains N member attributes named  "aaa1",
   "aaa2", ..., "aaaN" ("aaaI" represents any one of these N member
   attributes).
   
   1. The name of the collection attribute MUST be specified  (e.g.,
      "xxx").  The selection of the name "xxx" MUST follow the same
      rules for uniqueness as for attributes of any other syntax type,
      (as defined by IPP/1.1) unless "xxx" is a member attribute of
      another collection.  Then the selection of the name "xxx" MUST
      follow the rules for uniqueness defined in item 5a) of this list.
  1. The collection attribute syntax MUST be of type 'collection' or '1setOf collection'.
  1. The context of the collection attribute MUST be specified, i.e., whether the attribute is an operation attribute, a Job Template attribute, a Job Description attribute, a Printer Description attribute, a member attribute of a particular collection attribute, etc.
  1. An "xxx-supported" attribute MUST be specified and it has one of the following two forms:

a) "xxx-supported" is a "1setOf collection", which enumerates all

of the supported collection values of "xxx". If a collection of this form contains a nested collection, it MUST be of the same form.

For example, "media-size-supported" might have the values {{x- dimension:210, y-dimension:297},{x-dimension:297, y- dimension:420}} to show that it supports two values of "media size": A4 (210x297) and A3 (297x420). It does not support other combinations of "x-dimension" and "y-dimension" member attributes, such as 210x420 or 297x297, and it does not support non-enumerated values, such as 420x595.

b) "xxx-supported" is a "1setOf type2 keyword", which enumerates

the names of all of the member attributes of "xxx": "aaa1", "aaa2", ..., "aaaN". If a collection of this form contains a nested collection, it MAY be of either form. See item 5f) below for details on supported values of member attributes.

For example, "media-col-supported" might have the keyword values: "media-size" and "media-color".

  1. The member attributes MUST be defined. For each member attribute, the definition document MUST provide the following information:
      a) The member attribute's name (e.g., "aaa") MUST be unique within
         the collection being defined and MUST either:

i) reuse the attribute name of another attribute (that is

unique across the entire IPP attribute name space) and have the same syntax and semantics as the reused attribute (if the condition of item 4b) above is met). For example, a member attribute definition could reuse the IPP/1.1 "media" attribute.

ii) potentially occur elsewhere in the entire IPP attribute

name space. (if the condition of item 4a) above is met). For example, a member attribute could be "x-dimension", which could potentially occur in another collection or as an attribute outside of a collection.

iii) be unique across the entire IPP attribute name space (if

the condition of item 4b) above is met). For example, a member attribute could be "media-color" which must be unique across the entire IPP attribute name space.

b) Whether the member attribute is REQUIRED or OPTIONAL for the

Printer to support.

c) Whether the member attribute is REQUIRED or OPTIONAL for the

client to supply in a request.

d) The member attribute's syntax type, which can be any attribute

syntax, including '1setOf X', 'collection', and '1setOf collection'. If this attribute name reuses the name of another attribute (case of item a1 above), it MUST have the same attribute syntax, including cardinality (whether or not 1setOf).

e) The semantics of the "aaa" member attribute. The semantic

definition MUST include a description of any constraint or boundary conditions the member attribute places on the associated attribute, especially if the attribute reuses the name of another attribute (case of item a1 above).

f) The supported values for each "aaaI" member attribute (of the 

         member attributes  "aaa1", "aaa2", ..., "aaaN") is specified by
         one of two mechanisms.

i) If "xxx-supported" is a "1setOf collection" (see item 4a)

above), the value for each "aaaI" is specified in each collection value of "xxx-supported", in the context of other member attributes. That is, "xxx-supported" enumerates all supported values of "xxx".

ii) If the value of "xxx-supported" is a "1setOf type2

keyword" (see item 4b) above), the supported values of "aaaI" are the values specified by either i) the "aaaI- supported" attribute or ii) the definition of the member attribute "aaaI" within the document defining the "xxx" attribute. The values of each member attribute "aaaI" are specified independently of other member attributes, though a Printer is not required to support all combinations of supported values.

For example, "media-col-supported" might have the keyword values: "media-size" and "media-color". Using the first method for defining supported values (an "aaaI-supported" attribute), the collection values of "media-col" are combinations of values of "media-size-supported" and "media-color-supported". If "media-size-supported" has the values of '210x297' and '297x420' and "media-color- supported" has the values of 'white' and 'pink', the

Printer might support only the combinations 'white- 210x297', 'pink-210x297' and 'white-297x420', and not 'pink-297x420'.

If a collection contains a member "aaaI", whose syntax type is "text", the supported values would probably be defined by the definition of "xxx" rather than by the attribute "aaaI-supported".

g) the default value of each "aaaI" member attribute if it is

OPTIONAL for a client to supply the "aaa" member attribute in a request. The default value is specified by the attribute's definition within a document and MUST be one of the following:

i) a fixed default

ii) a mechanism by which the Printer determines default

iii) an indefinite default that is left to the implementation.

iv) an attribute that the Printer uses to determine the 

              default
  1. The default value of "xxx", if a client does not supply it. The default value is specified by the attribute's definition within a document and MUST be one of the following: a) a fixed default

b) a mechanism by which the Printer determines default

c) an indefinite default that is left to the implementation

d) a Printer attribute "xxx-default" which is a collection with

the same member attributes as "xxx". If optional member attributes are absent, the Printer uses the defaulting rules of item 5g) above.

  1. The "xxx-ready (1setOf collection)" attribute, if human intervention is required to make many of the supported values available. For example, "media-col" is an attribute which has a "ready" attribute. Most attributes do not have a "ready" attribute.

3.2 Nested Collections

A member attribute may have a syntax type of 'collection' or '1setOf collection', in which case it is called a nested collection attribute. The rules for a nested collection attribute are the same as for a collection attribute as specified in section 3.1.

4 Collection Attributes as Attributes in Operations

4.1 General Rules

A collection value is like any other IPP/1.1 value, except that it is structured. The rules for attributes with collection values are the same as for attributes of any other syntax type (see IPP/1.1), be they in any group of a request of a response.

4.2 Unsupported Values

The rules for returning an unsupported collection attribute are an extension to the current rules:

  1. If the entire collection attribute is unsupported, then the Printer returns just the collection attribute name with the 'unsupported' out-of-band value (see the beginning of [RFC2911] section 4.1) in the Unsupported Attributes Group.
  1. If a collection contains unrecognized, unsupported member attributes and/or conflicting values, the attribute returned in the Unsupported Group is a collection containing the unrecognized, unsupported member attributes, and/or conflicting values. The unrecognized member attributes have an out-of-band value of 'unsupported' (see the beginning of [RFC2911] section 4.1). The unsupported member attributes and conflicting values have their unsupported or conflicting values.

5 Example definition of a collection attribute

   In some printing environments, it is desirable to allow the client to
   select the media by its properties, e.g., weight, color, size, etc.,
   instead of by name.  In IPP/1.1 (see [RFC2911]), the "media (type3
   keyword | name) Job Template attribute allows selection by name.  It
   is tempting to extend the "media" attribute syntax to include
   "collection", but then existing clients could not understand default
   or supported media values that use the collection value.  To preserve
   interoperability, a new attribute MUST BE added, e.g., "media-col
   (collection)".  The following subsections contain a sample definition
   of a simplified "media-col" attribute.  The definition follows the
   rules in section 3.

All of the example attribute definitions in this document are illustrative examples, rather than actual definitions. These examples are intended to illustrate how to define collection attributes. Other documents MUST define collection attributes for use in actual interchange. Such definitions may be very similar to the examples in this document, since we attempted to pick useful examples.

Note: we picked the name "media-col" because the name "media" is already in use. Ordinarily the collection attribute would have a name like any other attribute and would not end in "col".

The member attributes of "media-col" attribute ("media-color (type 3 keyword)" and "media-size (collection)") both follow the naming rules of item 4a3 of section 3, i.e., the names are unique across the entire IPP attribute name space. The member attributes of the "media-size (collection)" member attribute ("x-dimension (integer(0:MAX))" and "y-dimension (integer(0:MAX))") both follow the naming rules of item 4a2 of section 3, i.e., they potentially occur elsewhere in the IPP attribute name space.

5.1 media-col (collection)

The "media-col" (collection) attribute augments the IPP/1.1 [RFC2911] "media" attribute. This collection attribute enables a client end user to submit a list of media characteristics to the Printer. When the client specifies media using the "media-col" collection attribute, the Printer object MUST match the requested media exactly. The 'collection' consists of the following member attributes:

Table 1 - "media-col" member attributes

        Attribute name  attribute syntax             request  Printer
                                                              Support

media-color type3 keyword | name (MAX) MAY MUST

media-size collection MUST MUST

The definitions for the member attributes is given in the following sub-sections:

5.1.1 media-color (type3 keyword | name(MAX)

This member attribute identifies the color of the media. Valid values are 'red', 'white' and 'blue'.

The "media-color-supported" (1setOf (type3 keyword | name(MAX))) Printer attribute identifies the values of this "media-color" member attribute that the Printer supports, i.e., the colors supported.

If the client omits this member attribute, the Printer determines the value in an implementation dependent manner.

5.1.2 media-size (collection)

This member attribute identifies the size of the media. The 'collection' consists of the member attributes shown in Table 2:

Table 2 - "media-size" collection member attributes

        Attribute name    attribute syntax      request   Printer
        
                                                          Support

x-dimension integer (0:MAX) MUST MUST

y-dimension integer (0:MAX) MUST MUST

The definitions for the member attributes are given in the following sub-sections:

5.1.2.1 x-dimension (integer(0:MAX))

This attribute identifies the width of the media in inch units along the X axis.

5.1.2.2 y-dimension (integer(0:MAX))

This attribute identifies the height of the media in inch units along the Y axis.

The "media-size-supported" (1setOf collection) Printer attribute identifies the values of this "media-size" member attribute that the Printer supports, i.e., the size combinations supported. The names of the member attributes are the same as the member attributes of the "media-size" collection attribute, namely "x-dimension", and "y- dimension", since they have the same attribute syntax and the same semantics.

5.2 media-col-default (collection)

The "media-col-default" Printer attribute specifies the media that the Printer uses, if any, if the client omits the "media-col" and "media". Job Template attributes in the Job Creation operation and the PDL do not include a media specification. The member attributes are defined in Table 1. A Printer MUST support the same member attributes for this default collection attribute as it supports for the corresponding "media-col" Job Template attribute.

5.3 media-col-ready (1setOf collection)

The "media-col-ready" Printer attribute identifies the media that are available for use without human intervention, i.e., the media that are ready to be used without human intervention. The collection value MUST have all of the member attributes that are supported in Table 1.

5.4 media-col-supported (1setOf type2 keyword)

The "media-col-supported" Printer attribute identifies the keyword names of the member attributes supported in the "media-col" collection Job Template attribute, i.e., the keyword names of the member attributes in Table 1 that the Printer supports.

6 A Second Example Definition Of A Collection Attribute

All of the example attribute definitions in this document are illustrative examples, rather than actual definitions. These examples are intended to illustrate how to define collection attributes. Other documents MUST define collection attributes for use in actual interchange. Such definitions may be very similar to the examples in this document, since we attempted to pick useful examples.

In some printing environments, it is desirable to allow the client to select the media for the job start sheet. The reason for not adding the 'collection' attribute syntax to the existing "job-sheets" Job Template attribute is the same as for "media". Instead, a new Job Template attribute is introduced, e.g., "job-sheet-col (collection)".

The member attributes of "job-sheet-col" attribute ("job-sheets (type 3 keyword)" and "media (type3 keyword | name)") both follow the naming rules of item 4a1 of section 3, i.e., they reuse existing IPP attributes. According to the rules, their supported values come from the existing IPP attributes: "job-sheets-supported" and "media- supported". However, their default values do not come from "job- sheets-default" and "media-default", respectively. Rather, the definition of "job-sheet-col" says that "job-sheets (type 3 keyword)" is required and if "media (type3 keyword | name)" is absent, the Printer uses the same media as the rest of the job uses.

If "job-sheet-col" attribute was defined to contain the member attribute "job-sheet-media (type3 keyword | name)" instead of "media (type3 keyword | name)", then the definition would also have to specify a "job-sheet-media-supported (1setOf (type3 keyword | name))" whose values would be independent of "media-supported (1setOf (type3 keyword | name))" and would be set separately by a System Administrator.

The actual text for the definition of the attribute is left as an exercise for the reader.

7 Encoding

This section defines the additional encoding tags used according to [RFC2910] and gives an example of their use. The encoding tags defined in this document MUST be used by all collection attributes defined in other documents. However, the example of their use is illustrative only.

7.1 Additional tags defined for representing a collection attribute

value

The 'collection' attribute syntax uses the tags defined in Table 3.

Table 3 - Tags defined for encoding the 'collection' attribute syntax 

        Tag name         Tag
        
                         value     Meaning
        
        begCollection    0x34      Begin the collection attribute value.
        
        endCollection    0x37      End the collection attribute value.
        
        memberAttrName   0x4A      The value is the name of the
                                   collection member attribute

When encoding a collection attribute "xxx" that contains an attribute "aaa" and is not inside another collection, the encoding follows these rules:

  1. The beginning of the collection is indicated with a value tag that MUST be syntax type 'begCollection' (0x34) with a name length and Name field that represent the name of the collection attribute ("xxx") as with any attribute, followed by a value. The Printer MAY ignore the value and its length MAY be 0. In the future, however, this field MAY contain useful information, such as the collection name (cf. the name of a C struct).
  1. Each member attribute is encoded as a sequence of two or more values that appear to be part of a single multi-valued attribute, i.e., 1setOf. The first value after the 'begCollection' value has the attribute syntax, 'memberAttrName' (0x4A), and its value holds the name of the first member attribute (e.g., "aaa"). The second value holds the first member's attribute value, which can be of any attribute syntax, except 'memberAttrName' or 'endCollection'. If the first member's attribute value is multi-valued, the third value holds the second value of the first member's value. Otherwise, the third value holds the name of second member attribute (e.g., "bbb"), and its attribute syntax is 'memberAttrName'. In this case, the fourth member's value is the value of "bbb".

Note that the technique of encoding a 'collection' as a '1setOf' makes it easy for a Printer that doesn't support a particular collection attribute (or the collection attribute syntax at all) to simply skip over the entire collection value.

  1. The end of the collection is indicated with a value tag that MUST be syntax type 'endCollection' (e.g., 0x37) and MAY have a zero name length and a zero value length. In the future, this field MAY contain useful information, such as the collection name that matches the one in the 'begCollection' .
  1. It is valid to have a member attribute that is itself, a collection attribute, i.e., collections can be nested within collections. This is represented by the occurrence of a member attribute that is of attribute syntax type 'begCollection'. Such a collection is terminated by a matching 'endCollection'. The name of such a member attribute is in the immediately preceding value, whose syntax type is 'memberAttrName'.
  1. It is valid for a collection attribute to be multi-valued, i.e., have more than one collection value. If the next attribute immediately following the 'endCollection' has a zero name length and a tag of 'begCollection', then the collection attribute is a multi-valued collection, as with any attribute. This statement applies to collections within collections and collections that are not in collections.

7.2 Example encoding: "media-col" (collection)

The collection specified in section 5 is used for the encoding example shown in Table 5. The example also shows nested collections, since the "media-size" member attribute is a 'collection. The encoding example represents a blue 4x6-index card and takes 216 octets. The Appendices contain more complex examples.

Additional examples have been included in the appendices.

The overall structure of the two collection values can be pictorially represented as:

"media-col" = 

        {  "media-color" =  'blue';
           "media-size" =
           {    "x-dimension" = 6;
                "y-dimension" = 4
             }
        },

The full encoding is in table 5. A simplified view of the encoding looks like this:

Table 4 - Overview Encoding of "media-col" collection

      Tag Value             Name                  Value
      
      begCollection         media-col             ""
      
      memberAttrName        ""                    media-color
      
      keyword               ""                    blue
      
      memberAttrName        ""                    media-size
      
      begCollection         ""                    ""
      
      memberAttrName        ""                    x-dimension
      
      integer               ""                    6
      
      memberAttrName        ""                    y-dimension
      
      integer               ""                    4
      
      endCollection         ""                    ""
      
      endCollection         ""                    ""

Table 5 - Example Encoding of "media-col" collection

      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x34         begCollection   value-tag  beginning of the "media-
                                              col" collection attribute
      
      0x0009                       name-      length of (collection)
                                   length     attribute name
      
      media-col    media-col       name       name of (collection)
                                              attribute
      
      0x0000                       value-     defined to be 0 for this
                                   length     type

no value (since value- length was 0) 

      0x4A         memberAttrName  value-tag  starts a new member
                                              attribute: "media-color"
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x000B                       value-     length of "media-color"
                                   length     keyword
      
      media-color  media-color     value      value is name of 1st
                                              member attribute
      
      0x44         keyword type    value-tag  keyword type
      
      0x0000                       name-      0 indicates 1setOf
                                   length

no name (since name-length was 0) 

      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x0004                       value-
                                   length
      
      blue         blue            value      value of 1st member
                                              attribute
      
      0x4A         memberAttrName  value-tag  starts a new member
                                              attribute: "media-size"
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x000A                       value-     length of "media-size"
                                   length     keyword
      
      media-size   media-size      value      Name of 2nd member
                                              attribute
      
      0x34         begCollection   value-tag  Beginning of the "media-
                                              size" collection attribute
                                              which is a sub-collection
      
      0x0000                       name-      0 indicates 1setOf
                                   length

no name (since name-length was 0) 

      0x0000                       value-     collection attribute names
                                   length     have no value

no value (since value- length was 0) 

      0x4A         memberAttrName  value-tag  starts a new member
                                              attribute: "x-dimension"
      
      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x000B                       value-     length of "x-dimension"
                                   length     keyword
      
      x-dimension  x-dimension     value      name of  1st sub-
                                              collection member
                                              attribute
      
      0x21         integer type    value-tag  attribute type
      
      0x0000                       name-      0 indicates 1setOf
                                   length

no name (since name-length was 0) 

      0x0004                       value-     length of an integer = 4
                                   length
      
      0x0006                       value      value of  1st sub-
                                              collection member
                                              attribute
      
      0x4A         memberAttrName  value-tag  starts a new member
                                              attribute: "y-dimension"
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x000B                       value-     length of the "y-
                                   length     dimension" keyword
      
      Octets       Symbolic Value  Protocol   comments
                                   field
      
      y-dimension  y-dimension     value      name of  2nd sub-
                                              collection member
                                              attribute
      
      0x21         integer type    value-tag  attribute type
      
      0x0000                       name-      0 indicates 1setOf
                                   length

no name (since name-length was 0) 

      0x0004                       value-     length of an integer = 4
                                   length
      
      0x0004                       value      value of  2nd sub-
                                              collection member
                                              attribute
      
      0x37         endCollection   value-tag  end of the sub-collection
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x0000                       value-     defined to be 0 for this
                                   length     type

no value (since value- length was 0) 

      0x37         endCollection   value-tag  end of the 1st collection
                                              value in 1setOf
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf
      
      Octets       Symbolic Value  Protocol   comments
                                   field

no name (since name-length was 0) 

      0x0000                       value-     defined to be 0 for this
                                   length     type

no value (since value- length was 0)

8 Legacy issues

IPP 1.x Printers and Clients will gracefully ignore collections and its member attributes if it does not understand the collection. The begCollection and endCollection elements each look like an attribute with an attribute syntax that the recipient doesn't support and so should ignore the entire attribute. The individual member attributes and their values will look like a 1setOf values of the collection attribute, so that the Printer simply ignores the entire attribute and all of its values. Returning unsupported attributes is also simple, since only the name of the collection attribute is returned with the 'unsupported' out-of-band value (see section 4.2).

9 IANA Considerations

The following table provides registration for the 'collection' attribute syntax defined in this document. This is to be registered according to the procedures in RFC 2911 [RFC2911] section 6.3. 

   Tag value:      Attribute Syntaxes:            Ref.      Section:
   collection                                     RFC 3382         3
   
     0x34          begCollection                  RFC 3382       7.1
     0x37          endCollection                  RFC 3382       7.1
     0x4A          memberAttrName                 RFC 3382       7.1
   
   The resulting attribute syntax registration will be published in the
   http://www.iana.org/assignments/ipp-registrations registry.

10 Internationalization Considerations

This attribute syntax by itself has no impact on internationalization. However, the member attributes that are subsequently defined for use in a collection may have internationalization considerations, as may any attribute, according to [RFC2911].

11 Security Considerations

This attribute syntax causes no more security concerns than any other attribute syntax. It is only the attributes that are subsequently defined, to use this or any other attribute syntax, that may have security concerns, depending on the semantics of the attribute, according to [RFC2911].

12 References

12.1 Normative References

   [RFC2910] Herriot, R., Butler, S., Moore, P. and R. Turner, "Internet
             Printing Protocol/1.1: Encoding and Transport", RFC 2910,
             September 2000.

[RFC2911] Isaacson, S., deBry, R., Hastings, T., Herriot, R. and P.

Powell, "Internet Printing Protocol/1.1: Model and Semantics", RFC 2911, September 2000.

12.2 Informative References

   [RFC2565] Herriot, R., Butler, S., Moore, P. and R. Tuner, "Internet
             Printing Protocol/1.0: Encoding and Transport", RFC 2565,
             April 1999.

[RFC2566] deBry, R., Hastings, T., Herriot, R., Isaacson, S. and P.

Powell, "Internet Printing Protocol/1.0: Model and Semantics", RFC 2566, April 1999. 

   [RFC2567] Wright, D., "Design Goals for an Internet Printing
             Protocol", RFC 2567, April 1999.
   
   [RFC2568] Zilles, S., "Rationale for the Structure and Model and
             Protocol for the Internet Printing Protocol", RFC 2568,
             April 1999.
   
   [RFC2569] Herriot, R., Hastings, T., Jacobs, N. and J. Martin,
             "Mapping between LPD and IPP Protocols", RFC 2569, April
             1999.
   
   [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter,
             L., Leach, P. and T. Berners-Lee, "Hypertext Transfer
             Protocol - HTTP/1.1", RFC 2616, June 1999.

[RFC3196] Hastings, T., Manros, C., Zehler, P., Kugler, C. and H.

Holst, "Internet Printing Protocol/1.1: Implementor's Guide", RFC 3196, November 2001.

Appendix A: Encoding Example of a Simple Collection (Informative)

The overall structure of the collection value can be pictorially represented as:

"media-size" = 

        {  "x-dimension" = 6;
           "y-dimension" = 4
        }

A simplified view of the encoding would look like this:

Table 6 - Overview Encoding of simple collection

      Tag Value             Name                  Value
      
      begCollection         media-size            ""
      
      memberAttrName        ""                    x-dimension
      
      integer               ""                    6
      
      memberAttrName        ""                    y-dimension
      
      integer               ""                    4
      
      endCollection         ""                    ""

Note:

"" represents a name or value whose length is 0.

Table 7 - Example Encoding of simple collection

      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x34         begCollection   value-tag  beginning of the "media-
                                              size" collection attribute
      
      0x000A                       name-      length of (collection)
                                   length     attribute name
      
      media-size   media-size      name       name of (collection)
                                              attribute
      
      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x0000                       value-     defined to be 0 for this
                                   length     type

no value (since value- length was 0) 

      0x4A         memberAttrName  value-tag  starts member attribute:
                                              "x-dimension"
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x000B                       value-     length of "x-dimension"
                                   length     keyword
      
      x-dimension  x-dimension     value      name of  1st collection
                                              member attribute
      
      0x21         integer type    value-tag  attribute type
      
      0x0000                       name-      0 indicates 1setOf
                                   length

no name (since name-length was 0) 

      0x0004                       value-     length of an integer = 4
                                   length
      
      0x0006                       value      value of  1st collection
                                              member attribute
      
      0x4A         memberAttrName  value-tag  starts a new member
                                              attribute: "y-dimension"
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x000B                       value-     length of the "y-
                                   length     dimension" keyword
      
      y-dimension  y-dimension     value      name of  2nd collection
                                              member attribute
      
      0x21         integer type    value-tag  attribute type
      
      0x0000                       name-      0 indicates 1setOf for
                                   length     media-size

no name (since name-length was 0) 

      0x0004                       value-     length of an integer = 4
                                   length
      
      0x0004                       value      value of  2nd collection
                                              member attribute
      
      0x37         endCollection   value-tag  end of the collection
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x0000                       value-     defined to be 0 for this
                                   length     type

no value (since value- length was 0)

Appendix B: Encoding Example of 1setOf Collection (Informative)

The overall structure of the collection value can be pictorially represented as:

"media-size-supported" = 

        {  "x-dimension" = 6;
           "y-dimension" = 4
        },
        {  "x-dimension" = 3;
           "y-dimension" = 5
        };

A simplified view of the encoding would look like this:

Table 8 - Overview Encoding of 1setOf collection

      Tag Value              Name                 Value
      
      begCollection          media-size-          ""
                             supported
      
      memberAttrName         ""                   x-dimension
      
      integer                ""                   6
      
      memberAttrName         ""                   y-dimension
      
      integer                ""                   4
      
      endCollection          ""                   ""
      
      begCollection          ""                   ""
      
      memberAttrName         ""                   x-dimension
      
      integer                ""                   3
      
      memberAttrName         ""                   y-dimension
      
      integer                ""                   5
      
      endCollection          ""                   ""

Table 9 - Example Encoding of 1setOf collection

      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x34         begCollection   value-tag  beginning of the "media-
                                              size-supported (1setOf
                                              collection" attribute
      
      0x00014                      name-      length of (collection)
                                   length     attribute name
      
      media-size-  media-size-     name       name of (collection)
      supported    supported                  attribute
      
      0x0000                       value-     defined to be 0 for this
                                   length     type

no value (since value- length was 0) 

      0x4A         memberAttrName  value-tag  starts member attribute:
                                              "x-dimension"
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x000B                       value-     length of "x-dimension"
                                   length     keyword
      
      x-dimension  x-dimension     value      name of  1st collection
                                              member attribute
      
      0x21         integer type    value-tag  attribute type
      
      0x0000                       name-      0 indicates 1setOf
                                   length

no name (since name-length was 0) 

      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x0004                       value-     length of an integer = 4
                                   length
      
      0x0006                       value      value of  1st collection
                                              member attribute
      
      0x4A         memberAttrName  value-tag  starts member attribute:
                                              "y-dimension"
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x000B                       value-     length of the "y-
                                   length     dimension" keyword
      
      y-dimension  y-dimension     value      name of  2nd collection
                                              member attribute
      
      0x21         integer type    value-tag  attribute type
      
      0x0000                       name-      0 indicates 1setOf
                                   length

no name (since name-length was 0) 

      0x0004                       value-     length of an integer = 4
                                   length
      
      0x0004                       value      value of  2nd collection
                                              member attribute
      
      0x37         endCollection   value-tag  end of the collection
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x0000                       value-     defined to be 0 for this
                                   length     type

no value (since value- length was 0) 

      0x34         begCollection   value-tag  beginning of the 2nd
                                              member of the 1setOf
                                              "sizes-avail " collection
                                              attribute
      
      0x0000                       name-      Zero length name indicates
                                   length     this is member of previous
                                              attribute
      
                                   name       no name (since name-length
                                              was 0)
      
      0x0000                       value-     defined to be 0 for this
                                   length     type

no value (since value- length was 0) 

      0x4A         memberAttrName  value-tag  starts member attribute:
                                              "x-dimension"
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x000B                       value-     length of "x-dimension"
                                   length     keyword
      
      x-dimension  x-dimension     value      name of  1st collection
                                              member attribute
      
      0x21         integer type    value-tag  attribute type
      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x0000                       name-      0 indicates 1setOf
                                   length

no name (since name-length was 0) 

      0x0004                       value-     length of an integer = 4
                                   length
      
      0x0003                       value      value of  1st collection
                                              member attribute
      
      0x4A         memberAttrName  value-tag  starts member attribute:
                                              "y-dimension"
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x000B                       value-     length of the "y-
                                   length     dimension" keyword
      
      y-dimension  y-dimension     value      name of  2nd collection
                                              member attribute
      
      0x21         integer type    value-tag  attribute type
      
      0x0000                       name-      0 indicates 1setOf
                                   length

no name (since name-length was 0) 

      0x0004                       value-     length of an integer = 4
                                   length
      
      0x0005                       value      value of  2nd collection
                                              member attribute
      
      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x37         endCollection   value-tag  end of the 1setOf
                                              collection value
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x0000                       value-     defined to be 0 for this
                                   length     type

no value (since value- length was 0)

Appendix C: Encoding Example of Collection containing 1setOf XXX

attribute (Informative)

The overall structure of the collection value can be pictorially represented as:

"wagons" = 

        {  "colors" = red, blue;
           "sizes" = 4, 6, 8
        }

A simplified view of the encoding would look like this:

Table 10 - Overview Encoding of collection with 1setOf value

Tag Value Name Value

begCollection wagons ""

memberAttrName "" colors

keyword "" red

keyword "" blue

memberAttrName "" sizes

integer "" 4

integer "" 6

integer "" 8

endCollection "" ""

Table 11 - Example Encoding of collection with 1setOf value

      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x34         begCollection   value-tag  beginning of the "wagons"
                                              collection attribute
      
      0x0005                       name-      length of (collection)
                                   length     attribute name
      
      wagons       wagons          name       name of (collection)
                                              attribute
      
      0x0000                       value-     defined to be 0 for this
                                   length     type

no value (since value- length was 0) 

      0x4A         memberAttrName  value-tag  starts a new member
                                              attribute: "colors"
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x0006                       value-     length of "colors" keyword
                                   length
      
      colors       colors          value      value is name of 1st
                                              member attribute
      
      0x44         keyword type    value-tag  keyword type
      
      0x0000                       name-      0 indicates 1setOf wagons
                                   length

no name (since name-length was 0) 

      0x0004                       value-
                                   length
      
      Octets       Symbolic Value  Protocol   comments
                                   field
      
      blue         blue            value      value of 1st member
                                              attribute
      
      0x44         keyword type    value-tag  keyword type
      
      0x0000                       name-      0 indicates 1setOf wagons
                                   length

no name (since name-length was 0) 

      0x0003                       value-
                                   length
      
      red          red             value      value of 1st member
                                              attribute
      
      0x4A         memberAttrName  value-tag  starts a new member
                                              attribute: "sizes"
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x0005                       value-     length of "length-avail"
                                   length     keyword
      
      sizes        sizes           value      Name of 2nd member
                                              attribute
      
      0x21         integer type    value-tag  attribute type
      
      0x0000                       name-      0 indicates 1setOf wagons
                                   length

no name (since name-length was 0) 

      0x0004                       value-     length of an integer = 4
                                   length
      
      Octets       Symbolic Value  Protocol   comments
                                   field
      
      0x0004                       value      1st value for 1setOf
                                              integer attribute
      
      0x21         integer type    value-tag  attribute type
      
      0x0000                       name-      0 indicates 1setOf
                                   length

no name (since name-length was 0) 

      0x0004                       value-
                                   length     length of an integer = 4
      
      0x0006                       value      2nd value for 1setOf
                                              integer attribute
      
      0x21         integer type    value-tag  attribute type
      
      0x0000                       name-      0 indicates 1setOf
                                   length

no name (since name-length was 0) 

      0x0004                       value-     length of an integer = 4
                                   length
      
      0x0008                       value      3rd  value for 1setOf
                                              integer attribute
      
      0x37         endCollection   value-tag  end of the collection
      
      0x0000                       name-      defined to be 0 for this
                                   length     type, so part of 1setOf

no name (since name-length was 0) 

      0x0000                       value-     defined to be 0 for this
                                   length     type
      
      Octets       Symbolic Value  Protocol   comments
                                   field

no value (since value- length was 0)

Appendix D: Description of the Base IPP Documents (Informative)

The base 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/1.1: Model and Semantics [RFC2911] Internet Printing Protocol/1.1: Encoding and Transport [RFC2910] Internet Printing Protocol/1.1: Implementer's Guide [RFC3196] 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 [RFC2566, RFC2565]. A few OPTIONAL operator operations have been added to IPP/1.1 [RFC2911, RFC2910].

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 specification documents, and gives background and rationale for the IETF IPP working group's major decisions.

The "Internet Printing Protocol/1.1: Model and Semantics" document describes a simplified model with abstract objects, their attributes, and their operations. The model introduces a Printer and a Job. The Job supports multiple documents per Job. The model document also addresses how security, internationalization, and directory issues are addressed.

The "Internet Printing Protocol/1.1: Encoding and Transport" document is a formal mapping of the abstract operations and attributes defined in the model document onto HTTP/1.1 [RFC2616]. It also defines the encoding rules for a new Internet MIME media type called "application/ipp". This document also defines the rules for transporting over HTTP a message body whose Content-Type is "application/ipp". This document defines the 'ipp' scheme for identifying IPP printers and jobs.

The "Internet Printing Protocol/1.1: Implementer's Guide" document gives insight and advice to implementers of IPP clients and IPP objects. It is intended to help them understand IPP/1.1 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.

Authors' Addresses

Roger deBry
Utah Valley State College
Orem, UT 84058 

   Phone: (801) 222-8000
   EMail: [email protected]
   
   Tom Hastings
   Xerox Corporation
   737 Hawaii St.  ESAE 231
   El Segundo, CA  90245
   
   Phone: 310-333-6413
   Fax: 310-333-5514
   EMail: [email protected]

Robert Herriot
Consultant
706 Colorado Ave
Palo Alto, CA 94303 

   Phone: 650-327-4466
   Fax: 650-327-4466
   EMail: [email protected]

Kirk Ocke
Xerox Corp.
800 Phillips Rd
M/S 128-30E
Webster, NY 14580 

   Phone: (585) 442-4832
   EMail: [email protected]

Peter Zehler
Xerox Corp.
800 Phillips Rd
M/S 128-30E
Webster, NY 14580 

   Phone: (585) 265-8755
   EMail: [email protected]
   
   IPP Web Page:  http://www.pwg.org/ipp/
   IPP Mailing List:  [email protected]

To subscribe to the ipp mailing list, send the following email:

1) send it to [email protected]
2) leave the subject line blank
3) put the following two lines in the message body:

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Implementers of this specification document are encouraged to join the IPP Mailing List in order to participate in any discussions of clarification issues and review of registration proposals for additional attributes and values. In order to reduce spam the mailing list rejects mail from non-subscribers, so you must subscribe to the mailing list in order to send a question or comment to the mailing list.

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