Network Working Group R. deBry

Network Working Group R. deBry
Request for Comments: 3382 Utah Valley State College
Updates: 2910, 2911 R. Herriot
Category: Standards Track 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 (C) 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

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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

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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

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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.

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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.

2. The collection attribute syntax MUST be of type 'collection' or
'1setOf collection'.

3. 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.

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4. 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".

5. 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.

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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

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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

6. 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.

7. 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.

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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.

2. 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.

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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'.

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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

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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.

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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).

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2. 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.

3. 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' .

4. 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'.

5. 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.

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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 "" ""

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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)

deBry, et. al. Standards Track [Page 16]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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"

deBry, et. al. Standards Track [Page 17]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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

deBry, et. al. Standards Track [Page 18]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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

deBry, et. al. Standards Track [Page 19]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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].

deBry, et. al. Standards Track [Page 20]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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.

deBry, et. al. Standards Track [Page 21]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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

deBry, et. al. Standards Track [Page 22]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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)

deBry, et. al. Standards Track [Page 23]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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)

deBry, et. al. Standards Track [Page 24]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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 "" ""

deBry, et. al. Standards Track [Page 25]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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)

deBry, et. al. Standards Track [Page 26]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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)

deBry, et. al. Standards Track [Page 27]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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

deBry, et. al. Standards Track [Page 28]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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

deBry, et. al. Standards Track [Page 29]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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)

deBry, et. al. Standards Track [Page 30]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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 "" ""

deBry, et. al. Standards Track [Page 31]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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

deBry, et. al. Standards Track [Page 32]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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

deBry, et. al. Standards Track [Page 33]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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

deBry, et. al. Standards Track [Page 34]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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.

deBry, et. al. Standards Track [Page 35]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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]

deBry, et. al. Standards Track [Page 36]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

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:
subscribe ipp
end

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.

deBry, et. al. Standards Track [Page 37]

RFC 3382 IPP: The 'collection' attribute syntax September 2002

Full Copyright Statement

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

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
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English.

The limited permissions granted above are perpetual and will not be
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This document and the information contained herein is provided on an
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.

deBry, et. al. Standards Track [Page 38]