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Internet Printing Protocol/1.1: Encoding and Transport
draft-sweet-rfc2910bis-00

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This is an older version of an Internet-Draft that was ultimately published as RFC 8010.
Authors Michael Sweet , Ira McDonald
Last updated 2015-04-25
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draft-sweet-rfc2910bis-00
IPP                                                             M. Sweet
Internet-Draft                                                Apple Inc.
Obsoletes: 2910 (if approved)                                I. McDonald
Intended status: Standards Track                        High North, Inc.
Expires: October 27, 2015                                 April 25, 2015

         Internet Printing Protocol/1.1: Encoding and Transport
                       draft-sweet-rfc2910bis-00

Abstract

   This document is one of a set of documents, which together describe
   all aspects of a new Internet Printing Protocol (IPP).  IPP is an
   application level protocol that can be used for distributed printing
   using Internet tools and technologies.  This document defines the
   rules for encoding IPP operations and IPP attributes into 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 a new
   scheme named 'ipp' for identifying IPP printers and jobs.

Editor's Note

   This draft is being submitted in preparation for a so-called "fast
   track" IETF IPP WG, with drafts being reviewed and edited by the
   IEEE-ISTO's Printer Working Group IPP WG, in order to correct known
   editorial issues and advance IPP/1.1 to IETF Internet Standard.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 27, 2015.

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Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conformance Terminology . . . . . . . . . . . . . . . . . . .   3
   3.  Encoding of the Operation Layer . . . . . . . . . . . . . . .   4
   3.1.  Picture of the Encoding . . . . . . . . . . . . . . . . . .   5
   3.1.1.  Request and Response  . . . . . . . . . . . . . . . . . .   5
   3.1.2.  Attribute Group . . . . . . . . . . . . . . . . . . . . .   5
   3.1.3.  Attribute . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.1.4.  Picture of the Encoding of an Attribute-with-one-value  .   6
   3.1.5.  Additional-value  . . . . . . . . . . . . . . . . . . . .   7
   3.1.6.  Alternative Picture of the Encoding of a Request Or a
           Response  . . . . . . . . . . . . . . . . . . . . . . . .   7
   3.2.  Syntax of Encoding  . . . . . . . . . . . . . . . . . . . .   8
   3.3.  Attribute-group . . . . . . . . . . . . . . . . . . . . . .  10
   3.4.  Required Parameters . . . . . . . . . . . . . . . . . . . .  11
   3.4.1.  Version-number  . . . . . . . . . . . . . . . . . . . . .  11
   3.4.2.  Operation-id  . . . . . . . . . . . . . . . . . . . . . .  11
   3.4.3.  Status-code . . . . . . . . . . . . . . . . . . . . . . .  12
   3.4.4.  Request-id  . . . . . . . . . . . . . . . . . . . . . . .  12
   3.5.  Tags  . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   3.5.1.  Delimiter Tags  . . . . . . . . . . . . . . . . . . . . .  12
   3.5.2.  Value Tags  . . . . . . . . . . . . . . . . . . . . . . .  14
   3.6.  Name-Length . . . . . . . . . . . . . . . . . . . . . . . .  17
   3.7.  (Attribute) Name  . . . . . . . . . . . . . . . . . . . . .  17
   3.8.  Value Length  . . . . . . . . . . . . . . . . . . . . . . .  17
   3.9.  (Attribute) Value . . . . . . . . . . . . . . . . . . . . .  18
   3.10. Data  . . . . . . . . . . . . . . . . . . . . . . . . . . .  19
   4.  Encoding of Transport Layer . . . . . . . . . . . . . . . . .  19
   4.1.  Printer-uri and job-uri . . . . . . . . . . . . . . . . . .  20
   5.  IPP URL Scheme  . . . . . . . . . . . . . . . . . . . . . . .  21
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  23
   7.  Internationalization Considerations . . . . . . . . . . . . .  24
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  24
   8.1.  Security Conformance Requirements . . . . . . . . . . . . .  24
   8.1.1.  Digest Authentication . . . . . . . . . . . . . . . . . .  24

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   8.2.  Using IPP with TLS  . . . . . . . . . . . . . . . . . . . .  26
   9.  Interoperability with IPP/1.0 Implementations . . . . . . . .  26
   9.1.  The "version-number" Parameter  . . . . . . . . . . . . . .  26
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
   10.1.  Normative References . . . . . . . . . . . . . . . . . . .  28
   10.2.  Informative References . . . . . . . . . . . . . . . . . .  30
   Appendix A.  Protocol Examples  . . . . . . . . . . . . . . . . .  32
   A.1.  Print-Job Request . . . . . . . . . . . . . . . . . . . . .  32
   A.2.  Print-Job Response (successful) . . . . . . . . . . . . . .  33
   A.3.  Print-Job Response (failure)  . . . . . . . . . . . . . . .  34
   A.4.  Print-Job Response (success with attributes ignored)  . . .  36
   A.5.  Print-URI Request . . . . . . . . . . . . . . . . . . . . .  37
   A.6.  Create-Job Request  . . . . . . . . . . . . . . . . . . . .  38
   A.7.  Get-Jobs Request  . . . . . . . . . . . . . . . . . . . . .  39
   A.8.  Get-Jobs Response . . . . . . . . . . . . . . . . . . . . .  40
   Appendix B.  Registration of MIME Media Type Information for
                "application/ipp"  . . . . . . . . . . . . . . . . .  42
   Appendix C.  Changes from IPP/1.0 . . . . . . . . . . . . . . . .  43
   Appendix D.  Acknowledgements . . . . . . . . . . . . . . . . . .  44
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  45

1.  Introduction

   This document contains the rules for encoding IPP operations and
   describes two layers: the transport layer and the operation layer.

   The transport layer consists of an HTTP/1.1 request or response.  RFC
   2616 [RFC2616] describes HTTP/1.1.  This document specifies the HTTP
   headers that an IPP implementation supports.

   The operation layer consists of a message body in an HTTP request or
   response.  The document "Internet Printing Protocol/1.1: Model and
   Semantics" [RFC2911] defines the semantics of such a message body and
   the supported values.  This document specifies the encoding of an IPP
   operation.  The aforementioned document [RFC2911] is henceforth
   referred to as the "IPP model document" or simply "model document."

   Note: the version number of IPP (1.1) and HTTP (1.1) are not linked.
   They both just happen to be 1.1.

2.  Conformance Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
   "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
   interpreted as described in RFC 2119 [RFC2119].

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3.  Encoding of the Operation Layer

   The operation layer is the message body part of the HTTP request or
   response and it MUST contain a single IPP operation request or IPP
   operation response.  Each request or response consists of a sequence
   of values and attribute groups.  Attribute groups consist of a
   sequence of attributes each of which is a name and value.  Names and
   values are ultimately sequences of octets.

   The encoding consists of octets as the most primitive type.  There
   are several types built from octets, but three important types are
   integers, character strings and octet strings, on which most other
   data types are built.  Every character string in this encoding MUST
   be a sequence of characters where the characters are associated with
   some charset and some natural language.  A character string MUST be
   in "reading order" with the first character in the value (according
   to reading order) being the first character in the encoding.  A
   character string whose associated charset is US-ASCII whose
   associated natural language is US English is henceforth called a US-
   ASCII-STRING.  A character string whose associated charset and
   natural language are specified in a request or response as described
   in the model document is henceforth called a LOCALIZED-STRING.  An
   octet string MUST be in "IPP model document order" with the first
   octet in the value (according to the IPP model document order) being
   the first octet in the encoding.  Every integer in this encoding MUST
   be encoded as a signed integer using two's-complement binary encoding
   with big-endian format (also known as "network order" and "most
   significant byte first").  The number of octets for an integer MUST
   be 1, 2 or 4, depending on usage in the protocol.  Such one-octet
   integers, henceforth called SIGNED-BYTE, are used for the version-
   number and tag fields.  Such two-byte integers, henceforth called
   SIGNED-SHORT are used for the operation-id, status-code and length
   fields.  Four byte integers, henceforth called SIGNED-INTEGER, are
   used for value fields and the request-id.

   The following two sections present the encoding of the operation
   layer in two ways:

   o  informally through pictures and description

   o  formally through Augmented Backus-Naur Form (ABNF), as specified
      by RFC 2234 [RFC2234]

   An operation request or response MUST use the encoding described in
   these two sections.

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3.1.  Picture of the Encoding

3.1.1.  Request and Response

   An operation request or response is encoded as follows:

   -----------------------------------------------
   |                  version-number             |   2 bytes  - required
   -----------------------------------------------
   |               operation-id (request)        |
   |                      or                     |   2 bytes  - required
   |               status-code (response)        |
   -----------------------------------------------
   |                   request-id                |   4 bytes  - required
   -----------------------------------------------
   |                 attribute-group             |   n bytes - 0 or more
   -----------------------------------------------
   |              end-of-attributes-tag          |   1 byte   - required
   -----------------------------------------------
   |                     data                    |   q bytes  - optional
   -----------------------------------------------

   The first three fields in the above diagram contain the value of
   attributes described in Section 3.1.1 of the Model document.

   The fourth field is the "attribute-group" field, and it occurs 0 or
   more times.  Each "attribute-group" field represents a single group
   of attributes, such as an Operation Attributes group or a Job
   Attributes group (see the Model document).  The IPP model document
   specifies the required attribute groups and their order for each
   operation request and response.

   The "end-of-attributes-tag" field is always present, even when the
   "data" is not present.  The Model document specifies for each
   operation request and response whether the "data" field is present or
   absent.

3.1.2.  Attribute Group

   Each "attribute-group" field is encoded as follows:

   -----------------------------------------------
   |           begin-attribute-group-tag         |  1 byte
   ----------------------------------------------------------
   |                   attribute                 |  p bytes |- 0 or more
   ----------------------------------------------------------

   An "attribute-group" field contains zero or more "attribute" fields.

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   Note, the values of the "begin-attribute-group-tag" field and the
   "end-of-attributes-tag" field are called "delimiter-tags".

3.1.3.  Attribute

   An "attribute" field is encoded as follows:

   -----------------------------------------------
   |          attribute-with-one-value           |  q bytes
   ----------------------------------------------------------
   |             additional-value                |  r bytes |- 0 or more
   ----------------------------------------------------------

   When an attribute is single valued (e.g. "copies" with value of 10)
   or multi-valued with one value (e.g. "sides-supported" with just the
   value 'one-sided') it is encoded with just an "attribute-with-one-
   value" field.  When an attribute is multi-valued with n values (e.g.
   "sides-supported" with the values 'one-sided' and 'two-sided-long-
   edge'), it is encoded with an "attribute-with-one-value" field
   followed by n-1 "additional-value" fields.

3.1.4.  Picture of the Encoding of an Attribute-with-one-value

   Each "attribute-with-one-value" field is encoded as follows:

   -----------------------------------------------
   |                   value-tag                 |   1 byte
   -----------------------------------------------
   |               name-length  (value is u)     |   2 bytes
   -----------------------------------------------
   |                     name                    |   u bytes
   -----------------------------------------------
   |              value-length  (value is v)     |   2 bytes
   -----------------------------------------------
   |                     value                   |   v bytes
   -----------------------------------------------

   An "attribute-with-one-value" field is encoded with five subfields:

   o  The "value-tag" field specifies the attribute syntax, e.g. 0x44
      for the attribute syntax 'keyword'.

   o  The "name-length" field specifies the length of the "name" field
      in bytes, e.g. u in the above diagram or 15 for the name "sides-
      supported ".

   o  The "name" field contains the textual name of the attribute, e.g.
      "sides-supported".

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   o  The "value-length" field specifies the length of the "value" field
      in bytes, e.g. v in the above diagram or 9 for the (keyword) value
      'one-sided'.

   o  The "value" field contains the value of the attribute, e.g. the
      textual value 'one-sided'.

3.1.5.  Additional-value

   Each "additional-value" field is encoded as follows:

   -----------------------------------------------
   |                   value-tag                 |   1 byte
   -----------------------------------------------
   |            name-length  (value is 0x0000)   |   2 bytes
   -----------------------------------------------
   |              value-length (value is w)      |   2 bytes
   -----------------------------------------------
   |                     value                   |   w bytes
   -----------------------------------------------

   An "additional-value" is encoded with four subfields:

   o  The "value-tag" field specifies the attribute syntax, e.g. 0x44
      for the attribute syntax 'keyword'.

   o  The "name-length" field has the value of 0 in order to signify
      that it is an "additional-value".  The value of the "name-length"
      field distinguishes an "additional-value" field ("name-length" is
      0) from an "attribute-with-one-value" field ("name-length" is not
      0).

   o  The "value-length" field specifies the length of the "value" field
      in bytes, e.g. w in the above diagram or 19 for the (keyword)
      value 'two-sided-long-edge'.

   o  The "value" field contains the value of the attribute, e.g. the
      textual value 'two-sided-long-edge'.

3.1.6.  Alternative Picture of the Encoding of a Request Or a Response

   From the standpoint of a parser that performs an action based on a
   "tag" value, the encoding consists of:

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   -----------------------------------------------
   |                  version-number             |   2 bytes  - required
   -----------------------------------------------
   |               operation-id (request)        |
   |                      or                     |   2 bytes  - required
   |               status-code (response)        |
   -----------------------------------------------
   |                   request-id                |   4 bytes  - required
   -----------------------------------------------------------
   |        tag (delimiter-tag or value-tag)     |   1 byte  |
   -----------------------------------------------           |-0 or more
   |           empty or rest of attribute        |   x bytes |
   -----------------------------------------------------------
   |              end-of-attributes-tag          |   1 byte   - required
   -----------------------------------------------
   |                     data                    |   y bytes  - optional
   -----------------------------------------------

   The following show what fields the parser would expect after each
   type of "tag":

   o  "begin-attribute-group-tag": expect zero or more "attribute"
      fields

   o  "value-tag": expect the remainder of an "attribute-with-one-value"
      or an "additional-value".

   o  "end-of-attributes-tag": expect that "attribute" fields are
      complete and there is optional "data"

3.2.  Syntax of Encoding

   The syntax below is ABNF [RFC2234] except 'strings of literals' MUST
   be case sensitive.  For example 'a' means lower case 'a' and not
   upper case 'A'.  In addition, SIGNED-BYTE and SIGNED-SHORT fields are
   represented as '%x' values which show their range of values.

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   ipp-message = ipp-request / ipp-response
   ipp-request = version-number operation-id request-id
            *attribute-group end-of-attributes-tag data
   ipp-response = version-number status-code request-id
            *attribute-group end-of-attributes-tag  data
   attribute-group = begin-attribute-group-tag *attribute
   version-number = major-version-number minor-version-number
   major-version-number = SIGNED-BYTE
   minor-version-number = SIGNED-BYTE
   operation-id = SIGNED-SHORT    ; mapping from model defined below
   status-code = SIGNED-SHORT  ; mapping from model defined below
   request-id = SIGNED-INTEGER ; whose value is > 0
   attribute = attribute-with-one-value *additional-value
   attribute-with-one-value = value-tag name-length name
       value-length value
   additional-value = value-tag zero-name-length value-length value
   name-length = SIGNED-SHORT    ; number of octets of 'name'
   name = LALPHA *( LALPHA / DIGIT / "-" / "_" / "." )
   value-length = SIGNED-SHORT   ; number of octets of 'value'
   value = OCTET-STRING
   data = OCTET-STRING
   zero-name-length = %x00.00              ; name-length of 0
   value-tag = %x10-FF                  ;see section 3.7.2
   begin-attribute-group-tag = %x00-02 / %04-0F ; see section 3.7.1
   end-of-attributes-tag = %x03                    ; tag of 3
                                   ; see section 3.7.1
   SIGNED-BYTE = BYTE
   SIGNED-SHORT = 2BYTE
   SIGNED-INTEGER = 4BYTE
   DIGIT = %x30-39    ;  "0" to "9"
   LALPHA = %x61-7A   ;  "a" to "z"
   BYTE = %x00-FF
   OCTET-STRING = *BYTE

   The syntax below defines additional terms that are referenced in this
   document.  This syntax provides an alternate grouping of the
   delimiter tags.

   delimiter-tag = begin-attribute-group-tag  / ; see section 3.7.1
             end-of-attributes-tag
   delimiter-tag = %x00-0F                      ; see section 3.7.1
   begin-attribute-group-tag = %x00 / operation-attributes-tag /
      job-attributes-tag / printer-attributes-tag /
      unsupported-attributes-tag /  %x06-0F
   operation-attributes-tag =  %x01                ; tag of 1
   job-attributes-tag      =  %x02                 ; tag of 2
   printer-attributes-tag =  %x04                  ; tag of 4
   unsupported-attributes-tag =  %x05      ; tag of 5

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3.3.  Attribute-group

   Each "attribute-group" field MUST be encoded with the "begin-
   attribute-group-tag" field followed by zero or more "attribute" sub-
   fields.

   The table below maps the model document group name to value of the
   "begin-attribute-group-tag" field:

   +----------------+--------------------------------------------------+
   | Model Document | "begin-attribute-group-tag" field values         |
   | Group          |                                                  |
   +----------------+--------------------------------------------------+
   | Operation      | "operations-attributes-tag"                      |
   | Attributes     |                                                  |
   +----------------+--------------------------------------------------+
   | Job Template   | "job-attributes-tag"                             |
   | Attributes     |                                                  |
   +----------------+--------------------------------------------------+
   | Job Object     | "job-attributes-tag"                             |
   | Attributes     |                                                  |
   +----------------+--------------------------------------------------+
   | Unsupported    | "unsupported-attributes-tag"                     |
   | Attributes     |                                                  |
   +----------------+--------------------------------------------------+
   | Requested      | (Get-Job-Attributes) "job-attributes-tag"        |
   | Attributes     |                                                  |
   +----------------+--------------------------------------------------+
   | Requested      | (Get-Printer-Attributes)"printer-attributes-tag" |
   | Attributes     |                                                  |
   +----------------+--------------------------------------------------+
   | Document       | in a special position as described above         |
   | Content        |                                                  |
   +----------------+--------------------------------------------------+

   For each operation request and response, the model document
   prescribes the required and optional attribute groups, along with
   their order.  Within each attribute group, the model document
   prescribes the required and optional attributes, along with their
   order.

   When the Model document requires an attribute group in a request or
   response and the attribute group contains zero attributes, a request
   or response SHOULD encode the attribute group with the "begin-
   attribute-group-tag" field followed by zero "attribute" fields.  For
   example, if the client requests a single unsupported attribute with
   the Get-Printer-Attributes operation, the Printer MUST return no
   "attribute" fields, and it SHOULD return a "begin-attribute-group-

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   tag" field for the Printer Attributes Group.  The Unsupported
   Attributes group is not such an example.  According to the model
   document, the Unsupported Attributes Group SHOULD be present only if
   the unsupported attributes group contains at least one attribute.

   A receiver of a request MUST be able to process the following as
   equivalent empty attribute groups:

   a.  A "begin-attribute-group-tag" field with zero following
       "attribute" fields.

   b.  An expected but missing "begin-attribute-group-tag" field.

   When the Model document requires a sequence of an unknown number of
   attribute groups, each of the same type, the encoding MUST contain
   one "begin-attribute-group-tag" field for each attribute group even
   when an "attribute-group" field contains zero "attribute" sub-fields.
   For example, for the Get-Jobs operation may return zero attributes
   for some jobs and not others.  The "begin-attribute-group-tag" field
   followed by zero "attribute" fields tells the recipient that there is
   a job in queue for which no information is available except that it
   is in the queue.

3.4.  Required Parameters

   Some operation elements are called parameters in the model document
   [RFC2911].  They MUST be encoded in a special position and they MUST
   NOT appear as operation attributes.  These parameters are described
   in the subsections below.

3.4.1.  Version-number

   The "version-number" field MUST consist of a major and minor version-
   number, each of which MUST be represented by a SIGNED-BYTE.  The
   major version-number MUST be the first byte of the encoding and the
   minor version-number MUST be the second byte of the encoding.  The
   protocol described in this document MUST have a major version-number
   of 1 (0x01) and a minor version-number of 1 (0x01).  The ABNF for
   these two bytes MUST be %x01.01.

3.4.2.  Operation-id

   The "operation-id" field MUST contain an operation-id value defined
   in the model document.  The value MUST be encoded as a SIGNED-SHORT
   and it MUST be in the third and fourth bytes of the encoding of an
   operation request.

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3.4.3.  Status-code

   The "status-code" field MUST contain a status-code value defined in
   the model document.  The value MUST be encoded as a SIGNED-SHORT and
   it MUST be in the third and fourth bytes of the encoding of an
   operation response.

   The status-code is an operation attribute in the model document.  In
   the protocol, the status-code is in a special position, outside of
   the operation attributes.

   If an IPP status-code is returned, then the HTTP Status-Code MUST be
   200 (successful-ok).  With any other HTTP Status-Code value, the HTTP
   response MUST NOT contain an IPP message-body, and thus no IPP
   status-code is returned.

3.4.4.  Request-id

   The "request-id" field MUST contain a request-id value as defined in
   the model document.  The value MUST be encoded as a SIGNED- INTEGER
   and it MUST be in the fifth through eighth bytes of the encoding.

3.5.  Tags

   There are two kinds of tags:

   o  delimiter tags: delimit major sections of the protocol, namely
      attributes and data

   o  value tags: specify the type of each attribute value

3.5.1.  Delimiter Tags

   The following table specifies the values for the delimiter tags:

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   +--------------+----------------------------------------------------+
   | Tag Value    | Meaning                                            |
   | (Hex)        |                                                    |
   +--------------+----------------------------------------------------+
   | 0x00         | reserved for definition in a future IETF standards |
   |              | track document                                     |
   +--------------+----------------------------------------------------+
   | 0x01         | "operation-attributes-tag"                         |
   +--------------+----------------------------------------------------+
   | 0x02         | "job-attributes-tag"                               |
   +--------------+----------------------------------------------------+
   | 0x03         | "end-of-attributes-tag"                            |
   +--------------+----------------------------------------------------+
   | 0x04         | "printer-attributes-tag"                           |
   +--------------+----------------------------------------------------+
   | 0x05         | "unsupported-attributes-tag"                       |
   +--------------+----------------------------------------------------+
   | 0x06-0x0f    | reserved for future delimiters in IETF standards   |
   |              | track documents                                    |
   +--------------+----------------------------------------------------+

   When a "begin-attribute-group-tag" field occurs in the protocol, it
   means that zero or more following attributes up to the next delimiter
   tag MUST be attributes belonging to the attribute group specified by
   the value of the "begin-attribute-group-tag".  For example, if the
   value of "begin-attribute-group-tag" is 0x01, the following
   attributes MUST be members of the Operations Attributes group.

   The "end-of-attributes-tag" (value 0x03) MUST occur exactly once in
   an operation.  It MUST be the last "delimiter-tag".  If the operation
   has a document-content group, the document data in that group MUST
   follow the "end-of-attributes-tag".

   The order and presence of "attribute-group" fields (whose beginning
   is marked by the "begin-attribute-group-tag" subfield) for each
   operation request and each operation response MUST be that defined in
   the model document.  For further details, see Section 3.7
   "(Attribute) Name" and 13 "Appendix A: Protocol Examples".

   A Printer MUST treat a "delimiter-tag" (values from 0x00 through
   0x0F) differently from a "value-tag" (values from 0x10 through 0xFF)
   so that the Printer knows that there is an entire attribute group
   that it doesn't understand as opposed to a single value that it
   doesn't understand.

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3.5.2.  Value Tags

   The remaining tables show values for the "value-tag" field, which is
   the first octet of an attribute.  The "value-tag" field specifies the
   type of the value of the attribute.

   The following table specifies the "out-of-band" values for the
   "value-tag" field.

   +------------+------------------------------------------------------+
   | Tag Value  | Meaning                                              |
   | (Hex)      |                                                      |
   +------------+------------------------------------------------------+
   | 0x10       | unsupported                                          |
   +------------+------------------------------------------------------+
   | 0x11       | reserved for 'default' for definition in a future    |
   |            | IETF standards track document                        |
   +------------+------------------------------------------------------+
   | 0x12       | unknown                                              |
   +------------+------------------------------------------------------+
   | 0x13       | no-value                                             |
   +------------+------------------------------------------------------+
   | 0x14-0x1F  | reserved for "out-of-band" values in future IETF     |
   |            | standards track documents.                           |
   +------------+------------------------------------------------------+

   The following table specifies the integer values for the "value-tag"
   field:

   +------------+------------------------------------------------------+
   | Tag Value  | Meaning                                              |
   | (Hex)      |                                                      |
   +------------+------------------------------------------------------+
   | 0x20       | reserved for definition in a future IETF standards   |
   |            | track document                                       |
   +------------+------------------------------------------------------+
   | 0x21       | integer                                              |
   +------------+------------------------------------------------------+
   | 0x22       | boolean                                              |
   +------------+------------------------------------------------------+
   | 0x23       | enum                                                 |
   +------------+------------------------------------------------------+
   | 0x24-0x2F  | reserved for integer types for definition in future  |
   |            | IETF standards track documents                       |
   +------------+------------------------------------------------------+

   NOTE: 0x20 is reserved for "generic integer" if it should ever be
   needed.

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   The following table specifies the octetString values for the "value-
   tag" field:

   +------------+------------------------------------------------------+
   | Tag Value  | Meaning                                              |
   | (Hex)      |                                                      |
   +------------+------------------------------------------------------+
   | 0x30       | octetString with an unspecified format               |
   +------------+------------------------------------------------------+
   | 0x31       | dateTime                                             |
   +------------+------------------------------------------------------+
   | 0x32       | resolution                                           |
   +------------+------------------------------------------------------+
   | 0x33       | rangeOfInteger                                       |
   +------------+------------------------------------------------------+
   | 0x34       | reserved for definition in a future IETF standards   |
   |            | track document                                       |
   +------------+------------------------------------------------------+
   | 0x35       | textWithLanguage                                     |
   +------------+------------------------------------------------------+
   | 0x36       | nameWithLanguage                                     |
   +------------+------------------------------------------------------+
   | 0x37-0x3F  | reserved for octetString type definitions in future  |
   |            | IETF standards track documents                       |
   +------------+------------------------------------------------------+

   The following table specifies the character-string values for the
   "value-tag" field:

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   +------------+------------------------------------------------------+
   | Tag Value  | Meaning                                              |
   | (Hex)      |                                                      |
   +------------+------------------------------------------------------+
   | 0x40       | reserved for definition in a future IETF standards   |
   |            | track document                                       |
   +------------+------------------------------------------------------+
   | 0x41       | textWithoutLanguage                                  |
   +------------+------------------------------------------------------+
   | 0x42       | nameWithoutLanguage                                  |
   +------------+------------------------------------------------------+
   | 0x43       | reserved for definition in a future IETF standards   |
   |            | track document                                       |
   +------------+------------------------------------------------------+
   | 0x44       | keyword                                              |
   +------------+------------------------------------------------------+
   | 0x45       | uri                                                  |
   +------------+------------------------------------------------------+
   | 0x46       | uriScheme                                            |
   +------------+------------------------------------------------------+
   | 0x47       | charset                                              |
   +------------+------------------------------------------------------+
   | 0x48       | naturalLanguage                                      |
   +------------+------------------------------------------------------+
   | 0x49       | mimeMediaType                                        |
   +------------+------------------------------------------------------+
   | 0x4A-0x5F  | reserved for character string type definitions in    |
   |            | future IETF standards track documents                |
   +------------+------------------------------------------------------+

   NOTE: 0x40 is reserved for "generic character-string" if it should
   ever be needed.

   NOTE: An attribute value always has a type, which is explicitly
   specified by its tag; one such tag value is "nameWithoutLanguage".
   An attribute's name has an implicit type, which is keyword.

   The values 0x60-0xFF are reserved for future type definitions in IETF
   standards track documents.

   The tag 0x7F is reserved for extending types beyond the 255 values
   available with a single byte.  A tag value of 0x7F MUST signify that
   the first 4 bytes of the value field are interpreted as the tag
   value.  Note this future extension doesn't affect parsers that are
   unaware of this special tag.  The tag is like any other unknown tag,
   and the value length specifies the length of a value, which contains
   a value that the parser treats atomically.  Values from 0x00 to
   0x37777777 are reserved for definition in future IETF standard track

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   documents.  The values 0x40000000 to 0x7FFFFFFF are reserved for
   vendor extensions.

3.6.  Name-Length

   The "name-length" field MUST consist of a SIGNED-SHORT.  This field
   MUST specify the number of octets in the immediately following "name"
   field.  The value of this field excludes the two bytes of the "name-
   length" field.  For example, if the "name" field contains "sides",
   the value of this field is 5.

   If a "name-length" field has a value of zero, the following "name"
   field MUST be empty, and the following value MUST be treated as an
   additional value for the attribute encoded in the nearest preceding
   "attribute-with-one-value" field.  Within an attribute group, if two
   or more attributes have the same name, the attribute group is mal-
   formed (see [RFC2911] Section 3.1.3).  The zero-length name is the
   only mechanism for multi-valued attributes.

3.7.  (Attribute) Name

   The "name " field MUST contain the name of an attribute.  The model
   document [RFC2911] specifies such names.

3.8.  Value Length

   The "value-length" field MUST consist of a SIGNED-SHORT.  This field
   MUST specify the number of octets in the immediately following
   "value" field.  The value of this field excludes the two bytes of the
   "value-length" field.  For example, if the "value" field contains the
   keyword (text) value 'one-sided', the value of this field is 9.

   For any of the types represented by binary signed integers, the
   sender MUST encode the value in exactly four octets.

   For any of the types represented by character-strings, the sender
   MUST encode the value with all the characters of the string and
   without any padding characters.

   For "out-of-band" "value-tag" fields defined in this document, such
   as "unsupported", the "value-length" MUST be 0 and the "value" empty;
   the "value" has no meaning when the "value-tag" has one of these
   "out-of-band" values.  For future "out-of-band" "value-tag" fields,
   the same rule holds unless the definition explicitly states that the
   "value-length" MAY be non-zero and the "value" non-empty

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3.9.  (Attribute) Value

   The syntax types (specified by the "value-tag" field) and most of the
   details of the representation of attribute values are defined in the
   IPP model document.  The table below augments the information in the
   model document, and defines the syntax types from the model document
   in terms of the 5 basic types defined in Section 3 "Encoding of the
   Operation Layer".  The 5 types are US-ASCII-STRING, LOCALIZED-STRING,
   SIGNED-INTEGER, SIGNED-SHORT, SIGNED-BYTE, and OCTET-STRING.

   +----------------------+--------------------------------------------+
   | Syntax of Attribute  | Encoding                                   |
   | Value                |                                            |
   +----------------------+--------------------------------------------+
   | textWithoutLanguage, | LOCALIZED-STRING                           |
   | nameWithoutLanguage  |                                            |
   +----------------------+--------------------------------------------+
   | textWithLanguage     | OCTET-STRING consisting of 4 fields: a. a  |
   |                      | SIGNED-SHORT which is the number of octets |
   |                      | in the following field, b. a value of type |
   |                      | natural-language, c. a SIGNED-SHORT which  |
   |                      | is the number of octets in the following   |
   |                      | field, and d. a value of type              |
   |                      | textWithoutLanguage.  The length of a      |
   |                      | textWithLanguage value MUST be 4 + the     |
   |                      | value of field a + the value of field c.   |
   +----------------------+--------------------------------------------+
   | nameWithLanguage     | OCTET-STRING consisting of 4 fields: a. a  |
   |                      | SIGNED-SHORT which is the number of octets |
   |                      | in the following field, b. a value of type |
   |                      | natural-language, c. a SIGNED-SHORT which  |
   |                      | is the number of octets in the following   |
   |                      | field, and d. a value of type              |
   |                      | nameWithoutLanguage.  The length of a      |
   |                      | nameWithLanguage value MUST be 4 + the     |
   |                      | value of field a + the value of field c.   |
   +----------------------+--------------------------------------------+
   | charset,             | US-ASCII-STRING                            |
   | naturalLanguage,     |                                            |
   | mimeMediaType,       |                                            |
   | keyword, uri, and    |                                            |
   | uriScheme            |                                            |
   +----------------------+--------------------------------------------+
   | boolean              | SIGNED-BYTE where 0x00 is 'false' and 0x01 |
   |                      | is 'true'                                  |
   +----------------------+--------------------------------------------+
   | integer and enum     | a SIGNED-INTEGER                           |
   +----------------------+--------------------------------------------+

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   | dateTime             | OCTET-STRING consisting of eleven octets   |
   |                      | whose contents are defined by              |
   |                      | "DateAndTime" in RFC 1903 [RFC1903]        |
   +----------------------+--------------------------------------------+
   | resolution           | OCTET-STRING consisting of nine octets of  |
   |                      | 2 SIGNED-INTEGERs followed by a SIGNED-    |
   |                      | BYTE. The first SIGNED-INTEGER contains    |
   |                      | the value of cross feed direction          |
   |                      | resolution. The second SIGNED-INTEGER      |
   |                      | contains the value of feed direction       |
   |                      | resolution. The SIGNED-BYTE contains the   |
   |                      | units value.                               |
   +----------------------+--------------------------------------------+
   | rangeOfInteger       | Eight octets consisting of 2 SIGNED-       |
   |                      | INTEGERs. The first SIGNED-INTEGER         |
   |                      | contains the lower bound and the second    |
   |                      | SIGNED-INTEGER contains the upper bound.   |
   +----------------------+--------------------------------------------+
   | 1setOf X             | Encoding according to the rules for an     |
   |                      | attribute with more than 1 value. Each     |
   |                      | value X is encoded according to the rules  |
   |                      | for encoding its type.                     |
   +----------------------+--------------------------------------------+
   | octetString          | OCTET-STRING                               |
   +----------------------+--------------------------------------------+

   The attribute syntax type of the value determines its encoding and
   the value of its "value-tag".

3.10.  Data

   The "data" field MUST include any data required by the operation.

4.  Encoding of Transport Layer

   HTTP/1.1 [RFC2616] is the transport layer for this protocol.

   The operation layer has been designed with the assumption that the
   transport layer contains the following information:

   o  the URI of the target job or printer operation

   o  the total length of the data in the operation layer, either as a
      single length or as a sequence of chunks each with a length.

   It is REQUIRED that a printer implementation support HTTP over the
   IANA assigned Well Known Port 631 (the IPP default port), though a
   printer implementation may support HTTP over some other port as well.

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   Each HTTP operation MUST use the POST method where the request-URI is
   the object target of the operation, and where the "Content-Type" of
   the message-body in each request and response MUST be "application/
   ipp".  The message-body MUST contain the operation layer and MUST
   have the syntax described in Section 3.2 "Syntax of Encoding".  A
   client implementation MUST adhere to the rules for a client described
   for HTTP1.1 [RFC2616] . A printer (server) implementation MUST adhere
   the rules for an origin server described for HTTP1.1 [RFC2616].

   An IPP server sends a response for each request that it receives.  If
   an IPP server detects an error, it MAY send a response before it has
   read the entire request.  If the HTTP layer of the IPP server
   completes processing the HTTP headers successfully, it MAY send an
   intermediate response, such as "100 Continue", with no IPP data
   before sending the IPP response.  A client MUST expect such a variety
   of responses from an IPP server.  For further information on
   HTTP/1.1, consult the HTTP documents [RFC2616].

   An HTTP server MUST support chunking for IPP requests, and an IPP
   client MUST support chunking for IPP responses according to
   HTTP/1.1[RFC2616].  Note: this rule causes a conflict with non-
   compliant implementations of HTTP/1.1 that don't support chunking for
   POST methods, and this rule may cause a conflict with non-compliant
   implementations of HTTP/1.1 that don't support chunking for CGI
   scripts

4.1.  Printer-uri and job-uri

   All Printer and Job objects are identified by a Uniform Resource
   Identifier (URI) [RFC2396] so that they can be persistently and
   unambiguously referenced.  The notion of a URI is a useful concept,
   however, until the notion of URI is more stable (i.e., defined more
   completely and deployed more widely), it is expected that the URIs
   used for IPP objects will actually be URLs [RFC1738]  [RFC1808].
   Since every URL is a specialized form of a URI, even though the more
   generic term URI is used throughout the rest of this document, its
   usage is intended to cover the more specific notion of URL as well.

   Some operation elements are encoded twice, once as the request-URI on
   the HTTP Request-Line and a second time as a REQUIRED operation
   attribute in the application/ipp entity.  These attributes are the
   target URI for the operation and are called printer-uri and job-uri.
   Note: The target URI is included twice in an operation referencing
   the same IPP object, but the two URIs NEED NOT be literally
   identical.  One can be a relative URI and the other can be an
   absolute URI.  HTTP/1.1 allows clients to generate and send a
   relative URI rather than an absolute URI.  A relative URI identifies
   a resource with the scope of the HTTP server, but does not include

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   scheme, host or port.  The following statements characterize how URLs
   should be used in the mapping of IPP onto HTTP/1.1:

   1.  Although potentially redundant, a client MUST supply the target
       of the operation both as an operation attribute and as a URI at
       the HTTP layer.  The rationale for this decision is to maintain a
       consistent set of rules for mapping application/ipp to possibly
       many communication layers, even where URLs are not used as the
       addressing mechanism in the transport layer.

   2.  Even though these two URLs might not be literally identical (one
       being relative and the other being absolute), they MUST both
       reference the same IPP object.  However, a Printer NEED NOT
       verify that the two URLs reference the same IPP object, and NEED
       NOT take any action if it determines the two URLs to be
       different.

   3.  The URI in the HTTP layer is either relative or absolute and is
       used by the HTTP server to route the HTTP request to the correct
       resource relative to that HTTP server.  The HTTP server need not
       be aware of the URI within the operation request.

   4.  Once the HTTP server resource begins to process the HTTP request,
       it might get the reference to the appropriate IPP Printer object
       from either the HTTP URI (using to the context of the HTTP server
       for relative URLs) or from the URI within the operation request;
       the choice is up to the implementation.

   5.  HTTP URIs can be relative or absolute, but the target URI in the
       operation MUST be an absolute URI.

5.  IPP URL Scheme

   The IPP/1.1 document defines a new scheme 'ipp' as the value of a URL
   that identifies either an IPP printer object or an IPP job object.
   The IPP attributes using the 'ipp' scheme are specified below.
   Because the HTTP layer does not support the 'ipp' scheme, a client
   MUST map 'ipp' URLs to 'http' URLs, and then follows the HTTP
   [RFC2616][RFC2617] rules for constructing a Request-Line and HTTP
   headers.  The mapping is simple because the 'ipp' scheme implies all
   of the same protocol semantics as that of the 'http' scheme
   [RFC2616], except that it represents a print service and the implicit
   (default) port number that clients use to connect to a server is port
   631.

   In the remainder of this section the term 'ipp-URL' means a URL whose
   scheme is 'ipp' and whose implicit (default) port is 631.  The term

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   'http-URL' means a URL whose scheme is 'http', and the term 'https-
   URL' means a URL whose scheme is 'https'.

   A client and an IPP object (i.e. the server) MUST support the ipp-URL
   value in the following IPP attributes:

   o  job attributes:

      *  job-uri

      *  job-printer-uri

   o  printer attributes:

      *  printer-uri-supported

   o  operation attributes:

      *  job-uri

      *  printer-uri

   Each of the above attributes identifies a printer or job object.  The
   ipp-URL is intended as the value of the attributes in this list, and
   for no other attributes.  All of these attributes have a syntax type
   of 'uri', but there are attributes with a syntax type of 'uri' that
   do not use the 'ipp' scheme, e.g. 'job-more-info'.

   If a printer registers its URL with a directory service, the printer
   MUST register an ipp-URL.

   User interfaces are beyond the scope of this document.  But if
   software exposes the ipp-URL values of any of the above five
   attributes to a human user, it is REQUIRED that the human see the
   ipp-URL as is.

   When a client sends a request, it MUST convert a target ipp-URL to a
   target http-URL for the HTTP layer according to the following rules:

   1.  change the 'ipp' scheme to 'http'

   2.  add an explicit port 631 if the URL does not contain an explicit
       port.  Note: port 631 is the IANA assigned Well Known Port for
       the 'ipp' scheme.

   The client MUST use the target http-URL in both the HTTP Request-Line
   and HTTP headers, as specified by HTTP[RFC2616][RFC2617] . However,
   the client MUST use the target ipp-URL for the value of the "printer-

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   uri" or "job-uri" operation attribute within the application/ipp body
   of the request.  The server MUST use the ipp-URL for the value of the
   "printer-uri", "job-uri" or "printer-uri-supported" attributes within
   the application/ipp body of the response.

   For example, when an IPP client sends a request directly (i.e. no
   proxy) to an ipp-URL "ipp://myhost.com/myprinter/myqueue", it opens a
   TCP connection to port 631 (the ipp implicit port) on the host
   "myhost.com" and sends the following data:

     POST /myprinter/myqueue HTTP/1.1
     Host: myhost.com:631
     Content-type: application/ipp
     Transfer-Encoding: chunked
     ...
     "printer-uri" "ipp://myhost.com/myprinter/myqueue"
            (encoded in application/ipp message body)
     ...

   As another example, when an IPP client sends the same request as
   above via a proxy "myproxy.com", it opens a TCP connection to the
   proxy port 8080 on the proxy host "myproxy.com" and sends the
   following data:

     POST http://myhost.com:631/myprinter/myqueue   HTTP/1.1
     Host: myhost.com:631
     Content-type: application/ipp
     Transfer-Encoding: chunked
     ...
     "printer-uri" "ipp://myhost.com/myprinter/myqueue"
            (encoded in application/ipp message body)
     ...

   The proxy then connects to the IPP origin server with headers that
   are the same as the "no-proxy" example above.

6.  IANA Considerations

   This section describes the procedures for allocating encoding for the
   following IETF standards track extensions and vendor extensions to
   the IPP/1.1 Encoding and Transport document:

   1.  attribute syntaxes - see [RFC2911] section 6.3

   2.  attribute groups - see [RFC2911] section 6.5

   3.  out-of-band attribute values - see [RFC2911] section 6.7

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   These extensions follow the "type2" registration procedures defined
   in [RFC2911] Section 6.  Extensions registered for use with IPP/1.1
   are OPTIONAL for client and IPP object conformance to the IPP/1.1
   Encoding and Transport document.

   These extension procedures are aligned with the guidelines as set
   forth by the IESG [IANA-CON].  The [RFC2911] describes how to propose
   new registrations for consideration.  IANA will reject registration
   proposals that leave out required information or do not follow the
   appropriate format described in [RFC2911].  The IPP/1.1 Encoding and
   Transport document may also be extended by an appropriate RFC that
   specifies any of the above extensions.

7.  Internationalization Considerations

   See the section on "Internationalization Considerations" in the
   document "Internet Printing Protocol/1.1: Model and Semantics"
   [RFC2911] for information on internationalization.  This document
   adds no additional issues.

8.  Security Considerations

   The IPP Model and Semantics document [RFC2911] discusses high level
   security requirements (Client Authentication, Server Authentication
   and Operation Privacy).  Client Authentication is the mechanism by
   which the client proves its identity to the server in a secure
   manner.  Server Authentication is the mechanism by which the server
   proves its identity to the client in a secure manner.  Operation
   Privacy is defined as a mechanism for protecting operations from
   eavesdropping.

8.1.  Security Conformance Requirements

   This section defines the security requirements for IPP clients and
   IPP objects.

8.1.1.  Digest Authentication

   IPP clients MUST support:

      Digest Authentication [RFC2617].

         MD5 and MD5-sess MUST be implemented and supported.

         The Message Integrity feature NEED NOT be used.

   IPP Printers SHOULD support:

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      Digest Authentication [RFC2617].

         MD5 and MD5-sess MUST be implemented and supported.

         The Message Integrity feature NEED NOT be used.

   The reasons that IPP Printers SHOULD (rather than MUST) support
   Digest Authentication are:

   1.  While Client Authentication is important, there is a certain
       class of printer devices where it does not make sense.
       Specifically, a low-end device with limited ROM space and low
       paper throughput may not need Client Authentication.  This class
       of device typically requires firmware designers to make trade-
       offs between protocols and functionality to arrive at the lowest-
       cost solution possible.  Factored into the designer's decisions
       is not just the size of the code, but also the testing,
       maintenance, usefulness, and time-to-market impact for each
       feature delivered to the customer.  Forcing such low-end devices
       to provide security in order to claim IPP/1.1 conformance would
       not make business sense and could potentially stall the adoption
       of the standard.

   2.  Print devices that have high-volume throughput and have available
       ROM space have a compelling argument to provide support for
       Client Authentication that safeguards the device from
       unauthorized access.  These devices are prone to a high loss of
       consumables and paper if unauthorized access should occur.

   8.1.2 Transport Layer Security (TLS)

   IPP Printers SHOULD support Transport Layer Security (TLS) [RFC2246]
   for Server Authentication and Operation Privacy.  IPP Printers MAY
   also support TLS for Client Authentication.  If an IPP Printer
   supports TLS, it MUST support the TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA
   cipher suite as mandated by RFC 2246 [RFC2246].  All other cipher
   suites are OPTIONAL.  An IPP Printer MAY support Basic Authentication
   (described in HTTP/1.1 [RFC2617]) for Client Authentication if the
   channel is secure.  TLS with the above mandated cipher suite can
   provide such a secure channel.

   If a IPP client supports TLS, it MUST support the
   TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA cipher suite as mandated by RFC
   2246 [RFC2246].  All other cipher suites are OPTIONAL.

   The IPP Model and Semantics document defines two printer attributes
   ("uri-authentication-supported" and "uri-security-supported") that
   the client can use to discover the security policy of a printer.

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   That document also outlines IPP-specific security considerations and
   should be the primary reference for security implications with regard
   to the IPP protocol itself.  For backward compatibility with IPP
   version 1.0, IPP clients and printers may also support SSL3 [SSL].
   This is in addition to the security required in this document.

8.2.  Using IPP with TLS

   IPP/1.1 uses the "Upgrading to TLS Within HTTP/1.1" mechanism
   [RFC2817].  An initial IPP request never uses TLS.  The client
   requests a secure TLS connection by using the HTTP "Upgrade" header,
   while the server agrees in the HTTP response.  The switch to TLS
   occurs either because the server grants the client's request to
   upgrade to TLS, or a server asks to switch to TLS in its response.
   Secure communication begins with a server's response to switch to
   TLS.

9.  Interoperability with IPP/1.0 Implementations

   It is beyond the scope of this specification to mandate conformance
   with previous versions.  IPP/1.1 was deliberately designed, however,
   to make supporting previous versions easy.  It is worth noting that,
   at the time of composing this specification (1999), we would expect
   IPP/1.1 Printer implementations to:

   understand any valid request in the format of IPP/1.0, or 1.1;

   respond appropriately with a response containing the same "version-
   number" parameter value used by the client in the request.

   And we would expect IPP/1.1 clients to:

   understand any valid response in the format of IPP/1.0, or 1.1.

9.1.  The "version-number" Parameter

   The following are rules regarding the "version-number" parameter (see
   Section 3.3):

   1.  Clients MUST send requests containing a "version-number"
       parameter with a '1.1' value and SHOULD try supplying alternate
       version numbers if they receive a 'server-error-version-not-
       supported' error return in a response.

   2.  IPP objects MUST accept requests containing a "version-number"
       parameter with a '1.1' value (or reject the request for reasons
       other than 'server-error-version-not-supported').

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   3.  It is recommended that IPP objects accept any request with the
       major version '1' (or reject the request for reasons other than
       'server-error-version-not-supported').  See [RFC2911] "versions"
       sub-section.

   4.  In any case, security MUST NOT be compromised when a client
       supplies a lower "version-number" parameter in a request.  For
       example, if an IPP/1.1 conforming Printer object accepts version
       '1.0' requests and is configured to enforce Digest
       Authentication, it MUST do the same for a version '1.0' request.

   9.2 Security and URL Schemes

   The following are rules regarding security, the "version-number"
   parameter, and the URL scheme supplied in target attributes and
   responses:

   1.  When a client supplies a request, the "printer-uri" or "job-uri"
       target operation attribute MUST have the same scheme as that
       indicated in one of the values of the "printer-uri-supported"
       Printer attribute.

   2.  When the server returns the "job-printer-uri" or "job-uri" Job
       Description attributes, it SHOULD return the same scheme ('ipp',
       'https', 'http', etc.) that the client supplied in the "printer-
       uri" or "job-uri" target operation attributes in the Get-Job-
       Attributes or Get-Jobs request, rather than the scheme used when
       the job was created.  However, when a client requests job
       attributes using the Get-Job-Attributes or Get-Jobs operations,
       the jobs and job attributes that the server returns depends on:
       (1) the security in effect when the job was created, (2) the
       security in effect in the query request, and (3) the security
       policy in force.

   3.  It is recommended that if a server registers a non-secure ipp-URL
       with a directory service (see [RFC2911] "Generic Directory
       Schema" Appendix), then it also register an http-URL for
       interoperability with IPP/1.0 clients (see Section 9).

   4.  In any case, security MUST NOT be compromised when a client
       supplies an 'http' or other non-secure URL scheme in the target
       "printer-uri" and "job-uri" operation attributes in a request.

   5.  . References

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10.  References

10.1.  Normative References

   [ASCII]    ANSI, "Information Systems - Coded Character Sets - 7-Bit
              American National Standard Code for Information
              Interchange (7-Bit ASCII)", June 2007.

   [ASME-Y14.1M]
              "ASME Y14.1M-1995: Metric Drawing Sheet Size and Format",
              1995.

   [IPP-IIG]  Hastings, T., Manros, C., Zehler, P., Kugler, C., and H.
              Holst, "Internet Printing Protocol/1.1: Implementor's
              Guide", RFC 3196, November 2001.

   [ISO10175]
              "ISO/IEC 10175 Document Printing Application (DPA)", June
              1996.

   [ISO10646-1]
              "ISO/IEC 10646-1:1993, "Information technology --
              Universal Multiple-Octet Coded Character Set (UCS) - Part
              1: Architecture and Basic Multilingual Plane, JTC1/SC2."",
              1993.

   [ISO8859-1]
              "ISO/IEC 8859-1:1987, "Information technology -- 8-bit
              One-Byte Coded Character Set - Part 1: Latin Alphabet Nr
              1"", 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC1738]  Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
              Resource Locators (URL)", RFC 1738, December 1994.

   [RFC1759]  Smith, R., Wright, F., Hastings, T., Zilles, S., and J.
              Gyllenskog, "Printer MIB", RFC 1759, March 1995.

   [RFC1766]  Alvestrand, H., "Tags for the Identification of
              Languages", RFC 1766, March 1995.

   [RFC1808]  Fielding, R., "Relative Uniform Resource Locators", RFC
              1808, June 1995.

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   [RFC1903]  McCloghrie, K., Case, J., Rose, M., and S. Waldbusser,
              "Textual Conventions for Version 2 of the Simple Network
              Management Protocol (SNMPv2)", RFC 1903, January 1996.

   [RFC1951]  Deutsch, P., "DEFLATE Compressed Data Format Specification
              version 1.3", RFC 1951, May 1996.

   [RFC1952]  Deutsch, P., Gailly, J-L., Adler, M., Deutsch, L., and G.
              Randers-Pehrson, "GZIP file format specification version
              4.3", RFC 1952, May 1996.

   [RFC1977]  Schryver, V., "PPP BSD Compression Protocol", RFC 1977,
              August 1996.

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              November 1996.

   [RFC2048]  Freed, N., Klensin, J., and J. Postel, "Multipurpose
              Internet Mail Extensions (MIME) Part Four: Registration
              Procedures", BCP 13, RFC 2048, November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 2234, November 1997.

   [RFC2246]  Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
              RFC 2246, January 1999.

   [RFC2279]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", RFC 2279, January 1998.

   [RFC2396]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifiers (URI): Generic Syntax", RFC 2396,
              August 1998.

   [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.

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   [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
              Leach, P., Luotonen, A., and L. Stewart, "HTTP
              Authentication: Basic and Digest Access Authentication",
              RFC 2617, June 1999.

   [RFC2817]  Khare, R. and S. Lawrence, "Upgrading to TLS Within
              HTTP/1.1", RFC 2817, May 2000.

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

   [RFC2911]  Hastings, T., Herriot, R., deBry, R., Isaacson, S., and P.
              Powell, "Internet Printing Protocol/1.1: Model and
              Semantics", RFC 2911, September 2000.

10.2.  Informative References

   [BCP-11]   Hovey, R. and S. Bradner, "The Organizations Involved in
              the IETF Standards Process", BCP 11, RFC 2028, October
              1996.

   [HTPP]     Barnett, J., Carter, K., and R. DeBry, "Initial Draft -
              Hypertext Printing Protocol - HTPP/1.0", 10 1996,
              <ftp://ftp.pwg.org/pub/pwg/ipp/historic/htpp/
              overview.ps.gz>.

   [IANA-CON]
              Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [IANA-CS]  "IANA Registry of Coded Character Sets",
              <ftp://ftp.isi.edu/in-notes/iana/assignments/character-
              sets>.

   [IANA-MT]  "IANA Registry of Media Types", <ftp://ftp.isi.edu/in-
              notes/iana/assignments/media-types/>.

   [LDPA]     Hastings, T., Isaacson, S., MacKay, M., Manros, C.,
              Taylor, D., and P. Zehler, "LDPA - Lightweight Document
              Printing Application", October 1996,
              <ftp://ftp.pwg.org/pub/pwg/ipp/historic/ldpa/
              ldpa8.pdf.gz>.

   [PSIS]     Herriot, R., "X/Open: A Printing System Interoperability
              Specification (PSIS)", August 1995.

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   [PWG]      "The Printer Working Group, a program of the IEEE-ISTO",
              <http://www.pwg.org/>.

   [RFC1179]  McLaughlin, L., "Line printer daemon protocol", RFC 1179,
              August 1990.

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [RFC2228]  Horowitz, M., "FTP Security Extensions", RFC 2228, October
              1997.

   [RFC2277]  Alvestrand, H., "IETF Policy on Character Sets and
              Languages", BCP 18, RFC 2277, January 1998.

   [RFC2278]  Freed, N. and J. Postel, "IANA Charset Registration
              Procedures", BCP 19, RFC 2278, January 1998.

   [RFC2316]  Bellovin, S., "Report of the IAB Security Architecture
              Workshop", RFC 2316, April 1998.

   [RFC2565]  Herriot, R., Butler, S., Moore, P., and R. Turner,
              "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, F., "Design Goals for an Internet Printing
              Protocol", RFC 2567, April 1999.

   [RFC2568]  Zilles, S., "Rationale for the Structure of the Model and
              Protocol for the Internet Printing Protocol", RFC 2568,
              April 1999.

   [RFC2569]  Herriot, R., Jacobs, N., Hastings, T., and J. Martin,
              "Mapping between LPD and IPP Protocols", RFC 2569, April
              1999.

   [RFC2579]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Textual Conventions for SMIv2", STD
              58, RFC 2579, April 1999.

   [RFC2639]  Hastings, T. and C. Manros, "Internet Printing
              Protocol/1.0: Implementer's Guide", RFC 2639, July 1999.

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   [SSL]      "The SSL Protocol, Version 3, (Text version 3.02)",
              November 1996.

   [SWP]      Moore, P., Jahromi, B., and S. Butler, "Simple Web
              Printing SWP/1.0", May 1997,
              <ftp://ftp.pwg.org/pub/pwg/ipp/new_PRO/swp9705.pdf>.

Appendix A.  Protocol Examples

A.1.  Print-Job Request

   The following is an example of a Print-Job request with job-name,
   copies, and sides specified.  The "ipp-attribute-fidelity" attribute
   is set to 'true' so that the print request will fail if the "copies"
   or the "sides" attribute are not supported or their values are not
   supported.

    Octets                  Symbolic Value       Protocol field

    0x0101                  1.1version-number    0x0002
    Print-Job               operation-id         0x00000001
    1                       request-id           0x01
    start operation-        operation-           0x47
    attributes              attributes-tag
    charset type            value-tag            0x0012
                            name-length          attributes-charset
    attributes-charset      name                 0x0008
                            value-length         us-ascii
    US-ASCII                value                0x48
    natural-language type   value-tag            0x001B
                            name-length          attributes-natural-
                                                 language
    attributes-natural-     name                 0x0005
    language
                            value-length         en-us
    en-US                   value                0x45
    uri type                value-tag            0x000B
                            name-length          printer-uri
    printer-uri             name                 0x0015
                            value-length         ipp://forest/pinetree
    printer pinetree        value                0x42
    nameWithoutLanguage     value-tag            0x0008
    type
                            name-length          job-name
    job-name                name                 0x0006
                            value-length         foobar
    foobar                  value                0x22
    boolean type            value-tag            0x0016

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                            name-length          ipp-attribute-fidelity
    ipp-attribute-fidelity  name                 0x0001
                            value-length         0x01
    true                    value                0x02
    start job-attributes    job-attributes-tag   0x21
    integer type            value-tag            0x0006
                            name-length          copies
    copies                  name                 0x0004
                            value-length         0x00000014
    20                      value                0x44
    keyword type            value-tag            0x0005
                            name-length          sides
    sides                   name                 0x0013
                            value-length         two-sided-long-edge
    two-sided-long-edge     value                0x03
    end-of-attributes       end-of-attributes-   %!PS...
                            tag
    <PostScript>            data

A.2.  Print-Job Response (successful)

   Here is an example of a successful Print-Job response to the previous
   Print-Job request.  The printer supported the "copies" and "sides"
   attributes and their supplied values.  The status code returned is
   'successful-ok'.

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   Octets                  Symbolic Value          Protocol field

   0x0101                  1.1                     version-number
   0x0000                  successful-ok           status-code
   0x00000001              1                       request-id
   0x01                    start operation-        operation-attributes-
                           attributes              tag
   0x47                    charset type            value-tag
   0x0012                                          name-length
   attributes-charset      attributes-charset      name
   0x0008                                          value-length
   us-ascii                US-ASCII                value
   0x48                    natural-language type   value-tag
   0x001B                                          name-length
   attributes-natural-     attributes-natural-     name
   language                language
   0x0005                                          value-length
   en-us                   en-US                   value
   0x41                    textWithoutLanguage     value-tag
                           type
   0x000E                                          name-length
   status-message          status-message          name
   0x000D                                          value-length
   successful-ok           successful-ok           value
   0x02                    start job-attributes    job-attributes-tag
   0x21                    integer                 value-tag
   0x0006                                          name-length
   job-id                  job-id                  name
   0x0004                                          value-length
   147                     147                     value
   0x45                    uri type                value-tag
   0x0007                                          name-length
   job-uri                 job-uri                 name
   0x0019                                          value-length
   ipp://forest/pinetree/1 job 123 on pinetree     value
   23
   0x23                    enum type               value-tag
   0x0009                                          name-length
   job-state               job-state               name
   0x0004                                          value-length
   0x0003                  pending                 value
   0x03                    end-of-attributes       end-of-attributes-tag

A.3.  Print-Job Response (failure)

   Here is an example of an unsuccessful Print-Job response to the
   previous Print-Job request.  It fails because, in this case, the
   printer does not support the "sides" attribute and because the value

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   '20' for the "copies" attribute is not supported.  Therefore, no job
   is created, and neither a "job-id" nor a "job-uri" operation
   attribute is returned.  The error code returned is 'client-error-
   attributes-or-values-not-supported' (0x040B).

   Octets                      Symbolic Value              Protocol
                                                           field

   0x0101                      1.1                         version-
                                                           number
   0x040B                      client-error-attributes-or- status-code
                               values-not-supported
   0x00000001                  1                           request-id
   0x01                        start operation-attributes  operation-
                                                           attributes
                                                           tag
   0x47                        charset type                value-tag
   0x0012                                                  name-length
   attributes-charset          attributes-charset          name
   0x0008                                                  value-length
   us-ascii                    US-ASCII                    value
   0x48                        natural-language type       value-tag
   0x001B                                                  name-length
   attributes-natural-language attributes-natural-language name
   0x0005                                                  value-length
   en-us                       en-US                       value
   0x41                        textWithoutLanguage type    value-tag
   0x000E                                                  name-length
   status-message              status-message              name
   0x002F                                                  value-length
   client-error-attributes-or- client-error-attributes-or- value
   values-not-supported        values-not-supported
   0x05                        start unsupported-          unsupported-
                               attributes                  attributes
                                                           tag
   0x21                        integer type                value-tag
   0x0006                                                  name-length
   copies                      copies                      name
   0x0004                                                  value-length
   0x00000014                  20                          value
   0x10                        unsupported (type)          value-tag
   0x0005                                                  name-length
   sides                       sides                       name
   0x0000                                                  value-length
   0x03                        end-of-attributes           end-of-
                                                           attributes-
                                                           tag

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A.4.  Print-Job Response (success with attributes ignored)

   Here is an example of a successful Print-Job response to a Print-Job
   request like the previous Print-Job request, except that the value of
   'ipp-attribute-fidelity' is false.  The print request succeeds, even
   though, in this case, the printer supports neither the "sides"
   attribute nor the value '20' for the "copies" attribute.  Therefore,
   a job is created, and both a "job-id" and a "job-uri" operation
   attribute are returned.  The unsupported attributes are also returned
   in an Unsupported Attributes Group.  The error code returned is
   'successful-ok-ignored-or-substituted-attributes' (0x0001).

   Octets                     Symbolic Value              Protocol field

   0x0101                     1.1                         version-number
   0x0001                     successful-ok-ignored-or-   status-code
                              substituted-attributes
   0x00000001                 1                           request-id
   0x01                       start operation-attributes  operation-
                                                          attributes-tag
   0x47                       charset type                value-tag
   0x0012                                                 name-length
   attributes-charset         attributes-charset          name
   0x0008                                                 value-length
   us-ascii                   US-ASCII                    value
   0x48                       natural-language type       value-tag
   0x001B                                                 name-length
   attributes-natural-        attributes-natural-language name
   language
   0x0005                                                 value-length
   en-us                      en-US                       value
   0x41                       textWithoutLanguage type    value-tag
   0x000E                                                 name-length
   status-message             status-message              name
   0x002F                                                 value-length
   successful-ok-ignored-or-  successful-ok-ignored-or-   value
   substituted-attributes     substituted-attributes
   0x05                       start unsupported-          unsupported-
                              attributes                  attributes tag
   0x21                       integer type                value-tag
   0x0006                                                 name-length
   copies                     copies                      name
   0x0004                                                 value-length
   0x00000014                 20                          value
   0x10                       unsupported  (type)         value-tag
   0x0005                                                 name-length
   sides                      sides                       name
   0x0000                                                 value-length

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   0x02                       start job-attributes        job-
                                                          attributes-tag
   0x21                       integer                     value-tag
   0x0006                                                 name-length
   job-id                     job-id                      name
   0x0004                                                 value-length
   147                        147                         value
   0x45                       uri type                    value-tag
   0x0007                                                 name-length
   job-uri                    job-uri                     name
   0x0019                                                 value-length
   ipp://forest/pinetree/123  job 123 on pinetree         value
   0x23                       enum  type                  value-tag
   0x0009                                                 name-length
   job-state                  job-state                   name
   0x0004                                                 value-length
   0x0003                     pending                     value
   0x03                       end-of-attributes           end-of-
                                                          attributes-tag

A.5.  Print-URI Request

   The following is an example of Print-URI request with copies and job-
   name parameters:

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   Octets                  Symbolic Value          Protocol field

   0x0101                  1.1                     version-number
   0x0003                  Print-URI               operation-id
   0x00000001              1                       request-id
   0x01                    start operation-        operation-attributes-
                           attributes              tag
   0x47                    charset type            value-tag
   0x0012                                          name-length
   attributes-charset      attributes-charset      name
   0x0008                                          value-length
   us-ascii                US-ASCII                value
   0x48                    natural-language type   value-tag
   0x001B                                          name-length
   attributes-natural-     attributes-natural-     name
   language                language
   0x0005                                          value-length
   en-us                   en-US                   value
   0x45                    uri type                value-tag
   0x000B                                          name-length
   printer-uri             printer-uri             name
   0x0015                                          value-length
   ipp://forest/pinetree   printer pinetree        value
   0x45                    uri type                value-tag
   0x000C                                          name-length
   document-uri            document-uri            name
   0x0011                                          value-length
   ftp://foo.com/foo       ftp://foo.com/foo       value
   0x42                    nameWithoutLanguage     value-tag
                           type
   0x0008                                          name-length
   job-name                job-name                name
   0x0006                                          value-length
   foobar                  foobar                  value
   0x02                    start job-attributes    job-attributes-tag
   0x21                    integer type            value-tag
   0x0006                                          name-length
   copies                  copies                  name
   0x0004                                          value-length
   0x00000001              1                       value
   0x03                    end-of-attributes       end-of-attributes-tag

A.6.  Create-Job Request

   The following is an example of Create-Job request with no parameters
   and no attributes:

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   Octets                  Symbolic Value          Protocol field

   0x0101                  1.1                     version-number
   0x0005                  Create-Job              operation-id
   0x00000001              1                       request-id
   0x01                    start operation-        operation-attributes-
                           attributes              tag
   0x47                    charset type            value-tag
   0x0012                                          name-length
   attributes-charset      attributes-charset      name
   0x0008                                          value-length
   us-ascii                US-ASCII                value
   0x48                    natural-language type   value-tag
   0x001B                                          name-length
   attributes-natural-     attributes-natural-     name
   language                language
   0x0005                                          value-length
   en-us                   en-US                   value
   0x45                    uri type                value-tag
   0x000B                                          name-length
   printer-uri             printer-uri             name
   0x0015                                          value-length
   ipp://forest/pinetree   printer pinetree        value
   0x03                    end-of-attributes       end-of-attributes-tag

A.7.  Get-Jobs Request

   The following is an example of Get-Jobs request with parameters but
   no attributes:

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   Octets                  Symbolic Value          Protocol field

   0x0101                  1.1                     version-number
   0x000A                  Get-Jobs                operation-id
   0x00000123              0x123                   request-id
   0x01                    start operation-        operation-attributes-
                           attributes              tag
   0x47                    charset type            value-tag
   0x0012                                          name-length
   attributes-charset      attributes-charset      name
   0x0008                                          value-length
   us-ascii                US-ASCII                value
   0x48                    natural-language type   value-tag
   0x001B                                          name-length
   attributes-natural-     attributes-natural-     name
   language                language
   0x0005                                          value-length
   en-us                   en-US                   value
   0x45                    uri type                value-tag
   0x000B                                          name-length
   printer-uri             printer-uri             name
   0x0015                                          value-length
   ipp://forest/pinetree   printer pinetree        value
   0x21                    integer type            value-tag
   0x0005                                          name-length
   limit                   limit                   name
   0x0004                                          value-length
   0x00000032              50                      value
   0x44                    keyword type            value-tag
   0x0014                                          name-length
   requested-attributes    requested-attributes    name
   0x0006                                          value-length
   job-id                  job-id                  value
   0x44                    keyword type            value-tag
   0x0000                  additional value        name-length
   0x0008                                          value-length
   job-name                job-name                value
   0x44                    keyword type            value-tag
   0x0000                  additional value        name-length
   0x000F                                          value-length
   document-format         document-format         value
   0x03                    end-of-attributes       end-of-attributes-tag

A.8.  Get-Jobs Response

   The following is an of Get-Jobs response from previous request with 3
   jobs.  The Printer returns no information about the second job
   (because of security reasons):

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   Octets                  Symbolic Value          Protocol field

   0x0101                  1.1                     version-number
   0x0000                  successful-ok           status-code
   0x00000123              0x123                   request-id (echoed
                                                   back)
   0x01                    start operation-        operation-attributes-
                           attributes              tag
   0x47                    charset type            value-tag
   0x0012                                          name-length
   attributes-charset      attributes-charset      name
   0x000A                                          value-length
   ISO-8859-1              ISO-8859-1              value
   0x48                    natural-language type   value-tag
   0x001B                                          name-length
   attributes-natural-     attributes-natural-     name
   language                language
   0x0005                                          value-length
   en-us                   en-US                   value
   0x41                    textWithoutLanguage     value-tag
                           type
   0x000E                                          name-length
   status-message          status-message          name
   0x000D                                          value-length
   successful-ok           successful-ok           value
   0x02                    start job-attributes    job-attributes-tag
                           (1st  object)
   0x21                    integer type            value-tag
   0x0006                                          name-length
   job-id                  job-id                  name
   0x0004                                          value-length
   147                     147                     value
   0x36                    nameWithLanguage        value-tag
   0x0008                                          name-length
   job-name                job-name                name
   0x000C                                          value-length
   0x0005                                          sub-value-length
   fr-ca                   fr-CA                   value
   0x0003                                          sub-value-length
   fou                     fou                     name
   0x02                    start job-attributes    job-attributes-tag
                           (2nd object)
   0x02                    start job-attributes    job-attributes-tag
                           (3rd object)
   0x21                    integer type            value-tag
   0x0006                                          name-length
   job-id                  job-id                  name
   0x0004                                          value-length

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   148                     149                     value
   0x36                    nameWithLanguage        value-tag
   0x0008                                          name-length
   job-name                job-name                name
   0x0012                                          value-length
   0x0005                                          sub-value-length
   de-CH                   de-CH                   value
   0x0009                                          sub-value-length
   isch guet               isch guet               name
   0x03                    end-of-attributes       end-of-attributes-tag

Appendix B.  Registration of MIME Media Type Information for
             "application/ipp"

   This appendix contains the information that IANA requires for
   registering a MIME media type.  The information following this
   paragraph will be forwarded to IANA to register application/ipp whose
   contents are defined in Section 3 "Encoding of the Operation Layer"
   in this document:

   MIME type name: application

   MIME subtype name: ipp

   A Content-Type of "application/ipp" indicates an Internet Printing
   Protocol message body (request or response).  Currently there is one
   version: IPP/1.1, whose syntax is described in Section 3 "Encoding of
   the Operation Layer" of [RFC2910], and whose semantics are described
   in [RFC2911].

   Required parameters: none

   Optional parameters: none

   Encoding considerations:

   IPP/1.1 protocol requests/responses MAY contain long lines and ALWAYS
   contain binary data (for example attribute value lengths).

   Security considerations:

   IPP/1.1 protocol requests/responses do not introduce any security
   risks not already inherent in the underlying transport protocols.
   Protocol mixed-version interworking rules in [RFC2911] as well as
   protocol encoding rules in [RFC2910] are complete and unambiguous.

   Interoperability considerations:

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   IPP/1.1 requests (generated by clients) and responses (generated by
   servers) MUST comply with all conformance requirements imposed by the
   normative specifications [RFC2911] and [RFC2910].  Protocol encoding
   rules specified in [RFC2910] are comprehensive, so that
   interoperability between conforming implementations is guaranteed
   (although support for specific optional features is not ensured).
   Both the "charset" and "natural-language" of all IPP/1.1 attribute
   values which are a LOCALIZED-STRING are explicit within IPP protocol
   requests/responses (without recourse to any external information in
   HTTP, SMTP, or other message transport headers).

   Published specifications:

   [RFC2911]  Isaacson, S., deBry, R., Hastings, T., Herriot, R.,
   Powell, P., "Internet Printing Protocol/1.1: Model and Semantics"
   draft-ietf-ipp-model-v11-07.txt, May 22, 2000.

   [RFC2910]  Herriot, R., Butler, S., Moore, P., Turner, R., "Internet
   Printing Protocol/1.1: Encoding and Transport", draft-ietf-ipp-
   protocol-v11-06.txt, May 30, 2000.

   Applications which use this media type:

   Internet Printing Protocol (IPP) print clients and print servers,
   communicating using HTTP/1.1 (see [RFC2910]), SMTP/ESMTP, FTP, or
   other transport protocol.  Messages of type "application/ipp" are
   self-contained and transport-independent, including "charset" and
   "natural-language" context for any LOCALIZED-STRING value.

Appendix C.  Changes from IPP/1.0

   IPP/1.1 is identical to IPP/1.0 [RFC2565] with the follow changes:

   1.  Attributes values that identify a printer or job object use a new
       'ipp' scheme.  The 'http' and 'https' schemes are supported only
       for backward compatibility.  See section 5.

   2.  Clients MUST support of Digest Authentication, IPP Printers
       SHOULD support Digest Authentication.  See Section 8.1.1

   3.  TLS is recommended for channel security.  In addition, SSL3 may
       be supported for backward compatibility.  See Section 8.1.2

   4.  It is recommended that IPP/1.1 objects accept any request with
       major version number '1'.  See Section 9.1.

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   5.  IPP objects SHOULD return the URL scheme requested for "job-
       printer-uri" and "job-uri" Job Attributes, rather than the URL
       scheme used to create the job.  See section 9.2.

   6.  The IANA and Internationalization sections have been added.  The
       terms "private use" and "experimental" have been changed to
       "vendor extension".  The reserved allocations for attribute group
       tags, attribute syntax tags, and out-of-band attribute values
       have been clarified as to which are reserved to future IETF
       standards track documents and which are reserved to vendor
       extension.  Both kinds of extensions use the type2 registration
       procedures as defined in [RFC2911].

   7.  Clarified that future "out-of-band" value definitions may use the
       value field if additional information is needed.

Appendix D.  Acknowledgements

   The authors would like to acknowledge the following individuals for
   their contributions to the original IPP/1.1 specification:

   Robert Herriot (original RFC 2910 editor) - Xerox Corporation, Paul
   Moore - Peerless Systems Networking, Sylvan Butler - Hewlett-Packard,
   Randy Turner - 2Wire, Inc., John Wenn - Xerox Corporation, Chuck
   Adams - Tektronix, Shivaun Albright - HP, Stefan Andersson - Axis,
   Jeff Barnett - IBM, Ron Bergman - Hitachi Koki Imaging Systems,
   Dennis Carney - IBM, Keith Carter - IBM, Angelo Caruso - Xerox,
   Rajesh Chawla - TR Computing Solutions, Nancy Chen - Okidata, Josh
   Cohen - Microsoft, Jeff Copeland - QMS, Andy Davidson - Tektronix,
   Roger deBry - IBM, Maulik Desai - Auco, Mabry Dozier - QMS, Lee
   Farrell - Canon Information Systems, Satoshi Fujitami - Ricoh, Steve
   Gebert - IBM, Sue Gleeson - Digital, Charles Gordon - Osicom, Brian
   Grimshaw - Apple, Jerry Hadsell - IBM, Richard Hart - Digital, Tom
   Hastings - Xerox, Henrik Holst - I-data, Stephen Holmstead, Zhi-Hong
   Huang - Zenographics, Scott Isaacson - Novell, Babek Jahromi -
   Microsoft, Swen Johnson - Xerox, David Kellerman - Northlake
   Software, Robert Kline - TrueSpectra, Charles Kong - Panasonic, Carl
   Kugler - IBM, Dave Kuntz - Hewlett-Packard, Takami Kurono - Brother,
   Rick Landau - Digital, Scott Lawrence - Agranot Systems, Greg LeClair
   - Epson, Dwight Lewis - Lexmark, Harry Lewis - IBM, Tony Liao - Vivid
   Image, Roy Lomicka - Digital, Pete Loya - HP, Ray Lutz - Cognisys,
   Mike MacKay - Novell, Inc., David Manchala - Xerox, Carl-Uno Manros -
   Xerox, Jay Martin - Underscore, Stan McConnell - Xerox, Larry
   Masinter - Xerox, Sandra Matts - Hewlett Packard, Peter Michalek -
   Shinesoft, Ira McDonald - High North Inc., Mike Moldovan - G3 Nova,
   Tetsuya Morita - Ricoh, Yuichi Niwa - Ricoh, Pat Nogay - IBM, Ron
   Norton - Printronics, Hugo Parra, Novell, Bob Pentecost - Hewlett-
   Packard, Patrick Powell - Astart Technologies, Jeff Rackowitz -

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   Intermec, Eric Random - Peerless, Rob Rhoads - Intel, Xavier Riley -
   Xerox, Gary Roberts - Ricoh, David Roach - Unisys, Stuart Rowley -
   Kyocera, Yuji Sasaki - Japan Computer Industry, Richard Schneider -
   Epson, Kris Schoff - HP, Katsuaki Sekiguchi - Canon Information
   Systems, Bob Setterbo - Adobe, Gail Songer - Peerless, Hideki Tanaka
   - Cannon Information Systems, Devon Taylor - Novell, Inc., Mike
   Timperman - Lexmark, Atsushi Uchino - Epson, Shigeru Ueda - Canon,
   Bob Von Andel - Allegro Software, William Wagner - NetSilicon/DPI,
   Jim Walker - DAZEL, Chris Wellens - Interworking Labs, Trevor Wells -
   Hewlett Packard, Craig Whittle - Sharp Labs, Rob Whittle - Novell,
   Inc., Jasper Wong - Xionics, Don Wright - Lexmark, Michael Wu -
   Heidelberg Digital, Rick Yardumian - Xerox, Michael Yeung - Canon
   Information Systems, Lloyd Young - Lexmark, Atsushi Yuki - Kyocera,
   Peter Zehler - Xerox, William Zhang- Canon Information Systems, Frank
   Zhao - Panasonic, Steve Zilles - Adobe, and Rob Zirnstein - Canon
   Information Systems.

Authors' Addresses

   Michael Sweet
   Apple Inc.
   1 Infinite Loop
   MS 111-HOMC
   Cupertino, CA  95014
   US

   Email: msweet@apple.com

   Ira McDonald
   High North, Inc.
   PO Box 221
   Grand Marais, MI  49839
   US

   Phone: +1 906-494-2434
   Email: blueroofmusic@gmail.com

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