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Internet Printing Protocol/1.1: Encoding and Transport
draft-sweet-rfc2910bis-03

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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 2015-05-27
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draft-sweet-rfc2910bis-03
IPP WG                                                          M. Sweet
Internet-Draft                                                Apple Inc.
Obsoletes: 2910,3382 (if approved)                           I. McDonald
Intended status: Standards Track                        High North, Inc.
Expires: November 28, 2015                                  May 27, 2015

         Internet Printing Protocol/1.1: Encoding and Transport
                       draft-sweet-rfc2910bis-03

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 November 28, 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.  Conventions Used in This Document . . . . . . . . . . . . . .   4
   2.1.  Requirements Language . . . . . . . . . . . . . . . . . . .   4
   2.2.  Printing Terminology  . . . . . . . . . . . . . . . . . . .   4
   2.3.  Abbreviations . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Encoding of the Operation Layer . . . . . . . . . . . . . . .   6
   3.1.  Picture of the Encoding . . . . . . . . . . . . . . . . . .   7
   3.1.1.  Request and Response  . . . . . . . . . . . . . . . . . .   7
   3.1.2.  Attribute Group . . . . . . . . . . . . . . . . . . . . .   8
   3.1.3.  Attribute . . . . . . . . . . . . . . . . . . . . . . . .   8
   3.1.4.  Attribute-with-one-value  . . . . . . . . . . . . . . . .   8
   3.1.5.  Additional-value  . . . . . . . . . . . . . . . . . . . .   9
   3.1.6.  Collection Attribute  . . . . . . . . . . . . . . . . . .  10
   3.1.7.  Member Attributes . . . . . . . . . . . . . . . . . . . .  11
   3.1.8.  Alternative Picture of the Encoding of a Request Or a
           Response  . . . . . . . . . . . . . . . . . . . . . . . .  12
   3.2.  Syntax of Encoding  . . . . . . . . . . . . . . . . . . . .  13
   3.3.  Attribute-group . . . . . . . . . . . . . . . . . . . . . .  15
   3.4.  Required Parameters . . . . . . . . . . . . . . . . . . . .  17
   3.4.1.  Version-number  . . . . . . . . . . . . . . . . . . . . .  17
   3.4.2.  Operation-id  . . . . . . . . . . . . . . . . . . . . . .  17
   3.4.3.  Status-code . . . . . . . . . . . . . . . . . . . . . . .  17
   3.4.4.  Request-id  . . . . . . . . . . . . . . . . . . . . . . .  18
   3.5.  Tags  . . . . . . . . . . . . . . . . . . . . . . . . . . .  18
   3.5.1.  Delimiter Tags  . . . . . . . . . . . . . . . . . . . . .  18
   3.5.2.  Value Tags  . . . . . . . . . . . . . . . . . . . . . . .  19
   3.6.  Name-Length . . . . . . . . . . . . . . . . . . . . . . . .  22
   3.7.  (Attribute) Name  . . . . . . . . . . . . . . . . . . . . .  22
   3.8.  Value Length  . . . . . . . . . . . . . . . . . . . . . . .  22
   3.9.  (Attribute) Value . . . . . . . . . . . . . . . . . . . . .  23
   3.10. Data  . . . . . . . . . . . . . . . . . . . . . . . . . . .  24
   4.  Encoding of Transport Layer . . . . . . . . . . . . . . . . .  24
   4.1.  Printer-uri and job-uri . . . . . . . . . . . . . . . . . .  25
   5.  IPP URI Schemes . . . . . . . . . . . . . . . . . . . . . . .  26

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   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  28
   7.  Internationalization Considerations . . . . . . . . . . . . .  29
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  29
   8.1.  Security Conformance Requirements . . . . . . . . . . . . .  29
   8.1.1.  Digest Authentication . . . . . . . . . . . . . . . . . .  29
   8.1.2.  Transport Layer Security (TLS)  . . . . . . . . . . . . .  30
   8.2.  Using IPP with TLS  . . . . . . . . . . . . . . . . . . . .  30
   9.  Interoperability with Other IPP Versions  . . . . . . . . . .  31
   9.1.  The "version-number" Parameter  . . . . . . . . . . . . . .  31
   9.2.  Security and URI Schemes  . . . . . . . . . . . . . . . . .  32
   10. Changes Since RFC 2910  . . . . . . . . . . . . . . . . . . .  32
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
   11.1.  Normative References . . . . . . . . . . . . . . . . . . .  33
   11.2.  Informative References . . . . . . . . . . . . . . . . . .  34
   11.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . . .  35
   Appendix A.  Protocol Examples  . . . . . . . . . . . . . . . . .  35
   A.1.  Print-Job Request . . . . . . . . . . . . . . . . . . . . .  35
   A.2.  Print-Job Response (successful) . . . . . . . . . . . . . .  36
   A.3.  Print-Job Response (failure)  . . . . . . . . . . . . . . .  38
   A.4.  Print-Job Response (success with attributes ignored)  . . .  39
   A.5.  Print-URI Request . . . . . . . . . . . . . . . . . . . . .  41
   A.6.  Create-Job Request  . . . . . . . . . . . . . . . . . . . .  43
   A.7.  Create-Job Request with Collection Attributes . . . . . . .  43
   A.8.  Get-Jobs Request  . . . . . . . . . . . . . . . . . . . . .  45
   A.9.  Get-Jobs Response . . . . . . . . . . . . . . . . . . . . .  47
   Appendix B.  Registration of MIME Media Type Information for
                "application/ipp"  . . . . . . . . . . . . . . . . .  48
   Appendix C.  Acknowledgements . . . . . . . . . . . . . . . . . .  49
   Appendix D.  Change History . . . . . . . . . . . . . . . . . . .  50
   D.1.  Changes In -03  . . . . . . . . . . . . . . . . . . . . . .  50
   D.2.  Changes In -02  . . . . . . . . . . . . . . . . . . . . . .  50
   D.3.  Changes In -01  . . . . . . . . . . . . . . . . . . . . . .  51
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  51

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 request and response.  All
   IPP implementations MUST support HTTP/1.1, the relevant parts of
   which are described in the following RFCs:

   o  Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing
      [RFC7230]

   o  Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content
      [RFC7231]

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   o  Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests
      [RFC7232]

   o  Hypertext Transfer Protocol (HTTP/1.1): Caching [RFC7234]

   o  Hypertext Transfer Protocol (HTTP/1.1): Authentication [RFC7235]

   o  HTTP Authentication: Basic and Digest Access Authentication
      [RFC2617]

   IPP implementations MAY support HTTP/2 which is described in the
   following RFCs:

   o  Hypertext Transfer Protocol Version 2 (HTTP/2) [RFC7540]

   o  HPACK - Header Compression for HTTP/2 [RFC7541]

   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" [RFC2911bis] defines the semantics of such a message body
   and the supported values.  This document specifies the encoding of an
   IPP operation.  The aforementioned document [RFC2911bis] is
   henceforth referred to as the "IPP model document" or simply "model
   document."

2.  Conventions Used in This Document

2.1.  Requirements Language

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

2.2.  Printing Terminology

   Client: Initiator of outgoing IPP session requests and sender of
   outgoing IPP operation requests (Hypertext Transfer Protocol --
   HTTP/1.1 [RFC7230] User Agent).

   Document: An object created and managed by a Printer that contains
   the description, processing, and status information.  A Document
   object may have attached data and is bound to a single Job.

   'ipp' URI: An IPP URI as defined in [RFC3510].

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   'ipps' URI: An IPP URI as defined in [RFC7472].

   Job: An object created and managed by a Printer that contains
   description, processing, and status information.  The Job also
   contains zero or more Document objects.

   Logical Device: A print server, software service, or gateway that
   processes Jobs and either forwards or stores the processed Job or
   uses one or more Physical Devices to render output.

   Output Device: A single Logical or Physical Device.

   Physical Device: A hardware implementation of an endpoint device,
   e.g., a marking engine, a fax modem, etc.

   Printer: Listener for incoming IPP session requests and receiver of
   incoming IPP operation requests (Hypertext Transfer Protocol --
   HTTP/1.1 [RFC7230] Server) that represents one or more Physical
   Devices or a Logical Device.

2.3.  Abbreviations

   ABNF: Augmented Backus-Naur Form [RFC5234]

   ASCII: American Standard Code for Information Interchange [ASCII]

   HTTP: HyperText Transfer Protocol [RFC7230]

   HTTPS: HTTP over TLS [RFC2818]

   IANA: Internet Assigned Numbers Authority

   IEEE: Institute of Electrical and Electronics Engineers

   IESG: Internet Engineering Steering Group

   IPP: Internet Printing Protocol (this document and [PWG5100.12])

   ISTO: IEEE Industry Standards and Technology Organization

   LPD: Line Printer Daemon Protocol [RFC1179]

   PWG: IEEE-ISTO Printer Working Group [1]

   RFC: Request for Comments

   TCP: Transmission Control Protocol [RFC793]

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   TLS: Transport Layer Security [RFC5246]

   URI: Uniform Resource Identifier [RFC3986]

   URL: Uniform Resource Locator [RFC3986]

   UTF-8: Unicode Transformation Format - 8-bit [RFC3629]

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

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   o  formally through Augmented Backus-Naur Form (ABNF), as specified
      by RFC 5234 [RFC5234]

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

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
   -----------------------------------------------

                       Figure 1: IPP Message Format

   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.

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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
   ----------------------------------------------------------

                    Figure 2: Attribute Group Encoding

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

   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
   ----------------------------------------------------------

                       Figure 3: Attribute Encoding

   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.  Attribute-with-one-value

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

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

                 Figure 4: Single Value Attribute Encoding

   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".

   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
   -----------------------------------------------

               Figure 5: Additional Attribute Value Encoding

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   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.  Collection Attribute

   Collection attributes create a named group containing related
   "member" attributes.  The "attribute-with-one-value" field for a
   collection attribute is encoded as follows:

   -----------------------------------------------
   |          value-tag (value is 0x34)          |   1 byte
   -----------------------------------------------
   |          name-length (value is u)           |   2 bytes
   -----------------------------------------------
   |                     name                    |   u bytes
   -----------------------------------------------
   |        value-length (value is 0x0000)       |   2 bytes
   -----------------------------------------------------------
   |               member-attribute              |   q bytes |-0 or more
   -----------------------------------------------------------
   |        end-value-tag (value is 0x37)        |   1 byte
   -----------------------------------------------
   |      end-name-length (value is 0x0000)      |   2 bytes
   -----------------------------------------------
   |      end-value-length (value is 0x0000)     |   2 bytes
   -----------------------------------------------

                  Figure 6: Collection Attribute Encoding

   Collection attribute is encoded with eight subfields:

   o  The "value-tag" field specifies the start attribute syntax: 0x34
      for the attribute syntax 'begCollection'.

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   o  The "name-length" field specifies the length of the "name" field
      in bytes, e.g. u in the above diagram or 9 for the name "media-
      col".  Additional collection attribute values use a name length of
      0x0000.

   o  The "name" field contains the textual name of the attribute, e.g.
      "media-col".

   o  The "value-length" field specifies a length of 0x0000.

   o  The "member-attribute" field contains member attributes encoded as
      defined in Section 3.1.7.

   o  The "end-value-tag" field specifies the end attribute syntax: 0x37
      for the attribute syntax 'endCollection'.

   o  The "end-name-length" field specifies a length of 0x0000.

   o  The "end-value-length" field specifies a length of 0x0000.

3.1.7.  Member Attributes

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

   -----------------------------------------------
   |          value-tag (value is 0x4A)          |   1 byte
   -----------------------------------------------
   |        name-length (value is 0x0000)        |   2 bytes
   -----------------------------------------------
   |          value-length (value is w)          |   2 bytes
   -----------------------------------------------
   |             value (member-name)             |   w bytes
   -----------------------------------------------
   |               member-value-tag              |   1 byte
   -----------------------------------------------
   |        name-length (value is 0x0000)        |   2 bytes
   -----------------------------------------------
   |      member-value-length (value is x)       |   2 bytes
   -----------------------------------------------
   |                member-value                 |   x bytes
   -----------------------------------------------

                    Figure 7: Member Attribute Encoding

   A "member-attribute" is encoded with eight subfields:

   o  The "value-tag" field specifies 0x4A for the attribute syntax
      'memberAttrName'.

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   o  The "name-length" field has the value of 0 in order to signify
      that it is a "member-attribute" contained in the collection.

   o  The "value-length" field specifies the length of the "value" field
      in bytes, e.g. w in the above diagram or 10 for the member
      attribute name 'media-type'.  Additional member attribute values
      are specifies using a value length of 0.

   o  The "value" field contains the name of the member attribute, e.g.
      the textual value 'media-type'.

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

   o  The second "name-length" field has the value of 0 in order to
      signify that it is a "member-attribute" contained in the
      collection.

   o  The "member-value-length" field specifies the length of the member
      attribute value, e.g. x in the above diagram or 10 for the value
      'stationery'.

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

3.1.8.  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
   -----------------------------------------------

                  Figure 8: Encoding Based On Value Tags

   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 [RFC5234] 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

   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
   status-code  = SIGNED-SHORT     ; mapping from model
   request-id   = SIGNED-INTEGER   ; whose value is > 0

   attribute-group          = begin-attribute-group-tag *attribute
   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

                   Figure 9: ABNF of IPP Message Format

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

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   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

                 Figure 10: ABNF for Attribute Group Tags

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:

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   +----------------+--------------------------------------------------+
   | 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        |                                                  |
   +----------------+--------------------------------------------------+

                           Table 1: Group Values

   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-
   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:

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   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
   [RFC2911bis].  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 consists of a major and minor version-
   number, each of which is represented by a SIGNED-BYTE.  The major
   version-number is the first byte of the encoding and the minor
   version-number is the second byte of the encoding.  The protocol
   described in this document has a major version-number of 1 (0x01) and
   a minor version-number of 1 (0x01).  The ABNF for these two bytes is
   %x01.01.

   Note: See Section 9 for more information on the "version-number"
   field and IPP version numbers.

3.4.2.  Operation-id

   The "operation-id" field contains an operation-id value as defined in
   the model document.  The value is encoded as a SIGNED-SHORT and is
   located in the third and fourth bytes of the encoding of an operation
   request.

3.4.3.  Status-code

   The "status-code" field contains a status-code value as defined in
   the model document.  The value is encoded as a SIGNED-SHORT and is
   located in the third and fourth bytes of the encoding of an operation
   response.

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   If an IPP status-code is returned, then the HTTP Status-Code MUST be
   200 (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 contains the request-id value as defined in
   the model document.  The value is encoded as a SIGNED-INTEGER and is
   located 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

   Tags are part of the IANA IPP registry [IANA-IPP]

3.5.1.  Delimiter Tags

   The following table specifies the values for the delimiter tags
   defined in this document:

   +---------------+---------------------------------------------------+
   | Tag Value     | Meaning                                           |
   | (Hex)         |                                                   |
   +---------------+---------------------------------------------------+
   | 0x00          | reserved for definition in a future 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 standards track |
   |               | documents                                         |
   +---------------+---------------------------------------------------+

                          Table 2: Delimiter Tags

   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 are attributes belonging to the attribute group specified by the
   value of the "begin-attribute-group-tag".  For example, if the value

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   of "begin-attribute-group-tag" is 0x01, the following attributes are
   members of the Operations Attributes group.

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

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 defined in this document:

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

                        Table 3: Out of Band Values

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

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

                           Table 4: Integer Tags

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

   The following table specifies the octetString values for the "value-
   tag" field defined in this document:

   +-------------+-----------------------------------------------------+
   | Tag Value   | Meaning                                             |
   | (Hex)       |                                                     |
   +-------------+-----------------------------------------------------+
   | 0x30        | octetString with an unspecified format              |
   | 0x31        | dateTime                                            |
   | 0x32        | resolution                                          |
   | 0x33        | rangeOfInteger                                      |
   | 0x34        | begCollection                                       |
   | 0x35        | textWithLanguage                                    |
   | 0x36        | nameWithLanguage                                    |
   | 0x37        | endCollection                                       |
   | 0x38-0x3F   | reserved for octetString type definitions in future |
   |             | standards track documents                           |
   +-------------+-----------------------------------------------------+

                         Table 5: octetString Tags

   The following table specifies the character-string values for the
   "value-tag" field defined in this document:

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   +------------+------------------------------------------------------+
   | Tag Value  | Meaning                                              |
   | (Hex)      |                                                      |
   +------------+------------------------------------------------------+
   | 0x40       | reserved for definition in a future standards track  |
   |            | document                                             |
   | 0x41       | textWithoutLanguage                                  |
   | 0x42       | nameWithoutLanguage                                  |
   | 0x43       | reserved for definition in a future standards track  |
   |            | document                                             |
   | 0x44       | keyword                                              |
   | 0x45       | uri                                                  |
   | 0x46       | uriScheme                                            |
   | 0x47       | charset                                              |
   | 0x48       | naturalLanguage                                      |
   | 0x49       | mimeMediaType                                        |
   | 0x4A       | memberAttrName                                       |
   | 0x4B-0x5F  | reserved for character string type definitions in    |
   |            | future standards track documents                     |
   +------------+------------------------------------------------------+

                           Table 6: String Tags

   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
   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 0x00000000 to
   0x3FFFFFFF are reserved for definition in future standards track
   documents.  The values 0x40000000 to 0x7FFFFFFF are reserved for
   vendor extensions.

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3.6.  Name-Length

   The "name-length" field consists of a SIGNED-SHORT and specifies 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 is empty and the following value is 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
   Section ?? of [RFC2911bis]).  The zero-length name is the only
   mechanism for multi-valued attributes.

3.7.  (Attribute) Name

   The "name" field contains the name of an attribute.  The model
   document [RFC2911bis] specifies such names.

3.8.  Value Length

   The "value-length" field consists of a SIGNED-SHORT which specifies
   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 binary signed bytes, the sender
   MUST encode the value in exactly one octet.

   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.  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     |
   |                      | SIGNED-SHORT which is the number of octets |
   |                      | in the following field, a value of type    |
   |                      | natural-language, a SIGNED-SHORT which is  |
   |                      | the number of octets in the following      |
   |                      | field, and 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     |
   |                      | SIGNED-SHORT which is the number of octets |
   |                      | in the following field, a value of type    |
   |                      | natural-language, a SIGNED-SHORT which is  |
   |                      | the number of octets in the following      |
   |                      | field, and 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                               |
   +----------------------+--------------------------------------------+
   | collection           | Encoding as defined in Section 3.1.6.      |
   +----------------------+--------------------------------------------+

                     Table 7: Attribute Value Encoding

   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 [RFC7230] is the REQUIRED transport layer for this protocol.
   HTTP/2 [RFC7540] is an OPTIONAL 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

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   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.

   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 [RFC7230].  A printer (server) implementation MUST adhere
   the rules for an origin server described for HTTP1.1 [RFC7230].

   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,
   consult the HTTP documents [RFC7230].

   An HTTP/1.1 server MUST support chunking for IPP requests, and an IPP
   client MUST support chunking for IPP responses according to HTTP/1.1
   [RFC7230].  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) [RFC3986] so that they can be persistently and
   unambiguously referenced.

   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 allows clients to generate and send a relative
   URI rather than an absolute URI.  A relative URI identifies a

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   resource with the scope of the HTTP server, but does not include
   scheme, host or port.  The following statements characterize how URIs
   should be used in the mapping of IPP onto HTTP:

   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 URIs are not used as the
       addressing mechanism in the transport layer.

   2.  Even though these two URIs might not be literally identical (one
       being relative and the other being absolute), they MUST both
       reference the same IPP object.

   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.

   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 URIs) 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 URI Schemes

   The IPP URI schemes are 'ipp' [RFC3510] and 'ipps' [RFC7472].  A
   client and an IPP object (i.e. the server) MUST support the ipp-URI
   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

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      *  printer-uri

   Each of the above attributes identifies a printer or job object.  The
   ipp-URI 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 URI with a directory service, the printer
   MUST register an ipp-URI.

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

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

   1.  change the 'ipp' scheme to 'http' or 'ipps' scheme to 'https'

   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' and 'ipps' schemes.

   The client MUST use the target http-URL in both the HTTP Request-Line
   and HTTP headers, as specified by HTTP [RFC7230][RFC2617].  However,
   the client MUST use the target ipp-URI for the value of the "printer-
   uri" or "job-uri" operation attribute within the application/ipp body
   of the request.  The server MUST use the ipp-URI 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-URI "ipp://printer.example.com/ipp/print/myqueue",
   it opens a TCP connection to port 631 (the ipp implicit port) on the
   host "printer.example.com" and sends the following data:

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

                       Figure 11: Direct IPP Request

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

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

                      Figure 12: Proxied IPP Request

   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 standards track extensions and vendor extensions to the
   IPP/1.1 Encoding and Transport document:

   1.  attribute syntaxes - see Section 6.3 of [RFC2911bis]

   2.  attribute groups - see Section 6.5 of [RFC2911bis]

   3.  out-of-band attribute values - see Section 6.7 of [RFC2911bis]

   These extensions follow the "type2" registration procedures defined
   in Section ?? of [RFC2911bis].  Extensions registered for use with
   IPP 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 [RFC2911bis] 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 [RFC2911bis].  The IPP/1.1
   Encoding and Transport document may also be extended by an
   appropriate standards track document that specifies any of the above
   extensions.

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7.  Internationalization Considerations

   See the section on "Internationalization Considerations" in the
   document "Internet Printing Protocol/1.1: Model and Semantics"
   [RFC2911bis] for information on internationalization.  This document
   adds no additional issues.

8.  Security Considerations

   The IPP Model and Semantics document [RFC2911bis] 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 SHOULD support:

      Digest Authentication [RFC2617].

         MD5 and MD5-sess MUST be implemented and supported.

         Use of the Message Integrity feature is OPTIONAL.

   IPP Printers SHOULD support:

      Digest Authentication [RFC2617].

         MD5 and MD5-sess MUST be implemented and supported.

         Use of the Message Integrity feature is OPTIONAL.

   The reasons that IPP Clients and 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

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       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.

   2.  Print devices that have high-volume throughput and have available
       ROM space are more likely 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) [RFC5246]
   [RFC7525] for Server Authentication and Operation Privacy.  IPP
   Printers MAY also support TLS for Client Authentication.  An IPP
   Printer MAY support Basic Authentication [RFC2617] for Client
   Authentication if the channel is secure.

   The IPP Model and Semantics document [RFC2911bis] defines two printer
   attributes ("uri-authentication-supported" and "uri-security-
   supported") that the client can use to discover the security policy
   of a printer.  That document also outlines IPP-specific security
   considerations and should be the primary reference for security
   implications with regard to the IPP protocol itself.

8.2.  Using IPP with TLS

   IPP uses the "Upgrading to TLS Within HTTP/1.1" mechanism [RFC2817]
   for 'ipp' URIs.  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.

   IPP uses the "HTTPS: HTTP over TLS" mechanism [RFC2818] for 'ipps'
   URIs.  The client and server negotiate a secure TLS connection
   immediately and unconditionally.

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9.  Interoperability with Other IPP Versions

   It is beyond the scope of this specification to mandate conformance
   with versions of IPP other than 1.1.  IPP was deliberately designed,
   however, to make supporting other versions easy.  IPP Printer
   implementations SHOULD:

   o  understand any valid request in the format of IPP/1.0, 1.1, 2.0,
      2.1, or 2.2;

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

   IPP Clients SHOULD:

   o  understand any valid response in the format of IPP/1.0, 1.1, 2.0,
      2.1, or 2.2.

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 the highest supported value, e.g., '1.1', '2.0',
       etc., 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').

   3.  It is recommended that IPP objects accept any request with the
       major version '1' or '2' (or reject the request for reasons other
       than 'server-error-version-not-supported').  See [RFC2911bis]
       "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.

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9.2.  Security and URI Schemes

   The following are rules regarding security, the "version-number"
   parameter, and the URI 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',
       'ipps', 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.  In any case, security MUST NOT be compromised when a client
       supplies an 'ipp' or other non-secure URL scheme in the target
       "printer-uri" and "job-uri" operation attributes in a request.

10.  Changes Since RFC 2910

   The following changes have been made since the publication of RFC
   2910:

   o  Added references to current IPP extension specifications.

   o  Added optional support for HTTP/2.

   o  Added collection attribute syntax from RFC 3382.

   o  Fixed typographical errors.

   o  Now reference TLS/1.2 and no longer mandate the TLS/1.0 MTI cipher
      suites.

   o  Updated all references.

   o  Updated document organization to follow current style.

   o  Updated example ipp: URIs to follow RFC 7472 guidelines.

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   o  Updated version compatibility for all versions of IPP.

   o  Updated HTTP Digest authentication to optional for Clients.

   o  Removed references to (experimental) IPP/1.0 and usage of
      http:/https: URLs.

11.  References

11.1.  Normative References

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

   [PWG5100.12]
              Sweet, M. and I. McDonald, "IPP/2.0, 2.1, and 2.2", April
              2015,
              <http://ftp.pwg.org/pub/pwg/ipp/wd/wd-ipp20-20150417.pdf>.

   [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.

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

   [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.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

   [RFC2911bis]
              Sweet, M. and I. McDonald, "Internet Printing
              Protocol/1.1: Model and Semantics", April 2015,
              <https://tools.ietf.org/html/draft-sweet-rfc2911bis-01>.

   [RFC3510]  Herriot, R. and I. McDonald, "Internet Printing
              Protocol/1.1: IPP URL Scheme", RFC 3510, April 2003.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

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   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC7230]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Message Syntax and Routing", RFC 7230, June
              2014.

   [RFC7231]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Semantics and Content", RFC 7231, June 2014.

   [RFC7232]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Conditional Requests", RFC 7232, June 2014.

   [RFC7234]  Fielding, R., Nottingham, M., and J. Reschke, "Hypertext
              Transfer Protocol (HTTP/1.1): Caching", RFC 7234, June
              2014.

   [RFC7235]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Authentication", RFC 7235, June 2014.

   [RFC7472]  McDonald, I. and M. Sweet, "Internet Printing Protocol
              (IPP) over HTTPS Transport Binding and the 'ipps' URI
              Scheme", RFC 7472, March 2015.

   [RFC7540]  Belshe, M., Peon, R., and M. Thompson, "Hypertext Transfer
              Protocol Version 2 (HTTP/2)", May 2015,
              <https://tools.ietf.org/html/rfc7540>.

   [RFC7541]  Peon, R. and H. Ruellan, "HPACK - Header Compression for
              HTTP/2", May 2015, <https://tools.ietf.org/html/rfc7541>.

   [RFC793]   Postel, J., "Transmission Control Protocol", STD 7, RFC
              793, September 1981.

11.2.  Informative References

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

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   [IANA-IPP]
              "IANA IPP Registry",
              <http://www.iana.org/assignments/ipp-registrations/>.

   [PWG5100.3]
              Ocke, K. and T. Hastings, "IPP Production Printing
              Attributes Set 1", February 2001,
              <http://ftp.pwg.org/pub/pwg/candidates/
              cs-ippprodprint10-20010212-5100.3.pdf>.

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

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, May 2015.

11.3.  URIs

   [1] http://www.pwg.org/

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                         1.1                  version-number
    0x0002                         Print-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     value-tag
                                   type
    0x001B                                              name-length
    attributes-natural-language    attributes-natural-  name

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                                   language
    0x0005                                              value-length
    en-us                          en-US                value
    0x45                           uri type             value-tag
    0x000B                                              name-length
    printer-uri                    printer-uri          name
    0x002C                                              value-length
    ipp://printer.example.com/ipp/ printer pinetree     value
    print/pinetree
    0x42                           nameWithoutLanguage  value-tag
                                   type
    0x0008                                              name-length
    job-name                       job-name             name
    0x0006                                              value-length
    foobar                         foobar               value
    0x22                           boolean type         value-tag
    0x0016                                              name-length
    ipp-attribute-fidelity         ipp-attribute-       name
                                   fidelity
    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-tag
    %!PDF...                       <PDF Document>       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   value-tag
                                     type
    0x001B                                              name-length
    attributes-natural-language      attributes-        name
                                     natural-language
    0x0005                                              value-length
    en-us                            en-US              value
    0x41                             textWithoutLanguag value-tag
                                     e type
    0x000E                                              name-length
    status-message                   status-message     name
    0x000D                                              value-length
    successful-ok                    successful-ok      value
    0x02                             start job-         job-attributes-
                                     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
    0x0030                                              value-length
    ipp://printer.example.com/ipp/pr job 123 on         value
    int/pinetree/123                 pinetree
    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

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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
   '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).

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   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

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

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   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
   0x02                       start job-attributes        job-
                                                          attributes-tag
   0x21                       integer                     value-tag
   0x0006                                                 name-length
   job-id                     job-id                      name

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   0x0004                                                 value-length
   147                        147                         value
   0x45                       uri type                    value-tag
   0x0007                                                 name-length
   job-uri                    job-uri                     name
   0x0030                                                 value-length
   ipp://printer.example.com/ job 123 on pinetree         value
   ipp/print/pinetree/123
   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     value-tag
                                   type
    0x001B                                              name-length
    attributes-natural-language    attributes-natural-  name
                                   language
    0x0005                                              value-length
    en-us                          en-US                value
    0x45                           uri type             value-tag
    0x000B                                              name-length
    printer-uri                    printer-uri          name
    0x002C                                              value-length
    ipp://printer.example.com/ipp/ printer pinetree     value
    print/pinetree
    0x45                           uri type             value-tag
    0x000C                                              name-length
    document-uri                   document-uri         name
    0x0019                                              value-length
    ftp://foo.example.com /foo     ftp://foo.example.co value
                                   m/foo
    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

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A.6.  Create-Job Request

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

    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     value-tag
                                   type
    0x001B                                              name-length
    attributes-natural-language    attributes-natural-  name
                                   language
    0x0005                                              value-length
    en-us                          en-US                value
    0x45                           uri type             value-tag
    0x000B                                              name-length
    printer-uri                    printer-uri          name
    0x002C                                              value-length
    ipp://printer.example.com/ipp/ printer pinetree     value
    print/pinetree
    0x03                           end-of-attributes    end-of-
                                                        attributes-tag

A.7.  Create-Job Request with Collection Attributes

   The following is an example of Create-Job request with the "media-
   col" collection attribute [PWG5100.3] with the value "media-
   size={x-dimension=21000 y-dimension=29700} media-type='stationery'":

   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

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   attributes-charset             attributes-charset   name
   0x0008                                              value-length
   us-ascii                       US-ASCII             value
   0x48                           natural-language     value-tag
                                  type
   0x001B                                              name-length
   attributes-natural-language    attributes-natural-  name
                                  language
   0x0005                                              value-length
   en-us                          en-US                value
   0x45                           uri type             value-tag
   0x000B                                              name-length
   printer-uri                    printer-uri          name
   0x002C                                              value-length
   ipp://printer.example.com/ipp/ printer pinetree     value
   print/pinetree
   0x34                           begCollection        value-tag
   0x0009                         9                    name-length
   media-col                      media-col            name
   0x0000                         0                    value-length
   0x4A                           memberAttrName       value-tag
   0x0000                         0                    name-length
   0x000A                         10                   value-length
   media-size                     media-size           value (member-
                                                       name)
   0x34                           begCollection        member-value-tag
   0x0000                         0                    name-length
   0x0000                         0                    member-value-
                                                       length
   0x4A                           memberAttrName       value-tag
   0x0000                         0                    name-length
   0x000B                         11                   value-length
   x-dimension                    x-dimension          value (member-
                                                       name)
   0x21                           integer              member-value-tag
   0x0000                         0                    name-length
   0x0004                         4                    member-value-
                                                       length
   0x00005208                     21000                member-value
   0x4A                           memberAttrName       value-tag
   0x0000                         0                    name-length
   0x000B                         11                   value-length
   y-dimension                    y-dimension          value (member-
                                                       name)
   0x21                           integer              member-value-tag
   0x0000                         0                    name-length
   0x0004                         4                    member-value-
                                                       length

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   0x00007404                     29700                member-value
   0x37                           endCollection        end-value-tag
   0x0000                         0                    end-name-length
   0x0000                         0                    end-value-length
   0x4A                           memberAttrName       value-tag
   0x0000                         0                    name-length
   0x000A                         10                   value-length
   media-type                     media-type           value (member-
                                                       name)
   0x44                           keyword              member-value-tag
   0x0000                         0                    name-length
   0x000A                         10                   member-value-
                                                       length
   stationery                     stationery           member-value
   0x37                           endCollection        end-value-tag
   0x0000                         0                    end-name-length
   0x0000                         0                    end-value-length
   0x03                           end-of-attributes    end-of-
                                                       attributes-tag

A.8.  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     value-tag
                                   type
    0x001B                                              name-length
    attributes-natural-language    attributes-natural-  name
                                   language
    0x0005                                              value-length
    en-us                          en-US                value
    0x45                           uri type             value-tag
    0x000B                                              name-length
    printer-uri                    printer-uri          name
    0x002C                                              value-length
    ipp://printer.example.com/ipp/ printer pinetree     value
    print/pinetree
    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

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A.9.  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):

   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)

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   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
   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 section is strictly informative.  The MIME media type listed in
   this section should not be re-registered by IANA when this document
   is published.

   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) whose syntax is described
   in Section 3 "Encoding of the Operation Layer" of [RFC2910bis], and
   whose semantics are described in [RFC2911bis].

   Required parameters: none

   Optional parameters: none

   Encoding considerations:

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

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   Security considerations:

   IPP protocol requests/responses do not introduce any security risks
   not already inherent in the underlying transport protocols.  Protocol
   mixed-version interworking rules in [RFC2911bis] as well as protocol
   encoding rules in [RFC2910bis] are complete and unambiguous.

   Interoperability considerations:

   IPP requests (generated by clients) and responses (generated by
   servers) MUST comply with all conformance requirements imposed by the
   normative specifications [RFC2911bis] and [RFC2910bis].  Protocol
   encoding rules specified in [RFC2910bis] 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 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:

   [RFC2911bis] Sweet, M., McDonald, I., "Internet Printing
   Protocol/1.1: Model and Semantics" draft-sweet-rfc2911bis-01.txt,
   April 26, 2015.

   [RFC2910bis] Sweet, M., McDonald, I., "Internet Printing
   Protocol/1.1: Encoding and Transport", draft-sweet-rfc2910bis-01.txt,
   April 27, 2015.

   Applications which use this media type:

   Internet Printing Protocol (IPP) print clients and print servers,
   communicating using HTTP (see [RFC2910bis]), 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.  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), Paul Moore, Sylvan Butler,
   Randy Turner, and John Wenn

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Appendix D.  Change History

D.1.  Changes In -03

   The following changes are in draft-sweet-rfc2910bis-03:

   o  New HTTP/2 RFCs: 7540, 7541

   o  Added informative reference to UTA BCP (RFC 7525)

   o  Culled list of people in acknowledgements to the original RFC 2910
      editors, per IPP F2F.

D.2.  Changes In -02

   The following changes are in draft-sweet-rfc2910bis-02:

   o  Sections 3.1.x: Dropped "Picture of the encoding of" from titles

   o  Section 3.4.1: Added reference to IPP version interoperability
      section.

   o  Section 3.4.2: Removed paragraph on status-code as operation
      attribute (already covered in 3.4 intro) and updated HTTP status
      code 200 name (OK)

   o  Section 3.5: Added reference to IANA IPP registry for tags.

   o  Section 3.8: Mention SIGNED-BYTE is 1 octet.

   o  Section 4.1: Drop mention of URIs not being widely implemented,
      and that implementations will pass around URLs (not true).  Also
      remove more "need not" text.

   o  Section 6: Fixed references.

   o  Section 8.1.1: Make Digest authentication a SHOULD for clients.

   o  Section 9: Reworked for generic IPP version compatibility.

   o  Section 9.1: Reworked for IPP 2.x compatibility.

   o  Section 9.2: Drop reference to IPP/1.0 and http/https URI schemes.

   o  Appendix A: Updated example URIs to follow IETF and IPP/IPPS URI
      examples

   o  Global: ipp-URL tp ipp-URI, URL to URI

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   o  Global: Don't use conformance language for statements of fact.

   o  Global: Change "NOTE:" to "Note:" for consistency.

D.3.  Changes In -01

   The following changes are in draft-sweet-rfc2910bis-01:

   o  Errata ID 4100: Cleaned up TLS references and recommendations - no
      longer include cipher suites.

   o  Errata ID 4172: Fixed range of standards-track value tags (to
      0x3ffffff not 0x37777777)

   o  Updated RFC references.

   o  Added HTTP/2 references, made it clear that only HTTP/1.1 is
      required and HTTP/2 is optional.

   o  Added collection attribute encoding from RFC 3382.

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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