INTERNET-DRAFT Robert Herriot (editor) Sun Microsystems Sylvan Butler Hewlett-Packard Paul Moore Microsoft. Randy Turner Sharp Labs November 7, 1997 Internet Printing Protocol/1.0: Protocol Specification draft-ietf-ipp-protocol-03.txt Copyright c The Internet Society (date). All Rights Reserved. Status of this Memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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". To learn the current status of any Internet-Draft, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). 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 technology. The protocol is heavily influenced by the printing model introduced in the Document Printing Application (ISO/IEC 10175 DPA) standard [dpa]. Although DPA specifies both end user and administrative features, IPP version 1.0 is focused only on end user functionality. The full set of IPP documents includes: Requirements for an Internet Printing Protocol [ipp-req] Internet Printing Protocol/1.0: Model and Semantics [ipp-mod] Internet Printing Protocol/1.0: Protocol Specification (this document) The requirements document takes a broad look at distributed printing functionality, and it enumerates real-life scenarios that help to clarify the features that need to be included in a printing protocol for the Internet. It identifies requirements for three types of users: end Herriot, Butler, November 7, 1997, [Page 1] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 users, operators, and administrators. The requirements document calls out a subset of end user requirements that MUST be satisfied in the first version of IPP. Operator and administrator requirements are out of scope for v1.0. The model and semantics document describes a simplified model with abstract objects, their attributes, and their operations. The model introduces a Printer object and a Job object. The Job object supports multiple documents per job. The protocol specification is formal document which incorporates the ideas in all the other documents into a concrete mapping using clearly defined data representations and transport protocol mappings that real implementers can use to develop interoperable client and printer (server) side components. This document is the "Internet Printing Protocol/1.0: Protocol Specification" document. Notice The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Herriot, Butler, November 7, 1997, [Page 2] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Table of Contents 1. Introduction........................................................4 2. Conformance Terminology.............................................4 3. Encoding of the Operation Layer....................................4 3.1 Picture of the Encoding.........................................5 3.2 Syntax of Encoding..............................................6 3.3 Version.........................................................8 3.4 Mapping of Operations...........................................8 3.5 Mapping of Status-code..........................................8 3.6 Tags............................................................. 3.6.1 Delimiter Tags.............................................8 3.6.2 Value Tags.................................................9 3.7 Name-Lengths...................................................11 3.8 Mapping of Attribute Names....................................11 3.9 Value Lengths..................................................12 3.10 Mapping of Attribute Values...................................12 3.11 Data............................................................ 4. Encoding of Transport Layer........................................14 4.1 General Headers................................................15 4.2 Request Headers...............................................16 4.3 Response Headers...............................................16 4.4 Entity Headers................................................17 5. Security Considerations............................................17 6. Copyright..........................................................18 7. References.........................................................19 8. Author's Address...................................................20 9. Other Participants:................................................20 10. Appendix A: Protocol Examples.....................................21 10.1 Print-Job Request.............................................21 10.2 Print-Job Response (successful)...............................22 10.3 Print-Job Response (failure)..................................23 10.4 Print-URI Request.............................................24 10.5 Create-Job Request............................................25 10.6 Get-Jobs Request..............................................25 10.7 Get-Jobs Response.............................................26 11. Appendix B: Mapping of Each Operation in the Encoding.............27 12. Appendix C: Hints to implementors using IPP with SSL3.............32 Herriot, Butler, November 7, 1997, [Page 3] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 1. Introduction This document contains the rules for encoding IPP operations and describes two layers: the transport layer and the operation layer. The transport layer consists of an HTTP/1.1 request or response. RFC 2068 [rfc2068] describes HTTP/1.1. This document specifies the HTTP headers that an IPP implementation supports. The operation layer consists of a message body in an HTTP request or response. The document "Internet Printing Protocol/1.0: Model and Semantics" [ipp-mod] defines the semantics of such a message body and the supported values. This document specifies the encoding of an IPP operation. The aforementioned document [ipp-mod] is henceforth referred to as the "IPP model document" 2. Conformance Terminology 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 RFC 2119 [rfc2119]. 3. Encoding of the Operation Layer The operation layer SHALL contain a single operation request or operation response. 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 SHALL be a sequence of characters where the characters are associated with some charset and some natural language. . A character string MUST be in "network byte 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 "network byte order" with the first octet in the value (according to reading order) being the first octet in the encoding Every integer in this encoding SHALL 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 SHALL be 1, 2 or 4, depending on usage in the protocol. Such one-octet integers, henceforth called SIGNED-BYTE, are used for the version and tag fields. Such two-byte integers, henceforth called SIGNED-SHORT are used for the operation, status-code and length fields. Four byte integers, henceforth called SIGNED-INTEGER, are used for values fields. Herriot, Butler, November 7, 1997, [Page 4] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 The following two sections present the operation layer in two ways . informally through pictures and description . formally through Augmented Backus-Naur Form (ABNF), as specified by draft-ietf-drums-abnf-02.txt [abnf] 3.1 Picture of the Encoding The encoding for an operation request or response consists of: ----------------------------------------------- | version | 2 bytes - required ----------------------------------------------- |operation (request) or status-code (response)| 2 bytes - required ----------------------------------------------------------- | xxx-attributes-tag | 1 byte | ----------------------------------------------- |-0 or more | xxx-attribute-sequence | n bytes | ----------------------------------------------------------- | data-tag | 1 byte - required ----------------------------------------------- | data | q bytes - optional ----------------------------------------------- The xxx-attributes-tag and xxx-attribute-sequence represents four different values of "xxx", namely, operation, job, printer and unsupported-job. The xxx-attributes-tag and xxx-attribute-sequence may be omitted if the operation has no attributes or it may be repeated with the same or different values of "xxx" in ways that are specific to each operation. The data is omitted from some operations, but the data-tag is present even when the data is omitted. Note, the xxx-attributes-tags and data-tag are called `delimiter-tags'. Note: the xxx-attribute-sequence, shown above may consist of 0 bytes, according to the rule below. An xxx-attributes-sequence consists of zero or more compound-attributes. ----------------------------------------------- | compound-attribute | s bytes - 0 or more ----------------------------------------------- A compound-attribute consists of an attribute with a single value followed by zero or more additional values. Note: a `compound-attribute' represents a single attribute in the model document. The `additional value' syntax is for attributes with 2 or more values. Each attribute consists of: Herriot, Butler, November 7, 1997, [Page 5] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 ----------------------------------------------- | value-tag | 1 byte ----------------------------------------------- | name-length (value is u) | 2 bytes ----------------------------------------------- | name | u bytes ----------------------------------------------- | value-length (value is v) | 2 bytes ----------------------------------------------- | value | v bytes ----------------------------------------------- An additional value consists of: ----------------------------------------------------------- | value-tag | 1 byte | ----------------------------------------------- | | name-length (value is 0x0000) | 2 bytes | ----------------------------------------------- |-0 or more | value-length (value is w) | 2 bytes | ----------------------------------------------- | | value | w bytes | ----------------------------------------------------------- Note: an additional value is like an attribute whose name-length is 0. From the standpoint of a parsing loop, the encoding consists of: ----------------------------------------------- | version | 2 bytes - required ----------------------------------------------- |operation (request) or status-code (response)| 2 bytes - required ----------------------------------------------------------- | tag (delimiter-tag or value-tag) | 1 byte | ----------------------------------------------- |-0 or more | empty or rest of attribute | x bytes | ----------------------------------------------------------- | data-tag | 2 bytes - required ----------------------------------------------- | data | y bytes - optional ----------------------------------------------- The value of the tag determines whether the bytes following the tag are: . attributes . data . the remainder of a single attribute where the tag specifies the type of the value. 3.2 Syntax of Encoding The syntax below is ABNF [abnf] except `strings of literals' SHALL be case sensitive. For example `a' means lower case `a' and not upper case Herriot, Butler, November 7, 1997, [Page 6] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 `A'. In addition, SIGNED-BYTE and SIGNED-SHORT fields are represented as `%x' values which show their range of values. ipp-message = ipp-request / ipp-response ipp-request = version operation *(xxx-attributes-tag xxx-attribute-sequence) data-tag data ipp-response = version status-code *(xxx-attributes-tag xxx-attribute-sequence) data-tag data xxx-attribute-sequence = *compound-attribute ; where "xxx" in the three rules above stands for any of the following ; values: "operation", "job", "printer" or "unsupported-job". version = major-version minor-version major-version = SIGNED-BYTE ; initially %d1 minor-version = SIGNED-BYTE ; initially %d0 operation = SIGNED-SHORT ; mapping from model defined below status-code = SIGNED-SHORT ; mapping from model defined below compound-attribute = attribute *additional-values attribute = value-tag name-length name value-length value additional-values = 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 operation-attributes-tag = %x01 ; tag of 1 job-attributes-tag = %x02 ; tag of 2 printer-attributes-tag = %x04 ; tag of 4 unsupported-job-attributes-tag = %x05 ; tag of 5 data-tag = %x03 ; tag of 3 value-tag = %x10-FF SIGNED-BYTE = BYTE SIGNED-SHORT = 2BYTE DIGIT = %x30-39 ; "0" to "9" LALPHA = %x61-7A ; "a" to "z" BYTE = %x00-FF OCTET-STRING = *BYTE The syntax allows an xxx-attributes-tag to be present when the xxx- attribute-sequence that follows is empty. The syntax is defined this way to allow for the response of Get-Jobs where no attributes are returned for some job-objects. Although it is RECOMMENDED that the sender not send an xxx-attributes-tag if there are no attributes (except in the Herriot, Butler, November 7, 1997, [Page 7] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Get-Jobs response just mentioned), the receiver MUST be able to decode such syntax. 3.3 Version The version SHALL consist of a major and minor version, each of which SHALL be represented by a SIGNED-BYTE. The protocol described in this document SHALL have a major version of 1 (0x01) and a minor version of 0 (0x00). The ABNF for these two bytes SHALL be %x01.00. 3.4 Mapping of Operations Operations are defined as enums in the model document. An operations enum value SHALL be encoded as a SIGNED-SHORT Note: the values 0x4000 to 0xFFFF are reserved for private extensions. 3.5 Mapping of Status-code Status-codes are defined as enums in the model document. A status-code enum value SHALL be encoded as a SIGNED-SHORT 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 SHALL NOT contain an IPP message-body, and thus no IPP status-code is returned. 3.6 Tags There are two kinds of tags: . delimiter tags: delimit major sections of the protocol, namely attributes and data . value tags: specify the type of each attribute value 3.6.1 Delimiter Tags The following table specifies the values for the delimiter tags: Tag Value (Hex) Delimiter 0x00 reserved 0x01 operation-attributes-tag 0x02 job-attributes-tag 0x03 data-tag 0x04 printer-attributes-tag 0x05 unsupported-job-attributes-tag 0x06-0x0F reserved for future delimiters Herriot, Butler, November 7, 1997, [Page 8] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 When an xxx-attributes-tag occurs in the protocol, it SHALL mean that the zero or more following attributes up to the next delimiter tag are xxx attributes as defined in the model document, where xxx is operation, job, printer, unsupported-job. Doing substitution for xxx in the above paragraph, this means the following. When an operation-attributes-tag occurs in the protocol, it SHALL mean that the zero or more following attributes up to the next delimiter tag are operation attributes as defined in the model document. When an job-attributes-tag occurs in the protocol, it SHALL mean that the zero or more following attributes up to the next delimiter tag are job attributes as defined in the model document. When an printer- attributes-tag occurs in the protocol, it SHALL mean that the zero or more following attributes up to the next delimiter tag are printer attributes as defined in the model document. When an unsupported-job- attributes-tag occurs in the protocol, it SHALL mean that the zero or more following attributes up to the next delimiter tag are unsupported- job attributes as defined in the model document. The operation-attributes-tag and data-tag SHALL each occur exactly once in an operation. The operation-attributes-tag SHALL be the first tag delimiter, and the data-tag SHALL be the last tag delimiter. Each of the other three xxx-attributes-tags defined above is OPTIONAL in an operation and each SHALL occur at most once in an operation, except for job-attributes-tag in a Get-Jobs response which may occur zero or more times. The order and presence of delimiter tags for each operation request and each operation response SHALL be that defined in the model document. For further details, see Section 3.8 Mapping of Attribute Names and Appendix B: Mapping of Each Operation in the Encoding. 3.6.2 Value Tags The remaining tables show values for the value-tag, which is the first octet of an attribute. The value-tag specifies the type of the value of the attribute. If the value-tag specifies a type of compoundValue, it represents a compound value whose type is the that of the last member of the compound value. The following table specifies the "out-of-band" values for the value-tag. Tag Value (Hex) Meaning 0x10 unsupported 0x11 reserved for future `default' 0x12 unknown 0x13 compoundValue 0x14-0x1F reserved for future "out-of-band" values. The "unsupported" value SHALL be used in the attribute-sequence of an error response for those attributes which the printer does not support. Herriot, Butler, November 7, 1997, [Page 9] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 The "default" value is reserved for future use of setting value back to their default value. The "unknown" value is used for the value of a supported attribute when its value is temporarily unknown. . The "compoundValue" SHALL be used to form a single value from a collection of values, and its value is the number of members forming the compound value, excluding the compoundValue. For example, a text value with a naturalLanguage override consists of 3 "values": a compoundValue with value 2, a naturalLanguage value and a text value. The following table specifies the integer values for the value-tag Tag Value (Hex) Meaning 0x20 reserved 0x21 integer 0x22 boolean 0x23 enum 0x24-0x2F reserved for future integer types NOTE: 0x20 is reserved for "generic integer" if should ever be needed. The following table specifies the octetString values for the value-tag Tag Value (Hex) Meaning 0x30 octetString with an unspecified format 0x31 dateTime 0x32 resolution 0x33 rangeOfInteger 0x34 reserved for dictionary (in the future) 0x35-0x3F reserved for future octetString types The following table specifies the character-string values for the value- tag Tag Value (Hex) Meaning 0x40 reserved 0x41 text 0x42 name 0x43 reserved 0x44 keyword 0x45 uri 0x46 uriScheme 0x47 charset 0x48 naturalLanguage 0x49 mimeMediaType 0x4A-0x5F reserved for future character string types NOTE: 0x40 is reserved for "generic character-string" if should ever be needed. Herriot, Butler, November 7, 1997, [Page 10] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 The values 0x60-0xFF are reserved for future types. There are no values allocated for private extensions. A new type must be registered via the type 2 process. 3.7 Name-Lengths The name-length field SHALL consist of a SIGNED-SHORT. This field SHALL specify the number of octets in the name field which follows the name- length field, excluding the two bytes of the name-length field. If a name-length field has a value of zero, the following name field SHALL be empty, and the following value SHALL be treated as an additional value for the preceding attribute. Within an attribute- sequence, if two attributes have the same name, the first occurrence SHALL be ignored. The zero-length name is the only mechanism for multi- valued attributes. 3.8 Mapping of Attribute Names Some attributes are encoded in a special position. These attribute are: . "printer-uri": The target printer-uri of each operation in the IPP model document SHALL be specified outside of the operation layer as the request-URI on the Request-Line at the HTTP level. . "job-uri": The target job-uri of each operation in the IPP model document SHALL be specified outside of the operation layer as the request-URI on the Request-Line at the HTTP level. . "document-content": The attribute named "document-content" in the IPP model document SHALL become the "data" in the operation layer. . "status-code": The attribute named "status-code" in the IPP model document SHALL become the "status-code" field in the operation layer response. The model document arranges the remaining attributes into groups for each operation request and response. Each such group SHALL be represented in the protocol by an xxx-attribute-sequence preceded by the appropriate xxx-attributes-tag (See the table below and Appendix B: Mapping of Each Operation in the Encoding). In addition, the order of these xxx-attributes-tags and xxx-attribute-sequences in the protocol SHALL be the same as in the model document, but the order of attributes within each xxx-attribute-sequence SHALL be unspecified. The table below maps the model document group name to xxx-attributes-sequence Model Document Group xxx-attributes-sequence Operation Attributes operations-attributes-sequence Job Template Attributes job-attributes-sequence Job Object Attributes job-attributes-sequence Unsupported Attributes unsupported-job-attributes-sequence Requested Attributes (Get- job-attributes-sequence Attributes of job object) Herriot, Butler, November 7, 1997, [Page 11] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Requested Attributes (Get- printer-attributes-sequence Attributes of printer object) Document Content in a special position as described above ISSUE: coordinate this with the model document. If an operation contains attributes from more than one job object (e.g. Get-Jobs response), the attributes from each job object SHALL be in a separate job-attribute-sequence, such that the attributes from the ith job object are in the ith job-attribute-sequence. See Section 11 "Appendix B: Mapping of Each Operation in the Encoding" for table showing the application of the rules above. 3.9 Value Lengths Each attribute value SHALL be preceded by a SIGNED-SHORT which SHALL specify the number of octets in the value which follows this length, exclusive of the two bytes specifying the length. For any of the types represented by binary signed integers, the sender MUST encode the value in exactly four octets.. For any of the types represented by character-strings, the sender MUST encode the value with all the characters of the string and without any padding characters. If a value-tag contains an "out-of-band" value which is not compoundValue, such as "unsupported", the value-length SHALL be 0 and the value empty " the value has no meaning when the value-tag has an "out-of-band" value. If a printer or client receives an operation with a nonzero value-length in this case, it SHALL ignore the value field. 3.10 Mapping of Attribute Values The syntax types and most of the details of their representation are defined in the IPP model document. The table below augments the information in the model document, and defines the syntax types from the model document in terms of the 5 basic types defined in section 3 Encoding of the Operation Layer. The 5 types are US-ASCII-STRING, LOCALIZED-STRING, SIGNED-INTEGER, SIGNED-SHORT, SIGNED-BYTE, and OCTET- STRING. Syntax of Encoding Attribute Value text, name LOCALIZED-STRING. The override natural language mechanism is encoded by syntactically preceding the text or name value by two values: first a value of type compoundValue whose value is 2 and second a value of type naturalLanguage whose value is the language override. From a protocol syntax view, Herriot, Butler, November 7, 1997, [Page 12] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Syntax of Encoding Attribute Value there are three separate values: the compoundValue, the naturalLanguage value and the text or name value, but from a semantic view, the Printer treats them as a single value where the naturalLanguage value overrides the language of the immediately following text or name value in the attribute. The override applies to just the text or name within the compound value. Other text or name values needing an override must be overridden with additional compoundValues. 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 compoundValue a SIGNED-INTEGER with a special meaning. If the value of a compoundValue is n, then the n following values of the attribute form a single value whose type is that of the last member of the compound value. For example, if an attribute has 3 successive values: compoundValue of 2, naturalLanguage of `fr-CA' and name of `chien', then these three "values" form a single value which is a name of `chien' in Canadian French.. dateTime OCTET-STRING consisting of eleven octets whose contents are defined by "DateAndTime" in RFC 1903 [rfc1903]. Although RFC 1903 also defines an eight octet format which omits the time zone, a value of this type in the IPP protocol MUST use the eleven octet format. [ transfer to model]. 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 unts value. rangeOfInteger Eight octets consisting of 2 SIGNED-INTEGERs. The first SIGNED-INTEGERs contains the lower bound and the second SIGNED-INTEGERs 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 Herriot, Butler, November 7, 1997, [Page 13] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 The type of the value in the model document determines the encoding in the value and the value of the value-tag. 3.11 Data The data part SHALL include any data required by the operation 4. Encoding of Transport Layer HTTP/1.1 shall be the transport layer for this protocol. The operation layer has been designed with the assumption that the transport layer contains the following information: . the URI of the target job or printer operation . 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 support HTTP over port 80, though a printer may support HTTP over port 516 or some other port. In addition, a printer may have to support another port for secure connections. Note: Consistent with RFC 2068 (HTTP/1.1), HTTP URI's for IPP implicitly reference port 80. If a URI references some other port, the port number must be explicitly specified in the URI. Each HTTP operation shall 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 shall be "application/ipp". The message-body shall contain the operation layer and shall have the syntax described in section 3.2 "Syntax of Encoding". A client implementation SHALL adhere to the rules for a client described in RFC 2068 [rfc2068]. A printer (server) implementation SHALL adhere the rules for an origin server described in RFC 2068.In the following sections, there are a tables of all HTTP headers which describe their use in an IPP client or server. The following is an explanation of each column in these tables. . the "header" column contains the name of a header . the "request/client" column indicates whether a client sends the header. . the "request/ server" column indicates whether a server supports the header when received. . the "response/ server" column indicates whether a server sends the header. . the "response /client" column indicates whether a client supports the header when received. . the "values and conditions" column specifies the allowed header values and the conditions for the header to be present in a request/response. The table for "request headers" does not have columns for responses, and the table for "response headers" does not have columns for requests. Herriot, Butler, November 7, 1997, [Page 14] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 The following is an explanation of the values in the "request/client" and "response/ server" columns. . must: the client or server MUST send the header, . must-if: the client or server MUST send the header when the condition described in the "values and conditions" column is met, . may: the client or server MAY send the header . not: the client or server SHOULD NOT send the header. It is not relevant to an IPP implementation. The following is an explanation of the values in the "response/client" and "request/ server" columns. . must: the client or server MUST support the header, . may: the client or server MAY support the header . not: the client or server SHOULD NOT support the header. It is not relevant to an IPP implementation. 4.1 General Headers The following is a table for the general headers. ISSUE: an HTTP expert should review these tables for accuracy. General- Request Response Values and Conditions Header Client Server Server Client Cache- must not must not "no-cache" only Control Connection must-if must must- must "close" only. Both if client and server SHOULD keep a connection for the duration of a sequence of operations. The client and server MUST include this header for the last operation in such a sequence. Date may may must may per RFC 1123 [rfc1123] Pragma` must not must not "no-cache" only Transfer- must-if must must- must "chunked" only . Encoding if Header MUST be present if Content-Length is absent. Upgrade not not not not Via not not not not Herriot, Butler, November 7, 1997, [Page 15] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 4.2 Request Headers The following is a table for the request headers. Request-Header Client Server Request Values and Conditions Accept may must "application/ipp" only. This value is the default if the client omits it Accept-Charset not not Charset information is within the application/ipp entity Accept-Encoding may must empty and per RFC 2068 [rfc2068] and IANA registry for content- codings Accept-Language not not . language information is within the application/ipp entity Authorization must-if must per RFC 2068. A client MUST send this header when it receives a 401 "Unauthorized" response and does not receive a "Proxy- Authenticate" header. From not not per RFC 2068. Because RFC recommends sending this header only with the user's approval, it is not very useful Host must must per RFC 2068 If-Match not not If-Modified- not not Since If-None-Match not not If-Range not not If-Unmodified- not not Since Max-Forwards not not Proxy- must-if not per RFC 2068. A client MUST send Authorization this header when it receives a 401 "Unauthorized" response and a "Proxy-Authenticate" header. Range not not Referer not not User-Agent not not 4.3 Response Headers The following is a table for the request headers. Response- Server Client Response Values and Conditions Header Accept-Ranges not not Age not not Location must-if may per RFC 2068. When URI needs Herriot, Butler, November 7, 1997, [Page 16] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Response- Server Client Response Values and Conditions Header redirection. Proxy- not must per RFC 2068 Authenticate Public may may per RFC 2068 Retry-After may may per RFC 2068 Server not not Vary not not Warning may may per RFC 2068 WWW- must-if must per RFC 2068. When a server needs to Authenticate authenticate a client. 4.4 Entity Headers The following is a table for the entity headers. Entity-Header Request Response Values and Conditions Client Server Server Client Allow not not not not Content-Base not not not not Content- may must must must per RFC 2068 and IANA Encoding registry for content codings. Content- not not not not Application/ipp Language handles language Content- must-if must must-if must the length of the Length message-body per RFC 2068. Header MUST be present if Transfer- Encoding is absent.. Content- not not not not Location Content-MD5 may may may may per RFC 2068 Content-Range not not not not Content-Type must must must must "application/ipp" only ETag not not not not Expires not not not not Last-Modified not not not not 5. Security Considerations When utilizing HTTP 1.1 as a transport of IPP, the security considerations outlined in RFC 2068 [rfc2068] apply. Specifically, IPP servers can generate a 401 "Unauthorized" response code to request client authentication and IPP clients should correctly respond with the proper "Authorization" header. Both Basic Authentication (RFC 2068) and Herriot, Butler, November 7, 1997, [Page 17] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Digest Authentication (RFC 2069) [rfc2069] flavors of authentication SHALL be supported. The server chooses which type(s) of authentication to accept. Digest Authentication is a more secure method, and is always preferred to Basic Authentication. For secure communication (privacy in particular), IPP SHOULD be run using a secure communications channel. For this purpose it is the intention to define standardization of IPP in combination with Transport Layer Security (TLS), currently under development in the IETF, when the TLS specifications are agreed and on the IETF standards track. As an intercept solution for secure communication, the Secure Socket Layer 3.0 (SSL3) could be used, but be warned that such implementations may not be able to interoperate with a future standardized IPP and TLS solution. Appendix C gives some hints to implementors wanting to use SSL3 as intercept solution. It is possible to combine the techniques, HTTP 1.1 client authentication (either basic or digest) with a secure communications channel. Together the two are more secure than client authentication and they perform user authentication. See further discussion of IPP security concepts in the model document [ipp-mod]. 6. Copyright This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Herriot, Butler, November 7, 1997, [Page 18] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 7. References [rfc822] Crocker, D., "Standard for the Format of ARPA Internet Text Messages", RFC 822, August 1982. [rfc1123] Braden, S., "Requirements for Internet Hosts - Application and Support", RFC 1123, October, 1989, [rfc1179] McLaughlin, L. III, (editor), "Line Printer Daemon Protocol" RFC 1179, August 1990. [rfc1630] T. Berners-Lee, "Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the Word-Wide Web", RFC 1630, June 1994. [rfc1759] Smith, R., Wright, F., Hastings, T., Zilles, S., and Gyllenskog, J., "Printer MIB", RFC 1759, March 1995. [rfc1738] Berners-Lee, T., Masinter, L., McCahill, M. , "Uniform Resource Locators (URL)", RFC 1738, December, 1994. [rfc1543] Postel, J., "Instructions to RFC Authors", RFC 1543, October 1993. [rfc1766] H. Alvestrand, " Tags for the Identification of Languages", RFC 1766, March 1995. [rfc1903} J. Case, et al. "Textual Conventions for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1903, January 1996. [rfc2046] N. Freed & N. Borenstein, Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types. November 1996. (Obsoletes RFC1521, RFC1522, RFC1590), RFC 2046. [rfc2048] N. Freed, J. Klensin & J. Postel. Multipurpose Internet Mail Extension (MIME) Part Four: Registration Procedures. November 1996. (Format: TXT=45033 bytes) (Obsoletes RFC1521, RFC1522, RFC1590) (Also BCP0013), RFC 2048. [rfc2068] R Fielding, et al, "Hypertext Transfer Protocol " HTTP/1.1" RFC 2068, January 1997 [rfc2069] J. Franks, et al, "An Extension to HTTP: Digest Access Authentication" RFC 2069, January 1997 [rfc2119] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119 , March 1997 [rfc2184] N. Freed, K. Moore, "MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations", RFC 2184, August 1997, Herriot, Butler, November 7, 1997, [Page 19] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 [abnf] D. Crocker et al., "Augmented BNF for Syntax Specifications: ABNF", draft-ietf-drums-abnf-04.txt. [char] N. Freed, J. Postel: IANA Charset Registration Procedures, Work in Progress (draft-freed-charset-reg-02.txt). [dpa] ISO/IEC 10175 Document Printing Application (DPA), June 1996. [iana] IANA Registry of Coded Character Sets: ftp://ftp.isi.edu/in- notes/iana/assignments/character-sets [ipp-req] Wright, F. D., "Requirements for an Internet Printing Protocol:" [ipp-mod] Isaacson, S, deBry, R, Hastings, T, Herriot, R, Powell, P, "Internet Printing Protocol/1.0: Model and Semantics" [ssl] Netscape, The SSL Protocol, Version 3, (Text version 3.02) November 1996. 8. Author's Address Robert Herriot (editor) Paul Moore Sun Microsystems Inc. Microsoft 901 San Antonio Road, MPK-17 One Microsoft Way Palo Alto, CA 94303 Redmond, WA 98053 Phone: 650-786-8995 Phone: 425-936-0908 Fax: 650-786-7077 Fax: 425-93MS-FAX Email: robert.herriot@eng.sun.com Email: paulmo@microsoft.com Sylvan Butler Randy Turner Hewlett-Packard Sharp Laboratories 11311 Chinden Blvd. 5750 NW Pacific Rim Blvd Boise, ID 83714 Camas, WA 98607 Phone: 208-396-6000 Phone: 360-817-8456 Fax: 208-396-3457 Fax: : 360-817-8436 Email: sbutler@boi.hp.com Email: rturner@sharplabs.com IPP Mailing List: ipp@pwg.org IPP Mailing List Subscription: ipp-request@pwg.org IPP Web Page: http://www.pwg.org/ipp/ 9. Other Participants: Chuck Adams - Tektronix Harry Lewis - IBM Ron Bergman - Data Products Tony Liao - Vivid Image Keith Carter - IBM David Manchala - Xerox Angelo Caruso - Xerox Carl-Uno Manros - Xerox Herriot, Butler, November 7, 1997, [Page 20] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Jeff Copeland - QMS Jay Martin - Underscore Roger Debry - IBM Larry Masinter - Xerox Lee Farrell - Canon Ira McDonald, Xerox Sue Gleeson - Digital Bob Pentecost - Hewlett-Packard Charles Gordon - Osicom Patrick Powell - SDSU Brian Grimshaw - Apple Jeff Rackowitz - Intermec Jerry Hadsell - IBM Xavier Riley - Xerox Richard Hart - Digital Gary Roberts - Ricoh Tom Hastings - Xerox Stuart Rowley - Kyocera Stephen Holmstead Richard Schneider - Epson Zhi-Hong Huang - Zenographics Shigern Ueda - Canon Scott Isaacson - Novell Bob Von Andel - Allegro Software Rich Lomicka - Digital William Wagner - Digital Products David Kellerman - Northlake Jasper Wong - Xionics Software Robert Kline - TrueSpectra Don Wright - Lexmark Dave Kuntz - Hewlett-Packard Rick Yardumian - Xerox Takami Kurono - Brother Lloyd Young - Lexmark Rich Landau - Digital Peter Zehler - Xerox Greg LeClair - Epson Frank Zhao - Panasonic Steve Zilles - Adobe 10. Appendix A: Protocol Examples 10.1 Print-Job Request The following is an example of a Print-Job request with job-name, copies, and sides specified. Octets Symbolic Value Protocol field 0x0100 1.0 version 0x0002 PrintJob operation 0x01 start operation- operation-attributestag attributes 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- attributes-natural- name language language 0x0005 value-length en-US en-US value 0x42 name type value-tag 0x0008 name-length job-name job-name name 0x0006 value-length foobar foobar value Herriot, Butler, November 7, 1997, [Page 21] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Octets Symbolic Value Protocol field 0x02 start job- job-attributes-tag attributes 0x21 integer type value-tag 0x0005 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 start-data data-tag %!PS... data 10.2 Print-Job Response (successful) Here is an example of a Print-Job response which is successful: Octets Symbolic Value Protocol field 0x0100 1.0 version 0x0000 OK (successful) status-code 0x01 start operation- operation-attributes-tag attributes 0x47 charset type value-tag 0x0012 name-length attributes- attributes- name charset charset 0x0008 value-length US-ASCII US-ASCII value 0x48 natural-language value-tag type 0x001B name-length attributes- attributes- name natural- natural-language language 0x0005 value-length en-US en-US value 0x41 text type value-tag 0x000E name-length status-message status-message name 0x0002 value-length OK OK value 0x02 start job- job-attributes-tag attributes 0x21 integer value-tag 0x0007 name-length job-id job-id name 0x0004 value-length Herriot, Butler, November 7, 1997, [Page 22] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Octets Symbolic Value Protocol field 147 147 value 0x45 uri type value-tag 0x0008 name-length job-uri job-uri name 0x000E value-length http://foo/123 http://foo/123 value 0x25 name type value-tag 0x0008 name-length job-state job-state name 0x0001 value-length 0x03 pending value 0x03 start-data data-tag 10.3 Print-Job Response (failure) Here is an example of a Print-Job response which fails because the printer does not support sides and because the value 20 for copies is not supported: Octets Symbolic Value Protocol field 0x0100 1.0 version 0x0400 client-error-bad-request status-code 0x01 start operation- operation-attribute tag attributes 0x47 charset type value-tag 0x0012 name-length attributes- attributes-charset name charset 0x0008 value-length US-ASCII US-ASCII value 0x48 natural-language type value-tag 0x001B name-length attributes- attributes-natural- name natural- language language 0x0005 value-length en-US en-US value 0x41 text type value-tag 0x000E name-length status-message status-message name 0x000D value-length bad-request bad-request value 0x04 start unsupported-job- unsupported-job- attributes attributes-tag 0x21 integer type value-tag 0x0005 name-length copies copies name 0x0004 value-length 0x00000014 20 value Herriot, Butler, November 7, 1997, [Page 23] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Octets Symbolic Value Protocol field 0x10 unsupported (type) value-tag 0x0005 name-length sides sides name 0x0000 value-length 0x03 start-data data-tag 10.4 Print-URI Request The following is an example of Print-URI request with copies and job- name parameters. Octets Symbolic Value Protocol field 0x0100 1.0 version 0x0003 Print-URI operation 0x01 start operation- operation-attributes-tag attributes 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- attributes- name language natural-language 0x0005 value-length en-US en-US value 0x45 uri type value-tag 0x000A name-length document-uri document-uri name 0x11 value-length ftp://foo.com/foo ftp://foo.com/foo value 0x42 name type value-tag 0x0008 name-length job-name job-name name 0x0006 value-length foobar foobar value 0x02 start job- job-attributes-tag attributes 0x21 integer type value-tag 0x0005 name-length copies copies name 0x0004 value-length 0x00000001 1 value 0x03 start-data data-tag %!PS... data Herriot, Butler, November 7, 1997, [Page 24] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 10.5 Create-Job Request The following is an example of Create-Job request with no parameters and no attributes Octets Symbolic Value Protocol field 0x0100 1.0 version 0x0005 Create-Job operation 0x01 start operation-attributes-tag operation- attributes 0x47 charset type value-tag 0x0012 name-length attributes- attributes- name charset charset 0x0008 value-length US-ASCII US-ASCII value 0x48 natural- value-tag language type 0x001B name-length attributes- attributes- name natural- natural- language language 0x0005 value-length en-US en-US value 0x03 start-data data-tag 10.6 Get-Jobs Request The following is an example of Get-Jobs request with parameters but no attributes. Octets Symbolic Value Protocol field 0x0100 1.0 version 0x000A Get-Jobs operation 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- attributes-natural- name language language 0x0005 value-length en-US en-US value 0x21 integer type value-tag 0x0005 name-length limit limit name 0x0004 value-length 0x00000032 50 value Herriot, Butler, November 7, 1997, [Page 25] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Octets Symbolic Value Protocol field 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 0x03 start-data data-tag 10.7 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. Octets Symbolic Value Protocol field 0x0100 1.0 version 0x0000 OK (successful) status-code 0x01 start operation- operation-attribute-tag attributes 0x47 charset type value-tag 0x0012 name-length attributes- attributes-charset name charset 0x0008 value-length ISO-8859-1 ISO-8859-1 value 0x48 natural-language value-tag type 0x001B name-length attributes- attributes-natural- name natural-language language 0x0005 value-length en-US en-US value 0x41 text type value-tag 0x000E name-length status-message status-message name 0x0002 value-length OK OK value 0x02 start job-attributes job-attributes-tag (1st object) 0x48 natural-language value-tag type 0x001B name-length attributes- attributes-natural- name natural-language language 0x0005 value-length fr-CA fr-CA value 0x21 integer type value-tag 0x0006 name-length job-id job-id name 0x0004 value-length 147 147 value Herriot, Butler, November 7, 1997, [Page 26] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Octets Symbolic Value Protocol field 0x42 name type value-tag 0x0008 name-length job-name job-name name 0x0003 name-length fou fou name 0x02 start job-attributes job-attributes-tag (2nd object) 0x02 start job-attributes job-attributes-tag (3rd object) 0x21 integer type value-tag 0x0006 name-length job-id job-id name 0x0004 value-length 148 148 value 0x13 compoundValue value-tag 0x0008 name-length job-name job-name name 0x0004 value-length 0x0002 2 value (number of values) 0x48 naturalLanguage value-tag 0x0000 multi-value marker name-length 0x0005 value-length de-CH de-CH value 0x42 name type value-tag 0x0000 multi-value marker name-length 0x0003 name-length isch guet isch guet name 0x03 start-data data-tag 11. Appendix B: Mapping of Each Operation in the Encoding The next three tables show the results of applying the rules above to the operations defined in the IPP model document. There is no information in these tables that cannot be derived from the rules presented in Section 3.8 "Mapping of Attribute Names". The following table shows the mapping of all IPP model-document request attributes to an appropriate xxx-attribute-sequence or special position in the protocol. The table below shows the attributes for operations sent to a Printer URI. Operation operation job attributes special position attributes Print-Job attributes- job-template document-content charset attributes attributes- natural- language job-name Herriot, Butler, November 7, 1997, [Page 27] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Operation operation job attributes special position attributes document-name ipp-attribute- fidelity document- natural- language Create-Job or attributes- job-template Validate-Job charset attributes attributes- natural- language job- name ipp-attribute- fidelity Print-URI attributes- job-template charset attributes attributes- natural- language job- name ipp-attribute- fidelity document-uri document- natural- language Send-Document attributes- document-content charset attributes- natural- language job-id last-document document-name document- natural- language Send-URI attributes- charset attributes- natural- language job-id last-document document-name document-uri document- natural- Herriot, Butler, November 7, 1997, [Page 28] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Operation operation job attributes special position attributes language Cancel-Job attributes- charset attributes- natural- language job-id message Get-Attributes attributes- (for a Printer) charset attributes- natural- language requested- attributes document-format Get-Attributes attributes- (for a Job) charset attributes- natural- language job-id requested- attributes Get-Jobs attributes- charset attributes- natural- language limit requested- attributes which-jobs The table below shows the attributes for operations sent to a Job URI. Operation operation job attributes special position attributes Send-Document attributes- document-content charset attributes- natural- language last- document document-name document- natural- language Send-URI attributes- charset Herriot, Butler, November 7, 1997, [Page 29] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Operation operation job attributes special position attributes attributes- natural- language last- document document-name document-uri document- natural- language Cancel-Job attributes- charset attributes- natural- language message Get-Attributes attributes- (for a Job) charset attributes- natural- language requested- attributes The following two tables shows the mapping of all IPP model-document response attributes to an appropriate xxx-attribute-sequence or special position in the protocol. Operation operation job- unsupported-job- special attributes attributes attributes position Print-Job, attributes- job-id unsupported status- Print-URI, charset job-uri attributes code Create-Job, attributes- job-state Send-Document natural- job-state- or Send-URI language reasons status- job-state- message message number-of- intervening -jobs Validate-Job attributes- unsupported status- charset attributes code attributes- natural- language status- Herriot, Butler, November 7, 1997, [Page 30] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 Operation operation job- unsupported-job- special attributes attributes attributes position message Note: the unsupported-job-attributes are present only if the client included some job attributes that the Printer doesn't support. Note: the job-attributes are present only if the server returns the status code of successful-ok or successful-ok-ignored-or-substituted- attributes. Operation operation job- printer- special attributes attributes attributes position Cancel-Job attributes- charset attributes- natural- language status- status-code message Get-Attributes attributes- requested status-code (of a job) charset attributes attributes- natural- language status- message Get-Attributes attributes- requested status-code (of a printer) charset attributes attributes- natural- language status- message Get-Jobs attributes- requested status-code charset attributes attributes- (see the natural- Note below) language status- message Note for Get-Jobs: there is a separate job-attribute-sequence containing requested-attributes for each job object in the response Herriot, Butler, November 7, 1997, [Page 31] Moore and Turner Expires May 7, 1998 INTERNET-DRAFT IPP/1.0: Protocol Specification November 7, 1997 12. Appendix C: Hints to implementors using IPP with SSL3 WARNING: Clients and IPP objects using intermediate secure connection protocol solutions such as IPP in combination with Secure Socket Layer Version 3 (SSL3), which are developed in advance of IPP and TLS standardization, might not be interoperable with IPP and TLS standards- conforming clients and IPP objects. An assumption is that the URI for a secure IPP Printer object has been found by means outside the IPP printing protocol, via a directory service, web site or other means. IPP provides a transparent connection to SSL by calling the corresponding URL (a https URI connects by default to port 443). However, the following functions can be provided to ease the integration of IPP with SSL during implementation. connect (URI), returns a status. "connect" makes an https call and returns the immediate status of the connection as returned by SSL to the user. The status values are explained in section 5.4.2 of the SSL document [ssl]. A session-id may also be retained to later resume a session. The SSL handshake protocol may also require the cipher specifications supported by the client, key length of the ciphers, compression methods, certificates, etc. These should be sent to the server and hence should be available to the IPP client (although as part of administration features). disconnect (session) to disconnect a particular session. The session-id available from the "connect" could be used. resume (session) to reconnect using a previous session-id. The availability of this information as administration features are left for implementors, and need not be standardized at this time Herriot, Butler, November 7, 1997, [Page 32] Moore and Turner Expires May 7, 1998