Network Working Group                                         R. Herriot
Request for Comments: 3510                                   I. McDonald
Updates: 2910                                            High North Inc.
Category: Standards Track                                     April 2003


                   Internet Printing Protocol/1.1:
                            IPP URL Scheme

Status of this Memo

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

Copyright Notice

  Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

  This memo defines the "ipp" URL (Uniform Resource Locator) scheme.
  This memo updates IPP/1.1: Encoding and Transport (RFC 2910), by
  expanding and clarifying Section 5, "IPP URL Scheme", of RFC 2910.
  An "ipp" URL is used to specify the network location of a print
  service that supports the IPP Protocol (RFC 2910), or of a network
  resource (for example, a print job) managed by such a print service.

Table of Contents

  1.  Introduction ...............................................  2
  2.  Terminology ................................................  3
      2.1.  Conformance Terminology ..............................  3
      2.2.  Model Terminology ....................................  3
  3.  IPP Model for Printers and Jobs ............................  3
  4.  IPP URL Scheme .............................................  4
      4.1.  IPP URL Scheme Applicability .........................  4
      4.2.  IPP URL Scheme Associated Port .......................  4
      4.3.  IPP URL Scheme Associated MIME Type ..................  5
      4.4.  IPP URL Scheme Character Encoding ....................  5
      4.5.  IPP URL Scheme Syntax ................................  5
      4.6.  IPP URL Examples .....................................  6
            4.6.1.  IPP Printer URL Examples .....................  6
            4.6.2.  IPP Job URL Examples .........................  6
      4.7.  IPP URL Comparisons ..................................  7




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  5.  Conformance Requirements ...................................  8
      5.1.  IPP Client Conformance Requirements ..................  8
      5.2.  IPP Printer Conformance Requirements .................  8
  6.  IANA Considerations ........................................  9
  7.  Internationalization Considerations ........................  9
  8.  Security Considerations ....................................  9
  9.  Intellectual Property Rights ............................... 10
  10. Normative References ....................................... 11
  11. Informative References ..................................... 11
  12. Acknowledgments ............................................ 12
  Appendix A - Registration of "ipp" URL Scheme .................. 13
  Authors' Addresses ............................................. 15
  Full Copyright Statement ....................................... 16

1.  Introduction

  This memo conforms to all of the requirements in Registration
  Procedures for URL Scheme Names [RFC2717].  This memo also follows
  all of the recommendations in Guidelines for new URL Schemes
  [RFC2718].

  See section 1, "Introduction", of [RFC2911] and section 1,
  "Introduction", of [RFC3196] for overview information about IPP.  See
  section 10, "Description of the Base IPP Documents", of [RFC3196] for
  a full description of the IPP document set.

  This memo updates IPP/1.1: Encoding and Transport (RFC 2910), by
  expanding and clarifying Section 5, "IPP URL Scheme", of RFC 2910,
  but does not define any new parameters or other new extensions to the
  syntax of IPP URLs.

  The IPP URL scheme defined in this document is based on the ABNF for
  the HTTP URL scheme defined in HTTP [RFC2616], which in turn is
  derived from the URI Generic Syntax [RFC2396] and further updated for
  IPv6 by [RFC2732].  An IPP URL is transformed into an HTTP URL
  according to the rules specified in section 5 of IPP Protocol
  [RFC2910].

  This document defines IPP URL scheme applicability, associated port
  (631), associated MIME type ("application/ipp"), character encoding,
  and syntax.

  This document is laid out as follows:

  -  Section 2 defines the terminology used throughout the document.

  -  Section 3 supplies references to the IPP Printer and IPP Job
     object model defined in IPP Model [RFC2911].



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  -  Section 4 specifies the IPP URL scheme.

  -  Section 5 specifies the conformance requirements for IPP Clients
     and IPP Printers that claim conformance to this document.

  -  Sections 6, 7, and 8 specify IANA, internationalization, and
     security considerations.

  -  Sections 9, 10, 11, 12, and 13 specify normative references,
     informative references, acknowledgements, authors' addresses, and
     full IETF copyright statement.

  -  Section 14 (Appendix A) is a completed registration template for
     the IPP URL Scheme (see section 6.0 of [RFC2717]).

2.  Terminology

     This specification document uses the terminology defined in this
     section.

2.1.  Conformance Terminology

     The uppercase terms "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].  These terms are used to specify conformance
     requirements for all implementations (both print clients and print
     services) of this specification.

2.2.  Model Terminology

     See section 12.2, "Model Terminology", in IPP Model [RFC2911].

3.  IPP Model for Printers and Jobs

     See section 2, "IPP Objects", section 2.1, "Printer Object", and
     section 2.2, "Job Object", in [RFC2911] for a full description of
     the IPP object model and terminology.

     In this document, "IPP Client" means the software (on some
     hardware platform) that submits, monitors, and/or manages print
     jobs via the IPP Protocol [RFC2910] to a print spooler, print
     gateway, or physical printing device.








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     In this document, "IPP Printer object" means the software (on some
     hardware platform) that receives print jobs and/or printer/job
     operations via the IPP Protocol [RFC2910] from an "IPP Client".

     In this document, "IPP Printer" is a synonym for "IPP Printer
     object".

     In this document, "IPP Job object" means the set of attributes and
     documents for one print job instantiated on an "IPP Printer".

     In this document, "IPP Job" is a synonym for "IPP Job object".

     In this document, "IPP URL" means a URL with the "ipp" scheme.

     Note:  In this document, "IPP URL" is a synonym for "ipp-URL" (in
     section 4, "IPP URL Scheme", of this document) and "ipp-URL" (in
     section 5, "IPP URL Scheme", of [RFC2910]).

4.  IPP URL Scheme

4.1.  IPP URL Scheme Applicability

     The "ipp" URL scheme MUST only be used to specify absolute URLs
     (relative IPP URLs are not allowed) for IPP print services and
     their associated network resources.  The "ipp" URL scheme MUST
     only be used to specify the use of the abstract protocol defined
     in IPP Model [RFC2911] over an HTTP [RFC2616] transport, as
     defined in IPP Protocol [RFC2910].  Any other transport binding
     for the abstract protocol defined in IPP Model [RFC2911] would
     require a different URL scheme.

     The "ipp" URL scheme allows an IPP client to choose an appropriate
     IPP print service (for example, from a directory).  The IPP client
     can establish an HTTP connection to the specified IPP print
     service.  The IPP client can send IPP protocol requests (for
     example, a "Print-Job" request) and receive IPP protocol responses
     over that HTTP connection.

4.2.  IPP URL Scheme Associated Port

     All IPP URLs which do NOT explicitly specify a port MUST be
     resolved to IANA-assigned well-known port 631, as registered in
     [IANA-PORTREG].

     See:  IANA Port Numbers Registry [IANA-PORTREG].
     See:  IPP Protocol [RFC2910].





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4.3.  IPP URL Scheme Associated MIME Type

     All IPP URLs MUST be used to specify network print services which
     support the "application/ipp" MIME media type as registered in
     [IANA-MIMEREG] for IPP protocol requests and responses.

     See:  IANA MIME Media Types Registry [IANA-MIMEREG].
     See:  IPP Protocol [RFC2910].

4.4.  IPP URL Scheme Character Encoding

     IPP URLs MUST use [RFC2396] encoding, as do their equivalent HTTP
     URLs.  Characters other than those in the "reserved" and "unsafe"
     sets [RFC2396] are equivalent to their ""%" HEX HEX" encoding.

4.5.  IPP URL Scheme Syntax

     The abstract protocol defined in IPP Model [RFC2911] places a
     limit of 1023 octets (NOT characters) on the length of a URI (see
     section 4.1.5, "uri", in [RFC2911]).

     Note:  IPP Printers ought to be cautious about depending on URI
     lengths above 255 bytes, because some older client implementations
     might not properly support these lengths.

  IPP URLs MUST be represented in absolute form.  Absolute URLs MUST
  always begin with a scheme name followed by a colon.  For definitive
  information on URL syntax and semantics, see "Uniform Resource
  Identifiers (URI): Generic Syntax and Semantics" [RFC2396].  This
  specification adopts the definitions of "host", "port", "abs_path",
  and "query" from [RFC2396], as updated for IPv6 by [RFC2732].

  The IPP URL scheme syntax in ABNF is as follows:

  ipp-URL = "ipp:" "//" host [ ":" port ] [ abs_path [ "?" query ]]

  If the port is empty or not given, port 631 is assumed.  The
  semantics are that the identified resource (see section 5.1.2 of
  [RFC2616]) is located at the IPP print service listening for HTTP
  connections on that port of that host, and the Request-URI for the
  identified resource is 'abs_path'.

  If the 'abs_path' is not present in the URL, it MUST be given as "/"
  when used as a Request-URI for a resource (see section 5.1.2 of
  [RFC2616]).






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4.6.  IPP URL Examples

  Note:  Literal IPv4 or IPv6 addresses SHOULD NOT be used in IPP URLs.

4.6.1.  IPP Printer URL Examples

  The following are examples of well-formed IPP URLs for IPP Printers
  (for example, to be used as protocol elements in 'printer-uri'
  operation attributes of 'Print-Job' request messages):

     ipp://example.com
     ipp://example.com/printer
     ipp://example.com/printer/tiger
     ipp://example.com/printer/fox
     ipp://example.com/printer/tiger/bob
     ipp://example.com/printer/tiger/ira

  Each of the above URLs are well-formed URLs for IPP Printers and each
  would reference a logically different IPP Printer, even though some
  of those IPP Printers might share the same host system.  The 'bob' or
  'ira' last path components might represent two different physical
  printer devices, while 'tiger' might represent some grouping of IPP
  Printers (for example, a load-balancing spooler).  Or the 'bob' and
  'ira' last path components might represent separate human recipients
  on the same physical printer device (for example, a physical printer
  supporting two job queues).  In either case, both 'bob' and 'ira'
  would behave as different and independent IPP Printers.

  The following are examples of well-formed IPP URLs for IPP Printers
  with (optional) ports and paths:

     ipp://example.com
     ipp://example.com/~smith/printer
     ipp://example.com:631/~smith/printer

  The first and second IPP URLs above MUST be resolved to port 631
  (IANA assigned well-known port for IPP).  The second and third IPP
  URLs above are equivalent (see section 4.7 below).

4.6.2.  IPP Job URL Examples

  The following are examples of well-formed IPP URLs for IPP Jobs (for
  example, to be used as protocol elements in 'job-uri' attributes of
  'Print-Job' response messages):

     ipp://example.com/printer/123
     ipp://example.com/printer/tiger/job123




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  IPP Job URLs are valid and meaningful only until Job completion and
  possibly an implementation defined optional period of persistence
  after Job completion (see IPP Model [RFC2911]).

  Ambiguously, section 4.3.1 'job-uri' of IPP Model [RFC2911] states
  that:

     "the precise format of a Job URI is implementation dependent."

  Thus, the relationship between the value of the "printer-uri"
  operation attribute used in a 'Print-Job' request and the value of
  the "job-uri" attribute returned in the corresponding 'Print-Job'
  response is implementation dependent.  Also, section 4.3.3 'job-
  printer-uri' of IPP Model [RFC2911] states that the 'job-printer-uri'
  attribute of a Job object:

     "permits a client to identify the Printer object that created this
     Job object when only the Job object's URI is available to the
     client."

  However, the above statement is false, because the transform from an
  IPP Job URL to the corresponding IPP Printer URL is unspecified in
  either IPP Model [RFC2911] or IPP Protocol [RFC2910].

  IPP Printers that conform to this specification SHOULD only generate
  IPP Job URLs (for example, in the "job-uri" attribute in a 'Print-
  Job' response) by appending exactly one path component to the
  corresponding IPP Printer URL (for interoperability).

4.7.  IPP URL Comparisons

  When comparing two IPP URLs to decide if they match or not, an IPP
  Client MUST use the same rules as those defined for HTTP URI
  comparisons in [RFC2616], with the sole following exception:

  -  A port that is empty or not given MUST be treated as equivalent to
     the well-known port for that IPP URL (port 631);

     See:  Section 3.2.3, "URI Comparison", in [RFC2616].












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5.  Conformance Requirements

5.1.  IPP Client Conformance Requirements

     IPP Clients that conform to this specification:

  a) MUST only send IPP protocol connections to the port specified in
     each given IPP URL (if present) or otherwise to IANA assigned
     well-known port 631;

  b) MUST only send IPP URLs used as protocol elements in outgoing IPP
     protocol request messages (for example, in the "printer-uri"
     operation attribute in a 'Print-Job' request) that conform to the
     ABNF specified in section 4.5, "IPP URL Scheme Syntax, of this
     document;

  c) MUST only convert IPP URLs to their corresponding HTTP URL forms
     according to the rules in section 5, "IPP URL Scheme", in
     [RFC2910].

5.2.  IPP Printer Conformance Requirements

  IPP Printers that conform to this specification:

  a) MUST listen for incoming IPP protocol connections on IANA-assigned
     well-known port 631, unless explicitly configured by system
     administrators or site policies;

  b) SHOULD NOT listen for incoming IPP protocol connections on any
     other port, unless explicitly configured by system administrators
     or site policies;

  c) SHOULD only accept IPP URLs used as protocol elements in incoming
     IPP protocol request messages (for example, in the "printer-uri"
     operation attribute in a 'Print-Job' request) that conform to the
     ABNF specified in section 4.5, "IPP URL Scheme Syntax", of this
     document;

  d) SHOULD only send IPP URLs used as protocol elements in outgoing
     IPP protocol response messages (for example, in the "job-uri"
     attribute in a 'Print-Job' response) that conform to the ABNF
     specified in section 4.5, "IPP URL Scheme Syntax", of this
     document;

  e) SHOULD only generate IPP Job URLs (for example, in the "job-uri"
     attribute in a 'Print-Job' response) by appending exactly one path
     component to the corresponding IPP Printer URL (for
     interoperability);



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  f) SHOULD NOT use literal IPv6 or IPv4 addresses in configured or
     locally generated IPP URLs.

6.  IANA Considerations

  This IPP URL Scheme specification does not introduce any additional
  IANA considerations, beyond those described in [RFC2910] and
  [RFC2911].

  See:  Section 6, "IANA Considerations" in [RFC2910]
  See:  Section 6, "IANA Considerations" in [RFC2911].

7.  Internationalization Considerations

  This IPP URL Scheme specification does not introduce any additional
  internationalization considerations, beyond those described in
  [RFC2910] and [RFC2911].

  See:  Section 7, "Internationalization Considerations", in [RFC2910].
  See:  Section 7, "Internationalization Considerations", in [RFC2911].

8.  Security Considerations

  This IPP URL Scheme specification does not introduce any additional
  security considerations, beyond those described in [RFC2910] and
  [RFC2911], except the following:

  a) An IPP URL might be faked to point to a rogue IPP print service,
     thus collecting confidential document contents from IPP clients.
     Server authentication mechanisms and security mechanisms specified
     in the IPP Protocol [RFC2910] are sufficient to address this
     threat.

  b) An IPP URL might be used to access an IPP print service by an
     unauthorized IPP client.  Client authentication mechanisms and
     security mechanisms specified in the IPP Protocol [RFC2910] are
     sufficient to address this threat.

  c) An IPP URL might be used to access an IPP print service at a print
     protocol application layer gateway (for example, an IPP to LPD
     gateway [RFC2569]) causing silent compromise of IPP security
     mechanisms.  There is no practical defense against this threat by
     a client system.  System administrators should avoid such
     compromising configurations.

  d) An IPP URL does not have parameters to specify the required client
     authentication mechanism (for example, 'certificate' as defined in
     section 4.4.2, "uri-authentication-supported", of IPP Model



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     [RFC2911]) and required security mechanism (for example, 'tls' as
     defined in section 4.4.3, "uri-security-supported", of IPP Model
     [RFC2911]).  Service discovery or directory protocols might be
     used to discover the required client authentication and security
     mechanisms associated with given IPP URLs.

  Historical Note:  During the development of this document,
  consideration was given to the addition of standard IPP URL
  parameters for the client authentication and security mechanisms.
  However, based on a strong IETF IPP Working Group consensus, no
  parameters were added to the "ipp" URL scheme as originally defined
  in IPP Protocol [RFC2910] in September 2000, for reasons of backwards
  compatibility with the many currently shipping implementations of
  IPP/1.1.

  See:  Section 8, "Security Considerations", in [RFC2910].
  See:  Section 8, "Security Considerations", in [RFC2911].

9.  Intellectual Property Rights

  The IETF takes no position regarding the validity or scope of any
  intellectual property or other rights that might be claimed to
  pertain to the implementation or use of the technology described in
  this document or the extent to which any license under such rights
  might or might not be available; neither does it represent that it
  has made any effort to identify any such rights.  Information on the
  IETF's procedures with respect to rights in standards-track and
  standards-related documentation can be found in BCP-11.  Copies of
  claims of rights made available for publication and any assurances of
  licenses to be made available, or the result of an attempt made to
  obtain a general license or permission for the use of such
  proprietary rights by implementors or users of this specification can
  be obtained from the IETF Secretariat.

  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.












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10.  Normative References

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

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

  [RFC2616]      Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
                 Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
                 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

  [RFC2732]      Hinden, R., Carpenter, B. and L. Masinter, "Format for
                 Literal IPv6 Addresses in URL's", RFC 2732, December
                 1999.

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

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

  [US-ASCII]     Coded Character Set -- 7-bit American Standard Code
                 for Information Interchange, ANSI X3.4-1986.

11.  Informative References

  [IANA-MIMEREG] IANA MIME Media Types Registry.
                 ftp://ftp.iana.org/in-notes/iana/assignments/media-
                 types/...

  [IANA-PORTREG] IANA Port Numbers Registry. ftp://ftp.iana.org/in-
                 notes/iana/assignments/port-numbers

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

  [RFC2717]      Petke, R. and I. King, "Registration Procedures for
                 URL Scheme Names", RFC 2717, November 1999.

  [RFC2718]      Masinter, L., Alvestrand, H., Zigmond, D. and R.
                 Petke, "Guidelines for new URL Schemes", RFC 2718,
                 November 1999.




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  [RFC3196]      Hastings, T., Manros, C., Zehler, P., Kugler, C. and
                 H. Holst, "Internet Printing Protocol/1.1:
                 Implementor's Guide", RFC 3196, November 2001.

12.  Acknowledgments

  This document is a product of the Internet Printing Protocol Working
  Group of the Internet Engineering Task Force (IETF).

  Thanks to Pat Fleming (IBM), Tom Hastings (Xerox), Harry Lewis (IBM),
  Hugo Parra (Novell), Don Wright (Lexmark), and all the members of the
  IETF IPP WG.

  Section 5, "IPP URL Scheme", in IPP Protocol [RFC2910] was the
  primary input to this IPP URL Scheme specification.




































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Appendix A - Registration of "ipp" URL Scheme

  Note:  The following registration obsoletes section 5, "IPP URL
  Scheme", of IPP Protocol [RFC2911].

  URL Scheme Name:  ipp

  URL Scheme Syntax:

     ipp-URL = "ipp:" "//" host [ ":" port ] [ abs_path [ "?" query ]]

  Character Encoding Considerations:

     IPP URLs MUST use [RFC2396] encoding, as do their equivalent HTTP
     URLs.  Characters other than those in the "reserved" and "unsafe"
     sets [RFC2396] are equivalent to their ""%" HEX HEX" encoding.

  Intended Usage:

     The intended usage of the "ipp" URL scheme is COMMON.

     An "ipp" URL is used to specify the network location of a print
     service that supports the IPP Protocol [RFC2910], or of a network
     resource (for example, a print job) managed by such a print
     service.  An IPP client can choose to establish an HTTP connection
     to the specified print service for transmission of IPP protocol
     requests (for example, IPP print job submission requests).

  Applications or Protocols which use this URL scheme:

     See:  Section 5, "IPP URL Scheme", in IPP Protocol [RFC2910].

  Interoperability Considerations:

     See:  Section 9, "Interoperability with IPP/1.0 Implementations",
     in IPP Protocol [RFC2910].

  Security Considerations:

     See:  Section 8, "Security Considerations", in IPP Protocol
     [RFC2910].

  Relevant Publications:

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




Herriot & McDonald          Standards Track                    [Page 13]

RFC 3510                     IPP URL Scheme                   April 2003


  [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter,
            L., Leach, P. and T. Berners-Lee, "Hypertext Transfer
            Protocol -- HTTP/1.1", RFC 2616, June 1999.

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

  Person & email address to contact for further information:

  Robert Herriot
  Consultant
  706 Colorado Ave
  Palo Alto, CA  94303

  Phone: +1 650-327-4466
  EMail: [email protected]

  Ira McDonald
  High North Inc
  221 Ridge Ave
  Grand Marais, MI  49839

  Phone: +1 906-494-2434
  EMail: [email protected]



























Herriot & McDonald          Standards Track                    [Page 14]

RFC 3510                     IPP URL Scheme                   April 2003


Authors' Addresses

  Robert Herriot
  Consultant
  706 Colorado Ave
  Palo Alto, CA  94303

  Phone: +1 650-327-4466
  EMail: [email protected]


  Ira McDonald
  High North Inc
  221 Ridge Ave
  Grand Marais, MI  49839

  Phone: +1 906-494-2434
  EMail: [email protected]

  Usage questions and comments on this IPP URL Scheme should be sent
  directly to the editors at their above addresses (and to the IPP
  mailing list, if you are a subscriber - see below).

  IPP Web Page:      http://www.pwg.org/ipp/
  IPP Mailing List:  [email protected]

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

  1) send it to [email protected]

  2) leave the subject line blank

  3) put the following two lines in the message body:  subscribe ipp

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











Herriot & McDonald          Standards Track                    [Page 15]

RFC 3510                     IPP URL Scheme                   April 2003


Full Copyright Statement

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Acknowledgement

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