IPP Mail Archive: RE: IPP> FW: Summary of PWG Document Objec

RE: IPP> FW: Summary of PWG Document Object issues

From: Hastings, Tom N (hastings@cp10.es.xerox.com)
Date: Thu Apr 24 2003 - 20:59:35 EDT

  • Next message: McDonald, Ira: "RE: IPP> FW: Summary of PWG Document Object issues"

    While it would be good to do an IPP/1.2 document, it really would be mainly
    a profile of IPP as Ira suggests. So we need to get the IPP Document object
    spec approved (and any other ones if we move some of the current stuff into
    a separate document) with its OPTIONAL features as currently specified so
    that we can do a last call. Then the IPP/1.2 Profile can be progressed
    after it.

    Tom

    -----Original Message-----
    From: McDonald, Ira [mailto:imcdonald@sharplabs.com]
    Sent: Thursday, April 24, 2003 15:07
    To: 'ipp@pwg.org'
    Subject: IPP> FW: Summary of PWG Document Object issues

    Hi folks,

    I sent the summary below to the Free Standards Group
    Open Printing Architecture mailing list earlier today.
    Most of the issues/topics below were discussed during
    this afternoon's continued review of the IPP Document
    Object spec in the PWG Semantic Model telecon.

    Most of these issues remain unsolved.

    Comments?

    Cheers,
    - Ira McDonald
      High North Inc

    -----Original Message-----
    From: McDonald, Ira [mailto:imcdonald@sharplabs.com]
    Sent: Thursday, April 24, 2003 1:12 PM
    To: printing-architecture@freestandards.org
    Subject: [Printing-architecture] Summary of PWG Document Object issues

    Hi,

    At today's FSG OP Architecture telecon, Claudia asked that I
    send out a summary of recent issues for IPP Document object.
    I used letters for the points below to avoid ambiguity with
    the many email notes on the PWG PSI, SM, and IPP reflectors.

    A) Print-by-reference authentication

       (IPP "Send-URI" <==> PSI "AddDocumentByReference")

       PWG PSI's design center is print-by-reference (a hand-held
       telling a PSI Print Service to print some document available
       on a Web or FTP server). But the necessary authentication
       credentials to _access_ the referenced file's URL must also
       be available (or no security exists). PSI actually sends
       these credentials (inside a TLS-secured session). But, as
       Michael Sweet (CUPS) has pointed out:
       a1) Simple end-user impersonation (username/password) is
           fragile and the print server may accidentally expose
           the user's security info - a liability for the vendor.
       a2) Stronger certificate-based public key authentication
           (usually used in TLS-secured sessions) may fail because
           some certificates are only valid if used _from_ the end
           user's home system (as identified by an FQDN stored in
           the certificate and validated by DNS lookup for source
           IP address for the transaction).
       a3) Without Kerberos-style single-use "tickets" the delegation
           of end user credentials to an intermediate server is an
           unsolved software problem (existing solutions only work in
           certain not-widely-deployed middleware).

    B) REQUIRED versus OPTIONAL operations and attributes

       PWG PSI/1.0 (now in working group 'last call') has only
       REQUIRED operations (including print-by-reference), but
       the IPP Document Object spec defines many operations and
       almost all Document Description attributes as OPTIONAL.
       This impacts any adoption of PSI by FSG PAPI, because
       interworking with IPP-based intermediate systems and
       printers will be degraded or will fail in some cases.

    C) Flat-file registries needed for key Document attributes
       
       IPP Document object (based on input from PWG PSI and from
       CIP4 JDF people) adds to the base "document-format" (MIME
       type values) the parallel qualifier "document-format-versions"
       (with values like "PDF/1.4" and "PDF/is-1.0"). The operation
       of the PWG IPPFAX protocol (soon to enter 'last call') and
       of IPP-based Document operations _depends_ on the presence
       of "document-format-versions".

       However, it remains to be settled whether the PWG will rent
       space on a commercial server (to avoid burdening our current
       host Lexmark with a file that might be downloaded by many
       clients) or the CIP4 will archive the file on their Web site.

       Several other attributes that can be present in the new
       "document-format-details" compound attribute also require
       registration of standard values, such as
       "document-source-application-version" ("MS Word 2000").

    D) Breaking IPP Document object into two (or more) specs

       Dennis Carney (IBM) recently suggested a compromise solution
       of making _two_ specs: one with only REQUIRED operations
       and attributes; and one with only OPTIONAL ones. It turns
       out (per Tom Hastings) that the first spec would be _very_
       skinny. Also, a whole bunch of important (but OPTIONAL)
       Document attributes would be delayed in the second spec
       (expected to move more slowly through the adoption process).
       There really should be a third spec (again, per Tom H) that
       contains the Job-level operation extensions and attributes.

    E) IPP/1.2

       Recently, Dennis Carney (IBM) observed that IPP Document
       object was starting to look a lot like "IPP/1.2".
       Michael Sweet suggested yesterday that perhaps we should
       be _writing_ an IPP/1.2 spec, and gathering up the numerous
       IPP extensions (several dozen) into one place (by reference,
       I hope) with a new set of conformance requirements.
       (I would collaborate on such a project, but I wouldn't
       take it on alone.)

    Predications:

    I predict that some part of IPP Document object will go to
    working group 'last call' pretty soon because it's holding up
    the release of both the PWG Semantic Model 1.0 (and schemas)
    and PWG PSI/1.0 (and WSDL headers), both of which want full
    Document object semantics in their content.

    I also predict that some/most of the IPP Job-level extensions
    and some/most of the "document-format-details" attributes will
    be delayed much longer (months at least) by the process and also
    by the bandwidth of the editors (basically Tom Hastings, with
    some help from Dennis Carney and a few others).

    Cheers,
    - Ira McDonald
      High North Inc

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