[IPP] WG Last Call of IPP Scan Service specification

[IPP] WG Last Call of IPP Scan Service specification

[IPP] WG Last Call of IPP Scan Service specification

Soma Meiyappan Soma.Meiyappan at conexant.com
Wed May 21 13:37:50 UTC 2014

Hi Mike,

Making printer-xxx-date-time & printer-current-time REQUIRED for consistency across the 3 primary specifications will be fine as long as devices that do not have a notion of calendar time can provide "no-value" as RFC 2911 allows for "printer-current-time" (and attributes whose value is derived from that). But, that is effectively making it STRONGLY RECOMMENDED, in principle, isn't it?

Personally, I feel that making something REQUIRED typically sets an expectation on the validity/accuracy of the data that the attribute provides although there is no explicit claim/requirement on the validity/accuracy made in the underlying specification.

Thanks and Regards,

From: Michael Sweet [mailto:msweet at apple.com]
Sent: Wednesday, May 21, 2014 8:54 PM
To: Soma Meiyappan
Cc: Ira McDonald; Peter Zehler; IPP at pwg.org
Subject: Re: [IPP] WG Last Call of IPP Scan Service specification


This is indeed something that needs to be documented in the implementor's guide, but in most cases the client just needs to see whether the date/time (or simply the up time in seconds) is different than last reported, and not if the change is newer.

But given that the printer-xxx-change-date-time attributes are required in IPP Everywhere, I think we still want them required for IPP Scan.

On May 20, 2014, at 11:09 PM, Soma Meiyappan <Soma.Meiyappan at conexant.com<mailto:Soma.Meiyappan at conexant.com>> wrote:

Hi Ira,

Thank you very much for the summary from the F2F discussions on this topic.

My question on the topic for FaxOut stems from the imaginable ways an IPP client may have been written to be dependent on printer-config-change-date-time for caching printer confifuation  and if it is a value that may be treated as trusted enough for that purpose. I am aware that 'no-value' is valid for these attributes (incl printer-current-time); but I am concerned about other valid (but inaccurate) dateTime values and the implications.

If 'printer-config-change-date-time' is used purely for informational purposes (as a value to display in a report or a web-page and not necessarily in caching the printer configuration), I'll not be too concerned. However, could it be used to determine if cached information about the printer needs to be refreshed? If yes, we may want to add a note targeted at IPP client writers, in the implementer's guide, that this information MUST not be used for caching printer capabilities without other precautions including protection against the possibility of the printer reported time being inaccurate [RFC 2911 does not place any accuracy requirements] and printer-current-time (and derived attribute values) going back to the past for a number of reasons.

Looking forward to hearing the forum's thoughts on the topic.

Thanks and Regards,

From: Ira McDonald [mailto:blueroofmusic at gmail.com]
Sent: Monday, May 19, 2014 11:23 PM
To: Soma Meiyappan; Ira McDonald; Peter Zehler
Cc: IPP at pwg.org<mailto:IPP at pwg.org>
Subject: Re: [IPP] WG Last Call of IPP Scan Service specification

Hi Soma,

Thanks for your careful reading of these IPP specs.
We discussed this comment during the Thursday IPP WG session
at the PWG F2F meeting last week, when looking at IPP Scan with
Pete Zehler.

The IPP F2F minutes state that this issue should be resolved on the
IPP mailing list, but there was unanimous consensus in the meeting:

(1) IPP FaxOut - these date-time attributes should remain REQUIRED
(because they satisfy regulatory requirements for a Fax service).

(2) IPP Scan - these date-time attributes should be changed to either
RECOMMENDED (i.e., best practice) or simply OPTIONAL.
Please note that in IPP Everywhere (PWG 5100.14), the attributes
printer-config-change-date-time and printer-state-change-date-time
attributes are REQUIRED in Table 6 for conformance (see notes 2
and 3 below the table).

Obviously, the underlying printer-date-time attribute should have
the same conformance level as the change-xxx attributes in IPP
Everywhere, IPP FaxOut, and IPP Scan.  This appears to me to
be an oversight in these specs.
Please comment further on this thread, to clarify your thoughts.
- Ira (co-chair of IPP WG)

Ira McDonald (Musician / Software Architect)
Co-Chair - TCG Trusted Mobility Solutions WG
Chair - Linux Foundation Open Printing WG
Secretary - IEEE-ISTO Printer Working Group
Co-Chair - IEEE-ISTO PWG Internet Printing Protocol WG
IETF Designated Expert - IPP & Printer MIB
Blue Roof Music / High North Inc
mailto: blueroofmusic at gmail.com<mailto:blueroofmusic at gmail.com>
Winter  579 Park Place  Saline, MI  48176  734-944-0094
Summer  PO Box 221  Grand Marais, MI 49839  906-494-2434

On Tue, May 13, 2014 at 10:34 PM, Soma Meiyappan <Soma.Meiyappan at conexant.com<mailto:Soma.Meiyappan at conexant.com>> wrote:
Hi Pete et al,

I have a concern about



These attributes figure in the REQUIRED table in section 4.3. The above attributes require the scan device to have a notion of wall clock time (whether it is accurate or not to the global wall clock time). To increase the chances of making use of that effectively & correctly, all clients would be required to use this somehow in reference to printer-current-time and not to the wall-clock time that the client might know through other sources. That makes me wonder if it is sufficient to have printer-state-change-time and printer-config-change-time as required and make xxxx-date-time as optional.

I have a similar question on FaxOut; but at least on FaxOut, the devices are expected to have a notion of wall-clock time although the point about how clients should use that information with reference to printer-current-time still seems applicable.


From: ipp-bounces at pwg.org<mailto:ipp-bounces at pwg.org> [mailto:ipp-bounces at pwg.org<mailto:ipp-bounces at pwg.org>] On Behalf Of Zehler, Peter
Sent: Friday, May 09, 2014 10:35 PM
To: IPP at pwg.org<mailto:IPP at pwg.org>
Subject: [IPP] WG Last Call of IPP Scan Service specification

This message initiates the IPP Working Group last call of the IPP Scan Service specification updated per prototype experience and subsequent discussions.


Please send all feedback to the IPP mailing list (reply-all works fine for this) and it will be collected and processed as quickly as possible.
Our intent is to move IPP Scan Service to PWG Formal Vote before the August 2014 F2F.

Peter Zehler

Xerox Research Center Webster
Email: Peter.Zehler at Xerox.com<mailto:Peter.Zehler at Xerox.com>
Voice: (585) 265-8755<tel:%28585%29%20265-8755>
FAX: (585) 265-7441<tel:%28585%29%20265-7441>
US Mail: Peter Zehler
Xerox Corp.
800 Phillips Rd.
M/S 128-25E
Webster NY, 14580-9701

ipp mailing list
ipp at pwg.org<mailto:ipp at pwg.org>

Michael Sweet, Senior Printing System Engineer, PWG Chair

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