Networked Products Business Unit
Email: Peter.Zehler at usa.xerox.com
Voice: (716) 265-8755
FAX: (716) 265-8792
US Mail: Peter Zehler
800 Phillips Rd.
Webster NY, 14580-9701
From: Stefan Andersson [mailto:stefan.andersson at axis.com]
Sent: Wednesday, March 24, 1999 9:46 AM
To: Zehler, Peter; ipp at pwg.org
Cc: Hastings, Tom N; anthony.porter at computer.org
Subject: RE: IPP> MOD - Use of time [and Bake Off 2 Issue 17]
On Wed, 24 Mar 1999, Zehler, Peter wrote:
> The HTTP layer requires a time stamp. Simple time protocols exist that
> are very light weight. A page can be made available in the embedded web
> server to set the current date and time. If all else fails the time can
> grabbed from incoming HTTP packets.
It is true that the HTTP layer requires a time stamp, but there is an
exception to this rule. From draft-ietf-http-v11-spec-rev-06.txt
3. If the server does not have a clock that can provide a
reasonable approximation of the current time, its responses MUST
NOT include a Date header field. In this case, the rules in
section 14.18.1 MUST be followed.
To add a page for setting the current date and time is not a good idea. If
a date is to be useful the client must be sure that the clock isn't
reseted between requests. The same argument can be used against grabbing
it from incoming HTTP packets, the server will have no way to control that
the incoming date/time is correct. The only way to get a date that would
work is to use for example NTP.
PZ> Software does not have to blindly accept a time change.
PZ> Timestamps can be adjusted based on the latest truth.
PZ> (I assume the client will ask for all the timestamps instead
PZ> of one at a time)
PZ> Across the Internet the chances of the Client and the Printer
PZ> having their time in sync is remote. A man with one watch
PZ> knows what time it is, a man with two is never really sure.
PZ> My point was that there are a number of methods to obtain the
PZ> current time. Each has certain advantages and disadvantages.
PZ> Let the method of obtaining the time be selected by the implementation
PZ> based on product requirements. There is a real end user advantage
PZ> to having the timestamps
Since the Date field probably is most useful for clients when the server
is spooling. I would recomend one of this alternatives:
1) Add optional attribute that gives the time in an absolute form.
2) If the server can answer in an absolute form it should do that
otherwise it will answer in an relative form as the protocol states
PZ> Are you suggesting alternate syntaxes for the same attribute?
PZ> Are you suggesting the following from the issues list?
> 1.Add to the IPP/1.1 Model and Semantics document OPTIONAL job
> description attributes: .date-time-at-creation (dateTime)., .date-
> time-at-processing (dateTime)., and .date-time-at-completion
PZ> It is statement 2 above that confuses me. Are you suggesting
PZ> the client ask for all attributes or both the absolute and relative
PZ> attributes or something else?
Stefan Andersson Software Engineer
Print Server Business Unit Stefan.Andersson at axis.com
AXIS Communications AB Phone: +46 46 270 19 85
Scheelevägen 16 Fax: +46 46 13 61 30
S-223 70 LUND, SWEDEN http://www.axis.com