I think that the window of time for holding events has to be different from
the "lease time" for the Subscription object. For example, an infinite
lease for the subscription object is allowed. This would mean that the
number of events coming back in each poll would grow forever.
The IPP notification specification [ipp-ntfy] is an OPTIONAL extension to
IPP/1.0 and IPP/1.1 that requires the definition of one or more delivery
methods for dispatching event notification reports to Notification
Recipients. This document describes the semantics and syntax of the 'ipp'
event notification delivery method. For this delivery method, the client
uses an explicit IPP Get-Notifications Printer operation in order to request
(pull) event Notifications from the IPP Printer.
When a Printer supports the 'ipp' delivery method, it holds each
Notification event for a certain length of time. The amount of time is
called the "lease time" and it is the same for all events in a Printer. If
a Notification Recipient does not want to miss events, the time between
consecutive polling of Subscription objects must be less than the lease
time. The Get-Notifications request indicates whether the client wants to
receive all pending events Notifications for (1) any Subscription for which
the client is the owner, (2) any Subscription associated with a Job or (3) a
particular Subscription object. With the Get-Notifications operation, the
Printer returns all existing Notifications along with two time intervals.
One specifies the length of the lease for all future events and the other
specifies the recommended interval to wait to the next Get-Notifications
operation. The second time interval is less than the first.
The Printer may keep the channel open if the recommended interval is
sufficiently short, but in any case the client performs a new
Get-Notifications operation each time it wants more Notifications. Since
the time interval between consecutive client requests is normally less than
the lease time,consecutive responses will normally contain some events that
are identical. The later ones in the previous response will become the
earliest in the next response. The client is expected to filter out these
duplicates which is easy to do because of the sequence number in each
From: Herriot, Robert [mailto:Robert.Herriot at pahv.xerox.com]
Sent: Tuesday, March 07, 2000 19:47
To: ipp at pwg.org
Subject: IPP>NOT lastest notify-poll document
I just downloaded the latest notify-poll document.
We may discuss the issues at the IPP teleconference tomorrow.