Here is a refinement to the solution for ISSUE 08: Allow the client to
supply a list of subscription-ids and notify-sequence-numbers so the Printer
filters out duplicates?
Ira, Marty, and I refined Marty and Michael's proposal to allow the client
to request the Printer to eliminate duplicate events in the
Get-Notifications responses when using Event No Wait mode.
Summary of changes from the 7/20/01 IPPGET Delivery Method:
1. Receiver NEED NOT support the Event Wait Mode, i.e., it can always return
the "notify-get-interval" meaning that it is not honoring Event Wait Mode.
Sub-ISSUE: Do we still RECOMMEND supporting Event Wait Mode or just make it
2. Receiver MUST support the following operation attributes:
3. REQUIRE Sender to always send "notify-recipients-uri" (uri) operation
attribute. If the client supplies only this attribute, the Printer searches
all Subscription Objects for a match.
4. Change "notify-subscription-id" (integer(1:MAX)) operation attribute to:
"notify-subscription-ids" (1setOf integer(1:MAX))
If the client supplies this attribute and "notify-search" = 'false' or
omitted, the Printer only access the identifies Subscription Objects; if
"notify-search" = 'true', the Printer also searches the Subscription Objects
for additional uri matches.
5. Add "notify-search" (boolean) operation attribute, 'true' means that the
Printer searches Subscription Objects to match the uri when the
"notify-subscription-ids" is supplied. If "notify-subscription-ids" isn't
supplied, then the Printer always does search to match URIs.
6. Add "notify-sequence-numbers" (1setOf integer(1:MAX)) operation
If supplied AND "notify-subscription-ids" MUST also be supplied, the Printer
only returns Events with that sequence number or higher sequence number for
the ith Subscription object identified by the ith subscription id in
"notify-subscription-ids", thereby, eliminating duplicates events on a
Subscription Object basis.
Note: this is a case of "parallel" attributes which we said we didn't want
to do again. However, these attributes are NOT on an object so there is not
problem with setting parallel attributes and these attributes can never get
into a directory (where the order might get changed). Most cases will be
just one value for each attribute as well.
Please send comments to the DL and consider at the IPP FAX WG meeting,
Tom, Marty, Ira
From: Hastings, Tom N [mailto:email@example.com]
Sent: Monday, July 30, 2001 17:57
To: ipp (E-mail)
Subject: IPP> NOT - 9 issues in the IPPGET spec [2 more than on original
So there are now two more issues for the IPPGET spec from the mailing list:
ISSUE 08: Allow the client to supply a list of subscription-ids and
notify-sequence-numbers so the Printer filters out duplicates? From Marty
Joel's Fri 07/27/2001 21:15 email:
Well, if a subscription ID is given with a Get-Notifications request, then
only one sequence number is (optionally) needed.
I'm thinking now that instead of Get-Notifications optionally taking a
single subscription ID, maybe that should be a list, and maybe there should
be another optional list with corresponding sequence numbers.
If that is done, then the 3 possibilities are that Get-Notifications takes
subscription IDs only and no recipient uri, a recipient uri and no
subscription IDs, or both. I propose that if Get-Notifications is given a
recipient uri, then a search will be made for matching subscriptions,
regardless of whether or not any subscription IDs are given. In the event
that the recipient uri is not given, then Get-Notifications will only
return events for the given subscription IDs. Whether or not a recipient
uri is given, if corresponding sequence numbers are given with the
subscription IDs, then the starting event sequence number will apply only
to those subscription IDs. For the case where recipient uri is not given,
the optional list of corresponding sequence numbers will apply to all
subscriptions being requested.
For the case where Get-Notifications is being called with a recipient uri,
then the first call would have no subscription IDs (since if the client
knows the subscription IDs, the search for those subscriptions having that
recipient uri can be avoided). The second call would contain that
recipient uri, and may include , for each subscription of the events
returned from the first call, the subscription IDs and a list of the
corresponding next sequence numbers to receive for each. As each
subsequent call is made, if an event is returned with a subscription ID
that was previously not returned, then that subscription ID and next
sequence number will be added to the lists for subsequent calls to
Get-Notifications. The client is not required to follow this procedure,
but if followed, it lowers the number of events the printer must process
and send, and eliminates the possibility of the client receiving duplicate
I realize this complicates the spec a bit, but I think it makes ippget more
versatile, and addresses Michael's excellent point of improving performance
ISSUE 09: Make Event Wait Mode OPTIONAL for a Sender and a Receiver?
Currently the spec REQUIRES the Receiver to support both values of the
"notify-wait" operation attribute ('true' and 'false').
With the Notification Recipient being able to request the Receiver to filter
out duplicates, is it ok to allow the Receiver to always force the
Notification Recipient back to Event No Wait Mode with the
"notify-get-interval" operation attribute of when to poll next?
Of should Event Wait Mode be RECOMMENDED for the Receiver?
What about RECOMMENDED for the Sender?
From: Hastings, Tom N [mailto:firstname.lastname@example.org]
Sent: Friday, July 27, 2001 17:48
To: ipp (E-mail)
Subject: IPP> NOT - 7 issues in the IPPGET spec
The IPPGET spec that was sent to the IETF last Friday, 7/20, has 7 issues
that have been raised since then. I've collected them into a single note
and sent them to the IPP FAX DL (email@example.com) for their IPPFAX WG meeting in
Toronto, August 1. IPPFAX REQUIRES support of IPPGET. However, the IPPGET
spec is an IPP document, so discussion of it should go on the IPP DL. So
here are the 7 issues.
If you have a comment think about whether or not to start a new thread. If
the comment is just about one issue, I suggest a new thread.
3. IPPGET Delivery Method (<draft-ietf-ipp-notify-get-04.txt>), I posted
Monday, 7/23, at:
ISSUE 01 (see section 12): Should we use application/multiplexed
(draft-herriot-application-multiplexed-03.txt) which can chunk mime types
using content lengths, instead of multi-part/related, which uses boundary
ISSUE 02: For Event Wait Mode, OK to make each successive response after
the first a complete IPP response, instead of just the Event Notification
Then each response looks like a complete response with its own status code.
Also complete responses might be necessary on some other transport. Also we
can move the "notify-interval" attribute back to the Operation Attributes
Group where it belongs, since it applies to all events being returned in
ISSUE 03: OK to clarify that the Per-Job Subscription Object and the
associated Job object MUST persist after the job completes (job completed,
canceled, or aborted) in the Job Retention or Job History phases (see
[RFC2911] section 18.104.22.168)?
Otherwise, a Notification Recipient that is polling would not get the Event
Notification, if it polled after the job completed, but before the Event
Lease Time expired.
ISSUE 04: OK to clarify that a client or a Printer MAY disconnect the
underlying transport connect for any operation, including the Event No Wait
Get-Notifications operation and the Event Wait Get-Notifications operation
when the Printer isn't willing to honor the initial request or reneges in a
So a client could keep the connection open for multiple Event No Wait
Get-Notifications. Before a Printer disconnects it needs to wait enough
time to make sure that any IPP response has had time to get back to the
client before disconnecting, otherwise the client might not see the
ISSUE 05: OK to add 'successful-ok-events-complete' status code for a
Get-Notifications response whether Event No Wait or Event Wait mode?
Here is more detail:
The Printer MUST return the 'successful-ok-events-complete' status code to
indicate when this return is the last return for all Subscription objects
that match the request, whether or not there are Event Notifications being
returned. This condition occurs for Event Wait Mode Notification Recipients
waiting for responses when the Subscription Object is: (1) canceled with a
Cancel-Subscription operation, (2) deleted when the Per-Printer Subscription
lease time expires, or (3) when the 'job-completed' event occurs for a
Per-Job Subscription. This condition also occurs for a Get-Notifications
request that a Notification Recipient makes after the job completes, but
before the Event Lease Time expires.
Here is a complete table of combinations of "notify-wait", "status-code",
"notify-interval", and Event Notification Attributes Groups for
Get-Notification initial (Wait and No Wait) Responses and subsequent Event
Wait Mode Responses (which may be staying in Wait Mode or may be requesting
the Notification Recipient to leave Wait Mode):
client sends: Printer returns: Notification
"notify-wait" "status-code" "notify-get-interval" Attribute Groups
------------- ------------- --------------------- ----------------
1.'false'/omitted 'successful-ok' MUST return N maybe
2.'false'/omitted 'not-found' MUST NOT MUST NOT
3.'false'/omitted 'busy' MUST return N MUST NOT
4.'false'/omitted 'events-complete' MUST NOT 'job-completed'
5. 'true' 'not-found' MUST NOT MUST NOT
6. 'true' 'busy' MUST return N MUST NOT
7. 'true' 'successful-ok' MUST NOT MUST
8. 'true' 'successful-ok' MUST return N maybe
9. 'true' 'events-complete' MUST NOT 'job-completed'
or maybe other
1-4: client requests Event No Wait
5-9: client request Event No Wait
2,5: Subscription object not found, or was canceled earlier; client should
NOT try again.
3,6: server busy, tells client to try later; client should try again in N
4: client polled after job completed, but before Event Lease Time expired,
and got the 'job-completed' event, so the client shouldn't bother trying
again; client should NOT try again later.
7: Printer returns one or more Event Notifications and is ok to stay in
Event Wait Mode; the client waits for more.
8: Printer wants to leave Event Wait mode. Can happen on the first
response (with events) or happen on a subsequent response with or without
Event Notifications; the client should try again in N seconds.
9. Printer either (1) returns 'job-completed' event or (2) the Subscription
Object was canceled by either a Cancel-Job or a Per-Printer Subscription
expired without being renewed. For case (1), at least one event MUST be
returned, while for case (2), it is unlikely that any Events are returned;
the client should NOT try again.
ISSUE 06: Section 12 says: "The Printer MAY chunk the responses, but this
has no significance to the IPP semantics." Is this sufficient, or is
HTTP/1.1 chunking REQUIRED in order to support the multi-part/related MIME
ISSUE 07: For Event No Wait mode, should we add a way for the Notification
Recipient to have the Printer filter out returning Event Notifications that
the Notification Recipient has already received in order to reduce the
duplicates (that will usually happen, else events will be lost)? Or should
we just depend on most usage using Event Wait Mode, so that there aren't
duplicates? It has been suggested on the mailing list that the Notification
Recipient could supply pairs of the "notify-sequence-number" and
"subscription-id" and the Printer would only return events with a higher
This archive was generated by hypermail 2b29 : Tue Jul 31 2001 - 02:43:58 EDT