We should not design a protocol that depends upon failure
of an operation in order for clients to know what to do next. If the
client doesn't know what the Printer is capable of doing it should
ask, not assume something works and wait to see if it does or not.
Sure, we have to consider what happens when an operation
fails, but we should not require failure to occur in order to do
simple operations.
The logic you suggest seems complex and poor design. It puts
extra burden on the client, which I would think we want to keep
as simple as possible.
The client logic ought to be:
Do I know I know about the Printer?
If no - query the printer, otherwise go ahead
Send a PrintJob operation with the job attributes
and the document(s) to be printed. If the response to
the query tells me that the Printer only supports one
document per job, I will do multiple PrintJobs, otherwise
I will put all of the documents in one PrintJob.
I don't view this as overloading the PrintJob operation.
Roger K deBry
Senior Techncial Staff Member
Architecture and Technology
IBM Printing Systems
email: rdebry at us.ibm.com
phone: 1-303-924-4080
---------------------- Forwarded by Roger K Debry/Boulder/IBM on 05/28/97 10:04
AM ---------------------------
don @ lexmark.com
05/28/97 09:22 AM
Please respond to don at lexmark.com @ internet
To: Roger K Debry/Boulder/IBM
cc: ipp @ pwg.org @ internet
Subject: Re: IPP>MOD - Too Many IPP Operations?
Roger:
My understanding is as follows:
-------------------
In the simple case of 1 job/1 document:
PrintJob - Creates a job and send it to be printed.
-------------------
Rather than overloading PrintJob we have added CreateJob
to support multiple documents per job.
CreateJob - Use to create a job on the server which
responds with some job identifier
SendDocument - Used multiple times to send the
multiple documents which make up the job
created with CreateJob
With a server that does not support multiple documents
per job, the CreateJob operation is rejected. The client
can either split the multiple document job into multiple
jobs or go look for a server that supports multiple
documents per job.
-------------------
ValidateJob is just as you describe.
------------------
Hope this helps!
Don
To: ipp%pwg.org @ interlock.lexmark.com
cc: (bcc: Don Wright)
From: rdebry%us.ibm.com @ interlock.lexmark.com @ LEXMTA
Date: 05/28/97 10:18:34 AM AST
Subject: IPP>MOD - Too Many IPP Operations?
You all must pardon me if I am covering ground that has been covered
before, but since I was not able to attend the IPP meetings last week my
thinking may be a bit behind where everyone else is at.
In reading through the minutes of the meeting and recent email on the
discussion list, it seems to me that we may have invented more
operations for IPP than we really need. It seems to me that we added
CreateJob to allow a client to validate job attributes prior to sending
all of the print data. The original send operation (which I think we are
back to) simply transmits the print data. The deBry/Carter proposal
to use multiple send Documents was not accepted. We are
depending upon http chunking to allow the client to send the
print data in pieces and upon tcp/ip to guarantee delivery.
We added Validate and PrintJob to provide for the simple print case
proposed by Microsoft. As I read the minutes and email it also seems
that we generally agreed that well behaved clients would always know
printer characteristics, either because the Printer has been "installed"
on the desktop or the client has queried the capabilities of the printer.
So as I see it, we are left with the following:
CreateJob - used to validate the print job
Validate - used to validate the print job
SendDocument - its only value is to transmit the job data
PrintJob - transmits the job data and the job attributes
What am I missing? In the spirit of simplification, it appears to me that
we
could get rid of CreateJob and SendDocument. I see little value to
these operations given the current set of proposals on the table. The
only thing I see is that I save resending the job attributes in the
sequence
CreateJob, SendDocument over the sequence Validate, PrintJob. Since
a well behaved client would know the capabilities of the Printer it would
normally not be necessary to validate job attributes and PrintJob
would almost always be the preferred method to use.
Roger K deBry
Senior Techncial Staff Member
Architecture and Technology
IBM Printing Systems
email: rdebry at us.ibm.com
phone: 1-303-924-4080