[Cloud] Simplified Cloud Imaging Diagram for a typical MFD

[Cloud] Simplified Cloud Imaging Diagram for a typical MFD

[Cloud] Simplified Cloud Imaging Diagram for a typical MFD

William A Wagner wamwagner at comcast.net
Wed Dec 11 16:58:21 UTC 2013

Michael and Ira,


I offer the following observation, subject of course to expert comment.

The IPP multifunction approach is evolving from IPP where there was just one
type of service and the client dealt just with a Printer Object, that it
accessed via a print service. Any necessary  information about the physical
"output" device came though the Service connection.  I am not sure how IPP
multifunction will evolve, but it could also have the normal user deal with
just the service he is interested in and any necessary  information about
the "endpoint" comes though the Service connection. The IPP "System Control
Service" would then be devoted to monitoring and management of the "Imaging
System" and any physical components that were a part of it.


True, the Semantic Model evolved from IPP. But the current version of the
Semantic Model specifically addressed an MFD, considering how to handle
multiple types of imaging services. So the Printer became expanded to an
Imaging System and a System Control Service was  defined to provide access
to System Elements. I have perhaps overstressed the "Imaging System"  and,
as Ira points out, the system may not relate to a device in the case of a
distributed .  Perhaps the basic imaging services user  need never even be
aware that there is a system.


So, if I drop my MFD mindset,  a reasonable network model has the Imaging
Services User just accessing the desire imaging service. Access to the
System Control Service is limited to supervisory/management/maintenance
users. As far as the basic User is concerned, there is no Imaging  System
and no *Imaging Device*; there are Services and elements in the Service
provide information on the location of the endpoint, the IPP *physical


However, for practical purposes, there may still be  justification for the
Proxy to access the Cloud System Control Service (or some other Cloud-based
component) that can provide/accept summary information for/from the Proxy
just as the Proxy can provide summary information for the Local  Services.
The alternative, which would be simpler but involve more traffic, would be
for the Proxy to just communicate with each Cloud Service independently.


So, the diagram would show the both Cloud and local Services (including
System Control Service) as being within Imaging Systems and the Proxy  would
interface with each Cloud Service and each local service. 

 Thanks, Bill Wagner


From: Michael Sweet [mailto:msweet at apple.com] 
Sent: Wednesday, December 11, 2013 9:04 AM
To: William A Wagner
Cc: <cloud at pwg.org>; <ipp at pwg.org>; Semantic Model 3.0 Workgroup discussion
Subject: Re: [Cloud] Simplified Cloud Imaging Diagram for a typical MFD




On Dec 11, 2013, at 1:24 AM, William A Wagner <wamwagner at comcast.net> wrote:



Thank you for the diagram. Some observations, rather that objections,
particularly in areas that appear different from the model  and diagram we
had previously agreed to and that seem inconsistent with the Semantic Model.

1.      We had avoided showing the interface between the proxy and  local
services, although the intention in defining the Proxy->Cloud  operations
was that the Proxy could communicate with the local services using the
standard client-imaging service operations.


True, but since we had our discussion in Monday's Cloud concall I felt it
might be useful to expose it, at least for a "big picture" diagram.  And
this *does* mirror the IPP model diagrams in RFC 2911 and IPPSIX (figures 1
and 3) where a local print service is connected to the IPP Server or IPP
Proxy.  IPP Server + Print Service == IPP Printer.


2.      But having shown these connections, I wonder about the dotted line
from the proxy to the Local System Control Service. I would expect that the
Proxy acts as a proxy for the Local System Control Service to the same
extent that it acts for the imaging services.


I made the line dotted mainly because we hadn't defined a concrete
relationship - the proxy might get a list of services to register from the
local system control service *or* it might get it from another source (web
interface, etc.), which gets it from the local system control service.
Architecturally we may not care beyond the fact that the Semantic Model
defines the local system control service in the model for an imaging
device/system - that is something we should probably decide on and document
in the Cloud model.

3.      According to the Semantic Model, there is an extensive client
interface to the System Control Service that provides access to both System
Control Service elements and System Object elements (SystemConfiguration,
SystemDescription, and SystemStatus). However, the diagram shows no System
Object either at the Cloud Level or the Local level ("Imaging System" in the
lower right  hand corner not withstanding.) The sort of information that a
User might want to know about the physical location of the "device" (however
one may wish to define it) is in the System Description. The UUID for the
imaging device is the System UUID. I suggest that, as in the previous
diagram,  there is both a Cloud Imaging System and, if we are showing things
beyond the Proxy, a Local Imaging System.


Adding the system object to the diagram would probably be useful.  I'm not
sure how we would show connections *to* this object, or whether we should
(for purposes of simplifying the diagram) just update the system control
service boxes to be "system control service and system object"?


4.      The diagram does not clear up the difference between a IPP Physical
Device and a Semantic  Model Device.  By the  SM definition  definition,
the Imaging Services  are physically embodied within one  or more physical
devices. In most cases ( and certainly for a basic MFD), the Imaging  System
represents the elements of the Device and the System Control Service
provides access to the values of these elements. Therefore, in an SM based
model, I suggest that there are no lines from Imaging Services to the
Device. Indeed, after the last Cloud call, I am eliminating all reference to
"Device"  as an actor in the cloud specification, in favor of System. 


Ira made some good comments, but I'll add one: you'll notice that the proxy
is only connected to services.  Only the local services are connected to the
physical device.  I believe that both mirrors our discussions and matches
the Semantic Model and IPP notions of separation.

5.      You presented a good argument for making IPP Identify Printer a
service operation, primarily by stating that a normal user would be using a
connection to a Imaging service not the System Control Service.  I am unsure
of the intent or limitations of the Client to Cloud System Control Service
path shown in the diagram (is ListAllServices the only operation allowed?)
However, although discovery is nominally of Imaging Services, it seems that
the in the Semantic Model physical elements of interest in discovery should
be accessed via the System Control Service, suggesting that a normal client
should have at least read access to the System Control Service.  It would
seem reasonable that it could also trigger an Identify via this path.


I should probably remove all of the operation names from the diagram and add
letter/number identifiers (as Smith has suggested).  I shows
"ListAllServices" as the most likely operation a client would use in order
to discover which imaging services are available, in preparation for
creating a job, etc. on a specific service. Clearly the client would be able
to perform any supported operation of the system control service, and I
agree IdentifyDevice is one of the expected operations.


So, the diagram appears to reflect a IPP model using IPP terminology and
does not reflect the Semantic Model of a System containing Services with
system specific elements accessed via a System Control Service. Am I missing


Actually, I believe the bottom half of the diagram looks a lot like Figure 6
of MFD Common Model (PWG 5108.1), just turned on its side and combining the
marker and scanner subunits as the "physical device" (also a SM term that is
shared with IPP - perhaps you would prefer "Multifunction Device" or
"Multifunction Device/Subunits" here?)




Please remember: Semantic Model came from IPP. While some of the terminology
was changed in the move to support multifunction services, and some of the
responsibilities are moved around (i.e. system control service), the overall
model remains the same.  The IPP Printer is an IPP Server talking to an
Imaging Service, just as a web service binding using the Semantic Model
schema and WSDL files is an XML-RPC server talking to an Imaging Service.
In both cases the imaging services are talking to the hardware subunits (as
needed) with implementation-defined coordination with the System Control


Michael Sweet, Senior Printing System Engineer, PWG Chair


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