Subject: Re: Service Access implementations (via SLP) requested

From: Michael Fischer <[email-masked]>
Date: Fri, 1 Dec 2000 14:10:47 +0100 (MET)

Jak,

Not exactly. I think I know, how the access procedure might look after
using SLP. But there is a large range of possibilities to do that.
I mentioned Jini, UPnP and Salutation not as service discovery but as
techniques for access, which could be done with them, too.
So I'd like to know if anybody already had done access, possibly has got a
implementation, which I might possibly have. :-)
This need not to be one of the 3 mentioned techniques, but might also
contain proprietary selfmade ones.
Or even any ideas and examples how access and templates (including access
attributes) might look like.

The most popular example is the access of a printer. E.G. how could the
access look like, after verifying the accessability and parameters (e.g.
color-capability) with SLP. 
Problems: 
- Loading drivers is not a good thing, especially Windows-Systems are
likely to get overloaded and crashy by buggy drivers.
- How should a document be transmitted

A testscenario for this might look like having a server in between the
client and printer to handle the SLP discovery and the access on the one
side and the printer on the other. This architecture shouldn't be
problematic, as printer spooler already are handled (via lp-Interface) by
such a server.

I trust, that there are already systems running using SLP for discovery
and any kind of access afterwards, as otherwise SLP would be quite
useless.

Am I right?

Thanks for your efforts
Michael

> I'm not sure I understand your question.
> 
> After discovering a service, you use the reachability information 
> in the service URL and (potentially) attributes to contact the
> service through opening a TCP or UDP socket and exchanging
> messages. You could also use attributes to configure the service,
> if there is no service-specific attribute discovery procedure.
> 
> All this is completely independent of SLP or any other service
> discovery protocol.
> 
> 		jak
> 
> >X-Authentication-Warning: wicked.neato.org: majordom set sender to 
> [email-masked] using -f
> >Date: Thu, 30 Nov 2000 19:48:50 +0100 (MET)
> >From: Michael Fischer <[email-masked]>
> >To: [email-masked]
> >Subject: Service Access implementations (via SLP) requested
> >MIME-Version: 1.0
> >
> >Hi out there,
> >
> >I'd like to know which simple (selfmade) implementations you made for
> >service access after discovery with SLP.
> >This should includes the service description and attributes needed for
> >the access parameters, as well as the access technology behind. Latter may
> >be public ones, like Salutation, UPnP, Jini or proprietary selfmade ones.
> >
> >Thats because I've got to implement such a service access myself, and like
> >to draw back on already available knowledge.
> >
> >Thanks
> >Michael
> >

---

From: James Kempf <[email-masked]>
Date: Fri, 1 Dec 2000 09:00:17 -0800 (PST)

>techniques for access, which could be done with them, too.

Most of these have built-in assumptions about location and access. SLP
is the opposite: there is no built-in assumption about access, only
location. As a result, SLP could be used to support any of the acccess
methods.

>attributes) might look like.

Well, SalutationV2 uses SLP for off-subnet discovery, I believe. They
have their own service type scheme, however, so they can't discover
arbitrary services. Jason Goldschmidt and I have done a prototype of
the Jini API on top of a library that uses SLP discovery instead of
RMI. It depends on the SLP Notification Protocol 
(draft-kempf-srvloc-notify-04.txt) to do Jini notifications. It also
uses its own service type scheme, so Java subtype location can
be supported. See the proceedings of last summer's INET 2000 for more 
information, we gave a paper there. Off and on, there have been discusions about
how to support UpNP style discovery/access with SLP, and it looks
doable with perhaps a couple of SLP extensions.

>- How should a document be transmitted

What kinds of printing protocols does the printer speak? The advantage
of a driver-loading approach, such as Jini, is that the application
doesn't have to care. The application writer only needs to write to
an API, and the driver can take care of adapting to the protocol.

Incidently, I believe that Windows currently allows driver loading
over SMB for a few restricted devices (like maybe two). One of these
is printing. More Windows-knowledgable folks can correct me if I am wrong.

With regard to crashing w (small) dow systems, if the window system
is properly written and the operating system architecture is properly
designed, this need not be the case. :-)

>and any kind of access afterwards, as otherwise SLP would be quite

I don't understand what you are proposing. It is certainly possible to
have a print spooler, sitting between the client and printer, use SLP
to locate printers if the printers support SLP or are advertised by
a surrogate. The client then only needs to locate the spooler, and 
it can do that by using SLP directly or by traditional mechanisms,
such as LPR.

It is also possible to have the client locate printers directly using
SLP. 

		jak

---

From: "McDonald, Ira" <[email-masked]>
Date: Mon, 4 Dec 2000 12:50:07 -0800

Hi Michael,

The IETF IPP (Internet Printing Protocol) WG has an IPP extension
for discovery of available drivers from the IPP-speaking printer
(AFTER discovery of the printer itself via the SLP or LDAP printer
schemes).

Novell has also extended the SLP/LDAP printer schemes to support
NDPS protocol access to printers.

You may wish to look at the specs and archives of the IETF IPP WG,
available from the Printer Working Group (PWG) home page and FTP
server at 'http://www.pwg.org' and 'ftp://ftp.pwg.org'.

The IETF IPP WG's mailing list is at [email-masked]' (see the above
Web server for info on joining that list).

Cheers,
- Ira McDonald, co-editor of SLP and LDAP printer schemes
  (consulting architect at Sharp and Xerox)
  High North Inc

-----Original Message-----
From: James Kempf [mailto:[email-masked]]
Sent: Friday, December 01, 2000 9:00 AM
To: [email-masked]; [email-masked]
Subject: Re: Service Access implementations (via SLP) requested

information, we gave a paper there. Off and on, there have been discusions
about

		jak