IPP> URLs within IPP operations

Mon Jun 1 19:46:36 EDT 1998

This is a multi-part message in MIME format.
--------------9233C429104D40AEF3E2F6F9
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

> You forget one thing, the IPP recipient must generate and give out addresses
> for new objects (Job-URI). it must therefore know its place in the
> addressing scheme of he underlying transport.
>
But it doesn't necessarily have to get that knowledge from the request
message.

http://www.pwg.org/hypermail/ipp/0541.html

--------------9233C429104D40AEF3E2F6F9
Content-Type: text/html; charset=us-ascii; name="0541.html"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline; filename="0541.html"
Content-Base: "http://www.pwg.org/hypermail/ipp/0541.
	html"

<title>IPP Mail Archive: RE: IPP&gt; URLs within IPP operations</title>
<h1>RE: IPP&gt; URLs within IPP operations</h1>
Paul Moore (paulmo at microsoft.com) 
Mon, 1 Jun 1998 15:41:14 -0700 

<ul>
<li> Messages sorted by: <a href="date.html#541">[ date ]</a><a href="index.html#541">[ thread ]</a><a href="subject.html#541">[ subject ]</a><a href="author.html#541">[ author ]</a>

<li> Next message: <a href="0542.html">Turner, Randy: "RE: IPP&gt; URLs within IPP operations"</a>
<li> Previous message: <a href="0540.html">Scott Isaacson: "IPP&gt; URLs within IPP operations"</a>

</ul>

You forget one thing, the IPP recipient must generate and give out addresses 
for new objects (Job-URI). it must therefore know its place in the 
addressing scheme of he underlying transport. 

&gt; -----Original Message----- 
&gt; From:	Scott Isaacson [SMTP:SISAACSON at novell.com] 
&gt; Sent:	Monday, June 01, 1998 2:41 PM 
&gt; To:	kugler at us.ibm.com 
&gt; Cc:	ipp at pwg.org 
&gt; Subject:	IPP&gt; URLs within IPP operations 
&gt; 
&gt; I changed the subject line. 
&gt; 
&gt; We do so seem to be confusing addressing vs payload. Addressing should 
&gt; be independent of payload. With URLs embedded within IPP operations, we 
&gt; are mixing addressing and payload. 
&gt; 
&gt; Since we chose HTTP for IPP we should rely on it for all of our addressing 
&gt; and routing, so we all seem to agree that for High Level Scenario 1 the 
&gt; URLs in the IPP operation are as you say "meaningless" In fact they were 
&gt; never there until late in the game and were added "just in case there is a 
&gt; mapping to some other transport other than HTTP" When that happens, no 
&gt; longer will IPP objects be identified with "http:" URLs, but some other 
&gt; type of addressing/naming scheme. In that case, we ought to make sure 
&gt; that there is enough info in that URL (URI, URN whatever) to get to the 
&gt; IPP printer object and not worry so much about including in the operation 
&gt; itself. 
&gt; 
&gt; I am becoming more and more convinced that it as a bad idea to put the 
&gt; URLs in there at all. We should rely on the addressing in the layer upon 
&gt; which IPP is mapped to solve the problem. I think we all agree that the 
&gt; URLs within IPP operations are not needed for HTTP. Then we try to guess 
&gt; if they are needed for other mappings? You suggest in scenarios 2 and 3 
&gt; that the embedded info might be needed for identifying a resource 
&gt; "underneath" or "behind" the IPP object. However, I wonder if this is 
&gt; true. The only addressable IPP objects are Printers and Jobs. Once a 
&gt; Printer gets a Printer request it should handle it as if it were supposed 
&gt; to get that request, and not have to check "is this really for me" That 
&gt; should be handled at a different layer. Same for a Job object. The HTTP 
&gt; level URL is all that is needed to route to the correct Job or Printer. 
&gt; So to me, scenarios 2 and 3 either collapse into one called "other" or 
&gt; expand into possibly many unexplored options. Let's not solve that 
&gt; problem now. 
&gt; 
&gt; Consider this example: 
&gt; 
&gt; If I get a postal service letter in my mail box, I open the evenlope and 
&gt; read it assuming it is for me. If I am at home, the address on the 
&gt; envelope is perhaps much simpler than if I am at work. If I am at home, 
&gt; it probably just has my name and street address. If I am at work, it 
&gt; probably has a street address, company name, mail/stop, building number, 
&gt; and my name. NOTE: **** In either case, the letter in the envelope can 
&gt; be exactly the same. **** 
&gt; 
&gt; What if the letter happens to have the address that was used at the top of 
&gt; the page? I usually just ignore it and read the letter, I don't care how 
&gt; it got to me. What if the letter happens to have the wrong address? ( 
&gt; the proxy case), I still ignore it and read the letter - the letter got to 
&gt; me, it must be for me. In the proxy case, who cares what the address 
&gt; printed at the top of the page is? 
&gt; 
&gt; Summary, why do we have a solution waiting for a problem that is causing a 
&gt; different problem? 
&gt; 
&gt; Scott 
&gt; 
&gt; &gt;&gt;&gt; Carl Kugler &lt;kugler at us.ibm.com&gt; 06/01 2:53 PM &gt;&gt;&gt; 
&gt; &gt; Scott - 
&gt; &gt; 
&gt; &gt; Maybe we need to step back and define the requirements before we nail 
&gt; down the 
&gt; &gt; specification. 
&gt; &gt; 
&gt; &gt; Consider some high-level scenarios: 
&gt; &gt; 
&gt; &gt; 1) IPP over HTTP: the simplest approach here, I think, would be to 
&gt; let the 
&gt; &gt; Request-URI take precedence. In this scenario, the IPP embedded target 
&gt; URI 
&gt; &gt; (printer-uri, job-uri, etc.) is essentially meaningless, since any 
&gt; entity in a 
&gt; &gt; position to read it has already been identified as the resource 
&gt; designated to 
&gt; &gt; receive this request by the HTTP Request-URI. But this scenario 
&gt; (IPP/HTTP) 
&gt; &gt; isn't the reason that the target URI was added to the IPP protocol. In 
&gt; fact, 
&gt; &gt; we know that IPP/HTTP can work without IPP embedded target URIs. 
&gt; &gt; 
&gt; &gt; 2) IPP over non-HTTP transport (e.g., IPP over SMTP): In this scenario, 
&gt; any 
&gt; &gt; entity in a position to read the IPP embedded target URI attributes is 
&gt; &gt; presumably an IPP Object. Therefore, the addressing of the request to 
&gt; the 
&gt; &gt; appropriate IPP Object is the responsibility of the transport layer 
&gt; (e.g., by 
&gt; &gt; email address). The IPP embedded target URI is used to identify a 
&gt; resource 
&gt; &gt; relative to the receiving IPP Object (e.g., a Job within the context of 
&gt; a 
&gt; &gt; Printer). So it is a Relative URI. 
&gt; &gt; 
&gt; &gt; 3) IPP Router: Apparently there are other scenarios involving some 
&gt; kind of 
&gt; &gt; IPP router capable of parsing an IPP request and retransmitting it to 
&gt; the 
&gt; &gt; resource identified by the embedded target URI. I haven't seen any of 
&gt; these 
&gt; &gt; re-route scenarios, but I think that only by working through some of 
&gt; them will 
&gt; &gt; we come to understand what the real requirements are. Maybe we need a 
&gt; new IPP 
&gt; &gt; embedded target URI attribute, of Absolute form, to identifiy the 
&gt; destination 
&gt; &gt; IPP Object in a router scenario. 
&gt; &gt; Scenario 1) could be modified to fit the general case of 2). Then the 
&gt; HTTP 
&gt; &gt; Request-URI would identify a Printer relative to a host, and the IPP 
&gt; embedded 
&gt; &gt; target URI would identify a resource relative to that Printer. 
&gt; &gt; 
&gt; &gt; - Carl 
&gt; 


<ul>

<li> Next message: <a href="0542.html">Turner, Randy: "RE: IPP&gt; URLs within IPP operations"</a>
<li> Previous message: <a href="0540.html">Scott Isaacson: "IPP&gt; URLs within IPP operations"</a>

</ul>

--------------9233C429104D40AEF3E2F6F9--