Re: Back-channel: What is it and where do I find it?

David,

Here's a fourth: each protocol that defines a binding to WS-Addressing 
identifies whether the term back-channel applies to it, and how. We have 
done so for the protocols we support (SOA 1.1 on HTTP, a more generic form 
for SOAP 1.2), and that proves that the concept is valid. 

The fact that in the WS-Addressing wg we are not going to settle that 
question for all protocols you can imagine does not prove anything. 

Paco




David Hull <dmh@tibco.com> 
Sent by: public-ws-addressing-request@w3.org
11/06/2006 04:03 PM

To
paul.downey@bt.com
cc
public-ws-addressing@w3.org
Subject
Re: Back-channel: What is it and where do I find it?






Paul,

Yours is the third eminently reasonable answer I've received on this. They 
all differ.

The points being 1) Of course we have to define it if we're going to use 
it.  2)  Agreeing on a definition is quite likely feasible, but certainly 
not trivial, so I'd like to know what we get for the effort if we go 
there.

paul.downey@bt.com wrote: 
Hi David,

Let me see if I can spring a few of your traps :-)

I assume that a "back-channel" is some magical combination of a 
return address and message correlation implicitly supplied by 
the underlying mechaninsm by which messages are being exchanged.

In other words, request-response just works.

I'm guessing you are asking for us to define that in more formal
terms in our spec, assuming we add the term?

 
   * Does email have a back-channel?
 

Reply-To, MessageId/In-Reply-To, it's certainly possible:

http://www.w3.org/TR/soap12-email

 
   * Does a raw TCP connection have a back-channel?
 

possibly, if you place significance on the order of messages.

 
   * Does a raw UDP packet have a back-channel?
 

nope.

 
   * Does BEEP have a back-channel?
 

er, possibly, depending on the profile. 
A bit like asking if Java has polynomials, no? 

RFC3288's http://iana.org/beep/soap supports the request/response MEP

 
   * Does XMLP <message/> have a back-channel?
 

er, SOAP abstracting away the transport is why we're here ..

 
   * Does XMLP <iq/> have a back-channel?
 

doesn't SOAP over XMPP use one?
http://www.xmpp.org/extensions/xep-0072.html#binding-operation-request-sendingreceiving


 
and finally ...

   * If a binding tells me "I have a back-channel", just what can I
     count on?
 

request-response. probably.

Paul