I like the idea of the client supplying, as part of a request,
the URL for notifications. In email, this address could be
supplied by the disposition-notification-to header, as with any
kind of receipt notification. For requests that get delivered
via IPP and POST, the address to which notifications get posted
could be supplied by the client via a URL, too. Clients would
have to know their own address, though, and make some kind of
service guarantee that they're willing to listen to responses
at that address. In some cases, the address of notification will
be different than the client address.
In email delivery for Internet Fax, we've also wanted to have
a notification protocol for "successful printing"; I'd like to
make sure that IPP and Internet Fax don't invent different
mechanisms for no good reason.
Larry
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http://www.parc.xerox.com/masinter