SMTP is not an application; end users don't use SMTP by itself.
MIME is only the latest in a series of versions of the
internet message format, which SMTP was tailor-made to carry.
But there is at least some precedent. ARPAnet email was originally
implemented by sending text messages over FTP and depositing them
in a file named after the recipient. But this didn't work very
well, and was soon replaced. Some TOPS-20 people layered their
SMTP implementations on top of telnet support in their kernel, but
eventually this turned out to be a Bad Idea. All of this was
long before the net had tens of millions of users, back when
casual experimentation had fewer risks associated with it.
It was also before there was a formal standardization process.
The belief in this case is that IPP is different enough from
ordinary HTTP traffic that the two should be distinguished.
> BTW, who determines whether an application can or cannot be layered
> on top of another? If is you who decides, we would have liked to hear
> this kind of strong objection much earlier in the project.
Ultimately, the IESG determines what is acceptable in an Internet
standards track protocol, with provision for appeal to the IAB.
I agree that earlier notification would have been better. But
IPP is trying to do something radically different than most
other working groups (even though it intended to be conservative),
and some of the implications of its approach were not apparent
until recently.
> If we are going to have these kind of discussions, it seems to me
> that the IAB should get involved, as they are rather fundamental
> Internet design decisions. Re-using existing infra-structure or not
> seems to be one important discussion point.
The IAB Chair participated in today's IESG conference call. A more
detailed response will be forthcoming, and the IAB Chair has requested
that IAB be in on the discussions.
Keith