[e2e] was Re: A message to authors - nsdi

[Michael Welzl]

On Thu, 2008-01-10 at 14:42 +0000, Jon Crowcroft wrote:
> so google do application layer retries in a
> lot of things
> 
> the problem with that approach
> is that automatic systems above
> the network layer have no meaningful
> equivalent to the RTT estimation process that
> drives the retransmit timer process, and 
> packet conservation mechanisms in transport
> that is a part of the congestion control
> loop, so we could end up either clobbering the
> net and the end system, or using incredily
> conservative timers for the retries...

IMO, incredibly conservative timers would do the
trick for email.


> with silent failure, we need to require
> positive acknowledgement in the application
> layer as you say- but i dont want to automate
> it:) there's problably some wonderful ways
> such a loop could interact with a vacation
> mail trigger too.....(can u say feature
> interaction? :-)

There are already special messages for that kind of
app-layer ACK, and I doubt ( = hope not  :-)  ) that
reasonably implemented automated vacation messaging
systems would react to them - as they could already
get them today.

I was just looking for the information that I once dug up - I'm
sure I had it in an email somewhere, but it seems I lost it
(ah, the irony  :-)   ). Seriously, let's assume that I'm
wrong and no such message exists: then we could still use
messages like the message-disposition-notification for the
ACK from the POP or IMAP server back to my SMTP, and such
a response would typically be ignored by current automated
answering systems.

Also, let's say that you only request that service by including
a special header - it's not a default method then, but something
that you choose if you want to be totally sure that the message
was reliably delivered (like marking an important email with a
"!" as most current mail clients allow you to do).


> hey, TCP on SMTP, anyone?

Count me in - I dig layers   :-)

Cheers,
Michael