MBOX-Line: From mrc+imap at panda.com  Mon Oct  4 10:56:08 2010
To: imap-protocol@u.washington.edu
From: Mark Crispin <mrc+imap@panda.com>
Date: Fri Jun  8 12:34:45 2018
Subject: [Imap-protocol] Fwd: iOS IMAP IDLE (Standard "Push Email")
	Deficiency, Explanation?
In-Reply-To: <4CAA0F5C.7030009@lists.grepular.com>
References: <352410DE-19D8-4EE4-8741-AB82741D7A18@sabahattin-gucukoglu.com>
	<4CAA0F5C.7030009@lists.grepular.com>
Message-ID: <alpine.OSX.2.00.1010041034520.392@hsinghsing.panda.com>

On Mon, 4 Oct 2010, Mike Cardwell wrote:
> This makes complete sense. In order to use IMAP Idle on a phone, it
> would have to keep a TCP connection open, and therefore a 3G connection
> open.

Say what?

Is that a UMTS requirement?  It certainly is not a TCP requirement.  TCP
is built on IP which is completely datagram.  I have built on-demand
networks which shut down until signaled back on, and then happily resumed
all the active TCP sessions even though the "network connection" had been
powered off for days.  The same signaling mechanism that is used for SMS
can be used to restart the mobile device radio.

That is how push works on BlackBerry.

The real problem with IDLE is that it is NAT-unfriendly.  Most NAT boxes
drop the mapping after a period of client inactivity, and send a TCP RST
to the server if the server resumes activity before the client.  Most
users don't see this, since if the client resumes activity first the same
mapping is created and no RST is sent.

No desktop client should ever use IDLE; it's unnecessary unless you using
radio.  Unfortunately, most desktop clients do implement IDLE, and then
any user who uses that client behind NAT complains about losing their
connection to the server.  A certain client that shall go unnamed (but for
which you should look out) just stops announcing new mail and shows a very
inconspicuous icon that indicates that there isn't a connection to the
server.

That, in turn, leads either to removing IDLE from the server or doing a
workaround in IDLE that makes IDLE pointless.

Notwithstanding any of the above, I stand by my previous statement.  It's
a waste of time and effort to worry overmuch about iOS4.  Android is the
way forward.

-- Mark --

http://panda.com/mrc
Democracy is two wolves and a sheep deciding what to eat for lunch.
Liberty is a well-armed sheep contesting the vote.

