Subject: RE: [lemonade] Mobile messaging clients barriers - IMAP4 "passiva tion"

From: Mendelovich Meir <[email-masked]>
Date: Mon, 16 Jun 2003 11:01:34 +0300

Hi,
 
 I want to reply to Greg and Ned about the session maintenance issue.
 
 Mobile clients are working in very "noisy" environments: they change cells,
bearers and sometimes get out of signal. Every time that there is a sudden
momentary disconnection, the old session hangs and new one should be
initiated. Though part of the problem would be solved by underlying
standards like mobile IP, disconnections will still be a problem.
 
We solved it by building proxy that gets HTTP requests and translate them to
IMAP4. But, if the IMAP4 will include a mechanism to "passivate" a session
and reinitiate; it will scientifically improve the system. It is also very
useful in WebMail environments where the server want to reduce the number of
open IMAP4 connections by passivating sessions.
 
About the RSERPOOL WG: If I understand their goals correctly, they try to
solve the problem of server availability. We are having problems with the
connection availability.
 
        Meir :->

-----Original Message-----
From: [email-masked] [ <mailto:[email-masked]>
mailto:[email-masked]] 
Sent: Sunday, June 15, 2003 6:33 PM
To: Lawrence Greenfield
Cc: Pete Resnick; Mark Crispin; IETF LEMONADE (E-mail)
Subject: Re: [lemonade] Mobile messaging clients barriers

I also would like to understand the long running session / session
initiation issue(s). I will also point out that if reliable connections to
servers really are an issue there is an entire IETF WG devoted to solving
this particular

problem:

 <http://www.ietf.org/html.charters/rserpool-charter.html>
http://www.ietf.org/html.charters/rserpool-charter.html

If the WG decides that work in this space is in order the RSERPOOL approach
needs to at least be considered.

 -----Original Message-----
From: Vaudreuil, Greg M (Greg) [mailto:[email-masked]] 
Sent: Friday, June 13, 2003 10:59 PM
To: 'Mendelovich Meir'; IETF LEMONADE (E-mail)
Subject: RE: [lemonade] Mobile messaging clients barriers

It sounds like you are asking for an IMAP "session" to extend across
multiple short-lived TCP connections?   Can you elaborate on why leaving the
TCP connection open is a burden for the client.... is it that a wireless
circuit must be maintained?  The cost of the TCP keep-alives?    
 
If the desire is to reduce the cost of "checking messages" over a circuit
data session, then something like a suspend command that would return from
the server a session token would be useful.  A new message-checking action
could rapid-start with this token as a means to access the last shared
state.... maybe check for new messages in just 3-4 round-trips.
 
Greg V.
 
-----Original Message-----
From: Mendelovich Meir [mailto:[email-masked]]
Sent: Friday, June 13, 2003 4:55 AM
To: IETF LEMONADE (E-mail)
Subject: [lemonade] Mobile messaging clients barriers

Hi, 
 I'm very happy to see that a consensus is forming about the need to add
message submission to IMAP4. 
 But, this is only one of several barriers that prevent us from building
good mobile messaging clients. I want to raise two major problems. All the
details are in section 7.1 of the requirements document that was presented
by Wong and me in San-Francisco (
<http://www.ietf.org/internet-drafts/draft-wong-umcli-02.txt>
http://www.ietf.org/internet-drafts/draft-wong-umcli-02.txt).

1. As Alan Stebbens mentioned, server-side processing of media is crucial.
We can't download 3 mega pixel image with 30bit color depth to device that
has 100X100 pixels screen and 8bit color depth. We don't expect mail servers
to implement image processing but it is needed to allow IMAP4 servers or
mobile messaging gateways to use external transcoding engines to provide
their mobile client better experience. 

In the MMS arena it is very hot issue. OMA prepares now a standard interface
for transcoding servers. 

2. It is very hard to maintain long sessions in mobile networks. The current
statefull nature of IMAP4 prevent many clients from providing good
experience. Most of the mobile handsets that has IMAP4 client open and close
new session for each command. This kind of behaviour cause enormous load on
the server and spend lots of bandwidth. We MUST solve this problem if we
want to see real mobile e-mail solution in GPRS and CDMA1X networks.

From our experience in mobile messaging clients these two problems must be
solve to fulfill the LEMONADE goals. 

        Meir :-> 

__________________________________ 

Meir Mendelovich 
Product Engineer 
Comverse 
              
Tel:     +972-3-765 5834 
Cell:    +972-5854-3834 
Fax:    +972-3-765 5834 
E-mail: [email-masked]

---

From: Mark Crispin <[email-masked]>
Date: Mon, 16 Jun 2003 07:54:58 -0700 (PDT)

> standards like mobile IP, disconnections will still be a problem.

This sounds like a bug in the TCP/IP implementation.  Abandoning a
perfectly good connection because of a momentary outage is, to my mind, a
bad idea.  Abandoning that connection to initiate a new one is a terrible
idea.

Back in the old days, we went to great effort to preserve sessions across
network outages, and to restore communication in the session promptly when
network connectivity is restored.  A fair amount of the architecture of
TCP becomes pointless if sessions (especially in highly stateful protocols
like IMAP) are destroyed before of a hiccup in a radio link.

Nor are the "noisy environment" problems new.  Refer to the old packet
radio work of 20-30 years ago.

-- Mark --

http://staff.washington.edu/mrc
Science does not emerge from voting, party politics, or public debate.
Si vis pacem, para bellum.
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