LEMONADE Working Group E. Burger
Internet-Draft BEA
Intended status: Informational G. Parsons
Expires: May 15, 2008 Nortel
November 12, 2007
LEMONADE Architecture - Supporting OMA Mobile Email (MEM) using Internet
Mail
draft-ietf-lemonade-architecture-00.txt
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Abstract
This document specifies the architecture for mobile email, as
described by the OMA, using Internet Mail protocols. This
architecture is the basis of the work of the LEMONADE WG and is a
guidleine for the LEMONADE Profile.
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Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. OMA Mobile Email (MEM) . . . . . . . . . . . . . . . . . . . . 5
2.1. OMA MEM Requirements . . . . . . . . . . . . . . . . . . . 5
2.2. OMA MEM Architecture . . . . . . . . . . . . . . . . . . . 5
2.2.1. OMA MEM logical Architecture . . . . . . . . . . . . . 5
2.2.2. OMA MEM Deployment Issues . . . . . . . . . . . . . . 7
2.3. OMA MEM Technical Specification . . . . . . . . . . . . . 8
3. IETF LEMONADE Architecture . . . . . . . . . . . . . . . . . . 9
3.1. Relationship between the OMA MEM and LEMONADE logical
architectures . . . . . . . . . . . . . . . . . . . . . . 10
3.2. LEMONADE realization of OMA MEM with non-LEMONADE
compliant servers . . . . . . . . . . . . . . . . . . . . 12
3.2.1. LEMONADE realization of OMA MEM with non-LEMONADE
IMAP servers . . . . . . . . . . . . . . . . . . . . . 12
3.2.2. LEMONADE realization of OMA MEM with non-IMAP
servers . . . . . . . . . . . . . . . . . . . . . . . 13
4. Filters and server to client notifications and LEMONADE . . . 14
5. Notifications objectives . . . . . . . . . . . . . . . . . . . 16
6. Security considerations . . . . . . . . . . . . . . . . . . . 17
7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 18
8. Version history . . . . . . . . . . . . . . . . . . . . . . . 19
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
Intellectual Property and Copyright Statements . . . . . . . . . . 24
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1. Introduction
This document describes the architecture of OMA mobile email (MEM)
using Internet Mail protocols defined by the IETF. Many of these
protocols have been enhanced by the LEMONADE work group for use in
the mobile environment and are summarized in the LEMONADE profile [5]
and its revision LEMONADE profile bis [6]. This document shows how
the OMA MEM Requirement document [3] , OMA MEM Architecture [2] and
OMA MEM Technical Specification [4] relate to the work of LEMONADE.
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2. OMA Mobile Email (MEM)
The OMA Mobile Email (MEM) sub-working group has spent some time
studying the requirements and architecture of mobile email. IETF
LEMONADE has been liaising with them and have based much of our
Internet Mail enhancements based on their input. This section
summarizes the output of the OMA.
2.1. OMA MEM Requirements
The OMA MEM activity has collected a set of use cases and derived
requirements for a mobile email enabler (MEM). the resulting work is
summarized in OMA MEM Requirements [3]. Some requirements relates to
email protocols, some involve other OMA technologies outside the
scope of IETF and some relate to implementations and normative
interoperability statements for clients and servers.
2.2. OMA MEM Architecture
This section gives a brief introduction to the OMA MEM Architecture.
2.2.1. OMA MEM logical Architecture
The OMA MEM activity has derived a logical architecture from the
requirements and use cases described in [3]. A simplification for
illustrative purposes is shown inFigure 1, where arrows indicate
content flows.
__________
| Other |
----| Mobile |<---
| | Enablers | |
| |__________| |
|ME-4 |ME-3
_v____ ___v____ ________
| | | | | |
| MEM |ME-1 | MEM | I2 | Email |
|Client|<------->| Server |<---->| Server |
|______| ME-2|________| |________|
^
|ME-5
|
Figure 1: Basic OMA MEM logical architecture
It identifies the following elements:
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o The MEM client which implements the client-side functionality of
the OMA Mobile Email Enabler. It is also responsible for
providing the mobile email user experience and interface to the
user and storing the email and data to be sent to the MEM server
when not connected.
o The MEM server which implements the server-side functionality of
the OMA Mobile Email Enabler (MEM).
o The MEM protocol between the MEM Client and MEM Server. It is
responsible for all the inband data exchanges that take place
between the MEM client and server in order to update the MEM
client with email server changes, the email server with changes in
the MEM client and to send new email from the email server.
o Other OMA enablers are needed to directly support the mobile email
enabler. They are out of scope of IETF but they may include
support for:
* Client provisioning and management for over the air
installation of the MEM client on the device, provisioning of
its settings and revocation
* Messaging enablers for outband notification, where outband
notifications that are server to client event exchanges not
transported by the MEM protocol but via other channels.
OMA identifies different interfaces:
o ME-1: MEM client interface to interact via the MEM protocol with
the MEM server
o ME-2: Corresponding interface of the MEM server
o ME-3: Outband MEM server interfaces (e.g. to support generation of
server to client notifications).
o ME-4: Outband MEM client interfaces (e.g. to receive server to
client notifications).
o ME-5: Interface for management of MEM enabler server settings,
user preferences and filters (globally and per account)
The MEM server enables an email server. In a particular
implementation, the email server may be packaged with (internal to
it) the MEM server or be in a separate component. In such cases,
interfaces to the email server are out of scope of the OMA MEM
specifications. In the present document, we focus on the case where
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the backend consists of IETF IMAP and Submit servers. However,
relationship to other cases are also discussed. The I2 interface is
an OMA notation to designate protocol / interfaces that are not
specified by the MEM enabler but may be standardized elsewhere.
2.2.2. OMA MEM Deployment Issues
The OMA MEM Architecture document [2] further identifies deployment
models.
2.2.2.1. OMA MEM proxy
The OMA MEM Architecture document [2] identifies OMA MEM server
proxies as server components that may be deployed ahead of firewalls
to facilitate traversa of firewalls.
2.2.2.2. OMA MEM deployment cases
OMA MEM identifies that each component (MEM client, MEM servers,
Other enablers and email server) may be deployed in different
domains, possibly separated by firewalls and other network
intermediaries. MEM proxies may be involved in front of firewall
that protects the MEM server domain.
OMA MEM target support of configurations where:
o All components are within a same domain (Mobile operator)
o MEM client and other enablers are in the mobile operator domain, a
MEM proxy is involved and MEM server and email server are in the
domain of the email service provider
o MEM client and other enablers as well as a MEM proxy are in the
mobile operator domain, MEM server and email server are in the
domain of the email service provider
o MEM client and other enablers are in the mobile operator domain, a
MEM proxy is in a third party service provider domain and MEM
server and email server are in the domain of the email service
provider
o MEM client, other enabler and MEM server are in the mobile
operator domain and email server is in the domain of the email
service provider
o MEM client and other enablers are in the mobile operator domain,
MEM server is in a third party service provider domain and the
email server is in the domain of the email service provider
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2.3. OMA MEM Technical Specification
The OMA MEM activity will conclude with a specification for a mobile
email enabler (MEM). The ongoing work is in OMA MEM Technical
Specification [4]. LEMONADE is a basis for the mechanism, however,
some additional details that are outside the scope of IETF will also
be included.
OMA provides ways to perform provisioning via OMA client provisioning
and device management. Other provisioning specifications are
available (e.g. SMS based).
OMA provides enablers to support outband notifications: the outband
notification mechanisms. Also, OMA XDM may be considered also for
outband filter changes. .
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3. IETF LEMONADE Architecture
This section gives a brief introduction to the LEMONADE Architecture.
The IETF LEMONADE activity has derived a LEMONADE profile [5] with
the logical architecture represented in Figure 2, where arrows
indicate content flows.
______________
| |
_________| Notification |
| | Mechanism |
| |______________|
|Notif. ^
|Protocol |
| ___|______
| | | _____
__v__ IMAP | LEMONADE | ESMTP | |
| |<----------->| IMAP |<---------------| MTA |
| MUA |- | Store | |_____|
|_____| \ |__________|
\ |
\ |URLAUTH
\SUBMIT |
\ ____v_____
\ | | _____
\ | LEMONADE | ESMTP | |
---->| Submit |--------------->| MTA |
| Server | |_____|
|__________|
Figure 2: LEMONADE logical architecture
The LEMONADE profile [5] assumes:
o IMAP protocol [7] including LEMONADE profile extensions [5]
o SUBMIT protocol (SMTP [9], ...) including LEMONADE profile
extensions
o LEMONADE profile compliant IMAP store connected to MTA (Mail
Transfer Agent) via ESMTP [8]
o LEMONADE profile compliant Submit server connected to MTA via
ESMTP
o Lemonade profile message store / submit server protocols (URLAUTH)
(see [5]).
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o Outband server to client notifications relying on external
notification mechanisms (and notification protocols) that may be
out of scope of the LEMONADE profile.
o A LEMONADE aware MUA (Mail User Agent). While use of outband
notification is described in the LEMONADE profile, support for the
underlying notifications mechanisms/protocols is out of scope of
the LEMONADE specifications.
Further details on the IETF email protcol stack and architecture can
be found in [16]
3.1. Relationship between the OMA MEM and LEMONADE logical
architectures
Figure 3 illustrates the mapping of the IETF LEMONADE logical
architecture on the OMA MEM logical architecture.
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_____________________
| Other_Mob. Enablers |
| |--------------| |
_________| Notification | |
| | | Mechanism | |
| | |______________| |
|Notif. |____________^________|
|Protocol ______|__________
ME-4 | | ___|_ME-3_ |
___|____ | | | | _____
| __v__ | IMAP | | LEMONADE | | ESMTP | |
|| |<----------->| IMAP |<-----------| MTA |
|| MUA || ME-2a | | Store | | |_____|
||_____||\ME-1 | |__________| |
| MEM | \ | | |
| Client| \ | |URLAUTH |
|_______| \SUBMIT | |
\ | ____v_____ |
\ | | | | _____
\ | | LEMONADE | | ESMTP | |
---->| Submit |----------->| MTA |
ME-2b | | Server | | |_____|
| |__________| |
|MEM Email |
|Server Server|
|_________________|
^
|ME-5
|
Figure 3: Mapping of LEMONADE logical architecture onto the OMA MEM
logical architecture.
As described in Section 3, the LEMONADE profile assumes LEMONADE
profile compliant IMAP stores and Submit servers. Because the
LEMONADE profile extends the IMAP store and the submit server, the
mobile enablement of email provided by the LEMONADE profile is
directly provided in these server. Mapped to OMA MEM logical
architecture, for the case considered and specified by the LEMONADE
profile, the MEM server and email server logically combined. They
are however split into distinct LEMONADE message store and LEMONADE
submit server. ME-2 consists of two interfaces ME-2a and ME-2b
associated respectively to IMAP extended according to the LEMONADE
profile and SUBMIT extended according to the LEMONADE profile.
The MUA is part of the MEM client.
External notifications mechanism can be part of the other OMA enabler
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specified by OMA (or other activities).
3.2. LEMONADE realization of OMA MEM with non-LEMONADE compliant
servers
The OMA MEM activity is not limited to enabling Lemonade compliant
servers. It explicitly identifies the need to support other
backends.
3.2.1. LEMONADE realization of OMA MEM with non-LEMONADE IMAP servers
Figure 4 illustrates the case of IMAP servers that are not (yet)
LEMONADE compliant. In such case, the I2 interface between the MEM
server components and the IMAP store and submit server are IMAP and
SUBMIT.
______________
| |
_________| Notification |
| | Mechanism |
| |______________|
|Notif. ^
|Protocol |
| ___|______ _____________
| | LEMONADE | | | _____
__v__ IMAP | MEM | IMAP |NON-LEMONADE | ESMTP | |
| |<--------->|Enabler |<------>|IMAP |<----->| MTA |
| MUA |\ ME-2a | Server | |Store | |_____|
|_____| \ |__________| |_____________|
\ |
\ |URLAUTH
\SUBMIT |
\ ____v_____ _____________
\ | | | | _____
\ | LEMONADE | SUBMIT |NON-LEMONADE | ESMTP | |
-->| MEM | |Submit | | |
| Enabler |------->|Server |------>| MTA |
ME-2b | Server | | | |_____|
|__________| |_____________|
Figure 4: Architecture to support non-LEMONADE IMAP servers with a
LEMONADE realization of OMA MEM enabler.
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3.2.2. LEMONADE realization of OMA MEM with non-IMAP servers
Figure 5 illustrates the cases where the message store and submit
servers are not IMAP store or submit servers. They may be POP3
servers or other proprietary message stores.
______________
| |
_________| Notification |
| | Mechanism |
| |______________|
|Notif. ^
|Protocol |
| ___|______ _____________
| | LEMONADE | | | _____
__v__ IMAP | MEM | I2 |Proprietary | ESMTP | |
| |<--------->|Enabler |<------>|Message |<----->| MTA |
| MUA |\ ME-2a | Server | |Store | |_____|
|_____| \ |__________| |_____________|
\ |
\ |URLAUTH
\SUBMIT |
\ ____v_____ _____________
\ | | | | _____
\ | LEMONADE | I2 |Proprietary | ESMTP | |
-->| MEM | |Submit | | |
| Enabler |------->|Server |------>| MTA |
ME-2b | Server | | | |_____|
|__________| |_____________|
Figure 5: Architecture to support non-IMAP servers with a LEMONADE
realization of OMA MEM enabler.
I2 designates proprietary adapters to the backends. They may invoved
functions performed in the message stores or submit server as well as
in the MEM enabler server.
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4. Filters and server to client notifications and LEMONADE
OMA MEM RD [3] and AD [2] emphasize the need to provide mechanisms
for server to client notifications of email events and filtering.
Figure 6 illustrates how notification and filterings are introduced
in LEMONADE profile [5].
______________
| |
_________| Notification |
| | Mechanism |
| |______________|
|Notif. ^
|Protocol -------\ _|_
| ______| ___\>|NF|____
| | | ---- | _____
__v__| IMAP |__ LEMONADE |___ ESMTP __| |
| |<-------->|VF| IMAP |DF |<--------|AF| MTA |
| MUA |\ ME-2a |-- Store |-^- --|_____|
|_____| \ |_____________| |
\_\_______________|_______|
\ |URLAUTH
\SUBMIT |
\ ____v_____
\ | | _____
\ | LEMONADE | ESMTP | |
---->| Submit |--------------->| MTA |
ME-2b | Server | |_____|
|__________|
Figure 6: Filtering mechanism defined in LEMONADE architecture
In Figure 6, four categories of filters are defined:
o AF: Administrative Filters - Set up by email service provider. AF
are typically not configured by the user and set to apply policies
content filtering, virus protection, spam filtering etc...
o DF: Deposit Filters - Filters that are executed on deposit of new
emails. They can be defined as SIEVE filters [10]. They can
include vacation notices.
o VF: View Filters - Filters that define which emails are visible to
the MUA. View filters can be performed via IMAP using the
facilities described in [6].
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o NF: Notification Filters - Filters that define for what email
server event an outband notification is sent to the client, as
described in [6].
The filters are manageable from the MUA:
o NF and DF: via SIEVE management protocol
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5. Notifications objectives
According to these analyses, there is a need to support: # Mechanisms
for event-based (server to client) synchronization: * Defines the
relationship between notification mechanisms and the IMAP4 protocol -
To minimize the latency observed for email events on the email server
to be reflected in the email client. - To avoid unnecessary polling
and requests from the e-mail clients: . To reduce the total amount
of data to be exchanged between email server and client, e.g. by
allowing the email client to select which messages to synchronize and
how to synchronize. . To reduce the amount of transactions. * Needs
to cope with possible lost or delayed notifications * Support in-band
(within IMAP band) and out-band notifications (Exchanged via other
servers / enablers). - Specified in ways that are network transport
independent but may contain some bindings to particular notification
channels (e.g. SMS binary, WAP Push, SIP Notification, ...) - When
the email client is connected to the email server, only inband
notifications is expected take place * Defines notification payload
for inband and outband mechanisms. # Server-side filtering to decide
which messages will be accessible by the email client. * Filtering
results into the following logical types: - Type A: Messages filtered
out and not accessible by the email client (no notification, no
header access, no access) - Type B: Messages that are accessible by
the mobile e-mail enabler client but no outband notification takes
place. Inband notification might however take place if email client
is already connected to email server. - Type C: Messages that are
accessible by the e-mail client for which notifications (outband or
inband) are always sent to the email client. # Notions of Filters: *
View filters: Filters that determine which email messages are of type
B and C or A * Notification filters: Filters that determine which
email messages are of type C or B * Event filters: Filters that
determines what events are to be notified to the client # Mechanisms
to allow the user to update the filters from the email client #
Mechanisms to allow configuration and exchange of settings between
the client and the server in band or outband: - Server to client:
e.g. server ID, account name, policies, ... - Client to server: e.g.
rules filters vacation notices, notification channel, ...
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6. Security considerations
This specification provides no security measures beyond those in the
referenced Internet Mail and LEMONADE documents.
We note however that there are security risks associated to:
o Outband notifications
o Server configuration by client
o Client configuration by server
o Presence of MEM proxy servers
o Presence of MEM servers as intermediaries
o Measures to addess the need to traverse firewalls
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7. IANA considerations
No specific IANA considerations have been identified that are not
covered by the different drafts and RFCs included in the realization
described in this document.
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8. Version history
Version 0: This document was extracted from sections of
draft-ietf-lemonade-profile-bis-05.txt and
draft-ietf-lemonade-notifications-04.txt.
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9. Acknowledgements
The authors acknowledge and appreciate the work and comments of the
IETF LEMONADE working group and the OMA MEM working group.
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10. References
[1] Bradner, S., "Key words for use in RFCs to Indicate
Requirements Levels", RFC 2119, BCP 14, March 1997.
[2] "Mobile Email Architecture Document",
OMA http://www.openmobilealliance.org/, June 2007.
[3] "Mobile Email RequirementS Document",
OMA http://www.openmobilealliance.org/, Oct 2005.
[4] "Mobile Email Technical Specification", OMA (Work in Progress),
http://www.openmobilealliance.org/, Oct 2007.
[5] Maes, S. and A. Melnikov, "LEMONADE profile", RFC 4550.
[6] Maes, S. and A. Melnikov, "LEMONADE profile bis",
draft-ietf-lemonade-profile-bis-0x (work in progress).
[7] Crispin, M., "IMAP4, Internet Message Access Protocol Version 4
rev1", RFC 3501, March 2003.
[8] Klensin, J., "SMTP Service Extensions", RFC 1861,
November 1995.
[9] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
April 2001.
[10] "SIEVE", Internet Draft draft-ietf-sieve-3028bis-12.
[11] Leiba, B., "IMAP4 IDLE command", RFC 2177, June 1997.
[12] Newman, C., "Internet Message Store Events",
draft-newman-lemonade-msgevent-0x (work in progress).
[13] "Open Mobile Alliance Email Notification Version 1.0",
OMA http://www.openmobilealliance.org/, August 2002.
[14] Maes, S. and et Al., "CONVERT", draft-ietf-lemonade-convert-0x
(work in progress).
[15] Melnikov, A. and et Al., "IMAP URL Scheme",
draft-ietf-lemonade-rfc2192bis-0x (work in progress).
[16] Crocker, D., "Internet Mail Architecture",
draft-crocker-email-arch-0x (work in progress).
[17] Melnikov, A. and et Al., "IMAP4 extension for quick reconnect",
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draft-ietf-lemonade-reconnect-0x (work in progress).
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Authors' Addresses
Eric Burger
BEA Systems, Inc.
Boston, MA
USA
Phone: +1 781 993 7437
Email: eburger@bea.com
Glenn Parsons
Nortel Networks
3500 Carling Avenue
Ottawa, ON K2H 8E9
Canada
Phone: +1 613 763 7582
Email: gparsons@nortel.com
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