ietf-lemonade-server-to-client-notifications-00.txt

Internet DRAFT - draft-ietf-lemonade-server-to-client-notifications

draft-ietf-lemonade-server-to-client-notifications

Last Version:	draft-ietf-lemonade-server-to-client-notifications-00.txt	Tracker Entry
Date:	`20-Jul-2004`
Disposition:	.draft-smaes-lemonade-s2c-notification-reqs

Lemonade
Internet Draft: Lemonade Server to Client S. H. Maes
Notifications
Document: draft-ietf-lemonade-server-to-client- C. Wilson
notifications-00.txt
Expires: January 2005 July 2004

Lemonade Server to Client Notifications

Status of this Memo

This document is an Internet-Draft and is subject to all provisions
of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

Abstract

Lemonade server to client notifications provides some extensions to
the IMAPv4 Rev1 protocol [RFC3501] for optimization in a mobile
setting, aimed at delivering extended functionality for mobile
devices with limited resources. These notifications support pushing
crucial changes actively to a client, rather than requiring the
client to initiate contact to ask for state changes.

Conventions used in this document

In examples, "C:" and "S:" indicate lines sent by the client and
server respectively.

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 [RFC2119].

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An implementation is not compliant if it fails to satisfy one or more
of the MUST or REQUIRED level requirements for the protocol(s) it
implements. An implementation that satisfies all the MUST or REQUIRED
level and all the SHOULD level requirements for a protocol is said to
be "unconditionally compliant" to that protocol; one that satisfies
all the MUST level requirements but not all the SHOULD level
requirements is said to be "conditionally compliant." When
describing the general syntax, some definitions are omitted as they
are defined in [RFC3501].

Table of Contents

Status of this Memo...............................................1
Abstract..........................................................1
Conventions used in this document.................................1
Table of Contents.................................................2
1. Introduction...................................................3
1.1. The Poll Model vs. the Push Model.........................3
1.2. The Server-Side Filtering in Lemonade.....................4
1.3. Synchronization Techniques................................5
1.3.1. State-Comparison-Based Synchronization...............5
1.3.2. Event-based Synchronization..........................6
2. The Lemonade Server to Client Notification Design..............7
2.1. Implementing Filters......................................7
2.1.1. The View Filter......................................8
2.1.2. The Priority/Notification Filter.....................8
2.1.3. The Syntax to define Priority/Notification Filters...8
2.2. Connectivity Models.......................................9
2.2.1. In-Response Connectivity.............................9
2.2.2. Inband Connectivity..................................9
2.2.3. Outband Connectivity................................10
2.3. Keeping the Client In Sync with the Mobile Repository....10
3. Events........................................................11
3.1. Message Events Sent During Inband and Inresponse Mode....11
3.2. Folder Events............................................12
3.3. PIM Events...............................................12
4. Interactions between the Lemonade Client and Lemonade Server..12
4.1. Revisions to IMAPv4 Rev1 Behavior........................12
4.1.1. UID.................................................12
4.1.2. Mobile Repository...................................12
4.1.3. IDLE................................................13
4.1.4. LEMONADESETPREF & LEMONADEGETPPREFS.................13
4.1.5. LEMONADEFILTER......................................13
Security Considerations..........................................15
References.......................................................15
Normative Appendices.............................................16
A. Event Payload..............................................16

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A.1. Event Payload in Clear Text for Lemonade Sessions.....16
A.2. Outband Channel Event Payload.........................16
Non-Normative Appendices.........................................17
B. Use Cases..................................................17
B.1. State Comparison-Based Sync...........................17
B.2. Event-Based Sync......................................18
Authors Addresses................................................19
Intellectual Property Statement..................................19
Full Copyright Statement.........................................19

1. Introduction

The Lemonade Server to Client Notifications extends IMAPv4 Rev1
[RFC3501]. The client devices in this document are assumed to be
wireless with limited resources. However, this should not be seen as
constraining. The Lemonade Server to Client Notifications can be
bound to any transport protocol for inband and outband connectivity.
These notifications inform the client of changes in an end user's
mailbox. This document will define what events and conditions
generate notifications, as well as how the server will inform the
client of these notifications. In addition, it covers how the client
will process these notifications to maintain email synchrony.

The organization of this document is as follows. The rest of this
section introduces the concepts of Lemonade Server to Client
Notifications so the reader can gain an understanding of the concepts
that drive this design. Section 2 discusses actual design decisions
for Lemonade Server to Client Notifications. Section 3 defines the
bindings for expressing events, while Section 4 is the main body of
the protocol, which describes the interactions between the Lemonade
server and client. Next are sections concerning security
considerations, and references. Finally, there are normative and
non-normative appendices, which provide useful information for those
who wish to implement the Lemonade Server to Client Notifications.

1.1. The Poll Model vs. the Push Model

This section discusses two different models for exchanging
notifications from the server to the client. Today, most of the
existing email clients implement a polling model, where the end user
is notified of changes to an email account only after the email
client polls the server for changes. How long it takes a client to
learn of a change on the server is thus dependent on how often the
client polls for changes. Many clients can poll at high rates so
that the client can quickly learn of changes and reflect them on the
client display to achieve a quasi-real time synchronization
experience for the end user. Because the client must continuously

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poll the server for changes, the bandwidth requirements can be quite
high and the connection quality must be good in order to provide a
quasi-real time experience to the user. The periodic poll model is
used on conventional email clients and is illustrated in Figure 1.

+--------------------+ Poll +--------------+
| | <------------ | |
| Mail Server | | Email Client |
| | ------------> | |
+--------------------+ Response +--------------+

Figure 1: Periodic Poll Model

Another way to achieve synchronization is for the email server to
initiate a session with the client when a crucial change to an email
occurs, which is the push model. When important events happen to a
userÆs email account, the server informs the client device about the
event, and then the client can respond to that event as necessary. In this case, the client device does not need to periodically poll
the mail server, so the push model is particularly effective in the
mobile computing environment when the cost of constant polling is
high. The Lemonade Server to Client Notification Specifications
define the semantics for pushing events to a client. The push model
is seen in Figure 2.

Event +----------------+ Push +--------------+
--------> | Mail Server | ---------> | Email Client |
+----------------+ +--------------+

Figure 2: Push Model

1.2. The Server-Side Filtering in Lemonade

The Lemonade profile and Lemonade Server to Client Notification
protocol is meant to support mobile client devices with memory and
connectivity constraints. Due to these constraints, an end user may
want to specify filters to limit the number of notifications sent.
These filters separate their emails into different sets that the
server should handle differently. All end users have a complete
repository, which includes all their email messages that are stored
on a server. The end user may want to receive a small subset of
these messages on their client device, which are to be included on
the mobile device. The messages on the device are split further into
two categories, lower priority messages that the user chooses to wait
for until it can poll the server and higher priority messages that
the user would like to be notified of as soon as possible by the
server. All three repositories have the same set of folders.

+----------------+ +--------------+ +------------+

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Figure 3: Filters and Repositories

Formally, a repository consists of a set of folders, and each folder
has both a name and a set of messages associated with it. While the
three repositories all have folders with the same name, there may be
different messages in them. The complete repository consists of all
folders of an end user and all the associated emails for each of
those folders. Messages in the complete repository that pass the
view filter make up the poll repository. An end user can specify
exactly one view filter per folder per device. In addition, there is
a second layer of filtering, called priority or notification filters,
and there is exactly one priority filter per folder per device. The
push repository is the set of all the messages in the complete
repository that pass both the view and the priority filters.

From this point forth, it can be assumed that an event in this
document refers to only and all changes to messages in the mobile
repositories. When the client connects to the server and polls for
messages, it can determine what changes have occurred to messages
that passed the view filters. Whenever an event occurs to a message
that passes the view and priority filters, the server actively pushes
a notification to the client.

1.3. Synchronization Techniques

After a client receives a notification that informs it that changes
have occurred to a mailbox, it needs to employ a synchronization
technique to reflect the server side changes onto the client device.
There are many techniques for determining what the changes between a
server and client are. In this section, two techniques are presented
that aim to keep a client device in sync with a given email account,
meaning the set of emails on the client device is the same as that in
the given email account.

1.3.1. State-Comparison-Based Synchronization

IMAPv4Rev1 clients use a state-comparison-based synchronization
technique to be in sync with an email account. This technique
requires the client to ask the server for information regarding all
the folders and all the messages in each folder stored on the server.
The client must then compute the difference between the server state

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and the client device state, and make all necessary changes so that
the client device state matches the server state. An example of the
interaction between the client and server in the IMAPv4 Rev1 protocol
for performing a state-comparison-based sync follows.

First, the client must retrieve the folders from the server.
C: A002 LSUB "" "*"
S: * LSUB () "/" "Drafts"
S: * LSUB () "/" "Friends"
S: * LSUB () "/" "INBOX"
S: A002 OK LSUB completed

The client must compare its folders with the responses of the command
above. If it does not have a folder, it must create that folder on
the client device. If there is a folder on the device that is not in
any of these responses, then the client must delete that folder.

Next, the client needs to make sure that the emails in each of its
folders match the server. It performs a SELECT and then a FETCH
command for each folder. A sample of a SELECT and FETCH command for
the inbox is as follows:
C: A003 SELECT ~/INBOX
S: * 60 EXISTS
S: ... more untagged responses with information about the folder
S: A003 OK SELECT completed
C: A004 FETCH 1:* (FLAGS UID)
S: * 1 FETCH (FLAGS (\Answered) UID 120)
S: * 2 FETCH (FLAGS (\Seen) UID 121)
S: ... flags for messages with message sequence numbers 3-59
S: * 60 FETCH (FLAGS () UID 250)
S: A004 OK FETCH completed

The client must go through the full list of email messages in each
folder. It must add an email in this list if it is not already on
the client. It must modify any email in this list on the client
device to reflect any changes to the mutable flags of that message.
Also, it should remove any emails on the client device not in this
list. After performing these operations, the client is in sync with
the server.

1.3.2. Event-based Synchronization

Another technique is event-based synchronization. Event-based
synchronization is used to keep the client device in sync with the
server. This method requires that the client has been fully
synchronized with the server at some earlier point. In the IMAPv4
Rev1 protocol, the client must perform a state-comparison-based sync
when it selects a folder, but then it can use event-based
synchronization to keep itself in sync after that. Although event-

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based synchronization cannot totally replace state-comparison-based
synchronization, it is a faster alternative for the client to
maintain synchrony when the server is capable of change tracking for
a client.

In event-based synchronization, the server keeps track of what
changes have occurred that are not yet reflected on the client
device. Such a change is called an event. When the client finishes
processing all events since the last time it was in sync with the
server, it is again in sync with the server. Event-based
synchronization is particularly effective when the server can push
events to the client for immediate processing. In this case, there
are likely to be only a small number of events the client needs to
process at one time.

When a Lemonade client drops a connection or accidentally disconnects
the server can retain the session and cache all events during the
time the client is disconnected. When the client reconnects it does
not need to perform a state-comparison-based synchronization again,
instead the server sends the list of pending events to the client.

2. The Lemonade Server to Client Notification Design

Lemonade Server to Client Notification assumes extensions of IMAP
with the same basic model, where the client connects to the server to
open a session to access its email account. A Lemonade client may
fetch the contents of the email account or make changes to it just as
in IMAP.

2.1. Implementing Filters

A Lemonade server should support multiple mobile devices for each
email user, and should allow each device to have one unique event
filter and a set of view filters and priority/notification filters.
The server only needs to support one connection per mobile device for
each email user. A mobile client connects to the Lemonade server by
supplying its LOGIN information, and then must inform the server of
this mobile clientÆs device ID, which is some unique identifier for
the client device. The server and client should agree on what
convention to use for this ID, and it could be a hash of IMEI. If no
device ID is given, then a regular IMAP session is initiated. The
LOGIN information is used to specify a user, while the device ID is
needed to specify the mobile client. Associated with the user and
device ID is exactly one view filter and exactly one
priority/notification filter for each folder. These filters are
saved and thus persist across Lemonade sessions. Filters can be
modified when a Lemonade session is open.

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2.1.1. The View Filter

View filters and priority/notification filters are used to filter out
email messages which match certain criteria. If an email passes
through the view filter, it is stored in the mobile repository. The
syntax for defining a view filter or notification filter includes any
combination of most of the search criteria as defined for the SEARCH
command of IMAP, in Section 6.4.4 and 7.2.5 of RFC 3501, or a days
filter. The days filter filters messages received starting a certain
number of days before the current day. The ALL search criteria, when
used alone, means that every email event satisfies the criteria. By
default, view filters are set to ALL.

Whenever a view filter is modified, the client needs to perform a
state-comparison-based sync to keep in sync with the mobile
repository since the messages in the mobile repository may have
changed.

2.1.2. The Priority/Notification Filter

Priority/Notification filters are used to select emails in the mobile
repository which match certain criteria. If an email passes through
the notification filter, it is stored in the push repository. The
syntax for defining a priority/notification filter is discussed
below. By default, priority/notification filters are set to NOT ALL
to reduce default traffic at the cost of some delays.

Because the view filter defaults to ALL and the priority/notification
filter to NOT ALL, the mobile repository will mirror the complete
repository, but none of the messages are added to the push
repository. This implies that the default behavior is equal to the
IMAPv4 Rev1 model.

The client does not need to do anything after it resets a
priority/notification filter or event filter, instead the server
should then only send out notifications that correspond to the most
up-to-date filters.

2.1.3. The Syntax to define Priority/Notification Filters

The syntax for defining a priority/notification filter is ALL, NONE,
or NEW. A priority/notification filter applies for all folders in a
push repository.
ALL -- All message events concerning messages of the push
repository will be sent to the client, such as if the message becomes
seen or deleted.
NONE -- No events should be pushed to the client.
NEW -- Only events that concern new messages arriving to the push
repository should be pushed to the client.

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This one event filter applies for all folders.

2.2. Connectivity Models

There are three connectivity models for Lemonade Server to Client
Notifications, depending on the capabilities of the Lemonade server,
the client, and the connection available between them. These models
include in-response, inband, and outband. It is explicitly stated in
what situations these three connectivity models arise.

2.2.1. In-Response Connectivity

The in-response binding scenario is the most basic one and implements
the poll model. In this case the client initiates the commands to the
Lemonade server and the server responds to client commands with
events. In this case there is no need for a persistent connection
between the client and the server. The client opens a connection only
when it needs to send commands to the Lemonade server, and that is
the only time it is notified of new events.
+--------+ +++ HTTP, etc. +--------+
| | Command +++ | |
| Client |--------------------+++--------------->|Lemonade|
| Device | +++ | Server |
| | Response + Event +++ | |
| |<-------------------+++----------------| |
+--------+ +++ +--------+
Figure 4: In-Response connection

An in-response connection can occur in several situations:
[1] HTTP/HTTPS binding
- Server Requires: HTTP/HTTPS listener for IMAPv4
- Client Requires: HTTP/HTTPS client with IMAPv4 processing
[2] TCP Binding
- Server Requires: IMAPv4
- Client Requires: IMAPv4 + no IDLE

2.2.2. Inband Connectivity

The inband binding scenario corresponds to a reliable push model. In
this case the server pushes events to the client whenever they occur.
To do so, it must have a reliable means of communication with the
client, and the client should be ready to accept such notifications.
In this case, there needs to be a persistent connection between the
client and the server so that the server can push an event at any
time. The client may optionally issue a request to retrieve more
information concerning an event.

+--------+ OOO TCP, Persistent +--------+
| | Push Event OOO HTTP, etc. | |

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| Client |<------------------OOO-----------------|Lemonade|
| Device | OOO | Server |
| | Optional Request OOO | |
| |...................OOO................>| |
+--------+ OOO +--------+
Figure 5: Inband Connection

An inband connection can occur in the following situations:
[1] TCP Binding, Always connected, IDLE
- Server Requires: IMAPv4 + IDLE
- Client Requires: IMAPv4 + IDLE, constant TCP connection
[2] Any other persistent two-way connection
- Server Requires: IMAPv4 + IDLE
- Client Requires: IMAPv4 + IDLE, constant connection

2.2.3. Outband Connectivity

The outband binding scenario corresponds to an unreliable push model.
In this case the server pushes events to the client whenever they
occur, to the best of its ability. To do so, it should be able to
send messages to the client without the need for a persistent
connection. However, the outband channel can possibly lose and
reorder messages, and there are no timing guarantees. Examples of
out-band channels include SMS, JMS, WAP Push, and UDP. As in the
inband scenario, the client may optionally open a Lemonade session
over an inband or in-response connection and send a command as a
result of receiving an event.

+--------+ Push Event XXX SMS +--------+
| |<--------------XXX---------------------| |
| Client | XXX |Lemonade|
| Device | Inband or | Server |
| | Request +O+ In-response | |
| |---------------O+O-------------------->| |
+--------+ +O+ +--------+
Figure 6: Outband Connection

Outband connectivity occurs in the following situations:
[1] A notification service from the server to the client
- Server Requires: A notification generator.
- Client Requires: A notification processor.

2.3. Keeping the Client In Sync with the Mobile Repository

Whenever a client device opens a new session, it must perform a
state-comparison-based sync with the email server so that its state
is the same as the mobile repository. Since the client has no way of

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directly detecting only changes to the repository since the last
login, it needs to retrieve information about every message in the
mobile repository and calculate the changes itself. After that
point, the client can use event-based synchronization to keep the
device in sync.

The Lemonade server can issue a session and track changes to a
selected folder for the duration of a session. Until the session is
expired, the server must log all events that occur while a client is
offline. This way, if the client temporarily loses a connection, it
does not have to worry about missing any events and needing to
perform another state-comparison-based sync. A client does have the
option though to prematurely end a session by issuing a LOGOUT
command. Additionally, Lemonade clients can remain inactive for at
least twenty four hours without being logged off the server and
without the session expiring.

3. Events

This section contains the syntax that the server uses to send events
to the client.

3.1. Message Events Sent During Inband and Inresponse Mode

The client can receive the following untagged responses from the
server:

[1] The client receives an EXISTS/RECENT event from the server
indicating a new message.
S: * 501 EXISTS
S: * 1 RECENT
Next, the client retrieves this new message using a FETCH command.
C: A02 FETCH 501 (ALL BODY[])
S: * 501 FETCH ...
S: A02 OK FETCH completed

[2] The client receives an EXPUNGE event from the server from a
message has been permanently removed from a folder.
S: * 25 EXPUNGE
The client deletes this message from the client device, as it has
been removed permanently from the folder. The client does not need
to send any command back to the server.

[3] The client receives an untagged FETCH event from the server,
which can contain just FLAG information if the event is regarding an
old message or possibly other information if the event is regarding a
new message. This event is received if a message's flags are

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changed, or in response to a new message if the user's preferences
are set to do so.
S: * 101 FETCH (FLAGS (\Seen \Deleted))
The client saves the information contained in this response
accurately in the client device.

3.2. Folder Events

This section will contain syntax for indicating folder events.

3.3. PIM Events

This section will contain syntax for indicating PIM events.

4. Interactions between the Lemonade Client and Lemonade Server

Interactions between Lemonade clients and servers are described in
[LEMONADEPROFILE].

The Lemonade Server to Client Notifications also define events to be
sent by the server to the client. These events notify the client
when there are changes to messages that match an end userÆs view
filters and notification filters, as well as any changes to a
clientÆs email folders. The syntax defined in this section is an
abstract syntax, and payloads may vary according to the communication
mechanism used. The normative appendix of this document describes
some specific payloads.

4.1. Revisions to IMAPv4 Rev1 Behavior

4.1.1. UID

The UID of email messages MUST not change across sessions. Changing
the UID of email messages requires a heavy computational burden on
the mobile client, so the server should avoid doing so. The UID of
email messages MUST not change for the duration of a session.

4.1.2. Mobile Repository

In a Lemonade session, the client can only access messages in the
mobile repository. This affects the messages returned by FETCH, UID
FETCH, etc. Message sequence numbers reflect the relative position
of messages within the given folders of the mobile repository, so the
message sequence number of an email while logged in to Lemonade may

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also differ from IMAP. When returning information about the email
account, only messages in the mobile repository are taken into
account.

4.1.3. IDLE

The server should implement the IDLE command from RFC 2177. When the
client issues this command, the server can push changes to a folder
to the client. The server may replace the EXISTS/RECENT message with
an untagged FETCH command as specified in [EXTENSIONS] (Section on
2.2.2. ¡ See LEMONADESETPREF & LEMONADEGETPPREFS). The client should
fire this command while in-session to enter inband mode, where the
server will actively push notifications to the client.

4.1.4. LEMONADESETPREF & LEMONADEGETPPREFS

The LEMONADESETPREF command is described in [EXTENSIONS]. It allows a
user to define certain configuration parameters, while the
LEMONADEGETPREFS command allows a user to retrieve the configuration
values. Any server that implements these commands must respond with
LEMONADEPREF as one of the capabilities in response to a CAPABILITY
command. It must also announce the values these parameters can be
set to in the LEMONADEPROVISION command (See [EXTENSIONS]). These
parameters affect how outband notifications are sent to the client,
as well as the format for sending new event notifications. If the
server supports LEMONADEPREF they are required to support all of the
following preferences with at least one value to set each preference
to. They are described in [EXTENSIONS].

4.1.5. LEMONADEFILTER

The LEMONADEFILTER command allows users to set up view filters and
priority/notification filters. LEMONADEFILTER can be fired when the
state is AUTHENTICATED or SELECTED. The first argument to this
command is the folder that that filter should be applied to, or "ALL"
for all folders. Next the user specifies "V", "N", or "B" to set
either a view filter or a priority/notification filter, or both.
Following this, it must specify the filter criteria using a
combination of search criteria as defined for the SEARCH command of
IMAP, in Section 6.4.4 and 7.2.5 of RFC 3501, or the days filter.
The ALL search criteria, when used alone, means that every email
message satisfies the criteria. Or it can specify "V" or "N" to get
a view filter or priority/notification filter. In this case, the
last argument is "GET" to retrieve the filter.
By default, view filters are set to ALL, while priority/notification
filters are set to NOT ALL. This means that the mobile repository
includes all the messages in the complete repository, but none are
pushed to the client, which is the IMAPv4 Rev1 model.

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Exactly one view filter and one priority/notification filter is
associated with each folder for each device. When a new view filter
or priority/notification filter is created, it replaces the previous
filter for that folder. When a view filter is modified, the client
needs to perform a state-comparison-based sync on the client in order
for the device to be in sync with the mobile repository. The server
always sends only notifications that correspond to the most up-to-
date view filters and priority/notification filters. All filters
persist across Lemonade sessions; once set, a filter on a folder
applies until the user changes it.

Lemonade introduces a filter, the days filter, which allows a user to
specify from how many days before today it would like to see emails.
To see only today's email, a 0 should be used for the int.

lemonadefilter_cmd = tag SP "LEMONADEFILTER" SP ("ALL" / folder) SP
(("V" / "N" / "B") SP lemonadefilter_criteria) /

(("V" / "N") "GET")
lemonadefilter_criteria = (IMAPv4Rev1_searching_criteria /
days_filter)
[SP lemonadefilter_criteria]
days_filter = "DAYSBEFORETODAY" SP int
Valid States: AUTHENTICATED or SELECTED
Responses: untagged responses: lemonadefilterGet_resp
lemonadefilterGet_resp = "*" SP "LEMONADEFILTER" SP folder SP
("V"/"N")
lemonadefilter_criteria
Result: OK - filter created
NO - can't create the filter
BAD - invalid arguments

Example: The client creates a priority/notification filter for all
messages in the Inbox from "John" since Jun. 1st, 2003.
C: A001 LEMONADEFILTER INBOX P SINCE 1-Jun-2003 FROM "John"
S: A001 OK LEMONADEFILTER completed

Example: The client asks for the view filter for all the folders.
C: A001 LEMONADEFILTER ALL V GET
S: * LEMONADEFILTER ~/INBOX V ALL
S: * LEMONADEFILTER ~/TRASH V NOT ALL
S: A001 OK LEMONADEFILTER completed

Example: Stop notifications on a particular device, fired while in
AUTHENTICATED mode.
C: A001 LEMONADEFILTER ALL P NOT ALL
S: A001 OK LEMONADEFILTER ALL P NOT ALL completed

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Security Considerations

The protocol calls for the same security requirements for an in-
response and inband connectivity mode as IMAP.

For the outband connectivity mode, servers should use encryption
methods for notifications if sensitive information is included in the
payload of that notification.

When an implementation of Lemonade is proxy-based, this may create
new security issues. These issues are discussed in detail in
Appendix C, because the issues are dependent on the implementation of
this protocol rather than inherent to the protocol itself.

References

[OMA-EN] Open Mobile Alliance Email Notification Version 1.0, August
2002. http://www.openmobilealliance.org/tech/docs/EmailNot/OMA-
Push-EMN-V1_0-20020830-C.pdf

[IMAP-DISC] Austein, R. "Synchronization Operations For Disconnected
Imap4 Clients", IMAP-DISC, November 1994.
http://asg.web.cmu.edu/cyrus/rfc/draft-ietf-imap-disc-01.html

[RFC2119] Brader, S. "Keywords for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
http://www.ietf.org/rfc/rfc2119

[RFC2180] Gahrns, M. "IMAP4 Multi-Accessed Mailbox Practice", RFC
2180, July 1997.
http://www.ietf.org/rfc/rfc2180

[RFC2234] Crocker, D. and Overell, P. "Augmented BNF for Syntax
Specifications", RFC 2234, Nov 1997.
http://www.ietf.org/rfc/rfc2234

[RFC2420] Kummert, H. "The PPP Triple-DES Encryption Protocol
(3DESE)", RFC 2420, September 1998.
http://www.ietf.org/rfc/rfc2420

[RFC2616] Fielding, R. et al. "Hypertext Transfer Protocol --
HTTP/1.1", RFC 2616, June 1999.
http://www.ietf.org/rfc/rfc2616

[RFC2617] Franks, J. et al. "HTTP Authentication: Basic and Digest
Access Authentication", RFC 2617, June 1999.
http://www.ietf.org/rfc/rfc2617

Maes Expires - January 2005 [Page 15]
<Lemonade Server to Client Notifications> July 2004

[RFC2683] Leiba, B. "IMAP4 Implementation Recommendations", RFC 2683
Sep 1999.
http://www.ietf.org/rfc/rfc2683

[RFC2177] Leiba, B. "IMAP4 IDLE Command", RFC 2177, June 1997.
http://www.ietf.org/rfc/rfc2177

[RFC2818] Rescorla, E. "HTTP over TLS", RFC 2818, May 2000.
http://www.ietf.org/rfc/rfc2818

[RFC2822] Resnick, P. "Internet Message Format", RFC 2822, April
2001. http://www.ietf.org/rfc/rfc2822

[RFC3501] Crispin, M. "IMAP4, Internet Message Access Protocol
Version 4 rev1", RFC 3501, March 2003.
http://www.ietf.org/rfc/rfc3501

[LEMONADEPROFILE] Maes, S.H. and Melnikov A., "Lemonade Profile",
draft-ietf-lemonade-profile-00.txt, (work in progress), July 2004.

[EXTENSIONS] Maes, S.H., Lima R., Kuang, C., Cromwell, R., Ha, V. and
Chiu, E., "Lemonade Command Extensions", draft-maes-lemonade-
command-extensions-00.txt, (work in progress), July 2004.

Normative Appendices

A. Event Payload

A.1. Event Payload in Clear Text for Lemonade Sessions

The event payload for a Lemonade session follows the general format
explained in Section 1.3.2, and is in clear text.

A.2. Outband Channel Event Payload

The suggested payload for notifications is that suggested by the OMA,
see [OMA-EN]. This notification informs the client that some push
event has happened on the server, so it must connect to fetch the
information.

When the client finally connects, the Lemonade server has opportunity
to send other pending events for this client.

Example: new message arrives on the server and this is notified via
outband.
S: pushes SMS with the following text:

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<emn
mailbox="mailat:joe@foo.com"
timestamp="2004-02-20T06:40:00Z">
</emn>
C: needs to connect and send any command to get the pending events
and act upon them.
C: A00 Login joe password
S: * SESSION SELECTED
S: * FOLDER INBOX
S: * 100 EXITS
S: * 87 EXPUNGE
S: * 90 FETCH (FLAGS \Seen)
S: A00 OK LOGIN completed
C: must now act on the events on the order they are received,
meaning, first perform a FETCH to get new message, then expunge
message 87 and change flags of message 90.

Non-Normative Appendices

B. Use Cases

In this section some use cases on Lemonade are presented so that it
is possible to correctly understand concepts and message flow.

B.1. State Comparison-Based Sync

Each time a client logs into a new Lemonade session, it must perform
a state comparison-based sync. To synchronize with the server, the
client needs to fetch all the new messages, and all the flags of the
old messages.

The client has N messages in a given folder with highest UID = X and
is disconnected from the Lemonade server. It connects to the server
and performs the following command:

First, it retrieves all the new messages.
C: A01 UID FETCH X+1:* ALL
S: * m FETCH ...
S: ... <more new messages if they exist>
S: A01 OK FETCH completed

The client stores all this information on the device and displays
it. Next, it wishes to sync up the old messages.
C: A02 FETCH 1:m-1 (UID FLAGS)
S: * 1 FETCH (UID 3242 FLAGS (\Seen ...))
S: ... <info for 2 through n-1>
S: * n FETCH (UID 3589 FLAGS (\Seen ...))
S: A02 OK FETCH completed

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B.2. Event-Based Sync

During a Lemonade session, the client will receive events in the form
of untagged EXISTS, RECENT, EXPUNGE, or FETCH responses. The client
must respond to these events. Sometimes, it will receive these
events by polling, by issuing a Lemonade command, such as NOOP. It
can also use IDLE so that the server can push events to the client.
The example following shows how the client acts during an IDLE
command, but it should also take the same actions (minus firing and
exiting IDLE mode) when it receives these events through polling.

A client can choose to issue an IDLE command to get events pushed to
it, or it can receive events from polling using NOOP or any other
IMAP command. First the client issues the IDLE command:
C: A02 IDLE
S: + Ready for argument

Now the client can receive any of the three following untagged
responses from the server.

When the client receives an EXISTS/RECENT response from the server:
S: * 501 EXISTS
First, the client must exit from this IDLE command.
C: DONE
S: A02 OK IDLE completed
Next, the client retrieves this new message using a FETCH command.
C: A02 FETCH 501 ALL
S: * 501 FETCH ...
S: A02 OK FETCH completed
The client returns to IDLE mode by issuing another IDLE command.
C: A03 IDLE
S: + Ready for argument

When the client receives an EXPUNGE response from the server:
S: * 25 EXPUNGE
The client deletes this message from the client device, as it has
been removed permanently from the folder. The client can remain in
IDLE mode.

When the client receives an untagged FETCH response from the server,
either signally a flag change to an old message or a new message:
S: * 101 FETCH (FLAGS (\Seen \Deleted))
The client updates the information on the device for this message
appropriately.

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Authors Addresses
Stephane H. Maes
Oracle Corporation
500 Oracle Parkway
M/S 4op634
Redwood Shores, CA 94065
USA
Phone: +1-650-607-6296
Email: stephane.maes@oracle.com

Corby Wilson
Enterprise Mobility Systems
Nokia
503 Martindale Street
Suite 610
Pittsburgh, PA 15212
USA
Phone: +1-412-576-5402
Email: Corby.Wilson@nokia.com

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Full Copyright Statement

Maes Expires - January 2005 [Page 19]
<Lemonade Server to Client Notifications> July 2004

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Acknowledgement

This document is based on the work in progress described in
draft-maes-lemonade-p-imap-03.txt.

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