Bearer +Mobility Overview

Bearer mobility allows the email Message Type Modules (MTM) to non-seamlessly +switch between networking bearers, such as, GPRS, WiFi, CDMA, GSM, and so +on. Switching between network bearers enables destination networks to connect +without dropping the connection with the remote server.

Settings

The email client MTM CEmailAccounts interfaces +are enhanced to configure the email account settings. These settings modify +the behaviour of the relevant server MTMs for the following functionality:

Non-seamless +bearer mobility

The IMAP4, POP3, and SMTP server MTMs are extended +to allow messaging applications to use the non-seamless network bearer mobility +when connecting to a destination network using the respective protocols. The +following functions are added to the CImBaseEmailSettings (CImPop3Settings, CImImap4Settings, and CImSmtpSettings) class:

SetBearerMobility
BearerMobility()

Per bearer-type +configuration for IMAP email accounts

Specifically for IMAP email +accounts, the CEmailAccounts class enables the following +per bearer-type configuration that affect the behaviour of IMAP accounts:

Download rules

Download +rules specify which parts of message to automatically download (according +to bearer type) when synchronising the contents of an IMAP email account. +You can configure an IMAP email account for IMAP download rules on each bearer +type and for each account using the CImapSyncDownloadRules class.

When +synchronising an IMAP email account you can do the following:
- Indicate that a list +of email download rules for each type of bearer must be used during the email +account synchronisations.
- Retrieve emails during +the synchronisation using the mail options specified in the list for the bearer +type that is currently in use by the connection to the server.
The CImapSyncDownloadRules class is used to store +per IMAP account sync download rules. This class describes the download rules +that provide the ability to automatically get the email content. This is configurable +on a per account and per bearer-type basis.
- Different download rules +can be specified for different bearers. For example, you can specify that +all text and attachments should be retrieved when connecting through a WiFi +connection; whereas, only text parts should be retrieved when connecting over +GPRS connection.
- Synchronisation is performed +in two stages: the email header synchronisation is performed first followed +by the email content retrieval. If the email account settings indicate that +the per-bearer-type list should not be used, or no per-bearer-type list is +defined, or the current bearer type is not listed in the per-bearer-type list, +then during the synchronisation the email headers for inbox and personal folders +are downloaded.
  
  Note: The per-bearer-type list is a set of +IMAP download and transport buffer size rules defined for each type of bearer.
- Messages that are not +previously populated are retrieved using this method. So a message that has +been populated according to GPRS settings will not be retrieved again according +to WiFi settings, if a subsequent connection is made.
- Messages that arrive +on the server while IMAP is in the IDLE state are also automatically +downloaded according to the Inbox download rules for the connected bearer +type.
- A single instance of +a set of download rules is applicable to multiple bearer types.
Transport buffer +size

Transport buffer size specifies the size of the data transferred +from server to client to get email body and attachments from an IMAP server +using a per bearer-type list of transport buffer sizes. You can configure +an IMAP account for IMAP transport buffer size on each bearer type using the CImapTransportBufferSizes class.
The +per-bearer-type list is a set of IMAP download and transport buffer size rules +defined for each type of bearer.
This class allows a client to +configure transport buffer sizes of IMAP accounts according to the bearer +type for retrieving large message parts. It is possible to specify in the +following:
- Maximum retrieve size. +Default is 20480 octets.
- Maximum outstanding +retrieve requests. Default is two outstanding requests.
Important considerations
- If there are is no bearer +type specific list defined, or the current bearer type is not listed in the +per-bearer-type list of transport buffer sizes, then the maximum retrieve +request size specified in the email account settings is used. The maximum +and default number of outstanding retrieve requests is two.
- The transport buffer +sizes that can be specified are the maximum retrieve request size sent in +IMAP retrieve requests.
- Download email body +and attachments from an IMAP server using the retrieve request buffer size +specific to the bearer type that the server connection is using.
- Download email body +and attachments from an IMAP server using the maximum number of outstanding +retrieve requests specific to the bearer type that the server connection is +using.
- A single instance of +a set of transport buffer sizes is applicable to multiple bearer types.

Bearer mobility policy plug-in

The bearer mobility +policy plug-in enables you to customise the migration behaviour of email accounts, +the bearer mobility policy plug-in is provided. It consists of an ECOM interface +class (CImMobilityPolicyPlugin) and a call-back class (MImMobilityPolicyHandler),which +allows the plug-in to issue policy decisions on an individual mobility events.