One of the new features in Exchange 2003 is Exchange ActiveSync.  Exchange ActiveSync allows you to synchronize your Windows Mobile 2003 Device with your Exchange mailbox over a wireless network without having to cradle the device.  The Up-to-date (UTD) feature notifies the device if there is a new item in the Exchange mailbox and the device will automatically initiate a synchronization with you mailbox.  This feature gives the user an always on and always current feeling.  The other benefits of this feature are better device resource utilization, a more consistent user experience when compared to device expectancies and this operation is done in the background without the device turning itself on.

What happens on the Device:

The UTD notification is an SMS message that is processed by the device at the TCP/IP level, so the user will never see the SMS message in their SMS Inbox.  It is a control message with a Globally Unique Identifier (GUID) in it.  The mobile client will match this GUID with the most current one that it has.  If they match, the device will schedule a synchronization to occur within 3 minutes.  The reason for the 3 minute wait is to handle the case when the device has been offline and the operator has queued up messages to be sent, when the device comes back on line all notifications are sent to the device.  We want the device to synchronize only once for these changes. 

How the message gets to the device:

The UTD notification will leave the Exchange environment as an SMTP message.  It is destine for a Mobile Operators SMTP front-end server.  This is not always available, especially in Europe and Asia.  Make sure to verify that the Mobile Operator being used does support inbound SMTP.  Once the operator receives this message, they will convert the SMTP packet into an SMS message and forward it on the the device.

How the Exchange Server 2003 processes the UTD notification:

Exchange monitors the mailbox with an Event Sink that runs in the Exchange Store.  There is an Event Registration Item in all folders that have been provisioned for Synchronization.  When a new item arrives in the folder, the Event Sink is called and creates a message containing all of the user information needed to get the message to the device.  It is then passed to the Exchange transport for verification and formatting.  A few things happen at this point.  1) The device has an expiry date assigned to it, which is checked.  If it is in the past, the notification is not sent. This expiry is set when the device synchronizes with the mailbox.  2)  The GUID in the message (mentioned above) is also verified, if it has already been sent, then the new notification will be dropped.  There is a time limit of 15 minutes for this in case the new notification is not received by the device.  3) the GUID is compressed and encoded before sending.  Once this has been accomplished, the notification is addressed to the devices SMTP address and send through the regular messaging transport.

- Steve Mattox