AUTD on Unreliable GPRS Networks becomes Almost-Up-To-Date

Published Jul 18 2006 06:14 PM 821 Views

Exchange Server 2003 provides a feature for users of Windows Mobile 2003 devices to receive their email on their device soon after it arrives in their mailbox.  We call this feature Always-Up-To-Date (AUTD) notifications and it can be enabled using the Mobile Services property page under Global Settings in Exchange System Manager. For users with mobile devices that are a bit older than those running on Windows Mobile 5 and the Microsoft Security and Features Pack, it's a step forward from scheduled sync.  Unfortunately, the feature relies on some technologies that can sometimes hinder its performance, and, in some cases, prevent it from working altogether.  I'll be discussing these setbacks below.  Exchange Direct Push, available in Service Pack 2 solves these problems. See Sami Khoury's blog post, Solving the Phone Synchronization Problem End-to-End, for a technical discussion of this new solution.

 

In the released version of Exchange Server 2003, AUTD makes use of SMTP-to-SMS technology that is provided by mobile operators in order to alert a Windows Mobile 2003 or later device that an item has arrived in the user's mailbox.  The SMS alert tickles the ActiveSync software on the device so that it connects back to Exchange Server and syncs down any new items that have arrived since the last sync session.  For many Exchange users, this feature works great but some issues have surfaced as enumerated below:

 

-      Not all mobile operators offer the SMTP-to-SMS service to their customers.  This is basically the ability to send messages to your device using an email address. We recognized this service barrier during the development of AUTD and were working on a parallel solution whereby Exchange enterprise customers would be able to send the SMTP messages to Microsoft's data center.  Microsoft would then convert these to SMS and send them to a mobile operator's SMS gateway.  Since most, if not all, modern day cell phones support SMS (aka Text Messaging), we thought we had this solved. However, the solution obviously would require connectivity agreements between Microsoft and mobile operators around the world.  Alas, we found that mobile operators were not interested enough in the feature to sign up. For Exchange customers of these mobile operators, AUTD is then not an option and schedule synchronization will have to do.

 

-      Connectivity can be hit-or-miss on wireless networks such as GPRS. Anyone who has a cell phone can attest to dropped calls every now and then. This can result in sync sessions that are disconnected or never initiated when out-of-range and also AUTD notifications being queued or altogether dropped when sent from the enterprise Exchange server.  Coupling this with the fact that users may be paying for their SMS text messaging on a per-message or per-byte basis, we needed to be careful about how often and when the Exchange server should initiate sync with an AUTD notification. The Windows Mobile guys were also thinking about this and built in a batching mechanism for dealing with incoming SMS from the Exchange server.  SMS messages are queued at the mobile operator's datacenter, and then sent when a user's device comes in to range.  ActiveSync on the device needs to swallow these queued messages and initiate just one sync back to the server.  So the device waits for three minutes once an AUTD notification is received before initiating server sync.  This can be fined tuned by changing the DWORD registry value (using a 3rd party registry editor) on the device:

 

HKCU\Software\Microsoft\AirSync\Settings\NotifySyncDelay

 

Since the release of Exchange Server 2003 three years ago, we've seen how these technological shortcomings have impacted some of our customers. With the release of Service Pack 2, you will see a radical change for the better in how we ensure that your mobile email remains up-to-date.  The SMTP/SMS technology is totally replaced with an "always connected" implementation.  I really shouldn't say "replaced" because the original feature will still be available for users of older devices.  However, any users of latter-day devices that support the new "always connected" technology should take advantage of the refinements that have been made.  I should mention that both of these features are available for implementation to all licensees of Exchange Active Sync so look for these features coming soon to your favorite device.

 

- Greg Bolles

7 Comments
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