How it works

Exchange ActiveSync is designed to synchronise e-mail, contact and calendar information with configurable filtering and truncation settings. E-mail support includes synchronisation for individual folders on demand, and smart reply and forward including configurable attachment handling - e. g. attachments can be forwarded from the server without downloading them to the device. Meeting requests are supported, as are client-side deletions.

Synchronisations are driven from the client, with client-side access to the server APIs achieved through HTTP or HTTPS POST requests - this avoids many issues with proxies and firewalls as the HTTP and HTTPS ports are rarely blocked. server responds to these POST requests with any required data, with most transactions using WBXML - a compressed binary tag version of XML, to reduce bandwidth.

The Exchange Server will supply identifiers for all objects to be synchronised, plus a key for each Exchange folder that determines the set of objects synchronised at that point. An Exchange ActiveSync Client will typically maintain a database of these identifiers and will send the last known synchronisation key to the Exchange Server on each synchronisation request - allowing the server to assume knowledge of what objects the device contains without the need to receive a complete list of object identifiers each time. If synchronisation fails part way through - say, due to a network failure - then the client can resend the previous synchronisation key to obtain any lost data.

Always-Up-To-Date

As already stated, synchronisations are driven from the client-typically by a manually started or scheduled synchronisation. However, Exchange ActiveSync also includes functionality to work as a push-solution.

In earlier versions of the protocol, Always-Up-To-Date (AUTD) synchronisation was implemented using SMS-based notifications. When new items appeared on the server an SMS was sent to the device and this would start an immediate sync. This required network support of SMTP e-mail to SMS conversion plus some clever message recognition on the client and had the potential to be cumbersome and costly to use.

However, Microsoft Exchange Server 2003 Service Pack 2 has recently been released and this new version provides an AUTD push mechanism based on an HTTP connection maintained by the device. The Exchange Server keeps the HTTP connection alive until an update occurs or a given timeout is reached, at which point it responds. If the response is a timeout rather than an update then the client has to resubmit the request for updates. Please visit the Microsoft Exchange Team Blog, for more details of how this works.

Other New Features of SP2

Exchange Server 2003 Service Pack 2 also provides the following useful enhancements:

• Additional support for task synchronisation and picture contacts
• Over-The-Air global address list lookup
• Over-The-Air IT policy setting and device wipe

This version, with built-in integration with Exchange Server 2003, support for "proper" push-synchronisation, advanced security features, minimum server administration overhead, multiple device support (as licensee's clients come to market) and the Microsoft brand name are likely to make this technology the Enterprise Solution of choice for many companies.

About EMCC Software Limited

EMCC Software is a leading Symbian, Series 60 and UIQ Competence Center, providing software development service and solutions to the mobile industry. They have been working closely with Symbian and the device manufactures for over seven years, helping to develop the Symbian OS platform, mobile phones and innovative applications and solutions. Building on their reputation for technical excellence, EMCC has recently received accredited certification against the ISO9001:2000 standard and TickIT Guidelines Issue 5. Further information about EMCC Software Ltd and the services they offer can be found at www.emccsoft.com.