Applies to: Exchange Server 2007 SP1, Exchange Server 2007
Topic Last Modified: 2007-02-01
The Microsoft Exchange Server 2007 Availability service improves information workers' calendaring and meeting scheduling experience by providing secure, consistent, and up-to-date free and busy information to computers running Microsoft Office Outlook 2007. Outlook 2007 uses the Autodiscover service to obtain the URL of the Availability service. The Autodiscover service is similar to the Domain Name System (DNS) Web service for Exchange 2007 Web services. Essentially, the Autodiscover service helps Outlook 2007 locate various Web services, such as the Unified Messaging (UM), Offline Address Book (OAB), and Availability services.
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If you have Outlook 2007 clients running on Exchange Server 2003 mailboxes, Outlook 2007 will use public folders for the free and busy information.
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The Availability service is part of the Exchange 2007 programming interface. It will be available as a public Web service to allow developers to write third-party tools for integration purposes.
Free and busy data is used extensively in meeting scheduling, which is one of the most frequent activities performed by information workers.
The following figure illustrates the process flow for the Availability service.
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Improvements Over Exchange 2003 Free and Busy
Table 1 lists the improvements to free and busy functionality that Exchange 2007 provides over Exchange 2003.
Table 1 Free and busy improvements
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Free and busy component
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Outlook 2003 running on Exchange 2003
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Outlook 2007 running on Exchange 2007
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Up-to-date information
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There was no guarantee that free and busy information was up-to-date. There were multiple factors that caused free and busy information to be outdated:
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By default, Outlook only updated free and busy information every 45 minutes. Furthermore, because of bandwidth and scalability issues, you could not decrease this interval.
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There were latencies that resulted from public folder replication.
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In cross-forest scenarios, there were delays when you used the Microsoft Exchange Inter-Organization Replication tool to replicate free and busy information across forests.
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Free and busy information is guaranteed to be up to date within a small time period (60 seconds) on all the data retrieved.
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Granularity
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The four meeting states (Free, Tentative, Busy, and Out-Of-Office) were available in one stream. To retrieve appointment details, additional MAPI calls were required.
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By default, free and busy information displays the start and end times for individual appointments. Additional calendar properties (such as Subject and Location) will be accessible through the Availability service.
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Security
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For any authenticated user, all free and busy data was available in a public folder. This meant that any authenticated user could delete, modify, or publish another user's free and busy information.
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Free and busy information provides increased security, similar to general calendar sharing. In compliance with your company's policy, you can specify the amount of free and busy information to share with a specific user. Because the Availability service reads directly from a user's mailbox, a user cannot modify or publish another user's free and busy information.
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Publishing frequency
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Office Outlook 2003 has a 45-minute default publishing interval.
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No publishing is required in an Exchange 2007 and Outlook 2007 organization.
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Out-of-Office Information
The Availability service also provides access to out-of-office messages for out-of-office appointments and global out-of-office information.
Information workers use the Out of Office feature in Outlook to alert others when they are unavailable to respond to e-mail messages. To improve out-of-office management, the Exchange 2007 implementation of the Out of Office feature makes configuring and managing out-of-office tasks easier and more flexible for both information workers and administrators.
For more information about the Out of Office feature, see Managing the Out of Office Feature.
Performance
You can use the Performance Monitor tool to automatically collect performance data from local or remote computers that are running Exchange 2007. You can define start and stop times for automatic log generation, manage multiple logging sessions from a single console window, and set an alert on a computer that enables a message to be sent or a log to be started when your criteria are met.
For information about using Performance Monitor, see Windows Server 2003 Monitoring Features and Tools in the Microsoft Exchange Service Management Guide.
You can use the following performance counters to collect information about the Availability service:
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Number of availability request serviced/second
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Number of availability request dropped/second
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Number of mailbox queried/second
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Number of availability service referrals/second
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Number of requests answered at none level/second
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Number of requests answered at F/B level/second
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Number of requests answered at detailed level/second
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Number of unique user’s mailbox opened
Distribution Group Handling
In Exchange 2007, distribution group expansion has been moved to the Exchange 2007 server. The primary benefit of moving distribution group expansion to Exchange 2007 is to provide consistent behavior for any Availability service consumer. In previous versions of Exchange, if the number of distribution group members was too large, the free and busy data for the distribution group members would display as busy when expanded.
In Exchange 2007, the following improvements have been made to the handling of distribution groups:
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The Availability service expands a distribution group up to only two-levels deep, regardless of the total number of distribution group members.
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A distribution group's free and busy data can expand up to a maximum of one hundred members.
Availability Service API
The Availability service is part of the Exchange 2007 programming interface. It will be available as a public Web service to allow developers to write third-party tools for integration purposes.
For more information about developing with Exchange 2007 Web services, see Development: Overview.
For More Information
For more information about the Autodiscover service, see the following topics:
For more information about providing secure Web communications on the Internet or intranet, see Creating a Certificate or Certificate Request for TLS.