How Outlook 2003 SP2 and Exchange Server 2003 SP2 OAB Version 4 Work TogetherPublished: November 2, 2005 This article goes into detail about how Microsoft® Office Outlook® 2003 Service Pack 2 (SP2) and Microsoft Exchange Server 2003 SP2 work together to take advantage of new OAB v4 functionality. This article supplements the Exchange Insider article, OAB Version 4 in Exchange Server 2003 Service Pack 2. On This Page
OverviewOutlook 2003 SP2 and Exchange Server 2003 SP2 introduce several new architectural changes to the offline address book. These changes included in Offline Address Book version 4 (OAB v4), include the following objectives.
This article focuses primarily on the client-side aspects of OAB v4, but an overview of the server-side changes is provided. Having a complete picture of this feature gives you the information you need to effectively troubleshoot offline address book issues. History of Offline Address Book IssuesTo fully understand the new architecture of OAB v4, it is important to understand the underlying reasons for the changes to the offline address book. This section covers the main support issues currently encountered by Exchange customers working with OAB v2 or v3a. Full Offline Address Book DownloadsThe biggest issue confronting administrators is the preponderance of unexpected full offline address book downloads in pre-OAB v4 environments. There are a variety of root causes for an unexpected full offline address book download, but the most prevalent causes in OAB v2 and v3a include:
Any one of these problems can cause a full offline address book download on every Outlook client that runs in cached mode in the Exchange organization, flooding the network in the process. Server-Side ChangesBefore introducing the client-side aspects of the changes in the OAB v., the server-side changes will be discussed. In this section the following topics are discussed.
OAB Version 4 GenerationOAB v4 is a new addition to the offline address book infrastructure. You must have Exchange Server 2003 Service Pack 2 installed on your computers that run Exchange Server if you are to use the new features. For Outlook 2003 clients to use these new OAB v4 features, they must be running Outlook 2003 SP2. For the most part, only the format of the offline address book data has changed in OAB v4. Exchange System Attendant is still responsible for generating the offline address book by calling Oabgen.dll and the Exchange Store is still responsible for storing the offline address book system folders. Throttling Full Offline Address Book Downloads (Not Specific to OAB v4)By default, every client request for a full offline address book download is served immediately, and the public store does not limit the number of concurrent full offline address book downloads that can occur. Because of this architecture for full offline address book downloads, Exchange Server 2003 SP1 introduced the ability to throttle full offline address book downloads. When you limit the bandwidth that is used by full offline address book downloads, this feature may extend the time elapsed until all clients receive their updated full offline address book data. Therefore, you should only use this feature if you have a very large offline address book and you must protect your LANs from overloading. For more information about the full offline address book throttling mechanism, see Microsoft Knowledge Base article 867623, Throttling full offline Address Book downloads to limit the effect on a LAN in Exchange Server 2003 The throttling mechanism included with Exchange Server 2003 SP1 is only mentioned in this bulletin because of the client-side response changes in Outlook 2003 SP2. This feature in Exchange Server 2003 SP1 does not rely on either the server or client using OAB v4. Smaller Full Offline Address Book File SizeOAB v4 files generated by Exchange Server 2003 SP2 will be up to 33 percent smaller than comparable files generated by earlier versions of Exchange Server. This file size reduction is primarily due to three architectural changes in the offline address book files.
OAB Version 4 Public Folder DataAs in earlier versions of the offline address book, a full offline address book and a differential offline address book are generated every morning, by default, at 05:00 local server time. The difference in the OAB v4 files is that they are generated using BinPatch technology. In contrast to pre-OAB v4 versions, the server checks to see if there have been any changes since the last generated full offline address book. If no changes occurred, the following two actions take place during the offline address book generation process:
Because the sequence numbers in this scenario do not change, this feature ensures clients do not download offline address book data that they do not need. Full Offline Address Book FilesAs in pre-OAB v4 versions, the offline address book public folder contains only one post for the full offline address book. Each offline address book post has the following file attachments:
Differential Offline Address Book FilesAs in pre-OAB v4 versions, the offline address book public folder contains one post for each of the last 30 days’ differential offline address book files (unless there are no offline address book changes and an offline address book is not built on a particular day). However, the post for the OAB v4 differential file has the following new characteristics:
Client-Side ChangesBecause of the architectural changes introduced by OAB v4, Outlook 2003 SP2 includes new capabilities and methods for working with the new OAB v4 files. In this section, the following aspects of the client-side offline address book feature set are discussed.
Downloading Offline Address Book filesAfter the SP2 update is installed on the computers that run both Office 2003 and Exchange Server 2003, Outlook will automatically download the full OAB v4. Note Outlook does not automatically upgrade to the OAB v4 if your profile is an American National Standards Institute (ANSI) (non-Unicode) profile that is using a OAB v2. In this scenario, if you want to upgrade to a OAB v4, you must create a new Outlook profile. The new profile should automatically be a Unicode mode profile and will download the OAB v4 file by default if it is available. If you work with OAB v4, Outlook will automatically fall back to OAB v3a if OAB v4 is missing on the server and to OAB v2 if both OAB v4 and OAB v3a are not available. You can control this behavior by editing the registry data on the Outlook client. Decompression and Extraction of the Offline Address Book DataBecause of the new BinPatch technology used with OAB v4, it is important to understand how Outlook decompresses and extracts the offline address book files after they are downloaded from Exchange Server.
Managing Offline Address Book DownloadsInvariably, customers need to modify the registry default settings for the different mechanisms involved in the offline address book download process. This section discusses only the new functionality available with OAB v4. Unless noted, all custom modifications for the OAB v2 or OAB v3a still apply to OAB v4. This section covers the following configuration settings:
Caution Incorrectly editing the registry can cause serious problems that may require you to reinstall your operating system. Problems resulting from editing the registry incorrectly may not be able to be resolved. Before editing the registry, back up any valuable data. Threshold for a Full Offline Address Book Download Instead of a Differential DownloadIn pre-OAB v4 versions of the offline address book, Outlook uses a default threshold of one-eighth to determine when to not perform a differential offline address book download and instead perform a full offline address book download. If you are using Outlook 2003 SP2 and OAB v4, this threshold has been increased to 50 percent. Note If you use Outlook 2003 SP2 and either OAB v2 or OAB v3a, Outlook uses the one-eighth threshold and not the new 50 percent threshold. Outlook calculates a percentage ratio of the total size of all the compressed differential offline address book files on the server to the current total size of the compressed full offline address book on the server. If the percentage ratio exceeds the threshold value, Outlook performs a full download instead of downloading the differentials. The threshold can be customized using the following client registry settings.
Server-Side Throttling Full Offline Address Book Downloads (Not Entirely Specific to SP2)In Exchange Server 2003 SP1 and later, you can override the default behavior and limit the bandwidth used by full offline address book downloads from a particular public server. After Exchange Server 2003 SP1, the server maintains a performance counter for full offline address book downloads. When Outlook is about to perform a full offline address book download, Outlook does a ropGetAttachmentTable Remote Procedure Call (RPC) and the server checks the performance counter to see whether the traffic is below the limit specified in the registry key. If the limit is exceeded, the server returns MAPI_E_BUSY. To customize this threshold, the following registry data is added to the Exchange server storing the offline address book data.
After you apply this registry setting, when an Outlook client tries to download a full offline address book, the public store determines the average full offline address book bytes that were downloaded over the previous 10 seconds. Then, one of the following events occurs.
Random Full Offline Address Book Request Timer (OAB 2, v3a, and v4)Outlook 2003 SP2 introduces a new registry policy setting that allows you to disperse full offline address book download requests to randomly start between 1 hour and a specified number of hours (which can span multiple days). If the registry policy is set and a full offline address book download is required, Outlook performs the full offline address book download in a random time between 1 hour and the number of hours specified in the registry. To implement this feature, use the following registry data.
Note The registry setting only applies to the case where Outlook already has a usable local offline address book. If Outlook does not have a usable offline address book (for example, you just upgraded to Outlook 2003), the registry settings are ignored until you have a usable offline address book. Policy to Download Only Unicode OAB v4 from the ServerThe following registry settings ensure Outlook will download only OAB v4 data from the Exchange server.
Note This registry data is not applicable to ANSI mode, which can only use OAB v2. It is ignored if you are not in Unicode mode. Name Resolution ImprovementsOAB v4 Browse and ANR indexing is based upon the locale setting (language and country) of the client and not the server. With OAB v4, the client generates the locale specific indexes for local .oab files regardless of what locales are on the server. These indexes are regenerated in their entirety after each full download or differential download. Note Manually changing the sort locale on the client computer or in the Office version does not automatically change the locale of the offline address book. The indexes are regenerated only when the offline address book download is successfully completed, either on a 24-hour basis, or when forced manually. The OAB v4 data also provides for improved name resolution and browsing by using the PR_GIVEN_NAME attribute. This attribute is a new property for Outlook 2003 SP2 to help resolve first names in directories where the display name is set to Lastname, Firstname. Here is one example where this behavior is a problem in non-OAB v4 clients. User Info: Pica Pica, Guido GPica gpica@exchange.contoso.com /o=Contoso/ou=APPS/cn=recipients/cn=gpica In pre-OAB v4 clients, you cannot find this user if you type "Guido” in the To field of a message. If you are using OAB v4, this same text will resolve the name for Pica, Guido. For More InformationFor more information see the following Exchange Server resources and Microsoft Knowledge Base articles:
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