New Additions to OAB Version 4
The following sections discuss the new additions to OAB v4.
Fewer Situations That Result in an Offline Address Book Full Download
In Exchange Server 2003 environments before Service Pack 2, two scenarios existed that caused full offline address book downloads.
Scenario 1: Parent Distinguished Name Changes
The addition or removal of a parent distinguished name in Active Directory® directory service can cause a full offline address book download. When the OAB Generation process (OABGen) is building an address list, it splits the exchangeLegacyDN and Simple Mail Transfer Protocol (SMTP) addresses into two separate parts. Currently the OAB Generation process has problems handling the addition and removal of the parent distinguished name, and this will cause OABGen to skip one day’s differential build.
-
End Result to Scenario1
When an Outlook client attempts to download the offline address book files and notices that the differential file is missing, the Outlook client is forced to download the full offline address book.
Scenario 2: One-Eighth Threshold Rule
Total directory changes exceeding one-eighth the size of the offline address book can cause a full offline address book download. This problem is one of the biggest client performance issues. The bigger the offline address book files become, the longer they take to download to the client. In the version of Exchange Server 2003 that was originally released, the offline address book differential files contain the entire users record, even if the changes were minimal.
-
End Result to Scenario 2
Clients are forced to download the entire offline address book.
OAB Version 4 Now Uses a Technology Called Binary Delta Compression
In OAB v4, we use Binary Delta Compression (Binpatch) technology to get around the issues discussed above. Read on.
Exchange Server 2003 Service Pack 2 introduces two new files, Binpatch.oab and Data.oab. The technology behind these files gives us the ability to apply multiple days' worth of differential files to a client.
-
Binpatch.oab Contains the incremental changes from the previous day.
-
Data.oab Contains the data from all merged differential files.
The following workflow discusses the new format used for downloading and applying offline address book files to an Outlook client.
-
Exchange Server generates a Binpatch.oab v4 file each day using the current Data.oab file and the Binpatch.oab file from the previous days’ Data.oab file. This new OAB v4 format follows the same sequence numbering as the current technology when using these new files. The Binpatch.oab file is nothing more than a delta of the Data.oab from the previous Data.oab file. It is completely unaware of the properties or records that changed.
-
Outlook downloads the Data.oab file from the server on the first day and subsequently downloads only the Binpatch.oab file from the Exchange server.
-
To allow an Outlook client to update its offline address book, the client needs to download all the Binpatch.oab files from the server to upgrade to that version. After this download is completed, Outlook applies these files to the Data.oab file.
-
After applying updates to the Data.oab file, the Outlook client regenerates new browse and ANR indexes based on the operating system user locale on the client.
OAB Templates Added to Differential Offline Address Book Downloads When They Are Updated
With the introduction of OAB v4, when an administrator changes or adds a template file to the Exchange server, Outlook clients will now have the ability to download this new template file when it downloads the differential file.
Failed Differential Files Won't Result in a Full Download
With OAB v4, Exchange Server no longer forces full downloads to the Outlook clients by intentionally not generating an offline address book differential file. The OABGen process has problems handling the addition or removal of the parent distinguished name and this causes the OAB Generation process to skip one day’s differential build. When the parent distinguished name addition or removal occurs, and when the Outlook client attempts to download the differential files, Outlook will notice the change and cause the client to do a full download of the offline address book files. When we use the new Binpatch technology, we are able to get around this problem.
.gif) Note: |
|---|
|
There is still a potential for a full download to occur. A failure to download one of the offline address book files, or a problem caused by file corruption will result in the Outlook client performing a full download.
|
Protection Against Offline Address Book Bloat
In OAB v4, Exchange Server now enforces limits to ensure that the OAB v4 does not grown needlessly. Now, if we find attributes that exceed one of the limits imposed, Exchange Server removes these attributes from the offline address book. After the attribute has been removed, Exchange Server adds an indicator to let Outlook know that some properties have been removed. Outlook 2003 SP2 treats the removed properties as "not present" in the record.
When retrieving necessary attributes from Active Directory that are required by Outlook to send mail, the Exchange OAB Generation process also has additional checks to make sure that these attributes are never removed from the offline address book.
Offline Address Book Indexing Based on the Client Locale Setting (Language and Country)
When building legacy offline address books (OAB v2 and OAB v3a) we would rely on the locale of the server to build the indexes for the offline address book files. With OAB v4, the client now generates the locale-specific indexes from the OAB v4 Data.oab file regardless of what locales are set on the server.