Throttling full offline Address Book downloads to limit the effect on a LAN in Exchange Server 2003

You may find that periods of very high network usage occur when many Microsoft Outlook clients in your company try to download the offline Address Book at the same time.

This problem may occur if you have very large offline Address Books.

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.

For example, if a public store that supports 10,000 users receives 3,000 requests in one hour and the offline Address Book size is 100 megabytes (MB), the server must deliver 300 gigabytes (GB) of data. This traffic could potentially overload a 100-megabits-per-second (Mbps) local area network (LAN) for longer than ten hours. This traffic could potentially overload a gigabit-per-second LAN for longer than one hour.

In Microsoft Exchange Server 2003 Service Pack 1 (SP1), the administrator can override the default behavior and limit the bandwidth that is used by full offline Address Book downloads from a particular public store.

To turn on this feature in a public store server that is used for offline Address Book distribution, follow these steps.

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

1. Click Start, click Run, type regedit in the Open box, and then click OK.
2. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem\
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type OAB Bandwidth Threshold (KBps) for the name of the DWORD, and then press ENTER.
5. Right-click OAB Bandwidth Threshold (KBps), and then click Modify.
6. In the Base area, click Decimal.
7. In the Value data box, type the value that you want to use, and then click OK.
   
   For example, type 5000 to configure the server to use 5000 kilobytes per second (KBps) as the bandwidth threshold for offline Address Book download throttling. 5000 KBps is approximately 40,960 kilobits per second (Kbps), or 40.96 megabits per second (Mbps).
   
   Use one of the following methods to determine the OAB Bandwidth Threshold data value to use:
   • Set the value preemptively. Based on your knowledge of the network topology and how full offline Address Book downloads from multiple servers can add up to overload the LAN, set the thresholds on the individual servers to the largest values that are consistent with not overloading the LAN.
   • Set the value after the fact. Watch the extended MSExchangeIS Performance Monitor counter OAB: Full downloads bytes/sec during a company-wide download that overloads the LAN. Note the bandwidth that is used by offline Address Book downloads on each server. Set the threshold values to a percentage of those values. For example, set the threshold values to 60% of those values.
8. Click OK, and then exit Registry Editor. You do not have to restart the Exchange services for this change to take effect.

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 ten seconds. One of the following two behaviors will occur:

• If the value is less than the OAB Bandwidth Threshold, the client can continue with the full offline Address Book download at full speed.
• If the value is more than the OAB Bandwidth Threshold, the client cannot continue with the full offline Address Book download, the extended MSExchangeIS Performance Monitor counter OAB: Full download attempts blocked is incremented by one, and the Outlook client receives the following error message:
  • Clients that are using Microsoft Office Outlook 2003 SP1 or earlier receive the following error message:
    'Microsoft Exchange Server' reported error (0x8004010B) : 'Unknown Error 0x8004010B'
  The Outlook client will try to download the full offline Address Book again, one time every hour, until it succeeds.

Notes

• To return to the default behavior, delete the registry value.
• This feature does not decrease the overall number of downloaded bytes.
• 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 Books. Therefore, you should only use this feature if you have very large offline Address Books and you must protect your LANs from overloading. Additionally, you should set the threshold value as high as possible.

For more information about high network usage that can occur while Outlook clients download the offline Address Book, click the following article number to view the article in the Microsoft Knowledge Base: