Throttling the OAB

Heck, I’ve wanted to throttle the OAB lots of times – but that’s not the reason for this blog entry🙂.  Chris had a challenge as the customer he was doing some work for wanted to manage the network bandwidth when all of the users in the company were downloading a full copy of the Offline Address Book.  When this happened, network activity went a bit crazy and the WAN became unworkable (not surprising – it was a big company).  Chris was trying to work out a way so that not all of the clients could download the OAB at the same time. 

I told Chris that before he started with anything drastic, it’s a good idea to read this article and learn how Outlook 2003 and Exchange 2003 OAB work together.  There are quite a few articles on this particular topic, and also a Best practices guide, so I had a look around for some extra pieces of info for him.

One way of throttling the full offline address book to limit the effect on the LAN is mentioned in this kb article.  You need to have Exchange 2003 SP1 installed, and you need to edit the registry and add a new value:

1:On the Edit menu, point to New, and then click DWORD Value. 
2:Type OAB Bandwidth Threshold (KBps) for the name of the DWORD, and then press ENTER.
3:Right-click OAB Bandwidth Threshold (KBps), and then click Modify. 
4:In the Base area, click Decimal.
5: 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).

 If you have Exchange SP2 however, you can take advantage of architectural changes in the OAB v4 and utilise LZX compression and Binary Delta compression Data. (Read about BDC here, and there’s a good blog entry on the Exchange team blog explaining how OAB v 4 works).  

 Hopefully this will give Chris good enough pointers to ease the WAN strain….