How does the OAB distribution happens in Exchange 2007?

The Exchange System Attendant service is responsible for the generation of oab. This service is available only on a server that has the mailbox role installed. The SA invokes a dll file called oabgen.dll. 

The oab files are stored in C:\Program Files\Microsoft\Exchange Server\ExchangeOAB. This folder is shared so that it can be replicated to the CAS server for web distribution.

The oab generation server opens the oab folders and updates the file. The oabgen.dll file is responsible for connecting to the public folder.

CAS server runs a service named Microsoft Exchange File Distribution Service which copies the oab files from the mailbox server (ExchangeOAB folder) to the web distribution point in the CAS server.

The web distribution folder is a folder on CAS Server where the copied oab files are placed. The default location is C:\Program Files\Microsoft\Exchange Server\ClientAccess\OAB. 

The web distribution point is updated once in 8 hours. If you want to force an oab update, restart the Exchange File Distribution Service.