A collaboration server can represent properties of known Address Book objects and make them available in an address book to its clients. When the client cannot reach the server because it is offline or due to high network costs to access the server, the client might keep a local copy of an offline address book (OAB). The Offline Address Book (OAB) Public Folder Retrieval Protocol enables OAB data to be located in and obtained from a shared location so that it can be retrieved by clients.
Clients can also obtain OAB version 4 files by using the Offline Address Book (OAB) Web Retrieval Protocol [MS-OXWOAB]. Note that the OAL data sequence number [MS-OXWOAB] is also used in public folder distribution, and any client use of that number applies to the public folder–distributed OAB as well.