2.1 Transport
This protocol uses one of the following as the underlying transport protocol when handling address books online on an address book server:
The Name Service Provider Interface (NSPI) Protocol, as specified in [MS-NSPI], or the Exchange Server NSPI Protocol, as specified in [MS-OXNSPI].<1>
The Messaging Application Programming Interface (MAPI) Extensions for HTTP, as specified in [MS-OXCMAPIHTTP].<2>
This protocol uses the OAB File Format and Schema, as specified in [MS-OXOAB], as the underlying structure when handling address books via a local offline address book (OAB).