How Exchange 2000 and MSN Instant Messaging Are Related

By Peter Pawlak

On the surface, the instant messaging (IM) capabilities of Exchange 2000 and MSN seem similar. In fact, the MSN Messenger 2.2 client software bundled with Exchange 2000 can simultaneously connect to both IM services, much like Outlook can connect to an Exchange mail server by using the Messaging Application Programming Interface (MAPI) and to any Simple Mail Transfer Protocol (SMTP) mail server by using the Post Office Protocol (POP3). Just as MAPI and POP3 are completely different, the two IM systems are also very different.

The MSN Instant Messaging Service, to which the MSN Messenger client software connects, is completely proprietary and is hosted on centralized Unix servers at MSN, while Exchange 2000’s IM service utilizes a “federated” architecture of loosely coupled servers that can scale to handle large numbers of users.

Unlike Exchange 2000 IM, the MSN Messenger Service does not communicate using the Rendezvous Protocol (RVP) or Instant Messaging and Presence Protocol (IMPP). It uses the “Buddy List Server Protocol” (BLSP), originally intended to be interoperable with America Online’s Instant Messaging. BLSP is not based on Web standards and many firewalls balk at passing messages that use this protocol.