Exchange 2000 Instant Messaging Architecture

The diagram below shows the core components of an Exchange 2000 Instant Messaging system. In the top row, workstations running a Windows 32-bit operating system and MSN Messenger 2.2 connect to their assigned “home servers” using HTTP1.1 and the XML-based RVP protocol. The home servers authenticate the users against Active Directory (AD) and maintain the users’ contact lists and presence information. The IM Router, which can be co-located with a home server or run on a separate server, consults with DNS and AD to route instant messages from one home server to another and provides a uniform IM namespace. If the IM users will access the system from the Internet, the firewall must be configured to “reverse proxy” HTTP IM requests to the IM Router. The IM Router redirects these requests to the appropriate home server. Users coming in from the Internet will provide AD credentials in their connection request. IIS’s Secure Sockets Layer (SSL) protocol keeps these credentials safe from eavesdroppers.