create a messaging system

Requirement is to create a 3 tier messaging system. There needs to be a Central Message Exchange that keeps track of each node and pass the message from one node to the other. The message will always go from one type of node (sender node) to the other type of node (recipient node) and on the recipient node, the message should pop up on the screen over all other open windows. All nodes will use the internet to connect to the Central Message Exchange and all communication must happen over a secure channel (using SSL). The authentication backend for all nodes is a MySQL server and all authentication must happen through the Central Message Exchange. Ideally the Central Message Exchange component will run on a linux server while the nodes will run on windows pcs. The nodes will be passing formatted data that it collects from local data stores.