Greetings, can someone give me some advices or links that will help me to implement to following scenario. Page will be written in asp.net mvc. Authorization is going to be implemented by Memberships. The scenario is as follows:

User1 has just logged in. After a while, User2 attempts to login with success. Then user1 should be notified that User2 has just logged in. Additionally User2 should be notified that User1 is online.

How can I achieve something like that? It should also be possible for these users to write messages to each other. (chat like).