Patent ID: 8166102

Claim:
In a client-server computer network, a method for determining when a particular user enters or exits the network, comprising the steps of: having a first user send a first request message to a server on the network, the first request message identifying at least one second user and requesting that the server notify the first user, via a notification message, upon detection of entry or exit of the at least one second user from the network; and having the server send the notification message to the first user when entry or exit of the at least one second user from the network is detected; wherein the first request message includes a user identifier identifying the at least one second user, the user identifier being independent of the at least one second user's location, the first request message requests subscription to a status notification service, subscription by the first user to the status notification service causes the server to send the notification message to the first user upon detecting entry or exit of the at least one second user from the network, and the first request message and the notification message are session initiation protocol (SIP) messages.