Technical Report

Google talk (Gtalk) is an instant messeger and voice over IP client developed by Google in 2005. Gtalk can work across firewalls and has very good voice quality. It encrypts calls end-to-end, and stores user information in a centralized fashion. This paper analyzes fundamental Gtalk functions such as login, firewall traversal, and call establishment under different network scenarios. The analysis is performed by both active and passive measurement techniques to understand the Gtalk network traffic. Based on our analysis, we devised algorithms for login and call establishment processes as well as data flow models.