Owing to a great expansion of broadband network access in recent years, the collaborative graphical desktop sharing systems (GDSS) have gained a considerable popularity and denote a non-negligible amount of data in today's internet traffic. Much research has been focusing on characterization of traffic load from different types of internet applications (such as Web, VoIP, Video streaming and Peer-to-Peer), while the remote desktop protocols have attracted very little attention, despite the fact that they belong to a group of real-time applications with very strict quality of service requirements. As with other complex interactive applications, a good understanding of user behavior workload is important to the design of GDSS systems. In this paper, we present characterization of user behavior workload for GDSS arrival process and develop models for interarrival time of user's sessions and the session duration. Our results not only provide an insight into users' activities and behavior to the collaborative virtual environments research community but they are also useful in the development of synthetic workloads in performance studies of GDSS systems.