Networked virtual environments (NVEs) have become a major trend in distributed computing, mainly due to the enormous popularity of multi-player online games in the entertainment industry. Nowadays, NVE systems are considered as the supporting technology for many networked and virtual organizations (NVO) (Singhal & Zyda, 1999), especially to those classified within the field of computer supported cooperative work (CSCW), where networked computer can be seen as a standard to provide the technological means to support the team design (Ott & Nastansky, 1997). These highly interactive systems simulate a virtual world where multiple users share the same scenario. The system renders the images of the virtual world that each user would see if he was located at that point in the virtual environment. Each user is represented in the shared virtual environment by an entity called avatar, whose state is controlled by the user through the client computer. Hundreds and even thousands of client computers can be simultaneously connected to the NVE system through different networks, and even through the Internet. NVE systems are currently used in many different applications (Singhal & Zyda, 1999) such as civil and military distributed training (Miller & Thorpe, 1995), collaborative design (Salles, Galli, Almeida et al., 1997) and e-learning (Bouras, Fotakis, & Philopoulos, 1998). Nevertheless, the most extended example of NVE systems are commercial multi-player online game (MOG) environments. These systems use the same simulation techniques that NVE systems do, and they are predicted to make up over 25 percent of local area network (LAN) traffic by 2010 (McCreary & Claffy, 2000).
Key Terms in this Chapter
Partition: Each one of the SN feasible solutions in which the “N” avatars connected to a NVE system can be assigned to the “S” servers of the simulation.
Awareness Problem: This problem consists of ensuring that each avatar is aware of all the avatars in its neighborhood. For example, a user provided with a non-coherent view of the virtual world could be shooting something that he can see although it is not actually there. In networked-server architectures, the existing servers easily solve the awareness problem, since they know the location of all avatars during all the time.
Jitter: The delay of the messages sent by the avatars (and also the ASR, in terms of average round-trip delay) to the servers where they are assigned is not regular along the simulation time. The jitter is the measure of how homogeneous the delay is and it is defined as the difference between the maximum and minimum values of delay registered by the avatar.
AOI (Area of Influence): As it occurs in the real world, when avatars are located within the virtual scene they cannot visualize completely all the objects and avatars situated on the virtual map. In order to model this feature, a circumference centered at the current position of the avatar (which ratio is used to be equal for all avatars) is used to define the portion of the virtual map that each avatar can visualize.
NVE: Abbreviation for networked virtual environment. In these systems (also called distributed virtual environments or DVEs), a set of users connected remotely from different computers share the same virtual scene. Although NVE systems are commonly classified into the research field of CSCW (computer-supported cooperative work) they can be considered as a general framework to support virtual organizations.
Avatar: Each user is represented in the shared virtual environment by an entity, whose state is controlled by the user through the client computer. It is very common to find in the literature of NVE systems that (for the sake of shortness) many authors use the term avatar to denote the client computer controlling that avatar.
Factor of Presence: A parameter for measuring the density of avatars located in different zones of the virtual scene. The factor of presence of an avatar Ai is the number of avatars in which AOI avatar Ai appears.