**4.3 Model of distributed virtual environment**

In terms of data consistency, the sharing of distributed virtual environments is closely related to the model of centralized virtual environment sharing. From a topological point of view, the same client–server architecture is deployed (**Figure 10**). It is extended by an additional (secondary) centralized virtual environment.

#### **Figure 10.**

*Consistency model of distributed virtual environment sharing.*

The primary centralized virtual/game environment, which provides the sharing of the main collaborative space, is considered to be the main one. The purpose of this space is to ensure the general existence of users/players and provide management of interactions and user/player entities.

Secondary environments provide an extension of virtual collaboration with specific virtual content. Their use would not be possible without primary environments since they are intended to broaden the context of collaboration. By combining the primary and secondary environments, a fully distributed collaborative virtual gaming space is created.

The algorithm of the data consistency management is identical to the algorithm of the centralized virtual environment model. Each of the users/players uses both the primary and the secondary environment, while the secondary environment work consists only of the content that is currently needed [43].

The main benefit of distributed virtual environments is the separation of general-purpose development from specifically defined functionality [44]. The same is true for mediating the virtual content and consistency at two levels of collaboration, which specifically controls user/player accesses and interactions. Due to the complexity of two interdependent environments in parallel, the application of such a consistency model is significantly challenging, mainly due to the problems of their joint synchronization [45]. Another negative is the need for duplicate development of system and user interfaces, especially if their intention is to support XR technologies.
