**4. Consistency models for sharing virtual game environments**

To use specific application architectures, it is important to ensure the correct consistency of the virtual environment. In collaborative virtual environments, users/ players perform various types of activities. These activities affect the modification of shared content, that is the virtual game environment. Ensuring consistency means that in case, any change is made to shared content by one user/player, this change will be visible to other users/players at the same time [37]. At the same time, the state of the virtual environment will be equivalent for all users/players after the change is made.

Consistency is directly related to the synchronization of virtual content between all users/players simultaneously. However, in this case, a problem arises if a group of users/players uses devices with different computing power as well as different network connection bandwidth. As stated in Ref. [38], there is a strong assumption that users with higher computing power and bandwidth could be prioritized when performing any interaction. This would strongly increase the number of conflicts between the activities of all users/players as well as misunderstandings in playing together.

To solve the mentioned issues, consistency models for sharing virtual environments are introduced, the main purpose of which is to manage and synchronize concurrency among user/player activities when working with virtual content.

#### **4.1 Model of centralized virtual environment**

Ensuring consistency of sharing through the centralized virtual environment model is primarily applicable to client–server application architectures (**Figure 8**). Every user/player accesses the centralized virtual environment through a network connection.

Consistency management is ensured by the following rules, as depicted in **Figure 8**:


The main benefit of the presented consistency model is the ability to synchronize users/players through a centralized node, tracking all the modifications of shared objects in real time [39]. This mechanism is suitable for the needs of concurrent collaboration management, where it is necessary to quickly record the modification of virtual content and then replicate its status. Every change in the state of the centralized virtual environment is continuously recorded. After users/players disconnection, the last modified state of the virtual environment is preserved and is available for future collaboration [38]. From an implementation point of view, the centralized environment is easily customizable and distributable among all users/players in real time.

*Collaborative XR Systems and Computer Games Development DOI: http://dx.doi.org/10.5772/intechopen.105555*

**Figure 8.**

*Consistency model of centralized virtual environment sharing.*

On the other hand, there are several principal limitations related to user access sharing and consistency management. A centralized virtual environment must be always available since it is the main source of virtual collaboration [40]. Although the service of this consistency model is easy to implement, it is important to optimize the centralized virtual environment for the needs of multiplatform access of users/players as well as XR technologies.
