Dev:Network Games Related Work

Terminology

• DIA = Distributed Interactive Applications
  • used by among others Delaney - Presence 2007
  • Includes any of the following:
• DIS = Distributed Interactive Simulations
  • Used by the military
• NVE = Networked Virtual Environment
  • Singhal & Zyda 99 <insert reference>
• DIM = Distributed Interactive Media
  • Mauve01 <insert reference>
• NIE = Networked Interactive Environment
  • Capps, McDowell, Zyda 01 <insert reference>
• DVE = Distributed Virtual Environment
  • Stytz96 <insert reference>
• CVE = Collaborative Virtual Environment
• DSE = Distributed Synthetic Environment
• SVE = Shared Virtual Environment
• CSCW = Computer Supported Cooperative Work

Consistency is the degree to which users share the same view of the application state. It includes Delaney - Presence 2007

• Synchronization: Time of events relative to other events are the same across the DIA
• Causality: cause/effect ordering is maintained
• Concurrency: Simultaneous execution of events by different users on same entity

Responsiveness is the time taken for the system to register and respond to a user event. Delaney - Presence 2007

Fidelity is the degree to which the virtual representations are similar to their real-world representations. Delaney - Presence 2007 & IEEE95

ISSUES IN SUPPORTING DIAs

Consistency vs Responsiveness

With 0 network latency and infinite bandwidth, a DIA could remain completely consistent and yet be highly responsive (i.e. change state rapidly). In the presence of network latency, however, the system will require time to reach a new consistent state. Thus when a state change is required, the system can either delay its response in order to fist reach a consistent state or it can process the change without guaranteeing complete consistency.
Fidelity is sacrificed in either case since fidelity represents how closely the simulation matches its real-world representation. Clearly inconsistencies harm fidelity as they lead to less accurate simulations. Decreased responsiveness also decreases fidelity since real events occur instantaneously. The importance of each aspect of fidelity is dependent upon the type of DIA. For instance, a fast-paced first-person shooter game must remain highly responsive but may tolerate certain types of inconsistencies. A shared whiteboard application, on the other hand, can tolerate some delay but should be consistent for all users.

It's important to notice that the fundamental problem to supporting DIAs is latency. Certain sources have found that for many DIAs, the variation in latency or "jitter", has the greatest impact on performance Delaney - Presence 2007. DIAs employ a wide range of Consistency Management Techniques, which are also known as latency hiding techniques, in order to maintain fidelity by balancing consistency with responsiveness in the face of latency. How best to manage this tradeoff depends on the requirements of the DIA.

Scalability

Scaling a DIA to support a larger number of users increases the computation that must be done by the nodes and increases the network bandwidth needed to communicate the state between the nodes. While the computational burden can usually be solved by adding more nodes, adding more nodes increases network bandwidth as more end points will need to share data. The exact architecture employed by each DIA will determine how the bandwidth requirements will increase with the number of users. To reduce the network bandwidth, DIAs employ a variety of Information Management Techniques.

TECHNIQUES

Consistency Management Techniques

• Lockstep Synchronization
• Imposed Global Consistency
• Delayed Global Consistency
• Time Warp
• Predictive Time Management
• Concurrency

Information Management Techniques

• Dead Reckoning
• Relevance Filtering
• Data Compression
• Packet Bundling/Aggregation