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The network must be capable of scaling smoothly when new nodes, or applications are added; the goal is to simply add resources to the system rather than change the technology. A desirable form of scalability is that resource costs be linear in some measure of performance or usage.
Networked applications are designed along the principles of either vertical or horizontal integration. In vertical integration, a dedicated infrastructure is designed for each application so that, for example, the telephone network is kept separate from the computer network.
In contrast, horizontal integration is based on open standards and provides for complexity, management, and portability. It has the following characteristics:
In general, vertically integrated networks are application-aware (e.g., videoconferencing networks in general know the media type), and horizontal networks are application-blind (e.g., the Internet). Networks are also sometimes content-aware (e.g., a video-on-demand network knows what video is being downloaded).
Several approaches to multimedia systems planning are available.8 Assuming that network resources will grow to meet the demand of the most-stringent combined user-applications, best-effort schemes are sufficient as currently used. Examples include low-profile, low-cost videoconferences, multimedia E-mail, and downloadable files. This approach, however, does not take the entire multimedia system into account.
Another alternative is to overengineer the networks, making bandwidth shortage a rare problem and access to services almost always available. This approach entails providing the user with the latest technologies and a high cost. In addition, leapfrogging computer power and applications resource requirements makes this approach highly susceptible to problems.
A third and generally more effective approach is to use either quality-of-service parameters or resource reservation, or both. For example, high-profile users (e.g., users of investment banking and medical applications) require that some form of resource reservation occur before the execution of multimedia applications.
As networking evolves and voice, video, and data are handled together, networking systems are expected to handle data streams with equal efficiency and reliability from the temporal, synchronization, and functional perspectives. Technology advancements have made users less tolerant of response delays, unreliable service, and lossy data occurring either at the network or at the desktop system.
For these reasons, it is essential that multimedia networks be designed with all computing resources in mind and provide some resource reservation or quality-of-service guarantee. The task before organizations is to find the most flexible, cost-effective method for delivering multimedia applications over networks while also providing for guaranteed quality of service.9
References
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