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Determining Service Levels

Several different types of service levels can be negotiated, including:

  Guaranteed service, which establishes quality of service within deterministic or statistical bounds.
  Predictive service, which estimates quality of service from past behavior.
  Best-effort service, which is used in the absence of available quality parameters.

SYSTEM CONSIDERATIONS

Designing networks to support multimedia applications involves more than just networking requirements; attention must also be paid to the entire system. Network configurations, for example, do not treat how the bandwidth is handled once it reaches the desktop. Bus speeds and I/O throughput are part of the link between the data source and the users’ screen. There are two possible approaches to handling bus speeds and throughput:

  Faster bus and I/O hardware.
  Desktop LANs that eliminate the workstation bus altogether and replace it with an internal packet switch linking the motherboard and peripheral system.

Bandwidth also is handled through compression techniques for images and video that radically reduce the amount of data transmitted and consequently lower bandwidth requirements. Multimedia information is bursty, meaning that some parts of it require higher bandwidth than others. Dynamic bandwidth allocation is useful to lessen the network burden.

Another consideration involves the accommodation of real-time requirements by the operating system. For example, the jitter and slowdown of a movie player may not be due to availability of resources but to a lack of proper scheduling. A music play program often picks up speed when contending programs terminate. Principal requirements for multimedia-capable operating systems are as follows:5

  Operating-system resource management must now be based on quality of service and respond to a new class of service that satisfies time constraints and negotiable service levels.6
  Real-time CPU scheduling, memory buffer and file management policies to support real-time processing, and support for real-time synchronization.
  Support for standard applications in addition to real-time multimedia applications.
  Low-overhead task management resulting from the need for frequent switching.

BARRIERS TO MULTIMEDIA NETWORKING

The extensive bandwidth and storage required to transmit multimedia streams coupled with the insufficient bandwidth of existing networks pose one of the major barriers to multimedia networking. The tendency of existing networks to treat individual streams as independent and unrelated units underscores the challenge of and need for effective synchronization.

Another major roadblock in networking existing applications is caused by proprietary development environments, data formats, and runtime environments, and by incompatible proprietary client-server models. The tight coupling among existing devices, data formats, and application program interfaces (API) makes it even more difficult to devise a standard. Heterogeneous delivery platforms pose networking challenges even when multimedia applications are not involved.

Other related concerns that aggravate existing problems associated with networked multimedia applications result from the lack of uniform standards in the following areas:

  Data capture and recording. Uniform data formats for graphics, sound, music, text, video, animation, and still images are needed.
  Data compression and decompression. Although there is no predominant standard, several organizations have proposed data compression and decompression standards. Among them are MPEG2 and JPEG (Joint Photographic Experts Group).
  Media storage and retrieval. In the case of CD-roms, digital video discs are needed for portability across platforms.
  Edit and assembly. Content description and container standards are either specified as universal object types or through the conventional method of surrounding dissimilar information types with wrappers. Scripted, structural tagging, identification tagging, and other language constructs have emerged as the conventional tools for cross-platform applications development and parameter passing.
  Presentation. Uniform customizable presentation standards are needed for maintaining a common look-and-feel across platforms.
  Transfer or networking. Asynchronous transfer mode (ATM) and TCP/IP-NG are emerging standards in this area.
  Multimedia signaling. Setting up a multimedia conference automatically, without being routed through a common conference bridge, requires a sequence of signaling events, such as call setup/connect and messages. New approaches are needed to support the capability of originating, modifying, and terminating sessions in a network.

ISSUES IN MULTIMEDIA SYSTEMS PLANNING

The challenge in networking applications is to develop a strategy that works with existing technology and enables management to provide gradual enhancements to the existing infrastructure. Both scalability and integration must be considered during the planning process. In terms of network management support, the technology chosen should support the entire infrastructure.


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