Distributed multimedia systems
Another important trend is the requirement to support multimedia services in distributed systems. Multimedia support can usefully be defined as the ability to support a range of media types in an integrated manner. One can expect a distributed system to support the storage, transmission, and presentation of what is often referred to as discrete media types, such as pictures or text messages. A distributed multimedia system should be able to perform the same functions for continuous media types such as audio and video; that is, it should be able to store and locate audio or video files, to transmit them across the network (possibly in real time as the streams emerge from a video camera), to support the presentation of the media types to the user and optionally also to share the media types of a group of users.
The crucial characteristic of continuous media types is that they include a temporal dimension, and indeed, the integrity of the media type is fundamentally dependent on preserving real-time relationships between elements of a media type. For example, in a video presentation, it is necessary to preserve a given throughput in terms of frames per second and, for real-time streams, a given maximum delay or latency for the delivery of frames (this is one example of the quality of service.
The benefits of distributed multimedia computing are considerable in that a wide the range of new (multimedia) services and applications can be provided on the desktop, including access to live or pre-recorded television broadcasts, access to film libraries offering video-on-demand services, access to music libraries, the provision of audio and video conferencing facilities and integrated telephony features including IP telephony or related technologies such as Skype, a peer-to-peer alternative to IP telephony. Note that this technology is revolutionary for challenging manufacturers to rethink many
consumer devices. For example, what is the core home entertainment device of the future – the computer, the television, or the games console?
Webcasting is an application of distributed multimedia technology. Webcasting is the ability to broadcast continuous media, typically audio or video, over the Internet. It is now commonplace for major sporting or music events to be broadcast in this way, often attracting large numbers of viewers (for example, the Live8 concert in 2005
attracted around 170,000 simultaneous users at its peak).
Distributed multimedia applications such as webcasting place considerable demands on the underlying distributed infrastructure in terms of:
• providing support for an (extensible) range of encoding and encryption formats, such as the MPEG series of standards (including, for example, the popular MP3 standard otherwise known as MPEG-1, Audio Layer 3) and HDTV;
• providing a range of mechanisms to ensure that the desired quality of service can be met;
• providing associated resource management strategies, including appropriate scheduling policies to support the desired quality of service;
• providing adaptation strategies to deal with the inevitable situation in open systems where the quality of service cannot be met or sustained.