Society is becoming more informationally and visually oriented every day. Personal computing facilitates easy access, manipulation, storage, and exchange of information. These processes require reliable transmission of data information. Communicating documents by images and the use of high resolution graphics terminals provide a more natural and informative mode of human interaction than just voice and data. Video teleconferencing enhances group interaction at a distance. High definition entertainment video improves the quality of picture at the expense of higher transmission bit-rates, which may require new transmission means other than the present overcrowded radio spectrum. A modern Telecommunications network (such as the broadband network) must provide all these different services (multi-services) to the user.
Differences between traditional (telephony) and modern communication services
Conventional telephony communicates using:
* the voice medium only
* connects only two telephones per call
* uses circuits of fixed bit rate
In contrast, modern communication services depart from the conventional telephony service in these three essential aspects. Modern communication services can be:
* point to point, and
These aspects are examined Individually in the following three sub-sections.
* Multi-media: A multi-media call may communicate audio, data, still images, or full-motion video, or any combination of these media. Each medium has different demands for communication qualities, such as:
o bandwidth requirement
o signal latency within the network, and
o signal fidelity upon delivery by the network
Moreover, the information content of each medium may affect the information generated by other media. For example, voice could be transcribed into data via voice recognition and data commands may control the way voice and video are presented. These interactions most often occur at the communication terminals, but may also occur within the network .
* Multi-point: A multi-point call involves the setup of connections among more than two people. These connections can be multi-media. They can be one way or two way communications. These connections may be reconfigured many times within the duration of a call. A few examples will be used to contrast point-to-point communications versus multi-point communications. Traditional voice calls are predominantly two party calls, requiring a point-to-point connection using only the voice medium. To access pictorial information in a remote database would require a point-to-point connection that sends low bit-rate queries to the database, and high bit-rate video from the database. Entertainment video applications are largely point-to-multi-point connections, requiring one way communication of full motion video and audio from the program source to the viewers. Video teleconferencing involves connections among many parties, communicating voice, video, as well as data. Thus offering future services requires flexible management of the connection and media requests of a multi-point, multi-media communication call .
* Multi-rate A multi-rate service network is one which allocates transmission capacity flexibly to connections. A multi-media network has to support a broad range of bit-rates demanded by connections, not only because there are many communication media, but also because a communication medium may be encoded by algorithms with different bit-rates. For example, audio signals can be encoded with bit-rates ranging from less than 1 kbit/s to hundreds of kbit/s, using different encoding algorithms with a wide range of complexity and quality of audio reproduction. Similarly, full motion video signals may be encoded with bit-rates ranging from less than 1 Mbit/s to hundreds of Mbit/s. Thus a network transporting both video and audio signals may have to integrate traffic with a very broad range of bit-rates.