Future telecommunication networks should have the following characteristics: Broadband, Multimedia, multi-point, multi-rate and economical implementation for a diversity of services (multi-services)[1][2]. The Broadband Integrated Services Digital Network (B-ISDN) provides these characteristics to a network. Asynchronous Transfer Mode (ATM) is a target technology for meeting these requirements and is widely deployed as a broadband network [2].

Modern Communication Services 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[3][4]. 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: Multimedia point to point, and multi-rate These aspects are examined Individually in the following three sub-sections[5]. 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: bandwidth requirement signal latency within the network, and 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 [2][3]. 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 [3][4]. 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 [3][5].

A single network for multiple services Traditional networks Traditionally, the various services mentioned above were carried via separate networks – voice on the telephone network, data on computer networks or local area networks (LANs), video teleconferencing on private corporate networks, and television on broadcast radio or cable networks. These networks are largely engineered for a specific application and are not suited for other applications. For example, the traditional telephone network is too noisy and inefficient for bursty data communication. On the other hand, data networks which store and forward messages using computers have very limited connectivity, usually do not have sufficient bandwidth for digitised voice and video signals, and suffer from unacceptable delays for the real-time signals. Television networks using the radio or the cable medium are largely broadcast networks with minimum switching facilities. Benefits of a single network for multiple services It is desirable to have a single network for providing all these communication services in order to achieve the economy of sharing. This economy motivates the general idea of an integrated services network. Integration avoids the need for many overlaying networks, which complicate network management and reduce the flexibility in the introduction and evolution of services. This integration is made possible with the advances in broadband technologies and high speed information processing

Broadband Traffic Types of Traffic carried by the network Modern networks have to carry integrated traffic consisting of voice, video and data. The Broadband Integrated Services Digital Network (B-ISDN) satisfies these needs [7]. The types of traffic supported by a broadband network can be classified according to three characteristics. Bandwidth: Is the amount of network capacity required to support a connection. Latency: is the amount of delay associated with a connection. Requesting low latency in the Quality of service (QoS) profile means that the cells need to travel quickly from one point in the network to another. Cell-delay variation: is the range of delays experienced by each group of associated cells. Low cell-delay variation means a group of cells must travel through the network without getting too far apart from one another Requirements of the different types of traffic The different types of traffic found in a broadband network (with examples) and their respective requirements are summarized in Table 1 [6]. Table 1. Network traffic types and their requirements. Traffic Type Example Required Bandwidth Cell-delay Variation Latency Constant Voice, guaranteed circuit emulation Minimal Low Variable Compressed Video Guaranteed Variable Low Available data Not guaranteed Widely variable Variable