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Paul Baran from the RAND Corporation first proposed the notion of a distributed communication network in 1964 [33] [42]. The aim of the proposal was to provide a communication network that could survive the impact of a nuclear war and employed a new approach to data communication based on packet switching. The Department of Defense (DoD) through the Advanced Research Projects Agency (ARPA) commissioned the ARPANET, in 1969. ARPANET was initially an experimental communication network that consisted of only four nodes: UCLA, UCSB, SRI, and the University of Utah. It?s popularity grew very rapidly over the next two decades and by the end of 1989, there were over 100,000 nodes connecting research universities and government organizations around the world. This network later came to be known as the ?Internet? and a layered protocol architecture (i.e. TCP/IP ref. Model) was adopted to facilitate services such as remote connection, file transfer, electronic mail, and news distribution over it. The proliferation of the Internet exploded over the past decade to over 10 million nodes since the release of the World Wide Web.

The current Internet infrastructure, however, behaves as a ?Best-Effort? delivery system. Simply put, it makes an honest attempt to deliver packets from a source to its destination, but provides no guarantees on the packet either being actually delivered and/or the time it would take to deliver it [22]. While this behavior is appropriate for textual data that requires correct delivery rather than timely delivery, it is not suitable for time-constraint multimedia data such as video and audio. Recently there has been a tremendous growth in demand for distributed multimedia applications over the Internet, which operate by exchanging ?multimedia? involving a myriad of media types. These applications have shown their value as powerful technologies that can enable remote sharing of resources or interactive work collaborations, thus saving both time and money. Typical applications of distributed multimedia systems include Internet based radio/television broadcast, video conferencing, video telephony, real-time interactive and collaborative work environments, video/audio on demand, multimedia mail, distant learning, etc.

The popularity of these applications has highlighted the limitations of the current best-effort Internet service model and viability of its associated networking protocol stack (i.e. TCP/IP) for the communication of multimedia data. The different media types exchanged by these applications have significantly different traffic requirements ? such as bandwidth, delay, jitter and reliability ? than the traditional textual data and demand different constraints or service guarantees from the underlying communication network to deliver an acceptable performance. In networking terminology, such performance guarantees are referred to as Quality of Service (QoS) guarantees, and can be provided only by suitable enhancements to the basic Internet Service model[22]. Circuit-switched networks, like the telephony system, Plain Old Telephone Service (POTS), have been designed from the ground-up to support such QoS guarantees. However, this approach suffers from many shortcomings like scalability, resource wastage, high complexity and high overhead [25]. Another approach, known as Asynchronous Transfer Mode (ATM), relies on cell switching to form virtual circuits that provide some of the QoS guarantees of traditional circuit-switched networks. Although ATM has become very popular as the backbone of high-bandwidth and local networks, it has not been widely accepted as a substitute for the protocol stack used on the Internet. Providing QoS in packet-switched Internet, without completely sacrificing the gain of statistical multiplexing, has been a major challenge of multimedia networking. In addition to the QoS guarantees, distributed multimedia applications also demand many functional requirements ? such as support for multicasting, security, session management, and mobility ? for effective operation, and these can be provided by introducing new protocols residing above the traditional protocol stack used on the Internet [48]. In this chapter, we discuss two popular protocol architectures (H.323 [44] [26] and SIP [17] [34]) that have been specifically designed to support distributed multimedia applications.

Apart from the Internet, cellular networks have also seen an unprecedented growth in its usage [13] and consequent demand for multimedia applications. The 2^nd Generation (2G) cellular systems like GSM, IS-95, IS-136 or PDC, which offered circuit-switched voice services, are now evolving towards 3^rd Generation (3G) systems that are capable of transmitting high-speed data, video and multimedia-traffic, to mobile users. IMT-2000 is composed of several 3G standards under development by the International Telecommunication Union (ITU) that will provide enhanced voice, data, and multimedia services over wireless networks. We discuss the layered QoS approach adopted by IMT-2000 to provide end-to-end QoS guarantees.

Section II starts with a general classification of media types from a networking/communication point of view. In this section, the reader is introduced to some common media types like text, audio, images, and video and a discussion about their traffic and functional requirements ensues. Section III discusses the inadequacy of the current best-effort Internet model to satisfy the multimedia traffic requirements and describes three enhanced architectures? Integrated Services [46], Differentiated Services [5], and Multi-Protocol Label Switching [30]? that have been proposed to overcome these shortcomings. Section IV presents some standard approaches to meet the functional requirements posed by multimedia traffic. Later in this section, we introduce the reader to two protocol architectures (H.323 and SIP) that have been introduced for the Internet protocol stack to satisfy these requirements. Section V describes current efforts to support multimedia traffic over the cellular/wireless networks and illustrates issues related to Inter-networking between wired and wireless networks.

:: [reports] Book Chapter: Multimedia Networks and Communication ::
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[reports] Book Chapter: Multimedia Networks and Communication