Network

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In very general terms, a network is defined as an interconnected system of people or things. Since the focus of this wiki is telecommunications, the type of network we are most interested in is the telecommunications network: an interconnection of equipment designed to convey information. Historically, the information we have tried to convey is either text, audio, images, video, or voice. To support these different information types, three different network types have emerged historically: data, video, and voice.

The voice network is characterized by the public switched telephone network (PSTN). It's primary purpose for existing is to interconnect telephones and make it possible for people to converse at a distance. The PSTN is the oldest network in existence, rooted back to the invention of the telephone and the formation of the Bell System in the late 1800s. Historically, the PSTN has operated on the circuit switching model, in which a communication channel with fixed bandwidth and delay characteristics must be established before communication can occur.

The video network has historically supported television services. Originally this was a wireless, broadcast technology. Televisions were equipped with antennas to receive the radio signal. Sometimes, this antenna had to be placed on top of a building in order to capture the signal adequately, requiring a length of coaxial cable to connect the antenna to the television. In the late 1940s, Community Antenna Television (CATV) systems began to emerge. These systems made it possible to extend this cable greater distances using amplifiers, and to have multiple residences or businesses sharing the same antenna. This gave rise to the cable television industry. The network has since migrated to a hybrid fiber/coax (HFC) technology. Unlike the original unidirectional cable network, the modern HFC network is now bidirectional and is being used to support data and voice services as well as video.

The data network emerged as point-to-point connections between mainframe and minicomputer systems in the 1950s and 1960s. Many of these early circuits were initially leased from the voice network. In 1969, however, the first packet network was launched. This network, called the ARPAnet, used a packet switching model. In a packet network, each of the packet switches in the network is able to receive packets of data from an attached computer system and, based on addressing information carried in the packet, forward that packet on to its intended destination. Such networks bring a great deal of flexibility to communication, but they can introduce variable delay and jitter when packets backlog in queues at the packet switches. This was not seen as a problem for data transmission (which includes text, images, and even unidirectional audio or video), but it made these packet networks unsuitable for interactive voice or video applications.

By the late 1990s, however, much progress had been made in provisioning class of service (CoS) and quality of service (QoS) capabilities in packet network environments. Technologies like ATM, MPLS, and advances in Ethernet and Wi-Fi technology made these data networks increasingly suitable to carrying all traffic types. This tendency for all traffic to converge to a single network environment is now the trend and is rapidly revolutionizing how communication occurs.

PodSnacks

<mp3>http://podcast.hill-vt.com/podsnacks/2007q4/network.mp3%7Cdownload</mp3> | Network