Asynchronous Transfer Mode (ATM) Networks

Asynchronous Transfer Mode, or ATM, is a network transfer technique capable of supporting a wide variety of multimedia applications with diverse service and performance requirements. It supports traac bandwidths ranging from a few kilobites per second (e.g., a text terminal) to several hundred megabits per second (e.g., high deenition video) and traac types ranging from continuous, xed-rate traac (e.g., le transfer) to highly bursty traac (e.g., interactive data and video). Because of its support for such a wide range of traac, ATM was designated by the telecommunication standardization sector of the International Telecommunications Union (ITU-T, formerly CCITT) as the transfer technique for Broadband, or high speed, ISDN (B-ISDN) 1]. ATM is a form of packet-switching technology. That is, ATM networks transmit their information in small, xed-length packets called \cells," each of which contains 48 octets (or bytes) of data and 5 octets of header information. The small, xed cell size was chosen to facilitate the rapid processing of packets in hardware and to minimize the amount of time required to ll a single packet. This is particularly important for real-time applications such as voice and video that require short packetization delays. ATM is also connection-oriented. In other words, a virtual connection must be established before a \call" can take place, where a call is deened as the transfer of information between two or more end-points. Virtual connection establishment entails the initiation of a signaling process, during which a route is selected according to the call's quality of service requirements, connection identiiers at each switch on the route are established, and network resources such as bandwidth and buuer space are reserved for the connection. Another important characteristic of ATM is that its network functions are typically implemented in hardware. With the introduction of high speed ber optic transmission lines, the communication bottleneck has shifted from the communication links to the processing at switching nodes and at terminal equipment. Hardware implementation is necessary to overcome this bottleneck, because it minimizes the cell processing overhead, thereby allowing the network to match link rates on the order of Gbit/s. Finally, as its name indicates, ATM is asynchronous. Time is slotted into cell-sized intervals, and slots are assigned to calls in an asynchronous, demand-based manner. Because slots are allocated to calls on demand, ATM can easily accommodate traac whose bit rate uctuates over time. Moreover, in ATM, no bandwidth is consumed unless information is actually …