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A challenging task of network technologies in the last decade has been to integrate multiple types of service over a single network. The Broadband Integrated Services Digital Network (B-ISDN), which is recently being vigorously researched and developed all over the world, is the telecommunication technology developed in the late 1980s that would be capable of adequately transporting data of all current and future applications at speeds typically in excess of 150 Mbps. This telecommunication technology requires a network architecture that can handle the differing requirement of these types of services and adapt to meet the Quality of Service (QoS) metrics required by each type of network traffic.
ATM technology, which promises to provide this type of adaptable network by providing flexible access to network while still guaranteeing specific QoS parameters, has been adopted by International Tele communication Union-Telecommunication (ITU-T) as a transport, multiplexing, and switching technology for B-ISDN (1), (2). The ability of the ATM technology to meet the adaptation requirement is attributed to the switching technology it adopts (3), called cell switching. The ATM cell is a fixed-length (53 octets) packet that constitutes every form of user information ranging from 64Kbps voice to several 100Mbps data. A key benefit of ATM is that it has in-built support for a diverse range of QoS categories. Within the ATM layer, the ATM Forum currently identifies five different classes (4), although the proposed version of the Traffic Management specification (5), includes a further service class known as guaranteed frame rate. These existing classes are stated below.
Constant bit-rate (CBR) service category is typically used by connections that require a static amount of bandwidth that is continuously available during the connection life's time. It is a deterministic service designed to support real-time applications requiring tightly constrained delay variations, minimal cell loss, and cell delay; such as circuit emulation, non-compressed voice traffic and continuous bit-rate video.
Variable bit-rate real time (VBR-rt) provides tightly constrained delay and delay variation for applications such as video and voice with silence removed. Variable bit-rate non-real time (VBR-nrt), is similar to VBR-rt except there are no delay bounds associated with this service category.
Unspecified bit-rate (UBR) is intended for non-real time applications such as file transfer and e-mail where the service provides best-effort delivery but offers no traffic-related guarantees. For a UBR connection, the peak transmission rate can be high, i.e., up to the maximum peak cell rate (PCR) value supported by a link, but the potential cell loss rate can also be high, resulting in a relatively low useful throughput for the UBR service.
Available bit-rate (ABR) is designed to support highly bursty non-real-time applications that are able to modify their data transfer rate dynamically during the life time of the connection according to network conditions whilst maintaining well-defined cell loss constraints. These elastic traffic services allow the network to operate at high utilization without undue risk of congestion, whilst exploiting transitory spare capacity for a relatively low tariff.
This dynamic adaptability of source transmission …