A novel ATM switch architecture for multimedia traffic

The ATM switch architecture described is the result of research by Ascom BroadNet which was commissioned for the EU RACE (Research and Development in Advanced Communications Technologies in Europe) funded HIPERNET (High Performance Networked Multimedia for Distributed Language Training) project at Cambridge University. A prototype network was installed and tested as part of the multimedia testbed, and following the completion of the HIPERNET project, the device was further developed as a product called ATM LightRing. Multimedia traffic in this paper is taken to mean VBR (variable bit rate) traffic with a large component of MPEG compressed video, and is characterised by a high “burstiness”, or peak-to-mean ratio of data rate. The traffic requires a very low CLR (cell loss ratio), typically less than 1 in 10⁶ or 1 in 10⁷ and has a strict CDV (cell delay variation) requirement. The motivation for developing a new switch architecture is discussed. To meet QoS requirements of multimedia traffic the network must be fully or nearly fully meshed, resulting in a large number of trunk ports and internodal links. The architecture devised was a single, geographically-dispersed switch, with a dual ring of dark fibre interconnecting the separate components and taking the place of the backplane in a conventional switch. The components of the switch intercommunicate using a cell-based protocol, which is similar to but not conformant with ATM. To support multimedia traffic a TDM-like service is provided