Architecture of PLAN: a pipelined-access local ATM network protocol for multimedia applications

This paper presents a shared media ATM LAN architecture known as PLAN (pipelined-access local ATM network) suitable for both LAN and MAN applications. The protocol has been designed for a bidirectional broadcast bus system topology. Stations can be connected at regularly spaced connection points along the bus. This segmentation allows to reduce the bus propagation delay between two successive transmissions to as little as the propagation delay of one segment. This feature helps to effectively reduce the overhead due to bus propagation delay and keep it fixed irrespective of the offered load. The protocol supports tree topology at the cost of slight increase in overhead. The protocol operates in two consecutive phases: one reservation and the other transmission. Although DQDB also limits the propagation delay overhead, the protocol requires the use of 2 buses. Moreover, 2 interfaces per station are required, tree topology networks are not supported, real time traffic is not supported, and an AAL is required to interface with ATM networks. The MLAN protocol addresses most of these problems but suffers from performance deterioration as the number of stations and bus length is increased-hence it is not suitable for the MAN environment. The proposed PLAN protocol (i) operates in the native ATM mode, (ii) guarantees continuous access to real-time traffic and high priority data traffic, (iii) achieves throughput approaching 100% for a 200 station LAN of 1 km length operating at 150 Mbps. The throughput decreases by a fraction of a percent for each kilometer increase in bus length. Based on these and other results, the proposed broadcast bus system PLAN architecture is seen to be well suited for high speed multimedia ATM LAN and MAN applications