The Distributed Queue Dual Bus (DQDB) system consists of a linear arrangement of N nodes that communicate with each other using two contra-flowing buses. The nodes use an extremely simple protocol to send messages on these buses. This simple, but elegant, system has been found to be very challenging to analyze. We consider a simple and uniform abstraction of this model to highlight the fairness issues in terms of average waiting time. We introduce a new approximation method to analyze the performance of DQDB system in terms of the average waiting time of a node expressed as a function of its position. Our approach abstracts the intimate relationship between the load of the system and its fairness characteristics, and explains all basic behavior profiles of DQDB observed in previous simulation. For the uniform DQDB with equal distance between adjacent nodes, we show that the system operates under three basic behavior profiles and a finite number of their combinations that depend on the load of the network. Consequently, the system is not fair at any load in terms of the average waiting times. We also show that the main theme of the analysis carries over to the general (nonuniform) DQDB. By suitably choosing the inter-node distances, the DQDB can be made fair around some loads, but such system will become unfair as the load changes. In the vicinity of a critical load, the uniform network runs into a state of instability, where its behavior fluctuates from one extreme to the other with small load variations. Our analysis is supported by simulation results.>

Considers a simple and uniform abstraction of the distributed queue dual bus (DQDB) system of N nodes to highlight the fairness issues in terms of average waiting time. For the uniform DQDB with equal distance between adjacent nodes, the authors show that the system operates under three basic behavior profiles and a finite number of their combinations that depend on the load of the network. Consequently, the system is not fair at any load in terms of the average waiting times. In the vicinity of a critical load of 1-4/N the uniform network runs into a state akin to chaos, where its behavior fluctuates from one extreme to the other with a load variation of 2/N. The analysis is supported by simulation results. The authors also show that the main theme of the analysis carries over to the general (non-uniform) DQDB.>

Recently protocols have been introduced that enable the integration of synchronous traffic (voice or video) and asynchronous traffic (data) and extend the size of local area networks without loss in speed or capacity. One of these is DRAMA, a multiband protocol based on broadband technology. It provides dynamic allocation of bandwidth among clusters of nodes in the total network. In this paper, we propose and evaluate a number of traffic placement policies for such networks. Metrics used for performance evaluation include average network access delay, degree of fairness of access among the nodes, and network throughput. The feasibility of the DRAMA protocol is established through simulation studies. DRAMA provides effective integration of synchronous and asynchronous traffic due to its ability to separate traffic types. Under the suggested traffic placement policies, the DRAMA protocol is shown to handle diverse loads, mixes of traffic types, and numbers of nodes, as well as modifications to the network structure and momentary traffic overloads.