A SIMULATION STUDY OF DQDB MAC PROTOCOL FOR FAIRNESS AND THROUGHPUT IMPROVEMENT

Abstract

In December 1990, the IEEE standard board accepted an IEEE 802.6 standard specifying the Distributed Queue Dual Bus (DQDB) subnetwork for a Metropolitan Area.Network (MAN). This dissertation does the extensive investigation of the asynchronous service of DQDB. When the network is overloaded or saturated some nodes get undesired bandwidth advantage over others. To overcome it a Bandwidth Balancing scheme is suggested in which system wastes some part of channel bandwidth and distributes rest of it equally among all the nodes. A new scheme called No Slot Waste Bandwidth Balancing (NSW_BWB) is analysed which balances the network without wasting any bandwidth. In basic DQDB the transmitted slots are never erased halfway through the bus, and only terminated at the end of bus. At first a special node called "Erasure Node" is introduced in basic DQDB network for slot reutilization. Due to placing of erasure nodes some latency is introduced and moreover erasing is dependent upon the traffic pattern. So a new scheme for slot erasing called Previous Slot Information (PSI) scheme is introduced. This scheme is fully compatible with IEEE 802.6 and does not add any latency to the network. The simulation technique is used to do the study the basic DQDB. This simulation is then extended to show the bandwidth saving with NSW_BSW. Along with that, throughput improvement and fairness performance is demonstrated with Erasure Nodes and PSI Scheme. Then the Erasure Nodes and PSI scheme is integrated and it is found that this gives still better , throughput performance.