Performance evaluation of two interconnected DQDB MANs

The primary service which will be provided by broadband networks in the metropolitan or regional area will be directed to LAN interconnection for business and research users. Work has been aimed at the analysis of different access methods (MAC protocols) suitable for high speed and higher round trip delay networks such as metropolitan area networks (MAN). Since they will represent the first technical solution towards a real B-ISDN network, this paper analyzes the performance of two interconnected DQDB MANs in a scenario which is similar to the real test-bed developed in the framework of the subproject V of 'Progetto Finalizzato Telecomunicazioni' (National Telecommunication Target Project) of the Italian National Council of Research (CNR). After a brief introduction, which shows the importance of MAN-internetworking in the perspective of a progressive realization of broadband Integrated Services Digital Network (B-ISDN), the authors describe the analyzed Network topology emphasizing the critical functionalities of the network elements acting as subnetwork routers. The simulations are based on the IEEE 802.6 standard considering the non-isochronous access class which is queue arbitrated. The authors show how they faced the central problem of interconnecting two networks characterized by different transmission capacities. To avoid saturation of the internetworking device, (i.e. their buffers), two flow-control mechanisms are directed to control the throughput of the faster MAN. The conclusion shows that some unfairness of the proposed mechanisms is due to the unfairness of the DQDB Access Protocol.