PERFORMANCE OF TCP OVER UBR IN ATM WITH EPD AND VIRTUAL QUEUING TECHNIQUES

While both available bit rate (ABR) and unspecified bit rate (UBR) ser vices can be used to support data traffic in asynchronous transfer mod e (ATM), many ATM switch vendors consider UBR to be more attractive be cause of its low implementation cost in comparison with ABR. However, since there is no congestion control at the cell level in UBR and cell s are simply discarded when buffer overflow occurs, the effective thro ughput of transmission control protocol (TCP) can degrade significantl y over UBR service in a congested network. Early Packet Discard (EPD) techniques have been proposed by Romanow and Floyd (Dynamics of TCP tr affic over ATM networks, IEEE Journal on Selected Areas in Communicati ons 13 (4) (1995) 633-641) and shown to improve the throughput of TCP over ATM. In our earlier work (A simulation study of TCP performance i n ATM networks with ABR and UBR services, in: Proceedings of the Inter national Phoenix Conference on Computers and Communications, March 199 6), we have shown that TCP with EPD can suffer significant degradation in fairness of throughputs among competing VCs in a congested ATM LAN environment, but the degree of fairness can be improved by using per- VC accounting/queuing techniques. In this paper, we continue our studi es in designing better and low cost methods for the support of TCP ove r ATM. We apply the virtual queuing technique proposed in Chiussi et a l. (Virtual queuing techniques for ABR service: improving ABR/VBR inte raction, Infocom'97) to emulate on a FIFO queue the service provided b y per-VC queuing. This technique requires low implementation cost and delivers performance of TCP over UBR comparable to the expensive per-V C queuing technique. Simulation results are presented to demonstrate t hat our technique combined with EPD can drastically improve the perfor mance of TCP over UBR service. (C) 1998 Elsevier Science B.V.