Performance of TCP over UBR in ATM with EPD and virtual queuing techniques

  • Authors:

  • Hong-Yi Tzeng;Kai-Yeung Siu

  • Affiliations:

  • High Speed Networks Research Department, Bell Laboratories, Lucent Technologies, Holmdel, NJ 07733, USA;d'Arbeloff Laboratory for Information Systems and Technology, MIT, 77 Massachusetts Ave., Cambridge, MA 02139, USA

  • Venue:
  • Computer Communications
  • Year:
  • 1998

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Abstract

While both available bit rate (ABR) and unspecified bit rate (UBR) services can be used to support data traffic in asynchronous transfer mode (ATM), many ATM switch vendors consider UBR to be more attractive because of its low implementation cost in comparison with ABR. However, since there is no congestion control at the cell level in UBR and cells are simply discarded when buffer overflow occurs, the effective throughput of transmission control protocol (TCP) can degrade significantly over UBR service in a congested network. Early Packet Discard (EPD) techniques have been proposed by Romanow and Floyd (Dynamics of TCP traffic over ATM networks, IEEE Journal on Selected Areas in Communications 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 in ATM networks with ABR and UBR services, in: Proceedings of the International Phoenix Conference on Computers and Communications, March 1996), 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 studies in designing better and low cost methods for the support of TCP over ATM. We apply the virtual queuing technique proposed in Chiussi et al. (Virtual queuing techniques for ABR service: improving ABR/VBR interaction, Infocom'97) to emulate on a FIFO queue the service provided by per-VC queuing. This technique requires low implementation cost and delivers performance of TCP over UBR comparable to the expensive per-VC queuing technique. Simulation results are presented to demonstrate that our technique combined with EPD can drastically improve the performance of TCP over UBR service.