A SIMULATION STUDY OF TCP PERFORMANCE OVER ABR AND UBR SERVICES IN ATM LANS

Both available bit rate (ABR) service and unspecified bit rate (UBR) s ervice with early packet discard (EPD) schemes have been considered fo r supporting data applications in ATM networks. Since transmission con trol protocol (TCP) is perhaps the most widely used transport layer pr otocol in existing data networks, the performance of TCP over ATM usin g ABR service and UBR service with EPD schemes is of great interest to ATM equipment vendors and service providers. In this paper, we presen t a simulation study of this interesting issue in a LAN environment us ing some benchmark network configurations proposed in the ATM Forum. O ur simulation results show the following: (1) With UBR service and EPD schemes, TCP suffers significant performance degradation in terms of fairness and requires relatively large switch buffer even with a small number of active virtual connections over a LAN configuration, and (2 ) for the same set of network configurations and with ABR service usin g explicit rate feedback schemes, TCP achieves good performance in ter ms of fairness and link utilization, and requires relatively small swi tch buffer.