Experimental TCP performance evaluation in an ABR access environment

The available bit rate (ABR) service category has a great potential in avoiding congestion in data communication networks. The ABR relies on a closed loop flow control mechanism, attempting to push buffer requirements towards the boundaries of the ABR aware network regions, be-it to the ATM end-systems in an ATM end-to-end environment or to the edge routers in a router based environment. On the other hand, Internet traffic is most often flow controlled at layer 4 by means of the transmission control protocol (TCP). Consequently it is of great importance to investigate the potential of the ABR in carrying TCP traffic efficiently. Most work reported in the literature is based on simulation studies. As interesting these simulation studies are, they can never capture all the real-world effects. The availability of an ABR ATM multiplexer and ABR network interface cards (NIC) gave us the unique opportunity to acquire hands-on experience in dimensioning an ABR system for Internet traffic. This paper studies the performance and buffer requirements of TCP traffic multiplexed with priority VBR background traffic in an ABR queue. We applied several modes of ABR responsiveness by changing the ABR connection parameters. We optimised the ABR node parameters, varied the amount of TCP sources and changed the VBR traffic profile. The outcome of this study is a set of guidelines for dimensioning an ABR access configuration for the efficient transport of Internet TCP traffic.