A study on accommodation of TCP/IP traffic using window scale option to international ATM network with VBR service category

For ATM Network, VER (Variable Bit Rate) service category is used to accommodate TCP/IP traffic. In an international ATM network with large propagation delay, higher TCP throughput can be obtained by use of window scale option. In order to accommodate TCP traffic with window scale option effectively, it is required to select optimum values of VER parameters, i.e. SCR (Sustainable Cell Rate) and MBS (Maximum Burst Size), and to evaluate the impact of UPC (Usage Parameter Control) function on TCP throughput. We have studied those technical issues for conventional TCP: but the results cannot be applied to TCP traffic with the window scale option due to the TCP terminal performance and the large window size. In this paper, we proposed VER parameter determination method for TCP with the window scale option and evaluated the values in each condition. These results shows that the optimum MBS is much smaller than the burst length of TCP segments especially using low performance TCP terminal or the PCR (Peak Cell Rate) below the calculated TCP throughput. Furthermore, we also discusses some experimental results of TCP throughput degradation due to UPC function. It shows that the throughput of TCP with large window size dramatically degraded when the SCR and MBS values used in ATM switch are smaller than the optimum values.