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

For an ATM network, the VBR (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 the window scale option. In order to accommodate TCP traffic with the window scale option effectively, it is required to select optimum values of VBR parameters, i.e. SCR (sustainable cell rate) and MBS (maximum burst size), and to evaluate the impact of the 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 propose a VBR parameter determination method for TCP with the window scale option and evaluate the values in each condition. The results show that the optimum MBS is much smaller than the burst length of TCP segments especially using a low performance TCP terminal or a PCR (peak cell rate) below the calculated TCP throughput. Furthermore, we also discuss some experimental results of TCP throughput degradation due to the UPC function. It is shown that the throughput of TCP with large window size dramatically degrades when the SCR and MBS values used in the ATM switch are smaller than the optimum values.