Abstract Recent advances in optical switching technology allows for the creation of networks in which data bursts are switched optically at each node, offering a greater degree of flexibility suitable for handling bursty Internet traffic. TCP-based applications account for a majority of data traffic in the Internet; thus understanding and improving the performance of TCP implementations over OBS networks is critical. Previously, several articles show that load-balanced routing improves loss-performance in OBS. In this paper, we identify the ill-effects of load-balanced OBS on TCP performance caused by false time-outs and false fastretransmits. We propose a source-ordering mechanism that significantly improves TCP throughput over a loadbalanced OBS network. Keywords Load-balancing · TCP · OBS