In TCP over OBS networks, packets from various IP sources assemble into a data burst at the ingress node and are transmitted to egress node cutting through the core network all-optically. The control packet always precedes the data burst by an offset time. This time gap between the control packet and the data burst is adequate to process the burst header packet and configure the switches at the core nodes. These switches down the route are configured only when the data burst arrives to facilitate the burst to cut through an all-optical path. The basic assumption of TCP variants is that the transmitting physical medium is electronic and packets are experiencing delay due to IP routers, but with TCP over OBS networks there will be a change in performance of TCP flavours due to the underlying network. In these conditions an experimental study was made to evaluate the performance of three popular TCP variants, TCP-Reno, TCP-Newreno and TCP-Vegas using NS-2.