Hi, I am running simulations using ns-2, and I have about 80 TCP flows and 80 UDP flows, with a bottleneck of 40 Mb and the UDP flows are CBR pumping 2MB. Some of the tcp flows receive "-1" number of acks, this is truly vague? And I am getting the number of acks that the flow receives frm the variable "_ack". Please enlighten. Smitha