Problem of the onOffAppliaction(using Tcp) Unexpected "weird" Packet-loss

[Tianye]

Hello Everyone,

I'm a novice to ns-3, I found an interesting result in my simple simulation. It contains three nodes (two clients use onOffApplication, one server uses Packetsink and pointToPoint is installed). I know that the average delay of packets would increase if the load were huge and I also want to verify this phenomenon. 

In my script I set the  DataRate of the channel to 20Mbps, the packet size to 100 Bytes and the DataRate of the onOffApplication to 1100 kBps. There is no packet-loss setting in my script.Keeping all other parameters the same, only the DataRate of onOffApplication is increased. When the DataRate of onOffApplication(in line 84) is larger than 1100 kBps, there are packet-loss. When the DataRate of onOffApplication increases to 1623 kBps the Ratio of lost packets will be the highest(about 99.3345%). I'm confused about why there would be packets lost? However, when I changed the protocol of the applications to UDP, no packet is lost. 

So may I ask what is the real reason of the packet-loss in my simulation? Thank you so much!

Best Regards,

Tianye