Measuring time at which an acknowledgement is received in TCP

[Amal Mohan]

I'm a beginner to ns3. Is there a way to know the time at which an acknowledgement is received in TCP. (My objective is to find the time difference between two consecutive acknowledgements received.)

Regards,
Amal

[Adil Alsuhaim]

TCP sockets have a TraceSource called "RTT", which I think is invoked every time an ACK is received. There's an example in the Traffic-Control module in the file
./src/traffic-control/examples/fqcodel-l4s-example.cc but if you think the example is too complicated, then try the 5th tutorial in the file ./examples/tutorial/fifth.cc which connects to the CongestionWindow trace of the socket, so what you can do is add connection to RTT trace

Ptr<Socket> ns3TcpSocket = Socket::CreateSocket (nodes.Get (0), TcpSocketFactory::GetTypeId ());

ns3TcpSocket->TraceConnectWithoutContext ("CongestionWindow", MakeCallback (&CwndChange));

So just add a connection to RTT and create the appropriate callback function (let's call it RttTrace)

ns3TcpSocket->TraceConnectWithoutContext ("RTT", MakeCallback (&RttTrace));

and create the function RttTrace as follows

void RttTrace (Time old_rtt, Time new_rtt)

{

     std::cout << Now().GetSeconds() <<  " : Received ACK. RTT=" << new_rtt.GetSeconds() << std::endl; 

}

Cheers,

Adil

[Amal Mohan]

Thanks a lot sir.
This one worked.
Similarly, can we know (by tracing) the time at which a packet is sent ?  (Our topology is a bottleneck link with few nodes on both sides. And we need the time interval between sending two consecutive packets by a particular node.)