Hi all: I have set up an experiment for TCP but I am puzzled by its results, so I thought maybe you can shed some light on it:
I have linear network with 4 nodes. 1 ----- 2 ----- 3 ------ 4 Link 1-2 and Link 3-4 are full duplex 100 Mb 1ms Link 2 -3 is full duplex 1Mb 1ms. I set up an FTP application sending from an Agent/TCP/Newreno in node 1 to an Agent/TCPSink in node 4. There's no other traffic. I would expect TCP to increase the transmisison window, and therefore, the throughput, until the queue in the link from 2 to 3 became full. Then, TCP should lose a packet and reduce the window. If I plot the cwnd_ of my TCP agent as a function of time, I see that indeed it keeps increasing until the simulation ends. However, the throughput reaches almost from the beginning a value close to the link capacity of 1 Mb, and the flow doesn't lose any packets (the queue does not get full). Is this caused by something specific of the TCP agent flow control, or am I missing something here? Thanks, -- Eduardo J. Ortega U.
