Tracing packets sent

[aaminaa01]

I'm unable to trace packets sent by applications. I'm using the "vehicular-simple-one.cc" example that the millicar module(built on ns3-mmwave) came with. The example traces packets received at the server with:
echoApps.Get(0)->TraceConnectWithoutContext ("Rx", MakeBoundCallback (&Rx, stream));

But using the same for transmitted packets isn't working.
Can someone please help me understand which trace source is being referred to by "Rx", since there are multiple modules with this particular trace source.

Thanks in advance!