>> When I plot a2b_tput.xpl I get two curves, one red and one blue
>> plus the yellow dots for packets. What is not clear for me is what
>> are the blue and red curves represents with respect to throughput?

Sorry, that stuff hasn't been documented very well, partly because I'm
not sure how to display it more clearly, but here's what it means:

The yellow dots are the instantaneous throughput samples.  They're
calculated by using the time since the last segment for the connection
and the size of the current segment to get bytes/second for this
sample.

The red line is the result of averaging together multiple yellow
dots.  By default (see -A), the red line uses the last 10 segments to
calculate a throughput.  Higher -A values give smoother curves.

The blue line is simply a running average throughput from the
beginning of the transfer, and it's final value is the same as what is
reported for the connection's transfer rate.

Hope that helps.  As I said, I'm not really sure what should be on
this graph.  What's there is the stuff that we've wanted here locally,
but I'd be glad to hear other ideas!

Shawn