> I'm curious whether we  shall take RTT Samples for each segment or
> not. AFAIK, the RFC encourage one RTT timer, which is started at
> least once a round.
> 
> An alternative way would be one timer per segment.

Our work suggests that multiple samples per RTT does not help the
estimator.

See:

  Mark Allman, Vern Paxson.  On Estimating End-to-End Network Path
  Properties.  Proceedings of the ACM SIGCOMM Technical Symposium,
  Cambridge, MA, September 1999.
  http://www.icir.org/mallman/papers/estimation.ps

allman