Re: TCP RTT esimates

[Natchu Vishnu Priya <vishnu@cs.ucr.edu>]

On Wed, 3 Mar 1999, David Lapsley wrote:

> Dear All,
> 
> I've been looking at the source code for the TCP Agent
> in tcp.cc and something does not seem right. 
> I would appreciate any help.
> 
> The lines that confuse me are:
> 
> 	if (t_srtt_ != 0) {
> 		register short delta;
> >>>>		delta = t_rtt_ - (t_srtt_ >> T_SRTT_BITS);	// d = (m - a0)
> 		if ((t_srtt_ += delta) <= 0)	// a1 = 7/8 a0 + 1/8 m
> 			t_srtt_ = 1;
> 
> Where t_srtt_ is the smoothed(average) round trip time, and t_rtt_ is the
> current round trip time sample.
> 
> According to this code, the final value of t_srtt_ is 7/8 of the previous
> t_srtt_ + the new round trip time sample t_rtt_.  It should be 7/8 of the 
> previous t_srtt_ + 1/8 of rtt_.

t_srtt_ is 8 * "smoothed round trip time" 
its easier to maintain it that way.. a little more presicion and less
shifts.


vishnu