RTT of TCP
Lloyd Wood <L.Wood@surrey.ac.uk>
Tue, 31 Aug 1999 12:36:54 +0100 (BST)
On Tue, 31 Aug 1999, Xiao Hannan wrote:
> What's the unit of variables for RTT estimations of TCP in NS?
* default 0.1,
* 0.3 for 4.3 BSD,
* 0.01 for new window algorithms,
> From the
> documentation, the RTT samples are computed as the difference between the
> current time and a "time echo" field in the ACK packet.
That's SACK/FACK only; otherwise you're relying on time of send/time
of receipt and Karn's algorithm.
> So is RTT in unit of time?
> I let a TCP session run over a link with 20ms delay. Then I monitor that
> the srtt_ of TCP is 8, and rttvar_ is 2 during a simulation time of 10s.
> Then, what's the relationship between these value?
rttvar_ is 2 x 0.01s
See e.g. RFC793 for srtt calculations.
> Thanks a lot