Dong Mo <montedong@gmail.com> writes:

> Thanks. My problem is solved.

Excellent. Do share your results :)

> It seems to me paping can sample for the RTT over this particular port, not the
> whole connection setup time. Maybe it only record for the sync time but I am not
> fully sure. From the latency result, it is quite close to RTT of the
> link.

Well, looking at the source code it seems to do a new connection each
time:
https://code.google.com/p/paping/source/browse/trunk/src/main.cpp#80

and

https://code.google.com/p/paping/source/browse/trunk/src/socket.cpp#106

It seems to call connect(), then measure the time until select() returns
with the socket ready to either read or write. Not sure when Linux
considers a TCP socket to be ready, but I guess it's probably after
receiving the SYN+ACK of connection setup, which would be one RTT after
calling connect(), and would fit with what you're seeing. :)

-Toke