[e2e] Minimum RTO values

Nicolas Christin christin at SIMS.Berkeley.EDU
Tue Nov 9 17:10:50 PST 2004


On Tue Nov 09, 2004, Preethi Natarajan <nataraja at cis.udel.edu> wrote:
> I am trying to probe webservers in the Internet for TCP Min RTO
> values. Based on my preliminary tests I saw the following results,
> which I want to validate.

Looking at the source code of the various OS's you refer to might

> Linux : around 200 ms

Sounds about right (at least for Linux 2.4). From

#define TCP_RTO_MIN     ((unsigned)(HZ/5))

where HZ is roughly equivalent to one second.

> FreeBSD : around 1s

It depends. Some versions of FreeBSD (e.g., 4.x) have 1s, indeed.
The value is in /usr/sys/include/netinet/tcp_timer.h:

#define TCPTV_MIN       (hz) 

but I also saw some branches which have a 3 in there instead,
e.g., the current branch (see

> Sun Solaris : around 4s

Solaris 8 has in /usr/include/netinet/tcp_timer.h:

#define TCPTV_MIN       (1*PR_SLOWHZ) 

which should indicate a 1 second minimum RTO.

Hope this helps!
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