Re: Recording RTT and RTO values

On Friday 26 December 2003 11:49, Tanmay Ganacharya wrote:
> Hello,
>
> I am a student from the University of Southern California. I am currently
> pursuing my master.
> I am working on a project in which I need to record the RTT and RTO values
> of a TCP connection.
> To achieve the same I first re-compiled my kernel to support debug mode.
> I then used a simple client server socket program to transfer a file. The
> sockets had the debug option set.
> Thus the kernel logs were then collected using the trpt command.
> But the problem is I am not able to figure out the required RTT and RTO
> values from the log.
>
> The log looks somewhat like the following
> 762 ESTABLISHED:input (src=128.8.126.6,32858,
> dst=204.57.0.2,1666)f5ac168b_at_5269bce1(win=f8e0)<ACK> -> ESTABLISHED
> rcv_nxt f5ac168b rcv_wnd e240 snd_una 5269bce1 snd_nxt 5269d381 snd_max
> 5269d381
> snd_wl1 f5ac168b snd_wl2 5269bce1 snd_wnd f8e0
>
> 762 ESTABLISHED:output (src=204.57.0.2,1666,
> dst=128.8.126.6,32858)[5269d381..5269d36d)_at_f5ac168b(win=e240)<ACK> ->
> ESTABLISHED
> rcv_nxt f5ac168b rcv_wnd e240 snd_una 5269bce1 snd_nxt 5269d929 snd_max
> 5269d929
> snd_wl1 f5ac168b snd_wl2 5269bce1 snd_wnd f8e0
>
> I am really not able to understand which are the RTT and RTO values in
> these.
> Please if anyone knows do let me know. It would really be useful.
> Also if anyone knows any other methods of recording the RTT and RTO values
> of a connection
> please do let me know abt it.
> I would really be grateful.

CC: net_at_ (current_at_ isn't exactly the list for this).

None of these values are the RTT or RTO values of the connection as the debug 
is rather sequence number centric. Take a look at "src/sys/netinet/tcp_var.h: 
struct tcpcb", where you will find short explainations for each field.

The value you might be looking for is "int t_rtttime". Modify the printf's in 
tcp_debug.c to give you the values you need and recompile your kernel.

Hope this helps.

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