From: Oumer Teyeb (oumer@kom.auc.dk)
Date: 08/18/04
Message-ID: <412302AB.4000909@kom.auc.dk> Date: Wed, 18 Aug 2004 09:18:03 +0200 From: Oumer Teyeb <oumer@kom.auc.dk> Subject: Re: tcptrace How to get the RTT _actually_ sampled by TCP?
I dont know if there is any option to output only the timestamps from
tcptrace.
I know that in tcpdump you can use -t and -tt switches to modify the way
timestamps are shown, but this timestamps refer to the time the kernel
sees the packets, not the ones you are interested in
Liangping Ma wrote:
>Hello Ouwer,
>
>Do you know how to easily get the timestamps using tcptrace? I have gone
>through the manual, but did not find the needed command. An indirect way
>is using
>tcptrace -R dump03
>and then extracting the timestamps from the output .xpl files.
>
>Thanks.
>
>Liangping
>
>
>
>
>
>>I think it might be using timestamps. If the timestamps options is
>>enabled every ACK will put the timestamp of the packet it acks, so even
>>though TCP might use only one RTT measure in a window, tcptrace can just
>>use the timestamps to tell you the RTTs.
>>
>>Liangping Ma wrote:
>>
>>
>>
>>>Hello,
>>>
>>>I measured the RTTs for a TCP connection using tcptrace. I found that the
>>>number of RTTs is almost equal to (in fact, a little bit less than) the
>>>number of packets sent. For example, in one TCP session,
>>>
>>>pure pkts sent: 7857
>>>sack pkts sent: 150
>>>
>>>The number of RTTs obtained by TCP is 7614. So tcptrace samples round-trip
>>>time almost once per packet.
>>>
>>>BUT, TCP only samples the round-trip time once per RTT (rather than once
>>>per packet). [see p. 468 Computer Networks, L. Peterson and B. Davie, 2nd
>>>Ed., 2000].
>>>
>>>How do you get the RTTs that are _actually_ sampled by TCP?
>>>
>>>Thanks.
>>>
>>>Liangping
>>>
>>>----------------------------------------------------------------------------
>>>To unsubscribe, send a message with body containing "unsubscribe tcptrace" to
>>>majordomo@tcptrace.org.
>>>
>>>
>>>
>>>
>>>
>>
>>
>
>
>
----------------------------------------------------------------------------
To unsubscribe, send a message with body containing "unsubscribe tcptrace" to
majordomo@tcptrace.org.
This archive was generated by hypermail 2.1.7 : 08/18/04 EDT