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stumbling over the use of io,stat,0,SUM

asked 2020-02-15 13:11:34 +0000

I don't understand the output I get when I try to sum tcp.time_delta in a trace

    C:\Temp>tshark -r P-Inside-sliced.pcapng -o tcp.calculate_timestamps:TRUE -Y tcp.dstport==443 -qz io,stat,0,SUM(tcp.time_delta)tcp.time_delta

============================================
| IO Statistics                            |
|                                          |
| Duration: 18.2 secs                      |
| Interval: 18.2 secs                      |
|                                          |
| Col 1: SUM(tcp.time_delta)tcp.time_delta |
|------------------------------------------|
|              |1           |              |
| Interval     |     SUM    |              |
|---------------------------|              |
|  0.0 <> 18.2 | 106.856631 |              |
============================================

C:\Temp>

The believe that the Total Time encompassed in this trace is 18.2s ... but then, how can the Sum of tcp.time_delta be ~106s?

And further, if I sum tcp_time.delta in the other direction (notice the change from tcp.dstport to tcp.srcport) ... I would have predicted that the SUM would be some other number ... not ~106s again

    C:\Temp>tshark -r P-Inside-sliced.pcapng -o tcp.calculate_timestamps:TRUE -Y tcp.srcport==443 -qz io,stat,0,SUM(tcp.time_delta)tcp.time_delta

============================================
| IO Statistics                            |
|                                          |
| Duration: 18.2 secs                      |
| Interval: 18.2 secs                      |
|                                          |
| Col 1: SUM(tcp.time_delta)tcp.time_delta |
|------------------------------------------|
|              |1           |              |
| Interval     |     SUM    |              |
|---------------------------|              |
|  0.0 <> 18.2 | 106.856631 |              |
============================================

C:\Temp>

See http://www.skendric.com/ask_wireshark for the pcaps

BTW: I have taken two pcaps, one from just inside a particular network device, the other from just outside same device, and I'm trying to use this technique to measure the device's impact on performance

--sk

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answered 2020-02-16 04:54:38 +0000

bubbasnmp gravatar image
tcp.time_delta  Time since previous frame in this TCP stream


If the capture has more than one stream in parallel then the sum can be larger than the elapsed time.
Changing the filter on the sum will sum data for a single stream.

-qz io,stat,0,SUM(tcp.time_delta)tcp.stream==0
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Ahh, got it -- thank you

Stuart Kendrick gravatar imageStuart Kendrick ( 2020-02-16 11:38:56 +0000 )edit

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Asked: 2020-02-15 13:11:34 +0000

Seen: 26 times

Last updated: Feb 16