Wireshark · Wireshark-bugs: [Wireshark-bugs] [Bug 2669] New: Negative values are not graphed correctly in IO Graphs/ Advanced

[bugzilla-daemon@xxxxxxxxxxxxx]

https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=2669

           Summary: Negative values are not graphed correctly in IO
                    Graphs/Advanced
           Product: Wireshark
           Version: 1.0.1
          Platform: PC
        OS/Version: Windows XP
            Status: NEW
          Severity: Normal
          Priority: Low
         Component: Wireshark
        AssignedTo: wireshark-bugs@xxxxxxxxxxxxx
        ReportedBy: greg.cook@xxxxxxxxxxx


Created an attachment (id=1943)
 --> (https://bugs.wireshark.org/bugzilla/attachment.cgi?id=1943)
PNG screen capture after graphing ppi.80211-common.dbm.antsignal

Build Information:
Version 1.0.1 (SVN Rev 25639)

Copyright 1998-2008 Gerald Combs <gerald@xxxxxxxxxxxxx> and contributors.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Compiled with GTK+ 2.12.8, with GLib 2.14.6, with WinPcap (version unknown),
with libz 1.2.3, without POSIX capabilities, with libpcre 7.0, with SMI 0.4.8,
with ADNS, with Lua 5.1, with GnuTLS 2.3.8, with Gcrypt 1.4.1, with MIT
Kerberos, with PortAudio V19-devel, with AirPcap.

Running on Windows XP Service Pack 2, build 2600, with WinPcap version 4.0.2
(packet.dll version 4.0.0.1040), based on libpcap version 0.9.5, without
AirPcap.

Built using Microsoft Visual C++ 6.0 build 8804

Wireshark is Open Source Software released under the GNU General Public
License.

Check the man page and http://www.wireshark.org for more information.
--
When using AirPCap, the PPI Packet Header Protocol can generate several fields
which are negative.  For example

ppi.80211-common.dbm.antsignal

generates values which are computed in dBm, and thus almost always negative. 
Typically, these values are between -100 and -20 dBm.  (As seen, for example,
when using the AirPcap classic.)

One common application after capturing 802.11 packets is to:

Statistics -> IO Graphs

Go to the "Y Axis" box and select "Advanced..." from the Unit: drop-down box.

Select MAX(*) from the Calc: drop-down box.

Paste  ppi.80211-common.dbm.antsignal into the box next to "MAX(*)".

Select Impulse from the Style: drop-down box.

Select Graph 1

This will result in something similar to the attached screen capture where all
the values are off-scale high.  The "Copy" button correctly outputs accurate
CSV data, so it seems it is the graph module and not the data where the problem
lies.  Clearly, the negative values are not being plotted correctly.

It would be very helpful to graph the received signal strength (and other
negative values) as given by PPI in Wireshark.  Using the "Copy" button does
allow a workaround for now, where the values may be saved and plotted by an
external program.


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