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Capturing MSTP network bus activity


How do I get a MSTP capture file so that I can analyze comm activity on an MSTP bus?

How can I determine if a site is using bad COV management?

How can I determine if a controller has poor bus design or installation?

How can I determine if a site has multiple BBMD's on the same subnet?





b3 controllers

Third party BACnet devices



Analyze MSTP traffic via capture.


To capture MSTP comm activity to a capture file that can be analyzed using a network sniffer application such as WireShark you will need the following.


MSTP Capture application  such as MSTPCap.exe


  • Connect the USB adapter cable to the usb port on a laptop PC
  • Connect the RS232/RS485 adapter to the 9 pin end of the USB adapter cable.
  • Attach a length of MSTP bus cable to the wire terminal on the RS485 adapter.
  • Copy the MSTP Capture application to C:\
  • Open a command window.
  • Launch the application by entering C:\> Mstpcap com# ###### where com# is the PC's serial port (Com1, Com2, etc.) and ##### is the current baud rate the BCX MSTP bus is configured for (19200, 38400, etc.).
  • The command window will indicate the name of the file the activity is being captured to.
  • Once you are done close the command line window

The capture data can be viewed by running WireShark.  Select File > Open and navigate to the folder the capture file was saved to and select the capture file. 

With the higher end MSTP capture tools such as tools developed by PolarSoft and Cimetrix, MSTP captures at 76.8K baud are possible.  Lower end capture applications like MSTPCap typically are only able to capture MSTP packets from networks running at buss speeds at or below 38.4K baud. 


Also check out the BACnet-Capturing MS/TP Traffic Quick-Help video on the Exchange.

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