Communication Troubleshooting in Ethernet (TCP / IP) networks


Question: Why SATEC device doesn't response Modbus TCP requests?


Such communication failure is possible for number of reasons:


1. Check continuity of power supplying SATEC devices during communication interruptions.


2. Violation of communication in the network.


  2.1 Check whether the instrument responds to PING requests. If the device answers PING, go to step 3.


  2.2 Check the for duplicate IP address in the network.

        Disconnect of the network cable for several seconds in order to verify 

        that this particular device is responding and not some other device in the network.


    Note:  Connecting new equipment to a specific Ethernet Switch port initializes Auto Negotiation process. 

           SATEC devices support a connection speed of up to 100 Mbp / sec.

   General recommendation :In order to increase the stability of the connection we recommend

                                to limit maximum connection speed to 100Mbps.

   SATEC BFM136 must be grounded. Check the quality of the ground.


    2.3 Check all network cables and the installation. The length of each cable must not exceed 100m.

         LAN cable must be twisted pair. Shielded cable is recommended.

         It is not allowed to coil spare cable into the bay during installation.


    2.4 Coordinate with local network administrator network setup for the device and check correctness of the definitions:

       2.4.1 IP Address

       2.4.2 Subnet Mask

       2.4.3 Default Gateway


   2.5 Define in a laptop same network setup except last segment of the IP address.

        Temporary, disconnect the SATEC device from Ethernet 

        and connect to laptop directly to the device and check communication to the device.

        

   2.6 Check the functionality and continuity of power for all switching devices.


3. Violation of communication using the Modbus protocol.

    SATEC devices are able to respond to requests of up to 4 clients simultaneously via Modbus or 2 by Modbus + 2 by DNP3.

    Each additional client will be able to connect to the device only when communication socked will be closed: 

   after 30 seconds (in some devices this time is set) from disconnecting time one of the 4 early connected clients.


4. Faults on the interrogating computer.

     4.1 Start the request for other devices in the system.

     4.2 Run the request for the same device from another computer.


5. Network problems in a certain segment of the network.

    Check the quality of communication for different devices in different segments of the network. Are there devices that stop responding to     requests in a certain segment of the network?


6. The time factor. Analyze starting time of communication interruptions.

    Check what changes in the network occur during these hours, including network overload.


7. How is communication restored: automatically or due of any actions by personnel?

    What is typical duration of communication interruptions?