Applies To:
  • CitectSCADA 5.xx
  • CitectHMI 5.xx

I am getting the error "wrong sequence of packets". What is the cause of this error? 

The "wrong sequence of packets" of packets error is displayed when the Citect Client/Server networking detects an invalid packet sequence. When packets larger than 512 bytes are sent between Citect clients and servers they are cut up into 512 sub packets and identified with a packet number. When the packets are received they are re-assembled on the other side using the packet sequence number. Packets should always be transferred in sequence and if not the "wrong sequence of packets" error is displayed.

This error can be caused by a multitude of problems, but usually relates back to the network transport. For example this problem occurred more often with the Windows 95 TCP/IP network protocol than with the Windows NT TCP/IP network protocol.

Other causes of this problem can be network dropouts, very high network loading or a temporary "hang" in Citect. Symptoms of this may be the Kernel errors "Out Of Buffers". Running out of read pool or write pool buffers can cause the Citect network connection to be dropped, causing a glitch in the sequence numbers resulting in this error.

You should not attempt to solve this by just increasing the read or write pool buffers as it suggests the real problem is with your network loading or network failures. One thing to do is check how much network traffic is occurring with your project. A typical Citect Client will send between 5 to 50 packets per second. Loads greater than 100 packets per second per client can be an indicator of a problem.

To verify your network rate type NETBIOS in the Citect kernel on a typical Client (This command will also work if you are using TCP/IP). This will display a window with all the Citect Client/Server network communications. Type 'v' to put the window in Verbose mode and you will see the Network Rate() at the bottom of the window. If you have high networking loading you should contact a Citect Certified Engineer to track down the cause of your networking loading problem.