Applies To:
  • CitectSCADA 1.00 1.01 1.10 1.11 1.20 2.00 2.01 3.00

When using NetBEUI protocol in the WFW3.11 for CITECT LAN communication, the response time on the client can cause slight delays on the server. This can cause an overall degrading of network performance on large or high speed Citect systems. If you have a small to median Citect system you will not notice this performance degradation, however it will have an effect on your response times.

This problem may show up in Citect with the Out of Buffers in lan.write.pool error message. This will occur as Citect cannot transmit the data fast enough across the network and Citects write buffers may overflow.


Microsofts NetBEUI protocol supports a sliding window feature including the piggybacking of acknowledges. These features are designed to make the most efficient use of the network bandwidth, however they may add slight delays to the network transfer. These extensions increase the performance when using file transfers however they degrade the performance of any application requiring real time communication. As Citect is a real time applications these extension will degrade the performance of Citect. If you have any other real time applications these extensions will also be degrading their performance as well.

You may disable these extensions via the piggybackack switch in the PROTOCOL.INI file. This switch is setup at the [NETBEUI] section of the PROTOCOL.INI file.


Setting this option will only have a very slight effect on the performance of file transfer between WFW nodes. The degrade in file transfer performance can be less than 1% while the increase in performance to real time applications can be up to and over 100%. See also Q1711 for same problem with IPX protocol.

You may also work around the real time limitation of the network protocol by increasing the number of transmit buffers Citect will use. You will only need to increase the transmit buffers on Citect which are sending a large number of network packets. For example increase on the I/O Server or Alarm/Trend/Report servers. You should not need to increase transmit buffers on a Citect client. You adjust the transmit buffers with the parameter [LAN]SesSendBuf. See online help for full documentation on this parameter. You must be careful when adjusting this parameter as you can cause the network protocol to run out of transmitt buffers if you set this number too high. If the protocol runs out of transmit buffers you will suffer a major degrade of network performance and you will get hardware errors. The default for this parameter is 2 and you should try to slowly increasing this parameter,. Values of 8 to 12 with NetBEUI will give good performance without causing the protocol to run out of transmit buffers