Socket Keep Alive

Each Geo SCADA Expert server can send polls to other servers or clients that are connected to the server via a TCP/IP connection. The poll is a request for a response, and is used to check that there are no open connections that should be closed.

During normal operation, the Geo SCADA Expert server has open connections to any other servers in the arrangement and each of the clients. If a client or server is shutdown, the TCP/IP connection to the Geo SCADA Expert server should be closed. However, sometimes there may be conditions on the network that result in the TCP/IP connection remaining open even though the client or server has been shutdown. As each open connection uses a Geo SCADA Expert license, this can result in users with valid licenses not being able to log on due to other connections remaining open (if the license limit has been reached).

The Geo SCADA Expert server uses the Socket Keep Alive feature to check that the servers and clients at the other end of the TCP/IP connections are still using the connection. If the clients or other servers respond to a poll that is sent, the TCP/IP connection is being used and is intentionally open. If there is no response, the Geo SCADA Expert server will send further polls (up to 5) to check that the connection is definitely not being used. If there are still no responses, the server will close the connection.

You can use the Socket Keep Alive settings to define whether the Send Poll feature is enabled or disabled.

When the feature is enabled, you can also define:

• The length of time that an open TCP/IP connection can remain inactive before it is closed.
• How long the server waits before sending another poll (if there was no reply to the first poll).

To configure the Socket Keep Alive settings:

1. Access the Geo SCADA Expert Server Configuration Tool.
2. Expand the Global Parameters branch of the tree structure.
3. Select the Advanced entry to display the Advanced section.
4. In the Socket Keep Alive section, define the required settings:

   • Send Poll—Use this check box to specify whether the Geo SCADA Expert server is to run checks to ascertain whether your system has any open connections to clients or servers that have shutdown. Such unnecessarily open connections could result in licensed users being unable to log on (if the license limit has been reached).

     Select the check box (the default) to enable the feature. The Geo SCADA Expert server will send regular polls to any servers or clients that are connected to it via a TCP/IP connection. It will use the polls to check whether there are any open connections to clients or servers that have shutdown. If the Geo SCADA Expert server detects an unused open connection, it will try to close that connection once it has determined that it is no longer required.

     Clear the check box to disable the feature. The Geo SCADA Expert server will not run checks to ascertain whether your system has any open TCP/IP connections to clients or servers that have shutdown. This could result in licensed users being unable to log on (if the license limit has been reached). When the check box is clear, the rest of the properties in the Socket Keep Alive section are 'grayed out' and unavailable for use.

   • Time between polls—Use this property to define the 'Keep Alive' time - the length of time during which a TCP/IP socket can remain idle before it is closed. The default setting of 300 seconds is usually appropriate.

     If there are system users that have valid licenses but are unable to log on, the Time between polls setting might be too slow. You can instruct the server to sends polls more quickly by decreasing the number of seconds.

     Before you decrease the Time between polls, you should assess your network, as lower Time between polls settings can result in increased traffic, which might have an impact on your network.

     If you do need to change the Time between polls, we recommend that the value is no less than 60 seconds.

     Alternatively, you might want to consider increasing the number of Geo SCADA Expert licenses on your system. Contact your Geo SCADA Expert provider to discuss your license requirements.

   • Interval—Define how often the server attempts to verify that a TCP/IP connection is being used. The server does this by sending a TCP Ack/Poll at this frequency to attempt to keep the socket alive when it is still required but is not currently being used by an application. Typically, the default setting of 1 second is appropriate.
5. Apply the changes to the server.

Now that you have defined the socket keep alive setting, you can proceed with other aspects of the server configuration.