Station-to-station communications
Station to station communications occur over port 1911 using the Fox protocol and primarily involve messaging for point, alarms, histories, and schedules.
Station-to-station communications can include communications from remote stations to a supervisor station as well as peer-to-peer station communications. It is possible to have a large number of stations communicating with a supervisor or involved in peer communications, or very likely, both types of communication occurring. When you are working with many stations and especially when a large number of points, alarms, histories, or schedules are involved, it is critical to look at the overall communications architecture of your application. There are many possible communication scenarios that can create a large volume of message traffic on the network. It is important to understand how to use NiagaraAX features that allow you to control and schedule the generation and quantity of station-to-station traffic.
In the Network component property sheet there are properties that display in most drivers, as shown in Figure 4-3.
Figure 4-3 Network parameters in the property sheet view
Status
This is a read-only property that indicates if the driver is capable of communications. For any configured driver, network Status is typically {ok}. However, when adding some networks, the initial Status may be {fault}. This might mean a communications port is unassigned, or there is a port conflict.
A fault status also occurs if the host platform is not properly licensed for the driver being used. If you have a network fault, see the Fault Cause property value for more details. If you set the Enabled property to false, the status reads {disabled}.
Enabled
By default, network Enabled is true--you can toggle this in the property sheet, or in the Driver Manager (by selecting the network and using the Edit button).
Whenever you set a network to disabled (Enabled = false), the network component and all child driver components (all devices, proxy points, etc.) change to a disabled status. If this is a field bus driver, communications routines like polling and device status pings also suspend. By default, disabled status color is gray text on a light gray background. This network-wide action may be useful for maintenance purposes to shut down communications across the driver network.
Note that Enabled is also individually available at the device-level and proxy point-level, using the Edit button or dialog box in the Device Manager or Point Manager, respectively. A disable at the device-level disables all child (proxy points), as well as polling to that points under that device. A disable at the proxy-point level disables the single point.
Health
This property simply displays advisory information about the “health” of the particular driver network. These read-only properties can help you recognize and troubleshoot a network problem but they provide no direct network management controls.
Alarm Source Info
A network's Alarm Source Info slot holds a number of common alarm properties that are used to populate an alarm if the network does not respond to a monitor ping. The Alarm Class option property may have impact on the network traffic since different alarm classes may be configured to impact network traffic to different degrees. For example, you may have an alarm class configured to route alarms simultaneously to multiple recipients across the network, including email, lineprinter and remote station recipients.
Each child device object also has its own Alarm Source Info slot, with identical (but independently maintained) properties.
Figure 4-4 Alarm class choice affects network traffic
Monitor
Monitor provides verification of the general health of the network, plus the network's “pingables” (typically, devices) by ensuring that each device is minimally “pinged” at some repeating interval.
You should leave Ping Enabled set to true in almost all cases. In this state, a ping occurs for each device under the network, as needed. While set to false, device status pings do not occur and device status message displays cannot change.
Specifies the interval between periodic pings of all devices. Typical default value is every 5 minutes (05m 00s), you can adjust differently if needed.
The network ping Monitor will only “ping” the device if the time of last health verification is older than the ping frequency. Therefore, in normal operation with most drivers, the proxy point polling mechanism actually alleviates the need for the monitor ping, providing that the ping frequency is long enough. The default setting of 5 minutes between “pings” should be good for most situations. If the ping frequency is set to some very low setting and you have a lot of devices on the network, the message traffic for pinging could be significantly higher.
If this is property is set to true (default), an alarm is recorded in the station's AlarmHistory upon each ping-detected device event (“down” or subsequent “up”). If false, device “down” and “up” events are not recorded in the station's AlarmHistory.
Specifies the period a station must wait after restarting before device “down” or “up” alarms are generated. Applies only if the Monitor's property Alarm On Failure is true.
Following, is a list of some of the network-level control options that are common across many of the drive networks. Each one of these child components has properties that are adjustable and can have network-wide impact.