# Network Polling Process

The points associated with each channel, by way of its SNA, are continuously monitored for alarm situations.

The Channel Polling Process consists of the following Steps:

1. A request for the current value of the point is transmitted across the network to the appropriate node.
2. That node then responds with the desired data. This transaction is referred to as polling the channel.
3. The current value of that point is then compared against the configured alarm violation criteria for that channel.
4. This process is endlessly repeated while the scan for that network is ON.
5. This entire process is referred to as the Channel Scan. The scan continues in an infinite loop. When a violation condition is detected, the RTU begins its alarming sequence, as described in Notification Alarm_Notification. The scan loop continues so those new alarm situations may be registered as they subsequently arise.

Because the scan depends upon transactions across the industrial network, alarm detection and reporting may be affected by various network failures. For example, a node may become disconnected or otherwise disabled. Other traffic on the network may cause arbitrary delays in the exchange of information packets. Ambient electrical disturbances can corrupt the information being transferred.

The Catalyst RTU has been carefully engineered to reliably detect and deal with the following situations:

- The protocol drivers all have state of the art error detection and correction algorithms, so data is guaranteed to be reliable.
- There are many timers and protocol-specific parameters to control traffic flow and adapt to specific networking environments.
- Polling delays for one channel will not delay the polling of other channels.
- Failed communications for an extended period will trip an alarm.