Unacknowledged Requests

Overview

The "Unacknowledged Requests” diagnostic fails when a BACnet device does not receive an acknowledgment (ack) after sending a message to another BACnet device in an OT network.
 

Causes

• The destination device is offline.
• The responding router is offline or busy.

Implications

• Communication Breakdown: Unacknowledged requests indicate that a device has not received a response from another device, leading to a breakdown in communication between devices.
• Data Loss: If messages are not acknowledged, data may not be received or updated correctly, leading to unreliable information being used for decision-making.
• Fault Detection Delay: Unacknowledged requests may indicate a device or sensor failure, but if not promptly addressed, faults and issues might go unnoticed.
• System Performance: Unacknowledged requests can lead to increased network traffic as devices attempt to resend messages, potentially slowing down the entire OT network.

How To Fix It

• Use OptigoVN Site Scope(s) to investigate the health of the devices involved in the unacknowledged requests. If a device is malfunctioning or disconnected, it might not be able to respond.
• Identify patterns of unacknowledged requests. This can help pinpoint specific devices or areas in the network that are experiencing communication issues. Look back at previous packet captures to see if the same devices and errors have been occuring at regular intervals, after a change in network state, etc. 
• Adjust retransmission parameters on devices to allow for a reasonable number of retries without overwhelming the network with unnecessary traffic.
• Review the network topology to ensure that there are no physical or logical barriers causing communication problems.
• Minimize the amount of unnecessary traffic on the network by optimizing communication patterns and avoiding excessive polling.
• Ensure that devices' clocks are synchronized to prevent timing issues that might lead to unacknowledged requests.
• Confirm that the devices' firmware are up to date, as newer versions might include improvements to communication reliability.
• Consider segmenting the network into smaller sub-networks to reduce the impact of network congestion and improve communication reliability.
• Regularly test devices' communication and monitor network traffic regularly to identify and address unacknowledged requests promptly.

Addressing unacknowledged requests requires a combination of troubleshooting techniques, network optimization, and careful configuration. By ensuring devices are healthy, network traffic is managed effectively, and communication parameters are appropriately set, you can minimize the occurrence of unacknowledged requests and maintain a robust BACnet network.