Which specific MQTT mechanism allows a broker to notify all subscribers of a device's sudden disconnection from the network?

The MQTT mechanism that allows a broker to notify subscribers of a device's sudden disconnection is called the Last Will and Testament, often abbreviated as LWT. When a client connects to an MQTT broker, it can define a Will Message, which is a specific message payload, and a Will Topic, which is the destination address for that message. The client also specifies a W....