@Override
    public PlcSubscriptionRequest.Builder subscriptionRequestBuilder() {
        if (!isSubscribeSupported()) {
            throw new PlcUnsupportedOperationException("The connection does not support subscription");
        }
        return new S7PlcSubscriptionRequest.Builder(this, getPlcTagHandler());        
    }
Subscriptions are only supported in a small subset of the S7 devices.

@return true, if the device supports subscriptions.
plc4j/drivers/s7/src/main/java/org/apache/plc4x/java/s7/readwrite/protocol/S7HPlcConnection.java