Setup:
Took nmqtt libraries from HG r460 into a WinForm TestApp.
Test App runs on win7
Mosquitto runs on another Win7 box and is monitored frequently.
If I have multiple sensors, they are sended in a burst.
The time between the bursts is controlled by an interval.
Behavior should be the same as the FakeTemperatureSensorCluster.hgx
172 bytes total, 46 in the topic and 126 in the message.

===========================================================================
Interval:1000ms
SensorCOunt:1

Everything seems fine, encountered a lost connection once.(after ca 1000 msg)

===========================================================================
Interval:50ms
SensorCOunt:1

Everything seems fine.(ca 5000 msg)

===========================================================================
Interval:1000ms
SensorCOunt:2

Sended 1000 message, had 495 exceptions, never saw sensor 2 arriving, but 5 times I could have missed.
A first chance exception of type 'Nmqtt.InvalidTopicException' occurred in Nmqtt.dll
Exception message: An item with the same key has already been added.

When Disposing MqttConnection, this happens:
System.ObjectDisposedException was unhandled
Message: An unhandled exception of type 'System.ObjectDisposedException' occurred in System.dll
Additional information: Cannot access a disposed object.

===========================================================================
Interval:1000ms
SensorCOunt:2
Started tweaking with Sleep to check how sensitive it is.

Sleep(100) 1000 messages, 1 exception
Sleep(50) 900 messages, 0 exceptions
Sleep(20) 538 messages, 0 exceptions
Sleep won't help me much further, testing on win7.

===========================================================================
Interval:1000ms
SensorCOunt:4

Sleep(20) 660 messages, 0 exceptions
No sleep 1004 messages, 494 exceptions (I expected 750)

===========================================================================
Interval:1000ms
SensorCOunt:4
No sleep

All previous tests were done with MqttQos.AtLeastOnce (=1)

MqttQos.AtMostOnce 756 messages, 0 exceptions
MqttQos.ExactlyOnce 728 messages, 366 exceptions
What the ****, Again!
MqttQos.AtMostOnce 1420 messages, 0 exceptions

===========================================================================
Interval:50ms
SensorCOunt:4
QOS:MqttQos.AtMostOnce

unhandled exceptions in PingRequired after 8000 messages couldn't continue
second run: 35000 messages, 0 exceptions

===========================================================================
Interval:50ms
SensorCOunt:16
QOS:MqttQos.AtMostOnce

Sending messages at 320 messages/sec now.
170000 messages, 0 exceptions

CPU load unnoticable on win7 box sending
CPU load on receiving win7 box displaying mqtt traffic to 40%

===========================================================================
Interval:50ms
SensorCOunt:200
QOS:MqttQos.AtMostOnce

Sending messages at 4000 messages/sec now.
1619000 messages, 0 exceptions

CPU load on sending win7 box 25%
CPU load on receiving win7 box displaying mqtt traffic to 25% (probably some overflooding protection)

Let's push it!

===========================================================================
Interval:50ms
SensorCOunt:2000
QOS:MqttQos.AtMostOnce

Sending messages at 40000 messages/sec now.
2302000 messages, 0 exceptions

CPU load on sending win7 box 50%
CPU load on receiving win7 box displaying mqtt traffic to 35%

===========================================================================
Interval:50ms
SensorCOunt:20000
QOS:MqttQos.AtMostOnce

Sending messages at 400000 messages/sec now.
15460000 messages, 0 exceptions

CPU load on sending win7 box 50%
CPU load on receiving win7 box displaying mqtt traffic to 35%

===========================================================================
This is what nmqtt says about the Quality of service

AtLeastOnce:
QOS Level 1 - Message is guaranteed delivery. It will be delivered at least one time, but may be delivered more than once if network errors occur.

AtMostOnce:
QOS Level 0 - Message is not guaranteed delivery. No retries are made to ensure delivery is successful.

ExactlyOnce:
QOS Level 2 - Message will be delivered once, and only once. Message will be retried until it is successfully sent..

===========================================================================

AtMostOnce is the mode that comes closest to guaranteed delivery, because the other modes are very buggy.