1. Building a conference attendee tracking system using DNN and MQTT
Peter Donker
DNN Connect 2017

2. First attempt at this using:
Last Year
First attempt at this using:
Raspberry Pi
HD44780 Display
RFID Cards and Scanner
Mono
WebAPI calls to server

3. Quite a few reliability issues
Last Year
Quite a few reliability issues
IoT app ran as console app
Network was not reliable

4. Console App
Because the card reader was a “USB keyboard”
Cannot read keyboard in a background process
So look for a reader that is not a keyboard

6. First Snag
Could only find “good” code in Python/C for the RC522 chip
In general: Python is the most ubiquitous for IoT code, then C
Subsequently it is *very* hard to do dotnetcore dev for IoT

7. The old cards didn’t “work” Many different RFID standards (?!?)
Another small snag ;-)
The old cards didn’t “work”
Many different RFID standards (?!?)
2016: low frequency EM4100 cards
2017: MiFare cards

8. Second challenge: network reliability
We have to assume the network is not always up
http web api calls (can be) relatively “demanding”
Most common protocol used in these situations: MQTT

9. MQTT
Message Queue Telemetry Transport
Traces back to IBM in the 90’s. First standard in 1999.
Focus on: limited bandwidth, reliability, simplicity
TCP – Ports 1883 or 8883 (SSL)
Widespread support

10. Follows so-called Pub-Sub pattern Message:
MQTT
Follows so-called Pub-Sub pattern
Message:
Topic (forward slash separated list)
Message (agnostic what it is)
QoS (0,1,2)
Clients publish and subscribe to topics
Everything runs through the “Broker” (i.e. the MQTT server) which does the dispatching of messages

11. MQTT
From

12. MQTT
From

13. MQTT
Header size up to 2-4 bytes (pub), for HTTP: bytes
Keep alive ping of 2 bytes
Client libraries are typically small and available in many languages
Simple to implement
Easy to find commercially available brokers
Reliable …

14. MQTT
From

15. MQTT Gotchas: Security is on connection level, not topic level
If you wish to have QoS > 0 then client must be able to reliably store queued messages

16. 2017 Conference Tracking System Design
Raspberry Pi Zero W
Satellite 1
DNN Connect Server
MQTT
Conference Site (DNN)
Satellite 2
Broker
MQTT
Satellite 3

17. 2017 Conference Tracking System Design
RFID DETECTOR
Node Red
Python
http
DNN
Memory
MQTT
Broker
DISPLAY

18. Demo time

19. Where one day DNN would incorporate a MQTT broker so
I have a dream
Where one day DNN would incorporate a MQTT broker so
We can have devices and modules on par
We can achieve a new level of extensibility
Obstacles
Use of non http protocol means it falls outside of IIS scope
MQTT is per host – you’d need to solve multiple sites/portals