Introduction to protocols for the Internet of Things. Constrained Environment. Constrained Application Protocol (CoAP) and MQTT Protocol.

1. An introduction to IoT
protocols
1
Vidhya Gholkar
@vgholkar

2. Constrained Device
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Class Rough Translation
0 Can’t run IP stack securely.
1
Integrated security but can’t employ full stack using
HTTP over TLS.
2
Small but benefit from efficient protocols that free
resources for application or reduce operational costs.

3. Constrained Environment
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10 kB RAM
100 kB Flash
40 MHz
Low Cost
Limited Processing
Battery to last many years
Network variable availability
Often low bitrate

4. Constrained Application Protocol
CoAP Requests/Response
Messages
application
UDP
logical model
Interaction with application
Interaction with UDP

5. CoAP Message
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
Ver T TKL Code Message ID
Token (if any, TKL Bytes)
Options (if any)
1 1 1 1 1 1 1 1 Payload (if any) …
Ver Version
T Transaction Type
TKL Token Length
Code Request Code
Message ID Identifier
Handle
Options
Mark/Payload
Base

6. CoAP Methods
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Message Code
GET 0.01
POST 0.02
PUT 0.03
DELETE 0.04

7. Request/Response
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COAP
client
COAP
server
COAP
client
COAP
Server
Confirmed Request
Non Confirmed
Request
ACK [0xbc90]
2.05 Content “19.8”
CON [0xbc90]
GET /temperature
NON [0x7a11]
GET /temperature

8. URI
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9. Resource Discovery
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10. Observe (example with CON)
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GET /temp Observe: (empty) Token 0x4a
ACK CON Observe: 1 Token 0x4a “26”
CON Observe: 24 Token 0x4a “28”
CON Observe: 56 Token 0x4a “26”
CLIENT
CON Observe: 56 Token 0x4a “26”

11. Security
! Datagram TLS
! Records are independent so that if the i’th record is lost i+1'th can still be decrptyed
! Handshake messages queued
! Application is responsible for dealing with loss and reordering
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12. Code to play with
! Cantcoap https://github.com/staropram/cantcoap
! C COAP Erbium github.com/contiki-os/contiki.git
! Firefox plugin https://addons.mozilla.org/en-US/firefox/copper-270430/
! Arduino https://github.com/dgiannakop/ Arduino-COAP
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13. Light Weight Device Management
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Device Configuration
Provisioning
Fault management
Upgrade Software

14. LWM2M deployment scenario
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from Whitepaper Feb 2014,Vodafone,ARM, Ericsson

15. MQTT
! Binary
! “Lightweight” - not much meta data
! PubSub, Broker is key
! Not a queue, cf. AMQP
- but most recent message can be stored by a broker and a Last Will and Testament can be
set.
! TCP with concomitant TLS/SSL
! (MQTT-S address TCP constraint)
! IBM driven. OASIS MQTT 3.1.1 expected approved in September 2014
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16. PubSub
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17. Topics and Wild Cards
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/Portland/North/BldA/hallway/temperature
/Portland/West/BldB/Concourse/humidity
/Portland/+/+/+/temperature
/Portland/West/#
Topic Publish:
Wildcard Subscribe:

18. Header and Payload
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bit 7 6 5 4 3 2 1 0
byte 1 Message Type DUP QoS Retain
byte 2 Remaining length (i.e. length of option + payload)
byte 3
Variable Header Component
byte n
byte m
Payload
byte n

19. Core MQTT messages
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Message Code Description
CONNECT 1 Client request to connect to Server
PUBLISH 3 Publish message
SUBSCRIBE 8 Client subscribe request
UNSUBSCRIBE 10 Client Unsubscribe
DISCONNECT 14 Client is disconnecting

20. Quality of Service
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for many constrained devices likely that only QoS 0 is available

21. Interesting Flags
! Last Will and Testament (if you think i am dead ….) .
- Optional message with CONNECT.
! Retained Message.
- e.g. New subscriber gets latest message
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22. Code to play with
! (C, JS, Python etc) http://git.eclipse.org/c/paho/
! Lots of client libraries including .NET, Erlang and Lua. Some are device specific. See
mqtt.org
! Broker http://mosquitto.org/
! More brokers: See http://mqtt.org/wiki/doku.php/public_brokers
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23. Semantics for IoT Objects
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24. Summary
! Go make things, do it wirelessly and use batteries.
! If you use a Broker look carefully at what assumptions you are making.
- Does an unknown client need full knowledge of the broker?
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25. Key References
! IETF RFC 7228 http://tools.ietf.org/html/rfc7228
! IETF RFC 7252 https://datatracker.ietf.org/doc/rfc7252/
! IETF draft http://tools.ietf.org/html/draft-ietf-core-observe-14
! IETF RFC 6690 http://tools.ietf.org/html/rfc6690
! OMA Lightweight M2M technical.openmobilealliance.org/Technical/release_program/docs/
LightweightM2M/V1_0-20131210-C/OMA-TS-LightweightM2M-V1_0-20131210-C.pdf
! OASIS http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.html
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