An introduction to IoT protocols

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Vidhya Gholkar @vgholkar

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.

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

Constrained Application Protocol

CoA

P Requests/Response

Messages

application

UDP

logical model

Interaction with application

Interaction with UDP

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 1Ver 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 VersionT Transaction Type

TKL Token LengthCode Request Code

Message ID Identifier

Handle

Options

Mark/Payload

Base

CoAP Methods

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Message Code

GET 0.01

POST 0.02

PUT 0.03

DELETE 0.04

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

URI

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Resource Discovery

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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”

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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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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Light Weight Device Management

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Device Configuration Provisioning Fault management Upgrade Software

LWM2M deployment scenario

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from Whitepaper Feb 2014, Vodafone, ARM, Ericsson

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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PubSub

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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:

Header and Payload

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bit 7 6 5 4 3 2 1 0byte 1 Message Type DUP QoS Retainbyte 2 Remaining length (i.e. length of option + payload)byte 3

Variable Header Componentbyte nbyte m

Payloadbyte n

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

Quality of Service

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for many constrained devices likely that only QoS 0 is available

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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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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Semantics for IoT Objects

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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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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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