ELEC-E7320 Internet Protocols, Spring 2020 Welcome! - Department of Communications and Networking (COMNET)
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ELEC-E7320 Internet Protocols, Spring 2020 Welcome! Department of Communications and Networking (COMNET) Yu Xiao 23.1.2020
Learning Outcomes
After this lecture, you will be able to
• Describe the key features of 6LoWPAN, MQTT and CoAP
• Summarize the design criteria of networking protocols for
constrained devices
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2
Internet of Things (IoT)
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3
IoT for Smart Cities
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4
Value is Created by Making Sense of
Data
Source: http://www.slideshare.net/mazlan1/current-trends-in-internet-of-things-iot
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5
IoT from an Embedded Systems Point
of View
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6
How to connect sensors to the Internet?
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7
IoT Protocols
Source: http://www.cse.wustl.edu/~jain/cse570-15/ftp/iot_prot.pdf
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8
6LoWPAN: IPv6 over Low Power Wireless Personal Area
Network
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9
6LoWPAN stack example
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10What are the advantages of IP?
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11Many Advantages of IP
• Extensive interoperability
• Other wireless embedded 802.15.4 network devices
• Devices on any other IP network link (Wi-Fi, Ethernet, …)
• Established naming, addressing, translation, lookup,
discovery
• Established proxy architecture for higher-level services
• NAT, load balancing, caching, mobility
• Established application level data model and services
• HTTP/HTML/XML/SOAP/REST
• Established network management tools
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12Many Advantages of IP
• Transport protocols
• End-to-end reliability in addition to link reliability
• Established security
• Authentication, access control and firewall mechanisms
• Most “industrial” standards support IP option
Source: http://voip.netlab.uky.edu/~fei/teaching/cs687_smartgrid/slides/4.6LoWPAN-tutorial.pdf
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13TCP/IP is not one size fits all
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146LoWPAN
• Try to optimize the transmission of IPv6 packets over low
power and lossy network such as 802.15.4
• RFC6282:
• Header compression: compresses the 40-byte IPv6 and 8-byte
UDP headers by assuming the usage of common fields
• Fragmentation and reassembly: The data link of IEEE
802.15.4 with a frame length of maximum 127 bytes does not match
the MTU of IPv6, which is 1280 bytes.
• Stateless auto configuration: the process where devices inside
the 6LoWPAN network automatically generate their own IPv6
address.
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15IPv6 Header Compression
• Defining some default values in IPv6 header
• Version==6, traffic class & flow-label == 0, hop-limit only well-known
values (1, 64, 255)
• Remove the payload length (available in 6LoWPAN fragment header or
data-link header)
• Addresses (link-local, global, multicast)
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16Header Compression
Send data to direct neighbors
In this example, assume that
interface ID is derived from
MAC address.
http://www.ti.com/lit/wp/swry013/swry013.pdf 22.1.2020
17Header Dispatch
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186LoWPAN stacked headers
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196LoWPAN
• A 6LoWPAN system is a low-power wireless mesh network where every
node has its own IPv6 address allowing it to connect directly to the
Internet
The compressed IPv6 header needs an intermediary
device to provide a conversion between 6LoWPAN
and standard IP header.
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206LoWPAN stack example
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21Design Principles of MQTT (MQ
Telemetry Transport)
• Minimize network bandwidth and device resource requirements
whilst also attempting to ensure reliability and some degree of
assurance of delivery.
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22MQTT (MQ Telemetry Transport)
• Publish/subscribe instead of request/response
• Many-to-Many communication
• Extremely simple and lightweight messaging protocol
• For constrained devices and low-bandwidth, high-
latency or unreliable networks
• MQTT v3.1.1 is an OASIS Standard
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23MQTT
• MQTT has a client/server model, where every sensor is a client
and connects to a server, known as a broker, over TCP.
• Publish/Subscribe
MQTT broker is in charge of dispatching all messages
between the senders and the rightful receivers.
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24Topic
• The topic is the routing information for the broker
• Clients don’t have to know each other, they only communicate
over the topic
https://www.hivemq.com/blog/how-to-get- 22.1.2020
started-with-mqtt/ 25Topic
• A topic is a simple string that can have more hierarchy levels,
which are separated by a slash
• Examples:
• House/living-room/temperature
• House/+/temperature
• House/#
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26MQTT Packets
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27MQTT Quality of Service
• The Quality of Service (QoS) level is an agreement between the
sender of a message and the receiver of a message that defines
the guarantee of delivery for a specific message.
ü At most once (0)
ü At least once (1)
ü Exactly once (2)
• Two sides of message delivery
ü Message delivery from the publishing client to the broker
ü Message delivery from the broker to the subscribing client
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28QoS 0, 1
QoS 0 (fire and forget)
QoS 1 – at least once
https://www.hivemq.com/blog/mqtt-essentials-part-6- 22.1.2020
mqtt-quality-of-service-levels/ 29QoS 2
QoS 2 –exactly once
(four-way handshake)
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30Packet Identifiers
• The packet identifier that MQTT uses for QoS 1 and QoS 2 is
unique between a specific client and a broker within an interaction.
• This identifier is not unique between all clients.
• Once the flow is complete, the packet identifier is available for
reuse. This reuse is the reason why the packet identifier does not
need to exceed 65535
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31Open Source Software
• Mosquitto https://www.eclipse.org/mosquitto/noteworthy/
• EMQtt: http://emqtt.io/
• Vernemq: https://vernemq.com/
• …
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32• Is TCP too expensive for a small device?
• How about TCP-less protocols?
• MQTT-SN (MQTT for Sensor Networks): UDP mapping of MQTT
and broker support for indexing topic names
• CoAP (Constrained Application Protocol)
• Inspired by HTTP, but use UDP
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33CoAP (Constrained Application
Protocol)
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34CoAP
• CoAP is a specialized web transfer protocol for use with
constrained nodes and constrained networks in the Internet of
Things
• The protocol is designed for machine-to-machine (M2M)
applications such as smart energy and building automation
• One-to-one communication protocol (RFC 7252)
• Based on REST model, like HTTP
• CoAP can carry different types of payloads, and can identify which
payload type is being used. CoAP integrates with XML, JSON, or
any data format of your choice.
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35CoAP Design Requirements
Source: ARM
https://tools.ietf.org/html/draft-shelby-core-coap-22.1.2020
req-04#page-3 36CoAP
• Embedded web transfer protocol (coap://)
• Asynchronous transaction model
• UDP binding with reliability and multicast support
• Built-in discovery
• Optional observation and block transfer
• Caching
• …
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37CoAP Messages
Each CoAP message has a unique id, this is useful to detect
message duplicates. A CoAP message is built by 3 parts:
ü a binary header
ü a compact options
ü payload
• Message types
ü Confirmable: a reliable message which is retransmitted until ACKed
ü Non-confirmable
ü Acknowledgement
ü Reset
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38CoAP Messages: Examples
https://www.survivingwithandroid.com/2018
/11/coap-protocol-tutorial.html
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39CoAP Request/Response
Tokens are chosen by the client and help to
identify request/response pairs that span several 22.1.2020
40
message exchangesMQTT vs. CoAP ?
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4122.1.2020
42Design criteria of network protocols for constrained devices
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43Designing Networking Protocols for
Constrained Devices
• Low cost, low speed, low power communication
• Limited transmit range -> multi-hop
• Compressed header -> compatibility
• Short message -> how to avoid message fragmentation
• Lossy network -> reliability?
• …
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44Challenges
• There are many competing technologies and standards
ü One size does not fit all!
ü Interoperability? How can devices be seamlessly connected?
• Connectivity
ü E.g. in industrial contexts (hot, humid environments with no
cell or Wi-Fi connectivity and/or far away from urban centers)
• Huge amount of data à local processing
• Security and privacy
• Regulations and laws
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45Questions?
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46You can also read
