My preliminary presentation on "RESTful Web Services for the Internet of Things". 2011. by Markku Laine, http://www.tinyurl.com/mplaine

1. Web Services for the Internet of
Things
T-106.5800 Seminar on Software Techniques (3 cr)
Presentation
Markku Laine, M.Sc. (Tech.)
markku.laine@aalto.fi
November 3, 2011

2. Presentation Outline
• Internet of Things
• CoAP
• CoAP protocol stack
• Web Services for the Internet of Things
• Conclusion
2

3. Internet of Things
3

4. What is Internet of Things?
(e.g., sensors)
(e.g., personal computers
and smart phones)
(e.g., routers
and servers)
Source: Sensinode
4

5. Gartner’s Hype Cycle for Emerging
Technologies, 2011
Source: Gartner
5

6. Challenges: How to…
• …connect physical environments/smart objects as part
of the Internet?
• …cope with trillions of smart objects?
• …handle the problems with smart objects/small devices
as they may have difficulties in dealing with protocols
and technologies designed for full-powered computers?
• …integrate devices in constrained networks with Web
applications?
6

7. Constrained Application Protocol (CoAP)
7

8. Google’s Hype Cycle for CoAP
CoAP v.00
Source: Google Insights for Search
8

9. Implementations
• libcoap (C), open source
– http://libcoap.sourceforge.net/
• OpenCOAP (C), open source
– https://code.google.com/p/opencoap/
• CoAPy (Python), open source, in progress
– http://coapy.sourceforge.net/
• Copper (Firefox addon)
– https://addons.mozilla.org/en-US/firefox/addon/copper-270430/
• Sensinode, The Contiki OS, TinyOS, etc.
9

10. CoAP Protocol Stack
10

11. Comparison of HTTP and CoAP Protocol
Stacks
XML Payload EXI
HTTP Application (L7) CoAP
TCP Transport (L4) UDP
IP Network (L3) 6LoWPAN
Ethernet MAC Data Link (L2) IEEE 802.15.4 MAC
Ethernet PHY Physical (L1) IEEE 802.15.4 PHY
11

12. Physical & Data Link Layers (L1 & L2):
Ethernet à IEEE 802.15.4 (PHY & MAC)
• Goal: Get rid of wires
• Methods: Wireless
• Solution: IEEE 802.15.4
– IEEE wireless standard (IEEE 802.15.4d), April 2009,
http://standards.ieee.org/getieee802/download/
802.15.4d-2009.pdf
– Specifies the physical layer and media access control for low-
rate wireless personal networks (LR-WPANs)
– Low-power, low-bandwidth communication technology
– Basis for extensions, such as ZigBee
12

13. Network Layer (L3):
IP à 6LoWPAN
• Goal: Integrate Wireless Sensor Networks (WSNs) and
smart objects with the Internet
• Method: Optional protocol
• Solution: IPv6 over Low-Power Wireless Personal Area
Networks (6LoWPAN)
– IETF Informational (RFC 4919), August 2007,
http://tools.ietf.org/html/rfc4919
– IETF Proposed Standard (RFC 4944), September 2007,
http://tools.ietf.org/html/rfc4944
– Brings IP to the smallest of devices, such as sensors
– Encapsulation and header compression mechanisms
13

14. Transport Layer (L4):
TCP à UDP
• Goal: Reduce the overhead for short-lived transactions
• Method: Optional protocol
• Solution: User Datagram Protocol (UDP)
– IETF Standard (RFC 768), August 1980,
http://tools.ietf.org/html/rfc768
– Fast but unreliable transport protocol
– Optimal for exchanging very small data units
– Supports multicasting
– Used with the IP network layer protocol
14

15. Application Layer (L7):
HTTP à CoAP
• Goal: Provide resource constrained devices with
RESTful web service functionalities
• Methods: Optional protocol
• Solution: Constrained Application Protocol (CoAP)
– IETF Internet Draft, November 2011,
https://tools.ietf.org/html/draft-ietf-core-coap-08
– REST-based architecture
– Optimized for resource constrained networks typical of IoT and
M2M applications
– Takes into account the low processing power and energy
consumption constraints of small embedded devices, such as
sensors
15

16. Payload:
XML à EXI
• Goal: Reduce the overhead of XML
• Methods: Compression and encoding
• Solution: Efficient XML Interchange (EXI)
– W3C Recommendation (EXI Format 1.0), March 2011,
http://www.w3.org/TR/exi/
– Very compact representation of the XML Information Set
– Optimizes the performance and utilization of computational
resources
– Extremely efficient schema-informed mode
16

17. Web Services for the Internet of Things
17

18. About Web Services
• Today’s Web Services are not suitable to be used with
the Internet of Things
– TCP, HTTP, XML (SOAP)
• What is needed is
– RESTful architecture for good Web integration
– Native push model with subscribe and notify
– UDP-based transport with multicast support
– Overhead suitable for constrained networks
– Complexity suitable for constrained nodes
– Build-in Web discovery and security
• CoAP comes to the rescue!
18

19. CoAP and Web Services
Source: Sensinode
19

20. Conclusion
20

21. Conclusion
• Traditional Web protocols and technologies are not
suitable for the Internet of Things
• The HTTP protocol stack needs to be optimized from the
bottom to the top
• CoAP is the key technology in accessing constrained
environments/nodes from Web applications
21

22. References
• Colitti, W., Steenhaut, K., and De Caro, N. Integrating
Wireless Sensor Networks with the Web. 2011.
• Shelby, Z. Embedded Web Services. In Journal of IEEE
Wireless Communications, 17(6):52-57, 2010.
• Castellani, A. et al. Web Services for the Internet of
Things through CoAP and EXI. In Communications
Workshops (ICC). IEEE, 2011, 1-6.
• Castellani, A. et al. Best Practices for HTTP-CoAP
Mapping Implementation. IETF Internet Draft, 2011.
22

23. Thank You!
Questions? Comments?
markku.laine@aalto.fi
23