This document discusses using web messaging and RESTful approaches to enable distributed sensing applications on heterogeneous networked devices. It proposes a RESTful Messaging System (RMS) to provide a pub/sub mechanism for devices to post sensor data and subscribe to channels in a scalable way. A live demo is shown of a smart meter publishing energy readings to an RMS channel and a browser client subscribing to receive the readings in real-time using Ajax long polling. The RMS approach leverages existing web technologies and tools to integrate physical devices and sensor data directly into the web.

1. Web Messaging for Open and Scalable
Distributed Sensing Applications
ICWE2010, Vienna, Austria - 6 July 2010
Vlad Trifa, Dominique Guinard, Vlatko Davidovski,
Andreas Kamilaris, and Ivan Delchev

2. The Internet of Things
Networked devices everywhere
Lots of different devices
‣ Capabilities/functions
‣ Applications/middleware
‣ Networking protocols
Internet connectivity
‣ Cheap
‣ Ubiquitous
‣ HTTP also possible

3. Web of Things [1]:
Use the Web to combine
heterogeneous mobile
devices to create interactive
ad-hoc applications!
[1] Online at: http://www.webofthings.com

4. Show Time!
RESTful SunSpot
Embedded NanoHTTPD
‣ Talks HTTP (over 802.15.4)
‣ Becomes a Web device
Properties and functions are
Web resources, so can be
‣ Browsed
‣ Bookmarked
‣ Shared
But also use twitter, send
emails, chat, etc..
D. Guinard, V. Trifa, T. Pham, and O. Liechti. Towards Physical Mashups in the Web of Things. In Proceedings of the 6th
International Conference on Networked Sensing Systems (INSS 2009), 2009.

5. Wait - what about eventing &
streaming ?
The Web wasn’t quite made
for that...

6. Need more than Pull, more than Push!
Web mainly request/response (HTTP)
Need for eventing & streaming for many users
‣ Sensor data represented as sequence of messages
Scalable pub/sub for devices as substrate
‣ Use the Web to build distributed event driven apps
Parameterized subscriptions (channels/queries)
‣ Specify what sensors, devices, locations, etc...
Many solutions (XMPP, etc....)
‣ None really integrate with the Web
‣ ATOM/ATOMpub is RESTful, but not push

7. Here comes the real-time Web!
Very active community expanding
Use the Web for distributed event driven apps
Comet
‣ Keeps the HTTP connection open
‣ Long polling
‣ Ajax push
Web Hooks
‣ Bi-directional
‣ Push from server to HTTP callbacks

8. RESTful Messaging System (RMS)
Similar to pubsubhubbub (PuSH) or RestMS
‣ But lighter (less options) to run on devices
Interested by a generic “Web push” mechanism
‣ Simple to use
‣ No complex client required
Minimal pub/sub support
‣ queues
‣ subscriptions

10. RMS
/rms/channels - every sub-resource represents a
hierarchical channel where entities can post data to,
ex: /rms/channels/ethz/ifw/floor/d/49.2
/rms/subscriptions - contains each subscription of
entities to individual channels
/rms/channels/x/publishers - contains all entities
that are publishing data on the channel x
/rms/channels/y/subscribers - contains all entities
that are subscribed to events on the channel y

11. Usage examples
Subscribe to a channel:
curl ­­request POST ­­data "rms­subscription­callback­
url=http://192.168.1.1/handler"
http://localhost:8080/aparat/rms/channels/simulation
Publish to a channel:
curl ­­basic ­­request POST ­­data "temperature=23"
http://localhost:8080/aparat/rms/channels/simulation

12. Show Time!
Live Demo
Plogg Smart Meter
‣ Talks HTTP (over Zigbee)
‣ Becomes a Web device
Posting through RMS
‣ /aparat/rms/channels/.../hifi
Browser client using Comet
(Ajax Long Polling)

13. Many devices - one receiver

14. Many receivers

15. Real deployment setup

17. Conclusion
Leverage REST as native API for devices
‣ Inherit all the tools & expertise in Web technologies
‣ Caching, security, scalability
Flexibility through real-time Web
‣ Loose coupling between application components
‣ Pub/sub helps to scale and is good for ad-hoc interactions
Good performances
‣ 100 msg/s delivered with low latency, 200 subscribers
notified with 360ms delay in average
‣ Real deployment 15 devices sampling@1Hz (< 60 ms delay)
Web of Things @ Vlad Trifa - SAP/ETH Zurich

18. Take away notes
Good performances for Web messaging and integrates
devices directly with existing Web (REST).
The Web goes physical!
Tools & best practices for Web-enabled things are
needed.
Web engineering can contribute a lot towards building
a programmable world.
We need applications (deployments) and testing!
Web of Things, 7.4.2010 Vlad Trifa - SAP/ETH Zurich

19. Thanks for your
attention !
www.webofthings.com