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GeoMQTT

The Message Queue and Telemetry Transport (MQTT [1]) protocol is a very lightweight protocol often used in the Internet of Things and Service (IoTS). It is especially suitable for constrained devices as well as low-bandwidth, high-latency and unreliable networks. Since 2013 it is standardized by the Organization for the Advancement of Structured Information Standards (OASIS[2]).

 The protocol implements the so-called publish/subscribe interaction scheme which is an event-based communication model between publishers that produce certain information and subscribers that register to these information. The term event is used for the act of publishing information whilst notification denotes the act of delivery to the consumer. A broker distributes the events according to the interests of subscribers. MQTT uses a topic-based publish/subscribe scheme for addressing.

We extended MQTT with new message types to support spatiotemporal tagging and filtering of events. Therefore, the extension is called GeoMQTT. It still uses a publish/subscribe interaction scheme although not exclusively topic-based but also timestamp and geometry-based. However, the topic mechanism is inherited from MQTT. Subscribers are able to specify their interests in geo events by the use of the topic, spatial and temporal filter. The broker only forwards the so-called GeoPublish message to subscribers if all three filters are satisfied. The following figure shows the basic principle of GeoMQTT.

The extension is compatible to MQTT, which means that different conflict strategies are used in the implementation of the broker to support also ordinary MQTT clients. For instance, if a client is subscribed to a topic with an MQTT subscription, the time stamp and geometry of incoming GeoPublish messages are ignored. If the topic name matches the topic filter of the subscription, the message is converted to an ordinary Publish message and forwarded.

 

In our projects, we deal with Wireless Geo Sensor Networks (WGSN) which uses ZigBee to communicate. Since GeoMQTT is based on TCP/IP we also implemented an extension to cope with connectionless communication protocols which is called GeoMQTT for Sensor Networks (GeoMQTT-SN). It extends the MQTT-SN[3] protocol with the spatiotemporal capabilities of GeoMQTT. The following figure shows the stacks of a GeoMQTT-SN architecture in the EarlyDike project.

In the figure, an Arduino-like device uses an intelligent geo textile to measure the deformation of a dike. The sensor measurements are sent to a Gateway using the GeoMQTT-SN protocol. The gateway translates the measurements into GeoMQTT messages and forwards them to a GeoMQTT Broker. From the broker’s perspective the sensor node is an ordinary GeoMQTT client and, therefore, is also able to act as a subscriber and receive messages.

[1]: http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.html

[2]: https://www.oasis-open.org/

[3]: http://mqtt.org/new/wp-content/uploads/2009/06/MQTT-SN_spec_v1.2.pdf

 

Ansprechpartner

 

M.Sc. Stefan Herle

Tel.: +49-241-80-95294
Fax: +49-241-80-92142