Multi-Sink WSN Gateway

Introduction

This page describes the WSN Gateway project developed for the Wireless Sensor Network Course 2007/2008.

This project aims to enable the remote access of sensors from one or more wireless sensor networks, through machines or devices that aren't directly connected to it.

Related Work

The IEEE 1451 standard main objective is to develop a standard (i.e., group of interfaces) that eases the integration of sensors or actuators with embedded systems and with other networks and systems.

The most important component from this standard is the NCAP (Network Capable Application Processor), illustrated in the following picture.

As one can see in the picture, the NCAP is composed by various groups of the IEEE 1451 standard.

In this way, this NCAP module, hardware implemented, enables monitoring applications to directly access sensors and actuators, independently of the communications medium and protocol used.

By observing the picture depicted above it's easy to understand the similarity between the IEEE 1451 NCAP and the WSN Gateway project.

It's important to notice, however, that the IEEE 1451 standard doesn't assume that sensors have processing capabilities, as is the case of motes of the MicaZ's family, which aren't more than embedded systems with reasonable processing capabilities associated with wireless communication capabilities. In this way it is possible to conclude that much of the components defined in the IEEE 1451 standard can be implemented in software in this new type of motes.

Requirements

1. Heterogeneous Access:

  • The developed project must allow the access to the information acquired by a sensor network in a remote fashion through a Gateway.
  • The Gateway must permit that a user that is outside from the WSN network can access to the sensors through a heterogeneous network.

2. WSN scalability:

  • The project has to permit the register of one or more WSN networks on the Gateway.
  • The developed project has also to allow the register of sink nodes on the gateway, to enable the possibility of future WSN networks that may have to be registered in this WSN Gateway.

3. Abstraction Layer:

  • The application must permit that a user abstracts from the communication protocols that are involved in a WSN network, transforming a data-centric communication in a identity-centric.
  • It's this work purpose that all of the querys are made using the known TCP/IP protocol. The application has to be capable of translating the querys created by identifying the network and the node that the client querys are destined for.

4. Security:

  • The access to the gateway should be accomplished in a secure way to assure the integrity and authorization of the communication being performed.
  • The gateway has to allow only registered users can access the gateway

5. Worksheet automation:

  • To make easier the access to the information from the registered WSN on the gateway, this has to enable the possibility of scheduling tasks.

System Description

This section presents the proposed system description to effectively reply to the requirements defined in the previous section. The logic architecture as well as the main functional blocks of the project are described next.

  • WSN Gateway This is the middle man between the Internet (or other network) where the user is making the querys, and the WSN network.
  • WSN Client Remote Machine from which the client makes the qurys to the WSN network.
  • Sink Node This is the node from the WSN network that makes the bridge between the WSN Gateway and the WSN network that we want to access.
  • WSN Network Network composed by a random number of sensors and by the sink node.

System Specification

Next the exchanged messages are presented.

As one can see from the above picture, the clients connect to the WSN Gateway through a SSH connection. Through this connection, the client access the WSN Gateway application where it can access to the information that is measured and acquired by the sensor network. The client specifies the WSN network that he wants, the node and the sensor he wants. The application tranforms this query to a TinyOS message and and makes the Query to the desired sensor. The gateway is then responsible to send the reply from the network to the client.

The WSN Gateway acts simply as a SSH server that is connected to at least one wireless sensor network. The client applications are merely SSH clients that connect to the referred WSN Gateway.

On what concerns the WSN Motes, these have a special software module installed, which acts as a proxy between the WSN Gateway and the sensing information or the actuation capabilities of the application already existent on those motes.

The following diagram depicts the registration process of WSN Motes on the WSN Gateway.

As soon as a mote is initialized, it starts by creating and sending a special registration packet called advertisement. This special packet identifies and outlines the capabilities of the referred mote, such as its identification, installed sensors/actuators and their respective applicable methods. This packet is then received by the sink node responsible for the wireless sensor network of the referred mote. this sink adds the network id to the received advertisement, creating a new special packet, called publish, which is then sent to the WSN Gateway. The WSN Gateway registers the referred on its database, followed by a confirmation of the successful registration through the use of a ACK packet.

References

  • Karl, H., Willig, A., “Protocols and Architectures for Wireless Sensor Networks”, John Wiley & Sons, Ltd., 2005
  • Lee, K., "IEEE 1451: A standard in support of smart transducer networking", Proceedings of the 17th IEEE, Volume 2, 2000, Pages:525 - 528?
  • http://www.tinyos.net/
  • http://ieee1451.nist.gov/

Abbreviations

  • NAT Network Address Translation
  • NCAP Network Capable Application Processor
  • SSH Secure Shell
  • STIM Smart Transducer Interface Module
  • TEDS Transducer Electronic Data Sheets
  • WSN Wireless Sensor Network

Group

João Matos

Luís Santos