A wireless sensor network (WSN) can comprise hundreds or maybe thousands of small size and low cost sensor devices working together to accomplish a commom task. There is a trend to incorporate these devices in several quotidian objects, realizing a vision of ambient networks where many different devices will collect and process information from many different sources to both control physical processes and to interact with human users.
The IEEE 802.15.4 standard was the first low-power standard for WSNs. Several solutions use IEEE 802.15.4 as the link layer technology, some of them proprietary, such as ZigBee and WirelessHART.
However, ZigBee and WirelessHART are not compatible with the IP protocol. Thus, in order to connect these networks to the Internet, it is necessary to develop complex gateway systems, that play the role of a proxy between Internet devices and wireless sensor nodes.
Hence, the end-to-end connectivity cannot be supported. Moreover, it is necessary to update the gateway when new functionalities are deployed on sensor nodes.
The use of IPv6 deals with some of these issues by providing a larger address space, autoconfiguration, security, among other advantages, but it imposes some requirements for sensor nodes, and reduces extensively its data payload length. Because of that, the IETF 6LoWPAN working group standardized an adaptation layer below IPv6 called IPv6 over Low-power Wireless Personal Area Net- works (6LoWPAN).
However, in order to enable end- to-end connectivity with 6LoWPAN-based sensor nodes and other Internet devices, it is necessary to design 6LoWPAN- compliant gateway systems.
This paper presents the construction of a new gateway device that enables end-to-end connectivity between 6LoWPAN- based sensor nodes and the Internet regular devices. This gateway acts like a router, forwarding IPv6 packets inside or outside the WSN. However, it performs additional tasks, such as 6LoWPAN header compression and packet fragmentation/reassembly.
The wireless sensor network will be the entity capable of sensing environ- mental conditions and communicating with other sensor nodes through the 6LoWPAN protocol. The IPv6 user represents the user which will interact directly with the WSN, i.e., he will receive sensor information or send queries or actions to the WSN.
The intermediator unit between the IPv6 network and the WSN is the 6LoWPAN gateway, which plays the role of compressing and decompressing IPv6 and transport layer headers, fragmenting packets in order to support IPv6 minimum MTU (Maximum Transmission Unit), and routing IPv6 packets inside the WSN or vice versa.
The gateway hardware is divided in four main components: i) the mother board where the processor and other components of the gateway are plugged; ii) the storage unit, which stores the operating system and the gateway programs;iii) an Ethernet port to connect the WSN gateway to the IPv6 network; iv) the base station plugged to the USB port to allow connectivity with the WSN.
An Intel desktop board D945GCLF with an integrated Intel Atom processor 1.6 GHz has been chosen to be the mother board of the gateway.
A laboratory testbed has been defined to evaluate the proposed gateway where two different sensor platforms compatible with IEEE 802.15.4 have been used.
The results show that the gateway allows end-to-end communication with the WSN, since no protocol translation is performed. Hence, it enables IPv6 hosts to get data from heterogeneous sensor nodes or execute actuation on them in real time.
The experimental results also shows that the gateway successfully enables communication between a WSN comprising distinct nodes and IPv6 clients, allowing IPv6 clients to read and show sensor nodes data and to actuate on their assets.
(****Other authors: Joel J. P. C. Rodrigues and Lucas D. P. Mendes, University of Beira Interior, Portugal; Lu´is M. L. Oliveira, Polytechnical Institute of Tomar, Portugal; and Eduardo F. Nakamura and Carlos Mauricio S. Figueiredo, Analysis, Research and Technological Innovation Center (FUCAPI), Manaus, Brazil.
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