25-08-2014, 03:34 PM
Integration of Wireless Sensor Network Services into
other Home and Industrial networks
Integration.pdf (Size: 304.21 KB / Downloads: 31)
Abstract—
Wireless sensor networks (WSN) have recently been
proposed for a large range of applications in home and industrial
automation, and for health and environment monitoring.
Especially the ZigBee standard is getting rising attention as it can
be used to implement wireless sensor networks, because of its low
data rate and low power consumption. Increasingly there is a
need to access wireless sensor network services from other IPbased networks. The DPWS has been chosen to implement the
integration of the different forms of networking services. DPWS
uses web services, xml, WSDL and SOAP protocol to connect
various devices and services in home and industrial applications.
It allows collaboration and dynamic reconfiguration of network
services and devices. This paper will describe our idea of how
DPWS can be used to integrate a wireless sensor network into
other IP-based networks.
INTRODUCTION
Recently, different types of networks can be seen in every
place in home, car, factories and companies. Furthermore,
wireless sensor networks (WSN) are becoming more and more
important for home and industrial applications, and the need to
access these networks from other existing networks is
continuously increasing. The benefit of WSN will be largest, if
the exchange of data between WSN and other networks is
bidirectional and happens in suitable time. In general SCADA
systems are used to manage real-time data in industrial
automation, where a gateway is used to exchange data between
MODBUS/TCP and WSN and such gateways are available on
the markets. In these solutions OPC and DCOM programming
technology are used.
Our idea is to benefit from the success of web services in
other distributed IT applications like SAP, ORACLE, which
offer data exchange between clients and web services using
J2EE or .Net and have achieved great success in connecting
business applications across corporate networks and the
Internet. The use of web services, WSDL and SOAP allows
developers of distributed industrial and home applications to
connect devices written in different programming languages
and from different manufacturers with each others. The paper describes how DPWS can be used to provide a secure model to
access a wireless sensor network from other IP-based
networks.
II. WIRELESS SENSOR NETWORK
Wireless sensor networks (WSN) have recently been
proposed for a large range of applications in home and
industrial automation. It consists of many tiny nodes, which
have several sensors and a radio interface that depends on the
IEEE 802.15.4 standard that supports large number of
embedded devices in one network. WSN can be used for many
applications such as environment monitoring, medical
applications, robotic systems and home and industrial
automation. WSN uses ZigBee standard (IEEE 802.15.4),
which is a standard for low-rate wireless personal area
networks (LoWPAN).
This IEEE 802.15.4 standard defines two layers of the OSI
model: the PHY (physical layer) and MAC (media accesses
control layer). The others layers of OSI model are left to the
developer.
The main features of a ZigBee standard device are:
• Low data rate (maximum 127bytes/s).
• Low power (usually uses 2 AA batteries for up to 2
years).
• Low cost.
• Uses three frequencies: 868, 915 MHz and 2.4 GHz.
• Low bandwidth (250 kbps in the 2.4 GHz band).
• Supports three network topologies (star, tree, mesh).
• Supports a large number of modes in the network.
• Uses Ad hoc networking.
• Establishes connections quickly.
• Supports large numbers of network nodes.
• Supports Built-in AES-128 encryption and
authentication.
III. SERVICE-ORIENTED ARCHITECTURE SOA
A service-oriented architecture (SOA) is a distributed
software architecture that depends on web services for building
systems. In this architecture the client looks up for the services
that are normally registered in the services directory, and the
data is usually exchanged in XML format. The web services
architecture is based on several protocols (SOAP, WSDL and
UDDI). The communication between the web services and the
client is based on the SOAP protocol and uses XML as data
format as shown in the Fig.
• XML (eXtensible Markup Language) is used to define
the data formats of the messages that are sent to and
received from services.
• UDDI [4] (Universal Description, Discovery and
Integration) is central services directory. In this
directory the client looks up for services.
• WSDL [5] (Web Services Description Language) has
XML format and is used to describe the services and
its binding to transport protocols.
• SOAP [6] (Simple Object Access Protocol) is used to
transfer messages between clients and services. The
services that use SOAP are independent of the system
platform and programming language. Usually the
messages transferred by SOAP are formatted regarding
to WSDL definitions. Using SOAP over HTTP allows
for easier communication behind proxies and firewalls.
IV. DEVICE PROFILE FOR WEB SERVICE
Device Profile for Web Services (DPWS) is a profile
designed for embedded systems and devices with small
resources. It is also called device-level protocol, and it is a new
SOA protocol and is considered as a successor for UPnP
(Universal Plug and Play) [12]
V. IPV6 /6LOWPAN MAPPING
There is a need to access the wireless sensor networks from
other IP-based networks. In order to achieve this need the
TCP/IP packets should be transferred through the ZigBee
packets, but there is a difference between the OSI model of
TCP/IP and the OSI model of ZigBee, this resulting into a need
for a new layer that makes the adaptation between the two
standards as shown in Fig.
This adaptation layer is defined by the 6LoWPAN work
group, which is responsible for standardization efforts of
6LoWPAN, and concerns about IPv6 over IEEE 802.15.4 [12].
• IPv6 (Internet Protocol Version 6): is a transport
protocol located in the third layer of the OSI Model. It
is the new version of the Internet Protocol (IP). It is the
successor to IPv4. The most significant change from
IPv4 to IPv6 is the size of IP addresses. IPv6 addresses
size is 128 bits instead of 32 bits in IPv4. IPv6
addresses consist of two logical parts, a 64-bit network
prefix, and a 64-bit host-addressing part, which is often
automatically generated from the interface MAC
address. IPv6 address consists of 8 groups of 16-bit
hexadecimal values separated by colons (.
IPv6 addresses are classified in three types:
o Unicast Address is applied to one network
interface and is delivered to the host with the
specified address.
o Multicast Address applied for multiple
network interfaces, and the packet is
delivered to all hosts with the same address.
o Anycast Address applied for multiple
network interfaces, but the actual packet is
delivered to one of them.
• 6LoWPAN: The WSN uses the standard IEEE 802.15.4
that supports a maximum frame size of 128 bytes. In
order to move the IPv6 packet over the ZigBee
network the IPv6 requires a support of packet sizes
larger than the 128 bytes. The 6LoWPAN standard
defines an adaptation layer for mapping from the IPv6
VI. DPWS GATEWAY SOLUTION
Our solution of DPWS gateway comprises a model of web
services that uses XML, WSDL and SOAP and enables the
exchange of data between WSN and other IP-based networks.
Fig. 4 shows the overall concept of a DPWS gateway,
which allows applications to read data from the WSN sensors
and to issue commands to the WSN devices. It is running on a
PC under Windows or Linux. The PC running a DPWS
gateway has access to an IP network and it connects to at least
one coordinating device in WSN which acts as a bridge
between other WSN devices and the PC.
A. The components of the systems
• Client: Each client may be an application that uses any
of TCP, UDP or HTTP that in turn are based on IP
protocol. The IP packets will be transferred to the
coordinator that converts the packets into 6LoWPAN
format and sends them to a specific sensor node. The
client can issue a request to a specific node, receive
responses and events from nodes, obtain service
descriptions and use the services of nodes.
• DPWS Gateway: It intermediates between the client
and the wireless sensor network and manages the
traffic on the network. The gateway registers the
sensor nodes in a routing table, obtains their WSDL
file, requests services from the wireless sensor nodes
and offers them to the client, collects and forwards the
events, the metadata and sensor data between the client
and the nodes.
• Wireless Sensor Nodes: Each node has a unique EUID-
64, it can join the LoWPAN and advertise its services
using WSDL file. The node can provide its data using
get-method of its services or can perform actions using
set-method of its services. The node is also able to send
and receive events.
• Coordinator: It is a ZigBee node connected to the
gateway using USB or serial port. Through this node
the gateway can connect with WSN. It takes the
packets from wireless sensor network and encapsulates
them into IPv6 Packets, or takes the packets from the
client through the Ethernet interface and translates it
from IPv6 into 6LoWPAN form, which can be
understood by WSN.
B. The functionality of the system
The interaction between client and wireless sensor network
can be done in a specific sequence as shown in Fig. 5.
The interaction can be arranged in the following stages:
• Addressing: The client and DPWS gateway have
specific IP addresses. Each sensor node also has a
unique EUID-64. When the wireless sensor is powered
on, it sends its EUID to the DPWS gateway that in turn
registers the EUID in a routing table. After that the
wireless sensor is part of the LoWPAN.
• Advertising and discovery of services: Once the
wireless sensor node has become part of the LoWPAN,
it sends a WSDL file containing the description of its
services. That means each node informs all other
network members of its services, and also it can be
informed about the presence of new members. When a
new client joins the network, it sends a search request
for other network members in order to get information
about their advertised services. Usually, search and
discovery of services are done using multicast method.
• Getting a service's description: Once the client has
discovered the wireless sensor nodes it needs to obtain
more information about the services of each node.
CONCLUSION
The presented paper has discussed the need and how to
integrate wireless sensor networks into other existing IP-based
networks.
Using the 6LoWPAN it is possible to connect a wireless
sensor network with the internet and other IP-based networks
in home and industrial environments. The 6LoWPAN also
implements the header compression and fragmentation as well
as reassembly of fragments in order to map from IPv6 to
ZigBee network.
The DPWS Profile was chosen to achieve the
implementation of a DPWS gateway because it is suitable for
embedded devices in home and industrial automation, and
because of its interoperability and its automatic networking and
discovery of services.