Study on Integrating BACnet with IPv6-based Wireless Sensor Networks

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Procedia

Engineering

www.elsevier.com/locate/procedia

2012 International Workshop on Information and Electronics Engineering

Study on Integrating BACnet with IPv6-based Wireless

Sensor Networks

Ping Zhou

a

, Xiangyu Lei

b

, Zhiyong Lv

c *

a,b,c_{Dept. Computer Science and Engineering, Guilin University of Electronic Technology, Guilin, 541004,}

China

Abstract

The wireless sensor network with BACnet (Building Automation and Control Networks) is the trend of intelligent building and building automation. In order to provide a new integrate solution for BACnet and WSN, An optimization for standard BACnet stack is proposed. In this paper, current technologies are presented. With the utilization of uIPv6 stack, the data communication between BACnet stack and hardware platform of WSN is realized. An evaluation is finally performed to show with evidence that the integrated system model is feasible.

Keywords: intelligent building; building automation and control networks; uIPv6 stack; integrated system

1. Introduction

With the rapid development of wireless communication technology, most of the fundamental supports for the implementation of automation are provided by computer network technologies. Especially in intelligent building, the market demand is moving rapidly in integrate technology direction. Currently, to meet the growing market demand flexibly and save the installation cost effectively, the field of commercial building automation is seeking for integrated wireless networks.

BACnet (A data communication protocol for Building Automation and Control Networks) is an international standard [1] in the automation field of intelligent building. The main goal of BACnet protocol is to provide a communication protocol (For Auto-Control System of Intelligent Building), which is open, extensible and interoperable. BACnet provides 6 kinds of wired data link layer protocol (such as

*

* Corresponding author. E-mail [email protected]

Open access under CC BY-NC-ND license.

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MS/TP, PTP, ARCnet, Ethernet, LonTalk and BACnet/IP). However, it did not provide wireless solutions. Therefore, to meet the market demand, BACnet need to define a new wireless communication solution. 6LoWPAN(IPv6 over Low power Wireless Personal Area Network) is a kind of wireless communication based on IEEE 802.15.4, which mainly utilized for wireless personal area network that is low-speed, short-distance and low-power-consumption. Combining the BACnet and 6LoWPAN can definitely popularize the standard of BACnet, and, furthermore, meet the needs of the auto-control field of intelligent building simultaneously [2, 3].

In this paper, we focus on the feasibility of executing the BACnet protocol on the WSN nodes based on IPv6. The operation is implemented for Readproperty and Writeproperty service in BACnet on Tmote Sky, and the result of the executed test are discussed.

2. Research Background 2.1. BACnet Standard

To consider the advancement and expandability of technology, ASHRAE SSPC 135P committee had established architecture (Fig. 1) according to ISO/OSI-RM. This architecture defines local area networks of different kinds, and describes the basic components of auto-control network system and its features, and develops object-oriented information model. Object-oriented analysis and design technique are also utilized. To promote the innovation of devices, functionalities of service that are related to equipment set up inside and structure are not customized [4].

Fig. 1. BACnet Architecture 2.2. Object and device of BACnet

BACnet uses object-oriented approach to describe function of each device. A BACnet object represents a specific device. Each object has encapsulated the element set of data. Objects are described by the data referred to as attribute, which is available and modifiable to the other objects.

The standard of BACnet-95 includes frequently-used basic function units in building automatic systems. This standard consists of eighteen defined objects: analog input, analog output, simulation value, digital input, digital output, digital value, commands, calendar, schedule, events, files, group, register ring, polymorphism input, polymorphism output, notice kind, procedures and equipment.

Three attributes are included in each object: object identifier, object name and object type. Among them, the object identifier used to characterize the object uniquely. By broadcasting the object name of a particular, self-contained object, the BACnet devices can establish connections with devices that include related objects. BACnet protocol calls for each device to include device object and, by loading its attributes, the network obtains all the device information.

2.3. Service and communication model of BACnet

BACnet Application Layer BACnet Network Layer ISO 8802-2 ISO 8802-3 ARCnet MS/TP EIA-485 PTP EIA-232 LonTalk BVLL IP UDP

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Service is used for conveying information between devices in BACnet protocol. The communication model that BACnet protocol used works in Client/Server mode. As Fig. 2 shows, each BACnet device indicates a server. The BACnet device is able to collect the information of the other devices and objects, or command a device to execute a particular operation, or notify the happened event to device. 35 services, defined in BACnet, have been classified into 6 categories: alarm and event service, file access service, object access service, remote device management service, virtual terminal service and network security service [5].

Fig. 2. The BACnet communication model

A device does not need to perform all the service operation. However, each device must be able to execute the Readproperty service that is used to access the device and its attribute.

Object access service is a series of services that access and modify the attribute of object, create and delete an object. Any attribute in the BACnet object is available to access through those services, including read and write property.

2.4. uIPV6 Protocol Stack

uIPv6 protocol stack [6] is built on the top of the Contiki OS [8], including the previously released uIP protocol stack [7]. The uIPv6 protocol stack does not rely on any special MAC or data link layer. The interface between the uIPv6 protocol stack and the underlying protocol consists of input/output function and data link layer address. This enables uIPv6 protocol stack to realize the integration of protocols in MAC layer and data link layer.

uIPv6 runs as original thread of Contiki system. uIPv6 will initialize the network interface at system startup. The node constructs IPv6 link-local address that is composed of fe80::0/64 (prefix) and the 802.15.4 MAC. Subsequently, it carries out DAD (Duplicate Address Detection) to ensure that this address is unique. Simultaneously, the node will request routing distribution information from routers in the network. The router advertises distributing routing information after receiving the request. According to the information received, the node constructs its global address and updates its network parameters. uIPv6 protocol stack send message one by one in DAD and process of routing discovery. Event triggered protocol stack, came from the underlying layer, handles incoming IPv6 packets, which include producing proper response information, and update different neighbor discovery information and data structure of interface. When a node needs to send a packet, it discoveries the right neighborhood node by executing next hop handler. If the MAC address of neighborhood node is not in its cache, the sender node needs to renew its routing table to obtain the MAC address of neighborhood node.

Server _Client

Read property

Present Value

notification

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3. Integrating System Model

The BACnet protocol can be simplified as application layer, network layer and BVLL (BACnet Virtual data link layer). BACnet application layer used to implement the service of Readproperty. The functionality of BACnet network layer is to enable the interconnection between BACnet networks, and BVLL provides an interface for BACnet network layer and uIPv6. The model is shown in Fig. 3.

Fig. 3. Integrating System Model

As Fig. 3 depicts, the BACnet operates as an upper level’s application of Contiki operating system. uIPv6 provides TCP/IP communication service. In this study, we choose the Tmote Sky as hardware platform. uIPv6 protocol stack achieve the process, BACnet protocol interfaces send and receive the data, by calling the Sky hardware platform.

4. Assessment on Integrating System Performance

Since the memory of WSN nodes is limited, when designing the system, the consumption of memory should be taken into account firstly. Table 1 shows the consumption of static memory in BACnet networking on sensor nodes.

Table 1. Memory consumption in different BACnet operation Memory consumption ReadProperty WriteProperty

ROM (Bytes) RAM (Bytes)

No No 30356 2564

Yes No 35765 3042

Yes No 41384 3169

Yes Yes 39743 3341

Yes Yes 40881 3398

As the test result describes, the memory consumption, only approximately 3KB RAM (Random Access Memory), is tiny in the integrating system we designed. As Table 1 describes, in the BACnet operation, the service possess the highest complexity when the read and write properties are both refer to ‘YES’. Furthermore, the consumption of RAM and ROM (Read Only Memory) increased with the complexity of service increasing. However, the total memory consumption meets the requirement of WSN node.

Contiki 2.4 OS uIPv6 Protocol Stack

BACnet Protocol Stack ReadProperty Network Layer BVLL

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5. Conclusion

In this paper, a new BACnet and IPv6-based WSN integrate model is presented. To optimize this model, a micro-BACnet protocol stack is designed and the interaction between the BACnet users is implemented by using uIPv6 protocol stack. According to the experiment in different BACnet operation, a solution with low memory consumption for the interconnection between BACnet and IPv6-based wireless sensor devices is provided in this study.

Acknowledgements

This paper is supported by the National Natural Science Foundation of China (60961002).

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