reliable ale middleware for rfid network applications

Received 17 June 2007Revised 3 November 2007

Copyright © 2008 John Wiley & Sons, Ltd. Accepted 9 March 2008

Reliable ALE middleware for RFID network applications

Nong-Kun Chen*†, Jiann-Liang Chen, Teng-Hsun Chang and Hsi-Feng Lu

Computer Science and Information Engineering Department, National Dong-Hwa University, Hualien, Taiwan, ROC

SUMMARY

Radio frequency identifi cation (RFID) technology adopts the air interface to deliver the information required for object identifi cation. The RFID system is convenient to manage and operate, and is widely encouraged by the large-scale chain industry. Additionally, electronic product code (EPC) network technology allows immediate, auto-matic identifi cation and sharing of information on items in the supply chain. This work proposes an RFID service middleware with a highly reliable and effi cient application-level event (ALE)-based prototype mechanism accord-ing to EPCglobal. A Student Muster Roll (SMR) application test bed is implemented in the proposed ALE-based scheme. The SMR system can be employed to manage the absentee records of students in a class, and can manage and control several operation multi-reader devices simultaneously. The proposed scheme can fi lter attendance accurately, eliminating the possibility of reduplication in student records. Performance evaluation results indicate that the proposed novel scheme is much more effi cient and reliable than a naive ALE scheme. Copyright © 2008 John Wiley & Sons, Ltd.

1. INTRODUCTION

Radio frequency identifi cation (RFID) technology adopts the air interface to deliver the information required for object identifi cation. Because the applicable technical RFID information is convenient to manage and operate, and is heavily promoted by the large-scale chain industry, application of this tech-nology is currently growing vigorously. The recent initiatives of Wal-Mart, Metro and Target, which require RFID object labeling, may seem trivial to the general public [1]. Information application industries can decrease the investment in management and enhance high-quality services by attaching smart RFID tags to objects [2]. Market surveys reveal that RFID is currently a fast-growing technology.

The RFID system architecture must be studied when designing an RFID application system. RFID applications have been investigated in real-world situations, such as pervasive services, sensor incorpo-ration and mobile employment [3–5]. Several RFID standards cover the terminology, such as the unique identifi er coding on RFID tags, the air interface, reader protocols and the middleware of an RFID system. The barcode is currently the most popular method of identifying objects for the logistic applications of goods. The price of RFID tags is likely to fall as technology advances, enabling RFID tags to replace bar-codes. RFID has the following advantages over barcodes: RFID is non-line-of-sight; tags can be written into information; tags can hold more information on items than barcodes; the reader must not read identifi ed code artifi cially; several objects can be read simultaneously; and it improves the visibility of a supplier’s goods.

EPCglobal is the faculty that promoted the electronic product code (EPC) network system to link all physical objects together for enterprise applications [6]. However, many RFID applications are still being

INTERNATIONAL JOURNAL OF NETWORK MANAGEMENTInt. J. Network Mgmt 2009; 19: 203–216Published online 6 June 2008 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/nem.698

*Correspondence to: Nong-Kun Chen, National Dong-Hwa University, Computer Science and Information Engineering, 1, Sec. 2, Da Hsueh Rd, Shou-Feng, Hualien, 97401, Taiwan, ROC.†E-mail: [email protected]

204 N.-K. CHEN ET AL.

Copyright © 2008 John Wiley & Sons, Ltd. Int. J. Network Mgmt 2009; 19: 203–216 DOI: 10.1002/nem

developed as non-EPC systems, owing to the high adaptability of RFID devices for different applications [7].

Various types of readers and tags can be adopted in RFID network applications. Feedback information from innumerable tags and various readers indicates that the raw data must be fi ltered and screened via the application-level event (ALE) mechanism, then sent back to the backend database. To ensure conve-nient management and security, powerful RFID middleware is required to manage the highly complex system environments. A highly effective ALE middleware can confront both integration and control over various tags and diverse function readers. Therefore, developing a reliable ALE-based middleware mechanism is very important. This study implements a service platform with a highly reliable and effi -cient ALE-based mechanism.

The remainder of this paper is organized as follows. Section 2 describes the background knowledge, which introduces the RFID system, RFID applications, EPC network and related research. Section 3 then introduces the proposed ALE middleware scheme. Next, Section 4 presents the implementation test bed of the proposed scheme. The performance results are discussed in Section 5. Conclusions are fi nally drawn in Section 6.

2. BACKGROUND KNOWLEDGE

As mentioned in Section 1, RFID tags carry a larger set of IDs and more information than barcodes. RFID readers can identify RFID tags from a distance without requiring a line of sight. Moreover, RFID application systems can distinguish among many different RFID tags in the same area without human help. Therefore, RFID is becoming a mainstream technology. The primary reason for the recent popular-ity of this technology is cost. To compete with the cheapest barcode technology, electronic identifi cation technology must be equally inexpensive, or add adequate added value to improve its applications [8,9]. This study surveys RFID theories and their applications, and the challenges for organizations that deploy this technology.

2.1 RFID system

RFID system technology has recently become a popular topic in academia and industrial research. The system component comprises two main parts: the RFID tag (electronic label) and the RFID reader (reading device). Tags are categorized into two types: passive and active. The power in an active tag is provided by batteries that continuously power the computing and transmitting circuits. Conversely, passive tags rely only on the RF energy induced by electromagnetic waves emitted by a reader [10]. The tag receives both information and operating energy from this RF signal when the reader broadcasts the requested command. The reader reads information about identifi ed objects using the RF interface from the tags. According to the ISO standard, the reader uses several radio frequency ranges as follows: low frequency (LF, 152 kHz), high frequency (HF, 13.56 MHz), ultra high frequency (UHF, 868–915 MHz) and microwave (2.45 GHz and 5.8 GHz). It utilizes electromagnetic waves to transmit energy and signals, and receives information by reading the ID from the tag. According to use the different frequency that will affect the transmission distance of reader successfully received the tags ID. For example, high frequency is suitable for smart card to use, while ultra high frequency is suitable for parking lot management.

2.2 RFID applications

The previous section relates to RFID hardware devices. The RFID system specifi cation was originally designed in the Auto-ID Center. However, the level of usage of an RFID system determines the effi ciency of its logistical management in enterprise applications and infl uences the speed of product information query. In Figure 1, after a reader has received the correct tag ID, it transmits this information to the backend database system or server to store it. Furthermore, the database system is combined with other

RELIABLE ALE MIDDLEWARE FOR RFID NETWORK APPLICATIONS 205


systems in an enterprise. Transmission or exchange of information through a standard Internet interface and computer network leads to an effi cient information integration function. The RFID system service currently applies to supply chain management, environmental monitoring, military, healthcare (patients) and transportation.

2.3 EPC network

The EPC was created by the Auto-ID Center, which was formerly known as EPCglobal Inc. The EPC is a unique object identifi er stored in RFID tags. RFID subscribers can obtain useful information about objects attached to RFID tags through the EPC network by scanning the tags [11]. The EPC network is a set of technologies enabling immediate, automatic identifi cation and sharing of information of items in the supply chain. EPCglobal has formed technical committees and action groups to maintain and study hardware and software development and business requirements [6]. Chris York has defi ned the EPC Network as a network ‘designed to ensure global interoperability along the supply chain, with benefi ts for manufacturers including labor and time savings’ [12].

The EPC network consists of three main components: object naming service (ONS), EPC information services (EPC-IS), and EPC discovery service (EPC-DS) [12,13].

The ONS is an entity to resolve EPC serial numbers in the EPC network. The global directory of EPC-IS is publicly available to query for product information. The ONS protocol, which resembles the domain name server (DNS) concept, has been proposed to enable Internet users to access the object informa-tion from RFID readers [14]. An EPC-IS is a company database containing product details including the manufacturer ID, object class, size, weight, price and various other data that appropriate for sharing with supply chain partners [12]. The EPC-DS is an electronic chain of custody for EPC tags. EPC-DS saves the location of the EPC-IS related to an object moving from one EPC-IS to another in the discovery server. Through this process, EPC-DS maintains a history of each status change for the EPC tag [12,15].

2.4 Related research

The EPC network model was created by the Auto-ID Center, which was a research project at the Massachusetts Institute of Technology (MIT) [16]. The main design purpose of the EPC network is to

Figure 1. RFID service network



link all objects in the world through the Internet. The EPC network application is the vital topic in RFID system services and has been discussed recently in the literature. An EPC network consists of three main elements, namely ONS, EPC-IS and EPC-DS, described in detail in the previous section.

Taesu Cheong et al. [17] demonstrated an implementation of the RFID middleware system that not only is compatible with the EPCglobal ALE specifi cation, but also can be adopted by both passive and active RFID readers. Lee and Kim [18] emphasized that RFID middleware plays a key role in applying RFID technology. Lee proposed an optimal set of performance parameters and designed RFID-specifi c tools for software performance testing. Y.I. Kim et al. [19] summarized current research on the RFID middleware framework, which is necessary for RFID application development in ubiquitous environ-ments, and analyzed the development of the RFID framework. Han et al. [15] investigated and recom-mended a framework to allow users of both EPC networks and mobile RFID application to seamlessly access information located in the other network. They also proposed an application-level gateway that transforms the protocols and content formats used in EPC networks to those specifi cally used in mobile RFID networks, and vice versa. That paper also proposed a combined mobile and RFID system network, a topic that will be investigated in this study to implement a highly reliable and effi cient ALE-based prototype mechanism.

3. PROPOSED ALE-BASED MIDDLEWARE

This study designed a highly reliable ALE middleware based on the EPCglobal standard. According to the ALE specifi cation, the middleware function needs to offer at least the following four functions:

• management of all application systems utilizing reader devices;• receiving tag information from multiple readers;• fi ltering information used for accumulating and eliminating information on redundancy;

and• combining and extracting information and, then responding to each application system with relevant

information.

Figure 2 illustrates the ALE-based middleware framework, which is divided into three layers: the applica-tion integration layer, the data monitoring and management layer, and the device monitor and manage-ment layer. This study focuses on designing the data monitoring and management layer, which is the major component of a system with a highly reliable ALE-based mechanism.

3.1 Reader framework

Various RFID readers with different protocol and signal carrier frequencies, called ‘heterogeneous readers’, are currently available. An integration platform that constructs one reader framework was built to handle heterogeneous readers. The structure requires additional modules for monitoring, uni-platform, and connection management. This design improves the reliability of the ALE-based mecha-nism. The relevant reader framework modules are introduced as follows.

3.1.1 Uni-platform moduleBecause various tags currently exist, readers have the use of different frequencies and protocols. Each reader manufacturer uses different control instructions for the same function, each of which must program in the middleware. The purpose of uni-platform design is to integrate the relevant instructions to uniform control interfaces for readers. That is, the uni-platform embeds the control instruction into the uni-platform module. Hence, the RUI can utilize the instructions in uni-platform to control corresponding reader hardware devices easily, thus effectively managing integrated heterogeneous readers.



3.1.2 Connection managementThe connection management mechanism consists of three modules, namely Connect Command, Logical Reader Naming System, and Reader Device Identifi er. These three modules are discussed in detail below.

A. Connect CommandThe RFID reader functions comprise Connect Command, Tag Interact Command, and Response Command. Each command may include a set of relevant instructions. These commands mainly set up the connected session with the RFID reader, receive a tag ID and write data to the tag ID.

1. Connect Command: this command is responsible for setting up a connected session with the reader. The Send Command and Get Response instructions are also performed, followed by termination of the connection.

2. Tag Interact Command: this command is mainly run to detect and identify tag IDs. After the adminis-trator assigns the command for reading the tag ID, the reader receives an ACK regardless of success or failure. If the information content is correct, then the reader receives a unique ID identifying the item.

3. Response Command: this is mainly used to control the reader device. As with the Tag Interact Command, the reader receives an ACK in response. The control instruction means that the reader device may receive some information such as reader status, antenna power control, operating temperature and antenna ON/OFF.

Figure 2. Enhanced ALE middleware structure



These instructions are part of the Connect Command, which is adopted in the management of various reader devices. Additionally, the Connect Command must communicate with scheduling schemes, which optimize the reader anti-collision schedules. The Connect Command then makes a connection with the reader devices according to the schedule.

B. Logical Reader Naming SystemAn RFID application system that covers a broad area to manage numerous reader devices effi ciently must provide Logical Reader functionality. For example, in warehouse management, a single reader is unable to read all items on one truckload of new product due to issues such as the directionality of the antenna, metal shield function and reader power. The system could allocate more than one reader device for one truckload of new product, to improve the identifi ed performance in the interrogation zone.

A large number of readers deployed at one block of items are combined to form a virtual reader. Starting a virtual reader name starts all the readers connected to it at the same time on the same block. The use of Logical Readers improves the effi ciency of system administration. This naming mechanism, independent of lower-layer reader entity, can further increase entity fl exibility in the reader allocation topology.

C. Reader Device Identifi erThe Reader Device Identifi er records the information about each reader entity, which comprises the reader type, allocated position, quantity and IP address. It can identify the unique reader entity, and can solve problems caused by changes in reader position or quantity.

3.1.3 Monitoring moduleTo acquire a better supply chain management, an RFID network must increase the allocated density and quantity of RFID reader devices. Therefore, the EPC network contains suffi cient information for this; the prospect can be realized on the inquiry of logistic objects and business applications. The reader scheme for gathering disconnection information is built to assist the system to manage the distributive broad zone and numerous RFID readers. The module mainly monitors the aliveness of each managed reader and notifi es abnormal events such as reader disconnections. The host system utilizes the ping instruction to test whether a reader exists, and records the message to the log. The message responds to the RUI scheme, in order to manage readers effi ciently.

3.2 Reader User Interface (RUI) module

The RUI module mainly offers one user interface with a simple and apt operation. The user can manage a set of readers easily through the interface. In the fi rst row in Figure 3 shows an RFID reader with number 01, an IP address of 192.168.1.90 and port 4000. The reader is triggered to read the tag ID every 300 ms. For example, the system can trigger the reader device of number 01 after the user pushes the Connect button. The reader device can read the tag ID once every 300 ms when the user pushes the Start Get SID button. The left textbox represents different readers with numbers from 01 to 04. The readers may be used for desktop computers, mobile PDA platforms and even RS232 port readers (Figure 4). Addition-ally, readers are divided into UHF and HF type, as described in Section 1.

3.3 ALE Message Agent

A transparent access scheme is the key to the entire application in an enterprise for connecting a conven-tional application system with an RFID network. A signifi cant issue in RFID system operation is whether the system can receive the appropriate tag information and guarantee data reliability. Therefore, RFID middleware provides interfaces for defi ning control and delivery of the fi ltered and accumulated tag data, thus giving outer applications access to ALE in order to obtain the tag data of interest. Hence, a highly effective ALE-based middleware can improve the effi ciency and transparency of EPC networks.



RFID middleware serves as the intermediary component between RFID tags and backend data appli-cations, making it important for promoting RFID technology. The middleware transfers tag data to application systems, and manages and monitors multi-readers by different communication protocols. In Figure 2 the ALE Message Agent contains two components: Filter Management and Message Management. Both modules are described in detail below.

3.3.1 Filter Management moduleThe fi lter mechanism is a function of the RFID middleware system. During fi lter processing, Filter Manage-ment consists of three functions: cleaning, consolidation and summarization. Clearing means eliminating the redundant data. Consolidation means collecting and extracting the data of interest according to the application requirement. These two functions enable the ALE to summarize the information to respond to application requirements. Figure 5 illustrates the Filter Management module interface. The binary search technique can be adopted to implement the fi lter mechanism.

Figure 3. RFID ALE user interface

Figure 4. Console of integrated heterogeneous readers



The ALE Message Agent mechanism enables application systems to obtain tag data by the Reader Agent control. The Reader Agent is an ALE middleware structure integrate module composed of three modules: Agent Management, Reader Framework and Reader User Interface.

3.3.2 Message Management moduleThe Message Management module accumulates and integrates data from the Filter Management module, and prepares the data for delivery to application systems. Additionally, Message Management must also cooperate with the function of the monitor component. The tag data are ready for delivery to every application system. However, if the tag data cannot be delivered immediately they are stored in the tem-porary storage area of the database. Until the application system connects with ALE, Message Management delivers the data by batch processing. The Message Management module not only supports retransmission management (RM) function operation, but also effi ciently decreases the risk of data loss. Furthermore, Message Management improves system accuracy and reliability by creating log fi les for temporary storage and retransmission of data.

The data fl ow chart in Figure 6 depicts how the ALE Message Agent modules process the system data. The RUI component can deliver tag information (raw data) to the Filter Mechanism while the reader device is in the power-on state. The Filter Mechanism module can eliminate/sift uninteresting and redundant data. The Message Management module then becomes responsible for transmitting and retransmitting data to application systems. If backend systems do not make a connection, then the module creates a log fi le to store the data. The module batch-processes the log fi le until the backend system recovers connection.

4. ALE-BASED TEST BED IMPLEMENTATION

This study implemented an EPC network test bed, which can be regarded as the infrastructure for devel-oping ALE middleware for RFID system applications (Figure 7). The platform comprises the following components: ONS, EPC-IS, EPC-DS, the manufacturer host and user front-end. The system can clearly provide the basic inquiries and processes for obtaining manufacturer information.

This experimental platform takes an EPC network as the backbone structure. The test bed employs Internet IP-based network application technology, and consults the EPC information query process. Figure 8 shows four cases of the EPC information query process. The user fi rst gets the tag EPC code, and then inquires about the retailer’s database using the company code in EPC. If the item information is obtained, then the EPC-IS can make the affi liated company serve the query directly (case 1). If the

Figure 5. Filter management interface



query is not successful, then upper-level ONS is queried to obtain the EPC-IS service affi liated to the company code (case 2). The hierarchical ONS can serve several EPC-ISs. If the ONS of the lower level cannot obtain the company code information, then the network queries the ONS of the upward level. If the network hits the query information, it transmits the information back to the user and records the information simultaneously (case 3). If it does not have the required information in Root-ONS, then the ONS structure does not contain the registration material of this company code, indicating that the company code is currently unable to obtain the correct EPC-IS service (case 4).

This study also developed an RFID system with high-reliability ALE middleware based on the EPC network test bed. This system is mainly used to manage the absence records of students for taking a subject. The system is called the Student Muster Roll System (SMR System). The three list boxes at the

Figure 6. ALE Message Agent data fl ow

Figure 7. EPC network test bed (left: manufacture server; right: local ONS)



Figure 8. Inquiry process of the EPC network test bed

bottom of Figure 9 show the presence or absence status of each student. The system can maintain total student fundamental data from the data manager menu (Figure 10).

The distribution becomes more extensive as more readers are used. For example, Figure 11 shows fi ve readers in a computer classroom, two readers in the laboratory and two readers in other places. Such a distribution requires a reader administrative system to manage and control the operation of every reader device. The device manager is divided into three parts: the device browser, subscribers and command area. Their functions are described as follows.

• Device browser: the readers are aligned according to their different places and functions, and are represented in a tree structure. In this example, the computer classroom has fi ve UHF readers.

• Subscribers: this component shows the detailed attributes of each reader, such as the Logical Reader name, the reader IP, port number and timer. Additionally, the component also provides some general operational functions, including New, Edit and Delete buttons. These buttons can control and browse device information.

• Command area: this area is composed of four parts: Display reader, Check reader connection, Show selected reader and Start selected on-line reader. The Display readers mainly refresh the reader alignment. The Check reader connection utilizes the ping instruction to check whether a reader exists. If no reader exists, then the off-line sign is depicted in the device browser to remind the administrator of its absence. The Show selected reader can assign an IP address to start the reader. The Start selected on-line reader makes the active reader prepare to receive data from tags.

5. PERFORMANCE EVALUATION

This section reports some results from the performance evaluation of the proposed ALE middleware mechanism. Tests are performed in the SMR application system. In the test environment, the system took



fi ve RFID reader devices and 100 RFID tags. A two-part experiment was undertaken to test the reliability and effi ciency of the proposed ALE middleware. First, the tags’ receipt time was calculated by the fi lter mechanism. The ratio of successfully read tags over the total number of tags was then measured by the retransmission mechanism (RM).

Figure 9. Student Muster Roll System: entrance menu

Figure 10. Student Muster Roll System: data manager menu



5.1 Filter mechanism

Figure 12 shows the time taken by the system to receive the RFID tag information. Fifteen samples were taken. In Figure 12, the line with square symbols represents the scheme with the fi lter, and the line with diamond symbols represents the scheme without the fi lter. The graph shows that the approach with the fi lter scheme takes less time than the approach without the fi lter, to deliver the RFID data to an appli-cation. The evidence reveals that an RFID system without fi ltering requires a reader device to transmit complete tag data to an application. The system thus delivers much data and takes a long time owing to the limited network bandwidth. Conversely, RFID systems with fi ltering sift the raw data in advance, thus eliminating largely redundant data and extracting the interesting data to the application. Figure 12 shows that the proposed fi lter mechanism takes less time than to deliver data to the application than the

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Figure 12. Tag receive time on fi lter mechanism

Figure 11. Student Muster Roll System: device manager menu



system without the mechanism. The proposed scheme clearly performs better than that without the fi lter mechanism, and improves the effi ciency of the RFID system.

5.2 Retransmission Mechanism (RM)

As mentioned above, the Message Management module not only supports RM but also effi ciently decreases the risk of data loss by temporarily storing the data. An experiment was performed to compare system performance with and without the RM function. The effect of the read frequency of various reader devices on system performance was also considered. Fifteen samples were taken. The read frequency was set to 200 ms at samples 1–5, 300 ms at samples 6–10 and 400 ms at samples 11–15.

In Figure 13, the read rate on the y-axis denotes the ratio of successfully read tags over the total tag numbers via the RM. The x-axis denotes the time of sampling. The line with triangular denotes the method with RM, and the line with red squares represents that without RM. Experimental results clearly indicate that the scheme with RM obtained a higher read rate than that without RM. The evidence also reveals that the scheme with RM obtained a higher accuracy than that without RM. Additionally, the highest read rate was obtained at a read frequency of 300 ms. The system with RM achieved a read rate of 100% at a read frequency of 300 ms. The scheme without RM could not achieve a read rate of 100%, because of RFID reader device failure, network disconnections or collision.

This performance evaluation demonstrates that the RFID system with the proposed novel ALE Message Agent mechanism obtained a read rate improvement of 19% over the system without RM. The evidence clearly indicates that the proposed ALE Message Agent mechanism is highly reliable and effi cient.

6. CONCLUSION AND FUTURE WORK

This work designs an EPC network system and RFID-based SMR application based on a highly reli-able and effi cient ALE scheme. These two system networks are based respectively on the standard EPC network model and the ALE standard of EPCglobal. Various enterprise applications will undoubtedly be available over the EPC network in the future. Therefore, this work presents an RFID system with a highly reliable ALE-based middleware framework for future applications. Performance evaluation results show that the RFID system with the proposed novel ALE Message Agent mechanism improves read rate performance by up to 19% over a method without RM.

Further investigation will combine the proposed scheme with mobile RFID technology. Therefore, the product authentication scheme in a mobile RFID environment allows Internet users to access information about objects with tags anytime and anywhere.

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Figure 13. Read rate of retransmission mechanism



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