Low Intrusion Active Hybrid Monitor for Nodes of Sensor Networks Marlon Navia, José Carlos Campelo, Alberto Bonastre, Juan José Serrano. IUI ITACA, Sensor Networks Lab, Universitat Politêcnica de Valência. Camino de Vera, s/n, 46022, Valencia, Spain.
[email protected]; {jcampelo,bonastre,jserrano}@itaca.upv.es
Abstract. Despite the growth of sensor networks development at last years, this kind of networks suffers problems in transmission due various factors. Several systems to monitor these networks have been proposed. In this paper a low intrusion active monitor node, focused on obtaining a log of sensor node operation, is presented. For this purpose, parallel transmission is used instead of serial transmission proposed by others similar approaches. Each event in the node is coded with few bits, adding timestamp information. This document starts with a brief about proposed monitors for sensor networks, after that the connection and operation scheme of the monitor node is described, and finally preliminary operation tests are presented. Keywords. Low intrusion, hybrid monitor, sensor networks.
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Introduction.
Sensors networks usually experience problems or errors in operation or data transmission. Several causes can be identified, such as interferences in the transmission medium, security attacks (specially in the wireless sensor networks - WSN -[1]), adverse environmental conditions, malfunctioning nodes, and others. Although during design or implementation of this type of network, debugging and operation testing is usually made, mainly in the development phase, the conditions during deployment can be very different and usually unanticipated events arise. To evaluate the performance of a sensor network, even in controlled conditions or in a real environment, the so called monitoring systems (or simply monitors) are used. Monitors can focus on many performance parameters, such as throughput, jitter, response time or reliability, and even sometimes, they are focused to security and intrusion detection in the network, as described in [2]. When a monitor measures any of these parameters, two approaches may be used. Active monitors involve hardware and/or software in the sensor nodes, interacting with it. This way, active monitors require the modification of the sensor nodes to be monitored, and thus interfering with its normal operation. Measured parameters may vary from unmonitored system, being greater the difference as the cost in the monitored node increases.
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C.Fernandez-Llatas and A. Bonastre (Ed.): Workshop on Innovation on Information and Communication Technologies (ITACA-WIICT 2014) ISBN 978-84-697-1166-8
to a central server for analysis, and can also works over more than a sensor network simultaneously. Memento [10] is an example of active monitor, which adds its code protocol to the node you want to monitor. It uses bitmaps to encode the event of a node and transmit, and can detect problems in a node based on the information provided by their neighbors in the network. A lightweight tracing, as an active monitor, is proposed in [11]. In this proposal node events are saved by using a very light coding (3 bytes in performed test) in nonvolatile memory for further reconstruction and debugging of node and network behavior. Passive diagnosis for WSN PAD [12] is a monitor system with little intrusion, based in a probabilistic diagnosis approach, based on a Belief (or Bayesian) Network, to infer the root causes of abnormal WSN function. This adds a probe in each node that marks packets with very little overhead (2 bytes in tests). Finally, in [13] a new three-layer reference model for WSN Monitor Platform (WSN-MP) is presented. It is based on the division of the monitoring issue in three independent layers. Monitoring Layer focuses on capturing, analyzing and visualizing information; Information Layer deals with information coherence and finally Interchange Layer supports information management.
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The Proposed Monitor
A Monitoring Platform for the evaluation of the operation and performance of a Sensor Network is currently being developed. This Monitoring Platform can be easily developed by following the methodology presented in [13]. In this first approach, the internal state of the node in each moment will be measured by the monitor, obtaining a detailed trace of the states reached by the mote. The main characteristics of the monitoring platform should be: ─ It must have the greatest possible independence between the application / network and monitor. ─ The intrusion in both software and hardware should be minimal. ─ The system must be able to record information of the nodes.
3.1
Monitoring Platform Architecture.
The first step in the design of the new WSN-MP, according to the purpose of [13], consists on the specification of the Monitoring Layer, where the MDP’s (Monitoring Data Points) which are relevant for the desired observation have to be identified. For each MDP, a probe must be considered, in order to capture the relevant information at the correct time. In this part of the Monitoring Platform, only the internal state of the mote is considered. This state is be obtained from the so-called State_MDP .
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Finally, Interchange Layer supports information management. This task includes data transmission and data storage. The storage of generated log data can be local or remote. In local mode it can use a non-volatile memory, e.g. a SD memory. In remote mode several ways can be used to implement it. We can use another network, wired or wireless, to transmit the information to a sink created for this objective; or we can connect another device, e.g. a computer, and transmit the information directly to it. In this Monitoring Platform a storage system is considered, implemented by means of a Secure Digital (SD) card. These SD will be manually carried and downloaded to the Analysis subsystem, where the appropriate algorithms will join and process all the traces obtained. 3.2
Monitor Implementation.
Our purpose is based on the left side of Fig. 1, this is the mote events capture, formatting and data storage. To test the proposed hybrid monitor node we have built an experimental node. For this we have used a sensor mote to be monitored, and the monitor node was implemented in a STM32F0Discovery board1. The hardware monitor is based on the STM32F051 microcontroller, a low cost and consumption ARM Cortex-M0 with several interfaces and functions, which has enough capacity to act as a monitor. The GPIO ports in the mote which are connected to the monitor node must be set up at output mode. The connection to the SD module is done through a SPI port. The connections of the mote with its transducers and RF communications devices are not relevant to the monitor node. Table 1. Defined codes.
Code #define Log_Reset #define Log_Sense0 #define Log_Sense1 #define Log_Sense2 #define Log_Wakeup #define Log_RxData #define Log_TxData #define Log_RxACK #define Log_RRoute #define Log_Sleep #define Log_Stop #define Log_LowBat #define Log_SinkRx #define Log_SinkTx #define Log_SinkEr #define Log_Error 1
Meaning 0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0A 0x0B 0x0C 0x0D 0x0E 0x0F
//Node Reset/Initialization //Read sensor 0 (first/unique) //Read sensor 1 (second if it’s) //Read sensor 2 (third if it’s) //Wake up from sleep/stop //Node receives data //Node sends data //Node receives ACK //Node reroutes data (if apply) //Node goes to sleep mode //Node goes to stop mode //Low battery indication //Sink receives data //Sink sends data //Error in sink //Error in node
http://www.st.com/web/catalog/tools/FM116/SC959/SS1532/PF253215
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The SD module is connected to the monitor, unlike [11] where it connects nonvolatile memory directly to the sensor node. To record the information on the SD memory the open source libraries FatFs, available in [14], are used. These libraries, which are generic to work with the FAT file system microcontroller, must be adapted to the characteristics of the used hardware. Figure 2 shows an example of events captured in a typical working cycle. During working time of the mote, several events are recorded: wake up, data capture (any sensor), data transmission, and change to sleep mode.
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Preliminary Test
Initial tests were made to verify the correct operation of the proposed monitor node. A wireless sensor node that measures temperature each 20 seconds and sends the measurement to its gateway was considered as the mote to monitor. The Fig. 3 shows a photograph of both mote and monitor node, and their connection for the tests. The lines between them include data lines (events and additional data), and an interruption line.
Fig. 3. Mote and developed monitor node.
The Fig. 4 shows a screen capture of content from log file generated by monitor node. Each element is separated by a semicolon. First column is the event timestamp with format hh:mm:ss.subss. The second column is the event code; and third column is an additional value (optional). It can be appreciated that the working cycle (when node is working) is very short, just a few milliseconds.
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by means of an application developed for this purpose. It is also possible to compare the log events generated with other motes or the gateway. This approach is a very interesting option for monitoring sensor networks, due to the very small interference caused in network operation. This monitor is being incorporated into a more complex monitoring platform, which may complement the captured information, using several sniffer nodes, in order to obtain a complete view of network behavior.
Acknowledgements This work was supported by the Technical University of Valencia Research Project SP20120889 and Spanish government under projects CTM2011-29691-C02-01 and TIN2011-28435-C03-0.
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