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Wireless Sensor Networks

1. y CHALMERS Se Wireless Sensor Networks an implementation using 6LoWPAN Master of Science thesis in the Integrated Electronic System Design programme NISVET JUSIC THILAK RATHINAVELU Department of Microtechnology and Nanoscience CHALMERS UNIVERSITY OF TECHNOLOGY Goteborg Sweden May 2011 Wireless Sensor Networks an implementation using 6LoWPAN Nisvet Jusic Thilak Rathinavelu Department of Microtechnology and Nanoscience CHALMERS University of Technology G teborg Sweden May 2011 The Author grants to Chalmers University of Technology and University of Gothenburg the non exclusive right to publish the Work electronically and in a non commercial purpose make it accessible on the Internet The Author warrants that he she is the author to the Work and warrants that the Work does not contain text pictures or other material that violates copyright law The Author shall when transferring the rights of the Work to a third party for example a publisher or a company acknowledge the third party about this agreement If the Author has signed a copyright agreement with a third party regarding the Work the Author warrants hereby that he she has obtained any necessary permission from
2. Processor Intel Celeron 2 80 GHz RAM Generic RAM 2 GB Harddisk Samsung SP0411N 40 GB NIC Intel 82562 EZ 10 100 Ethernet Controller Table 11 PC specification The operating system used was Ubuntu 37 There were several reasons for this choice the main one being Contiki was well tested with Ubuntu Windows was considered in the early stages of the project as some of the supporting software only was available for Windows for example Atmel Studio a programming environment for Atmel hardware Similar software was available for Linux though the Linux equivalent often proved more difficult to use as well as having less functionality However it was decided that the advantages of using Linux would outweigh the initial convenience of using Windows One significant advantage is the greater flexibility in system configuration which Linux offers 5 2 Jackdaw 30 Figure 10 RZUSBSTICK Jackdaw was chosen as the 802 4 15 wireless NIC 38 Jackdaw is the codename for a hardware software combination developed by the Contiki team The hardware part is an Atmel RZUSBSTICK see figure 10 32 The RZUSBSTICK is equipped with an Atmel AT90USB1287 microcontroller The main task of the MCU is to manage usb communication and the onboard AT86RF230 radio transceiver The AT90USB1287 has 8KB of internal ROM which can be extended to 32KB The RAM size is the main constraint for amount of routes that can be mapped With the def
3. r en av de ledande operativsystemen f r str msn la enheter Contiki skeppas med SICSlowpan vilket r SICS implementering av 6LoWPAN Contiki visade sig vara ett avancerat och kapabelt operativ system Att utveckla for Contiki forenklas dessutom genom anv ndadet av Cooja Cooja ar en n tverkssimulator utvecklat av SICS Kod kan simuleras och debuggas innan den laddas upp till hardvara pa vilken det ofta ar mycket svarare att fels ka En annan f rdel med Contiki r programmeringsspraket applikationskod f r Contiki ar skriven i C Detta till skillnad fran vissa av konkurrenterna dar koden m ste skrivas i en speciell dialekt eller spr k Slutligen r Contiki for tillf llet det enda operativ systemet som st djer TCP protokollet vilket kr vs f r vissa av implementeringarna i denna tes 11 Acknowledgements We would like to thank SenseAir for the opportunity to conduct this thesis especially Joakim Enerud and Henrik R djeg rd for their support and guidance We would also like to thank Kjell Jeppsson at Chalmers University of Technology for his help in writing this report Finally we would like to thank Carl Bengtsson for putting us in touch with SenseAir and making this thesis possible 111 Table of Content is A O a RR OSES SR Vee rey ae erate 1 ER e RN 1 ES tte 1 1 37 D limitatiod S dl e ri rd 1 E EE A Osa ta De a kee Tle SNRA Tala ae ei arsed ih Vs RR Meat 2 2 E ee 3 2 1 Wireless Zaepert a a ds cda 3 Zed Netwo
4. Figure 15 Servicebean for database operations 6 3 3 Data collection This section will describe the procedure used for data collection and describe the three implementations included in the project Aside from collecting data the system must also be able to indicate when the data was collected One straightforward solution would be to register at what time the data arrives at the server and assume the transmission time to be negligible Unfortunately this can incur a rather large error as TCP is used for transmission TCP utilizes retransmission when a packet is lost this means a packet may arrive at its destination much later than expected A better solution is to transmit a 37 timestamp along with the data the system clock of the node is excellent for this purpose The system clock measures time in seconds since boot up hence if the node is rebooted the system clock is reset The server and node clocks must therefore be synchronized Wait for message Calculate offset Figure 16 Server workflow Calculate ts Synchronization is achieved through an offset message sent by the node transmitted shortly after boot up The offset message contains the current node clock upon reception the server subtracts this value from the current server time and storing it to the database as the offset value see section 6 3 1 Figure 16 show this work flow This offset value will be added to the timestamps of all future incoming dat
5. events When an event timer expires an event will be posted to the process which set the timer in this case the main process The main process controls the application flow based on what events are triggered When an event is triggered for example a timer expires or an event is posted from another thread the Contiki kernel will activate the main process and pass the information regarding the event Depending on the event type the main process will enter different states All the actions within the state will be executed after which the main process will block and wait for 20 another event The main process consists of four states which are activated by four different events two user defined event types and two timer events The four states are SENSOR REQUEST TRANSMIT PERIOD TCP_ COMPLETE and SOFT RESET SENSOR_REQUEST This state s main task is to initiate sensor requests to the sensor A sensor request is a hard coded frame that is sent over serial line to the sensor requesting specific sensor data Sensor data could for example be CO temperature or humidity value Each sensor data can be fetched with separate sensor request implementations Therefore all sensor requests has to be processed within this state before transmitting to data collection server All the different sensor requests that are issued in this state are called a request chain Presently CO and temperature value are fetched from the sensor The byte values representi
6. 3290P MCUs JTAG interface on the Raven as shown in figure 25 Note that the location of JTAG interface of 3290P is shown in figure 26 Open a terminal on the PC and navigate to the cd folder Positioned in the cd folder run the following commands make clean make avr split ravenlcd_3290 elf avrdude pm3290p cjtag2 Pusb u Uflash w ravenlicd_3290 elf hex a Ueeprom w ravenlcd_3290 elf eep a Ulfuse w 0xE2 m Uhfuse w 0x99 m Uefuse w 0xFF m 56 CEA Raven Figure 26 Raven LCD Operation This manuals purpose is to aid the user with navigating the LCD on AVR Raven board When the node is powered on the 3290P MCU which controls the LCD will get the id from the 1284P and show it on the LCD The id is the last eight bits of the IP address When sensor data is fetched from the K30 the LCD will enter a cycling mode where it cycles between displaying CO and the temperature value on the LCD AVR Raven has a joystick positioned to the right just below the LCD marked in figure 26 This joystick is used to navigate in the LCD options menu The joystick can be moved in four directions up down left and right Pressing left up or down on the joystick when in cycling mode will switch between sensor data types shown on the LCD Pressing right on the joystick when in cycling mode enters the options menu The options in options menu are aligned to the right on the LCD and a key symbol is turned on see figure 26 which shows
7. Contiki and all the implementation is written in standard C which makes it easy to understand and modify 4 1 2 TinyOS TinyOS is maybe one of the most known operating systems today designed for small embedded resource constrained devices 26 TinyOS started initially as a research project at the University of California Berkeley but has since been developed by a large group of academic and commercial developers and users also called TinyOS Alliance TinyOS is open source and supports the 6LoWPAN standard TinyOS s 6LoWPAN implementation is part of the Berkeley Low power IP BLIP stack BLIP is equivalent to Contiki s uIPv6 stack There are some similarities between Contiki and TinyOS like the event driven programming and RPL support The TinyOS kernel works in a similar way as Contiki s event based kernel Tasks are run until completion and appropriate event handlers are signaled when an event 12 happens Tasks can be posted and will be scheduled by the kernel Some of the RPL developers are also TinyOS developers and the RPL implementation for TinyOS is currently in progress TinyOS uses a combination of Berkeley MAC BMAC and X MAC to achieve low power communication BMAC is another low power MAC layer protocol designed for duty cycled low traffic WSN BMAC is a Carrier Sense Multiple Access CSMA based technique developed at the University of California at Berkeley The adaption protocol exploit LPL to lower the power consumption b
8. The sensor data array will contain the system clock of the 27 last time a sensor value was acquired from the sensor This information will be stored at same position as for the offset mark packet 1 4 The remaining 6 bytes are used for CO value temperature and humidity two bytes for each sensor value CO is stored at position 5 6 temperature at 7 8 and humidity at 9 10 The present application functionality uses soft reset variable at position 9 10 Status 1 byte 4 bytes 2 bytes 2 bytes 2 bytes Table 10 An 11 byte packet containing sensor data UDP collection For the UDP collection slightly more modification was necessary Because UDP gives no assurance that the packets will reach the server the node does not receive any confirmation from the server and thus can not know if the packet has been delivered successfully Hence no need for the TCP_ COMPLETE and SOFT_RESET events within the main process Besides from this the functionality of the main process is the same as before The state diagram for the network process is shown in figure 9 The network process uses UDP protocol to transmit the sensor data The sensor data packaging is the same as for TCP implementation where the size of the packets were five bytes for offset and 11 bytes for sensor data Data collection server will respond on the offset mark letting the network process know that the offset mark has been delivered Upon receiving confirmation the network p
9. a 16 bit values Before posting the SENSOR DATA event to the main process the request pointer is increased to point at the next request which is needed within the SENSOR_ DATA state The second request is temperature and the third request is humidity All sensor values will be stored at specified position in the array Those values will later be accessed when HTTP transmission is performed 26 Presently only CO and temperature are fetched A reset value used for debugging which counts the number of soft resets performed by a node is stored instead of the humidity value On receiving the SENSOR_DATA event the main process enters the SENSOR_REQUEST and sends the next sensor request until the whole request chain has been successfully received When all sensor data is acquired the main process will post the DATA_AVAILAIBLE event to the network process The network process will go through the same procedure as before Though this time the DATA_SENT event will not be posted by the send_data function instead the network process will post the event when a connection at the server side is closed When the main process receives the DATA SENT event it will reset the soft reset counter that counts the number of consecutively aborts When the transmit_timer expires next time a new request chain will be started SOFT_RESET state is reached 25 seconds after each request chain is issued by the TRANSMIT_TIME state which is 5 seconds before the transmit
10. a lot of excessive venting is done by tenants to improve air quality in the apartment This increases the cost of heating for the landlords to investigate and survey this behaviour the Bosmart project will create a WSN sensing CO in each apartment An rapid decrease in CO concentration will indicate excessive venting Data is gathered from all apartments and is presented through a web interface 2 Technologies 2 1 Wireless Sensor Networks What differentiates WSN from other wireless networks is the sensing and controlling capability 9 Wireless sensor network are usually deployed in inaccessible environments to monitor conditions or gather sensor data that can be used for further analysis Sensor networks are built up of several small devices each device connected to a sensor These devices are required to be very small power efficient and cost effective but at the same time have sensing computation storage and communication capabilities This has a big impact on the resource constraints which differs dramatically from a typical wired network Wireless sensor networks are commonly self organized self configurable and should last for years without maintenance The latter being a very difficult demand where power consumption is the critical factor A lot of research is done regarding power efficiency for small resource constrained devices of particular interest are improvements that reduce power consumptions in radio transmissions
11. an event queue and will shortly after trigger the main process again TCP_COMPLETE The TCP_COMPLETE state is triggered by the DATA_SENT event The DATA_SENT sent is posted from the network process every time a TCP connection with the server has been closed Reaching this state means that everything went according to the plan and it is now up to the transmit_timer to trigger another request when it expires Should it be the first time the main process enters this state it means the offset mark has just been successfully sent to the server The offset mark is the system clock of the node in seconds which is used on the server side to adjust the time see section 6 3 3 At this point an offset flag offset sent will be set that implies the offset mark has been transmitted and the reset timer is set to 25 seconds This part of the state is only executed when an offset mark has been transmitted to the server All the other times this state is reached it indicates that a transmission with the server has been finalized and therefore the soft reset variable is zeroed The soft reset variable is used within the SOFT_RESET state to determine if a soft reset should be performed or not Soft reset is performed by shutting down the network process and start it up afresh This way the system clock and time synchronization are still intact A hard reset on the other hand refers to rebooting the node which will restart everything from scratch including the syste
12. clicked the SensorView bean creates and transmits an UDP multicast to all nodes in a network Finally the SensorView bean also allows all settings in the form on the web page to be cleared through the Reset link 43 7 Results The purpose of this thesis was to evaluate 6LoWPAN as a viable alternative for a SenseAir WSN implementation Though the performance proved to be dependent on what protocols were used higher up in the network protocol stack Hence this section will compare the performance of the three different implementations created in the project A WSN containing five nodes was deployed in an office environment The nodes were placed five to ten meters apart from each other and were placed in the same location for each test run The lowest index node was closest to the edge router distance increasing with node index Node one was therefore closest and node five the farthest away The nodes that were farthest away routed through a middle node Three test batches were run one for each of the implementations each run took three days The data is shown in table 12 and figure 23 The reference row indicates the theoretical number of data points which a node should have delivered It can be concluded that the heavyweight REST protocols performance suffers compared to TCP and UDP particularly for nodes with weak links Transmitted amount of data points RESTful TCP UDP Reference 8075 8233 8316 Node 1 7936 8
13. have in mind when reading the remaining of this section where the basic node application behavior will be described 18 Main process Initialize USART amp set event timers Wait for an event Less All sensor requests fetched w H Post DATA_AVAILABLE event SENSOR_REQUEST to the network process o Issue next sensor request Offset flag set Za Post SENSOR_DATA event to the main process TRANSMIT_PERIOD LZ Offset flag set S TCP COMPLETE Reset the soft reset counter Set the offset flag Increase soft reset LZ Offset flag set K counter SOFT_RESET Perform a soft reset Post ABORT event to PEEN A the network process counter reached maximum value Perform a soft reset amp Post DATA_AVAILABLE event to the network process Figure 7 Main process state diagram 19 Network process Wait for an event Initiate connection with the server bs ABORT event H dE Wait for an event Connection with the server established SE No Transmit sensor data LZ Connection closed D No z3 H D H Post DATA SENT to No Yes Yes a WW L Se Figure 8 Network process state diagram Wait for an event Main process The purpose of the main process is to initiate transmission of sensor data at specified time intervals This is achieved by event timers provided by Contiki which are used to generate timed
14. in which corresponding sensor values are inserted If an offset mark is to be sent no sensor values are needed The current system clock time in seconds is transmitted to the data collection server within an HTTP request see table 7 During this transmission the send_data function will block until an acknowledgment is received from the server When a confirmation is received the send_data function will post the DATA_SENT event to the main process and then close the current connection on the node side Should sensor data be transmitted an HTTP request containing the sensor data values is transmitted to the server see table 7 During this transmission no confirmation is needed instead the function closes the connection and let s the network process send the DATA_SENT event when the whole connection is closed Packet type Packet layout Data PUT sensenet sensor ts 120 amp co2 550 amp te 26 amp hu 0 ATTP 1 1 r n PUT sensenet sensor offset ts 50 HTTP 1 1 r n Table 7 HTTP offset and sensor data request layout The first time node contacts the server the DATA_SENT event will be posted within the send_data function Because it is the first time the main process enters this state the offset_sent flag will be set and the reset_timer is set to 25 seconds The next event that triggers the main process will be the transmit_timer When the transmit timer puts the main process into the TRANSMIT PERIOD state the timer will be reset as alwa
15. is wrong with the sensor communication 58 Appendix C Edge Router Manual Programming Jackdaw For a general reference on programming the Jackdaw see the Contiki web page 53 Before carrying on with this manual ensure step one and two of Appendix B Programming 1284P has been performed 1 Extract the jackdaw folder from the jackdaw tar gz to the same place where contiki folder is located 2 Open a terminal and navigate to the jackdaw folder 3 Run the following commands make clean make avr split ravenusbstick elf 4 Connect the RZUSBSTICK to a USB port on the PC 5 Connect the JTAGICE mkII to the JTAG interface of the RZUSBSTICK and turn on the JTAGICE 6 Use the following command line to program the RZUSBSTICK with Jackdaw code and to set correct fuse bits required for the RZUSBSTICK avrdude pusb1287 cjtag2 Pusb u Uflash w ravenusbstick elf hex a Ueeprom w ravenusbstick elf eep a Ulfuse w 0xDE m Uhfuse w 0x99 m Uefuse w 0xFB m Installation 1 Ensure that Ubuntu is installed as operating system 37 2 Install radvd by running sudo apt get radvd 3 Copy etc radvd conf from the project s software directory to etc 4 In etc sysctl conf Uncomment line net ipv6 conf all forwarding 1 Add line net ipv6 conf default rp_filter 0 Add line net ipv6 conf all rp_filter 0 5 Copy netconf sh to a suitable location for execution Typically either your home directory or usr bin 59 6 Edit net
16. on the node instead will reduce the overhead and might also increase performance But for small frequent transmissions REST is not recommended Finally efforts to adapt application level protocols for low power wireless networks are being made by 6LoWAPP a sister IETF work group to 6LoWPAN REST may therefore be worth revisiting in the future 46 8 2 TCP collection TCP collection offers significantly lower overhead compared to RESTful collection However a custom application protocol has to be specified which in most cases is not desirable TCP collections also offers a measure of safety in data transmissions but this comes at a cost Even though the overhead is lower compared to the RESTful collection the overhead to payload ratio is still high Despite this TCP collection offers quite good performance and should be considered the implementation of choice 8 3 UDP collection UDP collection is the most lightweight of the implementations This is due to the UDP protocol which does not use hand shaking and therefore offers much lover overhead But this also comes with the drawback that no guarantee is given for a successful transmission 47 9 Future Work A number of improvements and additions can be made to the prototype a short list will be presented in this section Presently only CO data is fetched But the prototype also supports temperature and humidity values with minor modifications to the node software Two way comm
17. rfc4944 txt Accessed 2011 01 24 Dunkels A amp Vasseur J P 2010 Interconnecting Smart Objects with IP The Next Internet Burlington Morgan Kaufmann ISBN 9780123751652 Deering S et al 1998 Internet Protocol Version 6 IPv6 Specification http www ietf org rfc rfc2460 txt Accessed 2011 01 24 Mid Sweden University Environmental Monitoring http www miun se en Research Our Research Centers and Institutes STC 1 Research within STC Wireless Sensor Systems Environmental monitoring Accessed 2011 01 24 Acreo AB Acreo http www acreo se Accessed 2011 01 24 Cook D amp Das S 2004 Smart Environments Technology Protocols and Applications Wiley Interscience ISBN 9780471544487 IEEE Institute of Electrical and Electronics Engineers http www ieee org Accessed 2011 01 24 IEEE 2006 Wireless Medium Access Control MAC and Physical Layer PHY Specifications for Low Rate Wireless Personal Area Networks LR WPANS http standards ieee org Accessed 2011 01 24 ITU 1994 ITU T Recommendation X 200 http www itu int rec dologin_pub asp lang e amp id T REC X 200 199407 I PDF E amp type items Accessed 2011 01 24 Bormann C amp Shelby Z 2009 6LoWPAN The Wireless Embedded Internet Chichester UK John Wiley amp Sons ISBN 9780470747995 Information Sciences Institute University of Southern California 1981 Internet Protocol DARPA Internet Program Protocol Specificat
18. schedule the processes within an application Though all events will be queued and handled by the kernel in a First In First Out FIFO order A blocking process will wait for an event to happen meanwhile the kernel continues by executing other processes When an event is triggered the kernel executes the corresponding process and passes associated event information The event based kernel protothreads and the blocking macros gives the user possibility to write programs with a sequential control flow Part of the Contiki operating system is a communication stack ulPv6 The ulPv6 communication stack is also partly developed by SICS and is one of the world s smallest open source TCP IP stacks SICSlowpan which is Contikis implementation of 6LoWPAN is included in ulPv6 11 Forwarding and routing can be done at either the data link layer mesh under or network layer route over of the OSI model Contiki implements the route over routing techniques This is enabled by ContikiRPL which is an implementation of the RPL routing protocol developed by the Routing over Low power and Lossy networks ROLL working group at IETF 24 The protocol is specifically designed for IPv6 routing in low power wireless sensor networks By implementing these different network standards and protocols designed for low power wireless networks the power consumption is decreased in comparison to original networking protocols To further decrease power consumption Cont
19. second task data presentation is to present the collected sensor data for the user in a user friendly form 1 3 Delimitations First delimitation is one way communication between nodes and server Only nodes will initiate communication the server s task is to collect the data from each node This decision was made to simplify the node functionality Second delimitation is power concerns No power saving features are implemented the nodes are always powered This delimitation was set by SenseAir The main reason is that the sensor itself consumes much more energy than the Microcontroller Unit MCU and radio Third delimitation is security There are no readily available technologies for securing low power wireless networks This effort might require a thesis of its own 1 4 Related work The research area of Wireless Sensor Networks have spawned a large number of projects each emphasizing different functional aspects Some are designed specifically for long battery life such as the Wireless Sensor Systems project at Mid Sweden University in Sundsvall 7 The environmental monitoring subproject aims to create a WSN with extremely long battery lifetime To achieve this everything from hardware to network protocols are custom made In contrast to this thesis where the main focus is to use existing standards An other project more closely related to this thesis is the Bosmart project at Acreo 8 It is suspected that during wintertime
20. the backing beans the bean will be created if it does not already exist Likewise the bean will be destroyed when its scope ends The two most commonly used scopes are request and session A request scoped bean will be destroyed when the web page request has ended a session scoped bean will be destroyed when the client s session ends When a client first connects to a web server a session is created on the server for that client the session holds data which should be persistent over several requests for that client All three backing beans in this project are request scoped SensorBean holds data regarding the choice of sensor The currently chosen sensor and a list of available sensors can be fetched from this bean ChartBean holds data configuring the chart 42 Settings such as type and color of the chart can be found in this bean Finally SensorView holds functionality for the two links Reset and Broadcast lt h selectOneMenu id sensor value sensorBean sensor ipAddress valueChangeListener sensorBean changeSensor gt lt f selectitems value sensorBean sensorsOptions gt lt h selectOneMenu gt Figure 22 JSF tags sample code Figure 22 shows an example where JSF tags and EL are used to create a drop down menu This specific code creates the drop down for selecting sensor The JSF tag is h selectOneMenu it creates the drop down itself The value attribute of this tag sets what value the drop down currently has EL all
21. the master and devices responding to the request are called slaves At any time only one master device may be connected to the Modbus serial line while up to 247 slaves are supported A request is always initiated by the master device which can not handle more than one request at a time Slave devices can not initiate requests and they will never transmit data without first receiving a request from the master device Furthermore the slaves can not communicate with each other Two transmission modes exist for serial lines Remote Terminal Unit RTU mode and American Standard Code for Information Interchange ASCII mode These defines the bit contents of message fields and how the information is decoded The transmission mode should correspond for all devices on a Modbus serial line Modbus Serial Line protocol adds additional fields to the Modbus PDU address and error checking field see figure 3 The address filed specifies the slave address In RTU mode error checking is performed by Cyclic Redundancy Check CRC CRC is an error detection code designed to detect accidental changes to raw data and is performed on every byte of the message content The receiving device also calculates the CRC on the same message content Should the calculated CRC not match against the acquired CRC from the sending device an error will occur e Modbus Application PDU gt d Modbus Serial Line PDU E Figure 3 Modbus Application and Serial Line PDUs 3 Syst
22. the time thus increasing the battery life time for end devices Though coordinator and router devices has to be powered all the time to fulfill their functionality 2 2 4 Internet Protocol The original version of IP was created in the early 1970s by Vint Cerf and Bob Kahn 14 It was designed in conjunction with the Transmission Control Protocol TCP see section 2 2 5 15 16 Together they form what is now known as the TCP IP stack see figure 1 IP is a so called connection less protocol it purpose is to provide a best effort transmission service Connection less means there is no setup time before transmitting data IP is best effort in the sense that there is no guarantee that data will arrive safely at the destination The result being hardware requirements for IP are quite low Routers supporting IP only need to forward incoming packets to a matching outgoing link The intelligence instead is placed in the end nodes where the upper layers of the stack exist These layers have the responsibility of dealing with the inherent unreliability issues of IP The majority of computers connected to the Internet today use Internet Protocol version 4 IPv4 IPv4 was first drafted in 1981 and is the first and only IP version to enjoy widespread adoption Unfortunately the requirements of the current Internet have started to outgrow the specifications of IPv4 namely the address space IPv4 features a 32 bit address which limits the number of addr
23. this third party to let Chalmers University of Technology and University of Gothenburg store the Work electronically and make it accessible on the Internet Wireless Sensor Networks an implementation using 6LoWPAN NISVET JUSIC nisvet 84 gmail com THILAK RATHINAVELU thilrat gmail com NISVET JUSIC 2011 THILAK RATHINAVELU 2011 Examiner KJELL JEPPSON Chalmers University of Technology University of Gothenburg Department of Microtechnology and Nanoscience SE 412 96 Goteborg Sweden Telephone 46 0 31 772 1000 Department of Microtechnology and Nanoscience G teborg Sweden May 2011 Abstract The past decade has seen a lot of research in the area of Wireless Sensor Networks The fruits of this research was a large number of proprietary network technologies the most successful of these being ZigBee However as the number of technologies have grown so had the need for standardization Added to this was the requirement of supporting large scale networks most of the existing technologies did not scale well with size The result was the IETF 6LoWPAN working group Their standards allow IPv6 to be operated on low power networks IPv6 being both a proven standard and reliable in large scale networking A simple but complete network where nodes deliver data to a central server will be implemented and examined by this thesis using Contiki Developed by SICS Contiki is one of the leading operating systems designed for low
24. 01 24 Buettner M et al 2006 X MAC A Short Preamble MAC Protocol For Duty Cycled Wireless Sensor Networks http www cs colorado edu rhan Papers xmac_sensys06 pdf Accessed 2011 02 14 TinyOS Alliance TinyOS http www tinyos net Accessed 2011 01 24 Real Time Engineers Ltd A FREE real time operating system RTOS for small embedded systems http www freertos org Accessed 2011 01 24 Sensinode Ltd Sensinode http www sensinode com Accessed 2011 01 24 Atmel Corporation Atmel Corporation http www2 atmel com Accessed 2011 01 24 Zolertia Zolertia http zolertia sourceforge net Accessed 2011 01 24 Atmel Corporation 2009 ZigBit 2 4 GHz Wireless Modules http www atmel com dyn resources prod_documents doc8226 pdf Accessed 2011 01 24 Atmel Corporation 2008 AVR2016 RZRAVEN Hardware User s Guide http www atmel com dyn resources prod_documents doc8117 pdf Accessed 2011 01 24 Atmel Corporation 2010 Atmega164A 164PA 324A 324PA 644A 644PA 1284 1284P http www atmel com dyn resources prod_documents doc8272 pdf Accessed 2011 01 24 Atmel Corporation 2011 ATmega329P 3290P Summary Preliminary http www atmel com dyn resources prod_documents doc8021 pdf Accessed 2011 01 24 Atmel Corporation 2009 AT86RF230 http www atmel com dyn resources prod_documents doc5131 pdf Accessed 2011 01 24 Atmel Corporation 2006 JTAGICE mkII Quick Start Guide http www atmel com dyn resou
25. 224 8304 Node 2 7907 8218 8271 Node 3 1523 8210 8210 Node 4 7071 7966 8092 Node 5 7169 8025 8009 Table 12 Transmission test results 44 100 00 98 00 96 00 94 00 92 00 90 00 Ml RESTful E TCP 88 00 H UDP 86 00 84 00 82 00 80 00 Node 1 Node 2 Node 3 Node 4 Node 5 Figure 23 Transmission test results in graph In addition to transmission performance accuracy of the Raven system clock was also proved to be a problem Due to a Contiki configuration issue on Raven hardware the system clock drift was roughly one second every 20 minutes Due to this the clocks had to be resynchronized quite often which was done by sending offset messages at regular intervals Another unsolved issue was the the reception of UDP traffic on the nodes Although the nodes sent out UDP segments without fail they did not receive them properly Due to this the UDP implementation differs somewhat from TCP and RESTful in the work flow In addition the broadcast functionality described in section 6 3 4 does not function properly 45 8 Conclusions The prototype system works as intended SICSlowpan proved to be a stable implementation of 6LoWPAN Furthermore it is well integrated into Contiki an operating system providing excellent support for low bandwidth devices Contiki also proved easy to work with although it did see a lot of development during the course of this project which made it slightly mor
26. A ota 35 Figure 14 JPQL sample A E A aseestaan 36 Figure 15 Servicsbe n tor database Operations vestir 37 Figure 16 Server WOW tence aio EEE AETA EEE AAE A A i 38 Figure 17 Webservice EE 39 Figure 18 TCP server classes nonon a cl een all one ta e a 39 Figure 19 UDP Server ds sa 40 Figure 20 Web page screenshots aicen i e iier ler eii 41 Fig re 217 B cking beans acere a yeas ssd eh cltiags Sy ateas a ure A VINER NESSER nse age NRA iy 42 Figure 22 JSF tags Sample COCO ee SE 43 Figure 23 Transmission test results in SraPli sssssersersersserserserrserssrrsrrsrrenrrsrrsrnernrsrrrsrrn e rn nn 45 Figure 24 Nerden 54 Figure 25 Programming a AO tati no ies 56 Figure 26 O e NR mins 57 vi List of Tables Table EE 6 Table 2 Common HTTP ques As 7 Table 3 Operating system COMPA ora 14 Table 4 Comparison of IP Stack ii a a 14 Table 5 Hardware E E E A dt 15 ebe e Platf fm dE SOS ee Ee ii 15 Table 7 HTTP offset and sensor data request lao sii id 25 Table 8 CO2 and temperature re qUe iia ei 26 Table 9 A five byte packet containing the offset mark 27 Table 10 An 11 byte packet containing sensor data ii rna 28 Table Ll EEN 30 Table 12 ransiission test results ci a 44 vil Abbreviations 6Lo WPAN API ASCII BLIP BMAC CRC CRUD CSMA CSS DC EEPROM EJB EL FIFO HTML HTTP IDE IEEE IETF IP IPv4 IPv6 ISM Java EE Java SE JDBC JSF JPA JPQL LAN LCD LPL LR WPAN MAC MCU MIPS MTU NIC OSI PC
27. Memory on each device is not large enough to store all gathered sensor data That means collected data has to be transported through the wireless network and be stored at a specified location Therefore the communication capability is needed Aside from a sensor each single device is required to contain its own microcontroller memory radio transceiver and power supply 2 2 Network Protocols 2 2 1 IEEE 802 15 4 Institute of Electrical and Electronics Engineers IEEE has developed standards for different wireless technologies such as IEEE 802 11 Wireless Local Area Network WLAN also known as WEFT IEEE 802 15 1 Bluetooth and IEEE 802 15 4 Low Rate Wireless Personal Area Network LR WPAN 10 The latter IEEE 802 15 4 is the most interesting where low power and low bandwidth is taken into account 11 The standard is defined at the Media Access Control MAC layer and physical layer specified in the seven layer Open System Interconnection OSI model see figure 1 12 MAC is a sublayer of the data link layer and provides addressing and channel access control mechanisms These mechanisms makes it possible for communication between nodes within a network IEEE 802 15 4 focuses on low speed and low cost communication between devices which results in a largest supported frame size of 127 bytes The standard provides a data transfer rate of up to 250 kb s at 2 4 GHz frequency El e 6LOWPAN es IEEE 802 15 4 Figure 1 Network
28. PCB PDU PHP PLC IPv6 over Low Power Area Networks Application Programming Interface American Standard Code for Information Interchange Berkeley Low power IP Berkeley MAC Cyclic Redundancy Check Create Read Update Delete Carrier Sense Multiple Access Cascading Style Sheets Direct Current Electrically Erasable Programmable Read Only Memory Enterprise JavaBeans Expression Language First In First Out Hypertext Markup Language Hypertext Transfer Protocol Integrated Development Environment Institute of Electrical and Electronics Engineers Internet Engineering Task Force Internet Protocol Internet Protocol version 4 Internet Protocol version 6 Industrial Scientific and Medical Java Enterprise Edition Java Standard Edition Java Database Connectivity Java Server Faces Java Persistence API Java Persistence Query Language Local Area network Liquid Crystal Display Low Power Listening Low Rate Wireless Personal Area Network Medium Access Control Microcontroller Unit Million Instructions Per Second Maximum Transmission Unit Network Interface Card Open System Interconnection Personal Computer Printed Circuit Board Protocol Data Unit PHP Hypertext Preprocessor Programmable Logic Controller viii POJO ppmv RADVD RAM REST ROLL ROM RPL RS 232 RTOS RTU SICS SLAAC SRAM SQL TCP UART UDP URI USART WLAN WSN WWW Plain Old Java Object parts per million by volume Linux IPv6 Router Advertisemen
29. RC of the sensor request payload The frame is then sent one byte at a time using the Contiki function rs232_send which prints one byte to the RS232 module No events are posted from here because the application now awaits response from the sensor which will be posted to the input handler sensor_input_handler initialized at main process start up The sensor_input_handler function will receive one byte at a time from the sensor as a response to the CO request The first two bytes sensor address and function code will be checked to match the expected response which should be the same as in the request Any unexpected byte will post an SENSOR_ DATA event to the main process which in return will issue the same request again because the request pointer has not yet been changed The third byte received will indicate payload data length in bytes This value will be stored in an array The last two bytes will contain a CRC of the whole response frame calculated by the sensor A new CRC calculation is performed on the incoming response which is why the first three bytes are also stored in the array The newly calculated CRC is compared against the received CRC Should there be a mismatch the main process will be notified just as before and same request will be issued again Should the CRC s match current system clock will be saved The saved system clock is the time the sensor data was acquired The received CO and temperature values will be stored as
30. Server class accepts incoming TCP connections and spawns a ServerThread for each connection The ServerThread class performs the same duties as the SensorWS class does in the RESTful collection It parses incoming messages and stores data to the database the latter is made possible by DBRemote DBRemote is the remote 39 interface for DBBean see figure 15 Two types of messages are sent by the node offset and data see section 4 3 3 The first byte of a received message is examined to determine the type of message In case an offset message was received a one byte response is sent to notify the node that the offset was successfully transmitted No response is sent for a data message Port 20000 is used both locally and remotely for the connection UDP Collection ServerThread Server SOURCE PORT int DESTINATION PORT int maintargs String 1 void socket DatagramSocket db DBRemote lt lt create gt gt ServerThread db DBRemote run void PacketHandler db DBRemote request DatagramPacket lt lt create gt gt PacketHandler db DBRemote request DatagramPacket runi void readAsShort buf byte index int short readAsint buf byte index int int Figure 19 UDP server classes UDP collection like TCP collection uses a stand alone Java server The Server class shown in figure 19 spawns a ServerThread which accepts inco
31. UR E 47 DELS Wa 48 o A A AN 49 Appendix A Software OO EE 52 EE KR AVR Si EE 32 ANI A de 52 BCID SC 0 sees 050 NS A SN da 52 el el Vert 52 Witesbark A A IN 52 Appendix B Node Marta austin A a ii at 53 O ic AS aaa 53 Lee Eu e 55 Application 1284P E 55 LEDO ira e 56 OPI A E SS OS 57 Appendix C Edge Router Mamnual ccscsssccssccserccsscssescessccsesccsaccsescesansseecesacesessenecesensenes 59 Programming Claessen A NS doesk 59 retten A a SEO O LEDEN NAMED ANA S sek ADR Ha DAKAR EA a SANT 59 E El 60 Appendix EE EE 61 A Eden ee erer EA 61 Op A VAN SR TEA a 61 List of Figures Figure 1 Network protOCOIlS essssessrsorserersorsrresrsreoreorerrerrsrerrsrrsrenrrrrsr rr ere reses ore nns ennen rr nen 4 Figure 2 HTTP tr l a O A tt sal AGES RENSA Ne 7 Figure 3 Modbus Application and Serial Line PDUS oonnoonncnnocanuconacoconanononcnononnconanononnnorncnonao conos 8 LE 42 Overview OF the EE 9 Rente INOS CEET et 10 Kuere A Ee 16 Figure TEMA process State A ee oa 19 Figure 8 Network process state Oagsranm eegesddeer inicial edi dai 20 Figure 9 UDP network process State Gia Oran 2 0 ccccsscscnnsosscdesecansecesnasectasdaceveagesdecesaceadsasehersanes 29 Pi RZ SS TER AS een sine Arena 31 Figure 11 Jackdaw network information c ccscsssesccecosesssnasnrsostenncsrnosneesesennsedseonsentssnncostessatoess 31 Figure 12 Databas Schema sisri A A A ES 35 Figure 13 Databaseabstr ction la O N
32. _timer expires Within this state the network process is either forced to its initial blocking state or completely restarted TCP collection To meet the server requirements for this approach minor changes were made within the node application The functionality of the application is the same as described for RESTful The differences were in packaging of the collected sensor data and the transmission protocol used RESTful collection stored sensor data as separate 16 bit values which can easily be inserted into the application level HTTP transmissions With TCP collection a custom protocol was designed to handle the transmission of sensor data between nodes and data collection server The collected sensor values are stored in an 8 bit array sensor_data When a transmission is made to the server the sensor data array is transmitted over TCP as raw data bytes For an offset mark the sensor_data array will be empty because no sensor values has been fetched The status code will be stored at position 0 assigned the value 0 which indicates an offset mark packet The current system clock will be stored as a 32 bit value at position 1 4 with the high order bytes first The length of the TCP segment will be 5 bytes see table 9 Status 1 byte 4 bytes Table 9 A five byte packet containing the offset mark For a sensor data packet the status bit will be set to 1 indicating sensor data The length of the TCP packet will be 11 see table 10
33. a EE 6 Glassfish 3 and JBoss AS6 43 44 Glassfish is 33 developed by Oracle and JBoss AS6 by JBoss supported by Redhat The two servers offer the same functionality but JBoss was chosen as it had better development tools such as better integration with Eclipse IDE 45 Though in a production environment Glassfish might prove the better choice as it is considered to be more lightweight a quality much appreciated when dealing with constrained hardware resources 6 2 2 Database server MySQL was chosen as the database server It is the prevailing open source SQL server widely used in web applications and has a reputation for being stable and fast 46 It is very easy to install and has some excellent tools such as phpMyAdmin for setting up and administrating the database 47 MySQL also has a stable Java Database Connectivity JDBC driver which is required for connecting to the database from Java 6 3 Software 6 3 1 Database The database schema consists of two tables sensors and datas shown in figure 12 The sensors table holds information about all the sensors in the system The id column is an auto incrementing primary key column Primary key means this column uniquely identifies each row in the table auto incrementing means this number will increment by one for each new row in the table The name column holds an optional string which describes the sensor The IP address holds the complete IPv6 address of the sensor This co
34. a transmissions calculating the approximate time of data collection on the node With this solution there can still be a discrepancy if the offset message suffers retransmissions which results in all future data transmissions having a delayed timestamp To mitigate this the node will only allow a windows of five seconds for the offset message to successfully be acknowledged else a new offset with an updated node time will be sent This allows the regular data transmissions to have a window as large as the interval at which data is sent That is since data is sent every thirty seconds the node may send retransmissions for up to thirty seconds before resigning In all three implementations the node is identified by its ipaddress The server examines the HTTP or TCP segments and extracts the source ipaddress simplifying traffic slightly by not requiring the transmission of an additional identifier RESTful collection 38 SensorwS db DBLocal request HttpServletRequest lt lt create gt gt Sensorws getSensorlipAddress String String setSensor name String void setSensorlipAddress String name String void setOffset timestamp long void setData timestamp long co2Concentration short temperature short humidity short void removeSensorfip ddress String void Figure 17 Webservice provider Data collection is performed through a RESTful web service It is implemented with RESTEasy wh
35. address varchar 255 offset bigint Figure 12 Database schema 6 3 2 Database layer Data serialVersionUID long Sensor FINDDATAS String FINDDATASCO2 String serialVersionUID long FINDDATASTE String id int FINDDATASHU String ipAddress String id DataPK DataPK name String co2Concentration short rialversionulD lon offset long humidity short EE datas Set lt Data gt 1l 0 temperature short sensorid int sensor Sensor 1 1 Fmestamp long lt lt create gt gt Sensor lt lt create gt gt DataPK getid int lt lt create gt gt Data etSensorid int setid id int void getld DataPK GE int void getipAddress String setld id DataPK void tTimest 0 lon y setipAddress ipAddress String void getCo2Concentration short Sm SE 2 a lona void getName String setCo2Concentration co2Concentration short void hashCode Serie eaves eeu setName name String void getHumidity short getOffset long setHumidity humidity short void setOffset offset long void getTemperature short getDatas Set lt Data gt setTemperature temperature short void getSensor Sensor setSensor sensor Sensor void Figure 13 Database abstraction layer The database layer provides access to the database through Java Persistence API JPA Source code for the database layer is found in the se senseair sensenet
36. art Date dateEnd Date queryLimit int offset int List lt Object gt getDatasHu sensor Sensor dateStart Date dateEnd Date queryLimit int offset int List lt Object gt setDatalipAddress String timestamp long co2Concentration short temperature short humidity short void removeDatal ipAddress String void lt lt interface gt gt DBRemote A lt lt realize gt gt I lt lt realize gt gt I em EntityManager getSensor ipAddress String Sensor getSensors List Sensor gt setSensor lipAddress String name String Sensor removeSensor ipAddress String void setOffset ipAddress String ts long void getDatas ipAddress String List Data gt getDatas sensor Sensor List lt Data gt getDatas sensor Sensor dateStart Date dateEnd Datei List lt Data gt getDatas sensor Sensor dateStart Date dateEnd Date limit int offset int queryName String List lt Object getDatascO2 sensor Sensor dateStart Date dateEnd Date limit int offset int List lt Object gt getDatasTelsensor Sensor dateStart Date dateEnd Date limit int offset int List lt Object gt getDatasHu sensor Sensor dateStart Date dateEnd Date limit int offset int List lt Object gt setDatalipAddress String timestamp long co2Concentration short temperature short humidity short void removeDatalipAddress String void
37. artDraggedListenerfevent ValueChangeEvent void session HitpSession ChartType lt create gt Tuplel bes rn eka etl i SSES void c02 a chartActionListener event ActionEvent voi DESTINATION PORT int TEMPERATURE SE Tuple key X value Y testChartDraggedAction dragEvent FlotChartDraggedEvent void lt lt create gt gt Sensorviewt HUMIDITY geken y E void destroySensorSession String GEET Eege gd i U H DEE SS setValue value Y void clear void Figure 21 Backing beans The web page is implemented with Java ServerFaces JSF JSF is a framework for simplifying front end integration in Java EE The content of the page is written with HTML JSF tags and Expression Language EL JSF tags and EL offer a substitute for scripting which is usually used when creating dynamic web pages A dynamic web page has content which the user may interact with such as a web form The JSF components allow access to the so called backing beans where the logic for the web page resides before being presented to the web client the JSF components are compiled to HTML The sensorview page refer to three backing beans SensorBean ChartBean and SensorView see figure 21 All three are so called managed beans Their entire life cycle creation to destruction is managed by the server The programmer need not explicitly create objects of these classes Instead when a web page is visited and said page requires access to one of
38. ault 8KB RAM the Jackdaw can map up to six routes hence it can support a network with up to six nodes This restriction arises from the fact that there is no 6LoWPAN stack available for Linux as a temporary solution the Jackdaw translates IEEE 802 15 4 frames to Ethernet frames before routing them Additionally this also places constraints on what MAC addresses can be used for the nodes 23 The software part consists of a Contiki installation configuring the usbstick as an edge router When connected to the PC the usbstick registered as usb0 The Jackdaw was recognized as an Ethernet device as such all the usual network configuration commands are usable on it Addresses 4 max bbbb 1 fe80 12 13ff fe14 Neighbors 6 max fe80 11 22ff fe33 4466 11 22ff fe33 4433 11 22ff fe33 4422 11 22ff fe33 4411 6 max 11 22ff fe33 4455 128 PLA 4422 11 22ff fe33 4466 128 SE S 4466 11 22ff fe33 4444 128 EE 4422 11 22ff fe33 4433 128 Sp oie 4411 11 22ff fe33 4422 128 Bape IC 4422 11 22ff fe33 4411 128 A S s 4411 Figure 11 Jackdaw network information The Jackdaw has a serial interface accessible through a terminal emulator Figure 11 shows a 31 screenshot of the main menu A number of settings can be made and inspected through this interface The neighbours menu is particularly interesting as it lists all neighbours and routes currently registered Figure 11 shows a typical setup with six nodes 5 3 C
39. base JPA requires queries to be performed in a certain manner First off queries are written in Java Persistence Query Language JPQL Though very similar to SQL in JPQL tables are not queried but Java classes as shown in figure 14 NamedQueries NamedQuery name findAllSensors query SELECT s FROM Sensor s ORDER BY s name NamedQuery name findSensorByIpAddress query SELECT s FROM Sensor s WHERE s ipAddress LIKE ipAddress D Figure 14 JPQL sample code Writing queries in JQPL allows the database layer to be database agnostic that is the type of database MySQL MSSQL Oracle etc can be exchanged without changing the code Merely the connection configuration of the data source need to be changed A data source is Java s representation of the database its connection configuration holds information such as the URI of the database the user and password with which to log onto the database and what type of database it is Each data source is associated to a persistence unit this links the models from figure 13 to the data source The persistence unit is managed by an entity manager on which JPQL queries are performed The entity manager is usually provided by the container but can also be programmatically created All operations on a database are handled through a single entity manager to allow for concurrency else race conditions might arise on the entities Finally operations on an entity manager must be
40. base package illustrated in figure 13 JPA allows the mapping of database tables to special Java classes called entities In general the instance variables of an entity map to a column in the table The type of the variable is chosen to be as close to the MySQL counterpart as possible A few of the instance variables listed might seem odd as they do not have a counterpart in the table The id variable in the Data class for example is of class DataPK PK short for Primary Key Since the datas table has a compound primary key it can not be represented by a simple variable A custom class had to be created to model the key In DataPK the two primary key columns for the datas table are found Associations are represented by additional variables with the class of the associated tables class For example the foreign key sensorid in the datas table is represented by the sensor instance variable in the Data class it has the type Sensor So instead of getting the foreign key first and execute a separate query manually into the sensors table one can immediately get the Sensor 35 object Respectively in the Sensor class the datas variable represents the collection of datas which are associated with each sensor The three classes depicted in figure 13 offer a complete model of the database and queries to the database can now return Java objects Each object represents a row in the database changing a value in the object will change the value in the data
41. conf sh if necessary to customize the ipaddress of eth0 and usb0 Operation 1 Boot computer and login 2 Ensure that the Jackdaw is connected to the computer and that is has been configured by the system by running sudo ifconfig There should be a post under usb0 which should be confirmed as a NIC 3 Run netconf sh 4 Ensure that ethO and usb0 has received global addresses by running sudo ifconfig 5 Optional radvd should start on boot up in case radvd did not start properly run sudo etc init d radvd restart 60 Appendix D Server Manual Installation 1 Ensure that Ubuntu is installed as operating system 37 2 Download and install MySQL database server 46 3 Create a mysql user senseuser with password sensepass create a database sensebase and grant all privileges to senseuser Consult MySQL web page for guides and references 46 4 Import the sensebase sql file found in the project s software directory to the sensebase database 5 Download and install JBoss AS 6 to opt jboss 6 0 0 44 6 Copy the contents of opt jboss 6 0 0 found in the project s software directory to opt jboss 6 0 0 on the server 7 Edit opt jboss 6 0 0 server default deploy mysql ds xml to match your database server configuration 8 Edit if necessary opt jboss 6 0 0 bin run conf to bind the web server to a different IP address Modify Djboss bind address variable 9 Make www data owner of jboss 6 0 0 by running sudo chown R www da
42. e collection of operating systems to three Contiki TinyOS and FreeRTOS 4 1 1 Contiki Contiki is a small open source event driven operating system designed for low power and memory constrained devices 23 The operating system was initially designed by Adam Dunkles in the Networked Embedded Systems group at the Swedish Institute of Computer Science SICS but has been further developed by a collaboration between developers from industry and academia The memory allocated by the system can be configured to be as small as 40 kB of ROM and 2 kB of RAM A Contiki process consists of a single protothread running an infinite loop Protothreads are lightweight stackless threads intended for very memory constrained systems They provide conditional blocking and thus also allow linear code execution All protothreads in the system run on the same stack in contrast to traditional threads where each thread requires an own stack hence the very small amount of memory allocation for each protothread The stack is rewound every time a protothread blocks which means the information contained by a protothread will be overwritten by other protothreads That is why all variables used within a protothread has to be globally declared in order to be preserved One of the many features in Contiki is provided by the event driven kernel The kernel is non preemptive which means it will execute a process until that process blocks Thus it is up to the programmer to
43. e difficult to test Still it should be noted that Contiki was the only operating system offering support for TCP at the time The data presentation works as intended It should be noted that data availability is obscured when longer time intervals are requested by the client As it is not interesting to present every single data point over longer intervals an average is calculated The first threshold is at three days when an interval greater than this is requested all data points are averaged to the nearest hour The second threshold is at one week an interval greater than this and only one data point per day will be shown However should only an hours worth of data be present for a day this hour will come to represent the entire day 8 1 RESTful collection The REST architecture is the de facto standard for lightweight machine to machine over the world wide web Though it may still be too heavyweight for low bandwidth networks such as 6LoWPAN On the other hand RESTful collection was very easy to implement With a framework supported by Java EE it integrated well into an Java EE application server It also uses an established application level protocol HTTP The programmer needs only to acquaint himself with a custom API The negative performance of REST is in this project partly due to the large overhead Since only a small amount of data is sent in each transmission it is not very effective Using a larger transmit interval and storing data
44. e posted by the uIPv6 stack Should the connection fail the process will try again until it succeeds or receives an ABORT event Should a successful connection with the server be established the network process will initiate a protosocket and enter a loop to complete the transmission Within this loop a protosocket function is called to send the data through the initiated protosocket However each time a data segment is transmitted the protosocket will block within the function and await permission from 23 ulPv6 stack to continue which is the reason for the loop in network process When a TCP event is received by the network process the protosocket function will be called again This loop will continue until the function runs to completion which will close the connection at node side and end the protosocket There are also two more TCP events that can end the loop those are if the connection was aborted or timed out Aside from these three TCP events the ABORT event is also acceptable which will abort the ongoing connection 4 3 3 Application functionality Three different implementations of the data collection part have been tested both on the node and the server side Those are RESTful TCP and UDP collection see section 6 3 3 RESTful collection performs transmission over the HTTP application layer protocol while TCP and UDP collection uses a custom made protocol In this section the application functionality and the differences between
45. e Jackdaw By default IPv6 is turned off on the Jackdaw this option is of course required Also by default a web server is compiled with Jackdaw where the user can examine various network information such as routing tables and neighbours This restricts the number of routes supported by the Jackdaw to two and therefore also the number of nodes supported in the network to two In order to increase the number of routes the web server was disabled A general configuration guide for the edge router can be found on the Contiki web page for further reference 23 32 6 Server The server has two main tasks or modules data collection and data presentation 6 1 Hardware To simplify matters the server runs on the same hardware as the edge router Though in concept the server is separated from the edge router and is designed to run on any computer connected to the edge router 6 2 Software Technologies A number technologies were considered for the server software the two main candidates were PHP and Java Enterprise Edition Java EE 40 41 PHP is a scripting language used for building websites and systems Its strength is simplicity it offers rapid development and a low learning curve However as it is a scripting language it is not suited for performing operations on large amounts of data Hence PHP would be excellent for the data collection module However as the presentation module would need to perform some kind of calculation after
46. em Overview This section will give an brief introduction to the system see figure 4 for an overview Three base components can be found in the system the node the edge router and the server The node is the 6LoWPAN equivalent of a router This means all nodes in the system are routers hence all nodes will forward data within the wireless network This is the foundation for the mesh network topology Each MCU is connected to a sensor and will govern the data collection from the sensor and transmit the data to the data collection server The edge router is the up link device Through this the 6LoWPAN network is connected to the outside Its only task is to receive data from the 6LoWPAN network and forward it to the Local Area Network LAN and in extension the Internet The server has two main tasks data collection and data presentation Data collection is performed through a web service the server will receive data transmitted by all the nodes and store them in a database The data presentation is performed through a website where a line graph will show transient data Router Mote Sensor Data collection DBMS server MySQL End User Client PC Smartphone Figure 4 Overview of the system 4 Node Nodes are sensor devices that build up the wireless sensor network These collect sensor data and send it to the server All nodes have router functionality which allows them to pass on data from other nodes within the net
47. enclosed in a transaction Transactions provide atomicity at the entity level All operations in a transaction are committed at the end of the transaction Enterprise JavaBeans EJB is a Java API for managing the business logic of a Java EE application EJBs simplify database access by for example automatically initiating and closing transactions at the start and end of a java function If a Plain Old Java Object POJO is used transactions would have to be manually marked in code The interface to the database layer is DBBean which is an EJB bean The operations found in this bean are shown in figure 15 Figure 15 also shows that DBBean has an interface DBLocal Generally an EJB will always have an 36 local or remote interface A local interface will allow the bean only to be accessed by local applications where as a remote interface allows external applications to access this bean lt lt interface gt gt DBLocal getSensor ipAddress String Sensor getSensors List lt Sensor gt setSensor ipAddress String name String Sensor removeSensorlipAddress String void setOffset ipAddress String ts long void getDatastipAddress String List Data gt getDatas sensor Sensor List Data gt getDatas sensor Sensor dateStart Date dateEnd Date List lt Data getDatasCO2 sensor Sensor dateStart Date dateEnd Date queryLimit int offset int List lt Object gt getDatasTe sensor Sensor dateSt
48. er compression is to remove the unnecessary part of the IPv6 address that is not needed and make the header smaller 2 2 3 ZigBee ZigBee was created in 2003 by a group of companies known as ZigBee Alliance 3 ZigBee Alliance work together to make low cost and low power wireless technology available in different markets ZigBee is the dominant low power network technology ZigBee is a protocol specification that builds upon the IEEE 802 15 4 standard ZigBee adds some extra features such as network and security layers and application protocol profiles The standard is designed for LR WPANSs and operates on the worldwide Industrial Scientific and Medical ISM 2 4 GHz radio band A ZigBee network is composed of three different type of devices ZigBee Coordinator ZigBee Router and ZigBee End Device The coordinator is the most intelligence device in the network and might also bridge to other networks There is only one coordinator in each ZigBee network The coordinator is tasked to control the security and formation of the network The Router allows the network to scale in size by acting as a traditional router and forward data from other devices But the router also contains the application code which performs the specific sensing or controlling tasks within a network The end device contains only the application code and can not route any data This means the end devices have less responsibility and thereby can be asleep a significant amount of
49. esses to roughly 4 3 billion With the rapid growth of the Internet the IPv4 address space is estimated to be depleted by march 2012 5 Although Network Address Translation NAT has alleviated the situation it does not solve the problem In addition devices providing NAT must hold network states breaking the end to end principle in the process 6 Internet Protocol version 6 IPv6 is next version of the Internet Protocol IP 6 With an address length of 128 bits its address space covers 3 4 10138 entries it effectively solves the address space issue for the foreseeable future IPv6 not only brings a larger address space but also a variety of new technologies Stateless Address Autoconfiguration SLAAC is one new technology used in this project SLAAC allows nodes to automatically configure themselves using router discovery messages A typical IPv6 address consists of a 64 bit network prefix and a 64 bit host address The network prefix 1s supplied by the router the host address is generated from the MAC address of the host A sample IPv6 address generated from SLAAC is shown in table X Network prefix Host address IPv6 address aaab 0 0 0 1122 3344 5566 7788 MAC address 11 22 33 44 55 66 77 88 Table 1 IPv6 address 2 2 5 Transmission Control Protocol Transmission Control Protocol TCP is a transport layer connection oriented protocol designed to address the shortcomings of IP 6 Connection oriented mea
50. fetching data most often calculating averages it would suffer in performance Java EE on the other hand is well suited for this task Java EE is the specification for a web development framework built on top of Java SE Java SE being the regular Java flavour Though programming in EE is quite a bit different than SE and the learning curve is steep compared to that of PHP Microsoft s NET framework offers much of the same benefits as Java EE but was not considered due to the licensing costs of their servers where as there are free open source Java EE implementations Mono which is an open source version of NET is quite a bit slower than Java EE and was therefore dismissed 42 Though it should be noted that the increased performance came at the cost of increased memory usage In an effort to use an unified platform for both of the servers main tasks Java EE was chosen This decision was made to simplify the development of the server software This allows all server software to be written in the same language Thus not only code can be shared between the two modules but run time resources can also be shared more easily An example is the database layer which both tasks utilize The data collection module uses the layer to store incoming data the presentation module uses it to fetch data 6 2 1 Application Server There are a number of application servers available for Java EE but at the time of this project only two were compatible with Jav
51. he value on the LCD TRANSMIT_PERIOD The TRANSMIT_PERIOD state keeps track of when to initiate a request chain that is when to transmit new sensor data to the data collection server This state is triggered by an event timer transmit_timer every 30 seconds Each time transmit_timer expires an event will be posted to the main process by the kernel When the main process reaches this state the transmit_timer will be reset with the same time interval It is important to distinguish the two terms reset and restart when talking about event timers in 21 Contiki Resetting an event timer in Contiki will set the starting point of the new interval to be the same as when the timer last expired For example if a timer expired five seconds ago and reset is used for that timer the new starting point will be five seconds ago Exactly the same time as it last expired even though that time is in the past The time interval of the event timer will be unchanged This feature enables event timers to be stable over time which is exactly what is needed in this case On the other hand when an event timer is restarted the starting point will be at that specific time the restart function was used In this state the transmit_timer is reset reset_timer is restarted and the request pointer is set to point at the first sensor request Then a request chain is initiated which means the SENSOR_DATA event is posted to the main process itself The event will be placed in
52. ic coding definitions 4 3 1 Setup environment Cooja is an advanced Java based simulation environment for Contiki operating system 23 The tool allows the programmer to simulate a wireless sensor network with user specified Contiki application The advantage of using a controlled environment is the possibility to observe and verify the application code before deploying it into hardware Cooja was used extensively during this project especially in the beginning when no hardware was available AVR Studio 4 software was provided with the RZRAVEN kit 29 This software is an Integrated Development Environment IDE that is used to build and debug applications for 8 bit AVR microcontrollers However the software could only be run under Windows operating systems while Contiki software tools were tested for Linux which is why the AVR Studio 4 was never fully explored Though it was useful for debugging code deployed on the hardware A C compiler is used to compile Contiki together with the node application code 17 4 3 2 Application states Contiki is a process based event driven operating system which means the node application is implemented with events and blocking macros This also means that the node application functionality can be illustrated as a sequential state machine The application consists of two processes network process and main process Two state diagrams of the processes are shown in figure 7 and 8 These figures are good to
53. ical issue Table 4 shows a brief comparison of the three IP stacks any deeper comparison between the stacks was not desirable All three stacks supports UDP protocol though Contiki s IP stack is the only one supporting TCP In order to properly examine 6LoWPAN different implementations were created in this thesis Due to the application protocols requiring TCP this feature was important 13 Operating system TinyOS FreeRTOS 6LoWPAN SICSlowpan BLIP NanoStack implementation Hardware platforms 20 12 26 supported Kernel Scheduler Run to completion Run to completion Real Time properties event based event based threads threads threads priority based FIFO priority based preemptive or non preemptive preemptive cooperative Table 3 Operating system comparisons TinyOS is written in nesC while Contiki and FreeRTOS was written in pure C language The time to learn a new language weighed against TinyOS However the later versions of TinyOS allows the programmer to write applications in C The operating system chosen for this project was Contiki the main reason being the TCP support Supported OS TinyOS FreeRTOS UDP Yes TCP Yes Route over Yes Mesh under Neighbor discovery Yes Table 4 Comparison of IP stacks 4 2 Node Hardware With 6LoWPAN as starting point the Contiki operating system was chosen and based on Contiki s platform support the hardware could be selected Two hardware platforms were con
54. ich is the JBoss implementation of JAX RS JAX RS is a Java API specification for RESTful web services 48 It allows the mapping of Java functions to a specific combination of Uniform Resource Identifier URI and REST operation Figure 17 shows the SensorWS class which implements the web service Each function in this class is mapped to its own combination of URI and REST operation The base URI used is sensenet the absolute location of the web service is http aaab 20f feff fe3c 4ca3 3080 sensenet all site URIs are relative this The SetOffset function is the first step in the time synchronization When a node comes online it will call this function first and supply it with the current node time SetOffset is mapped to the a PUT on sensor offset The node then starts delivering data by sending the current node time and sensor data This triggers the SetData function SetData is mapped to a PUT on sensor The response on a successful REST request is always a HTTP 204 No Content indicating there is no message body 18 TCP collection ServerThread Server socket Socket SOURCE_PORT int db DBRemote mainfargs String void lt lt create gt gt ServerThread socket Socket db DBRemote runi void Figure 18 TCP server classes This implementation uses a TCP link for data collection A stand alone TCP server was written in Java figure 18 shows the class diagram The
55. iki implements an adaption MAC layer protocol called X MAC 25 X MAC is an adaptive short preamble low power MAC layer protocol designed for duty cycled WSNs Preamble is a signal used in WSNSs to synchronize transmission timing between sender and receiver Duty cycle referrers to periodically cycling between awake and sleep mode X MAC uses an asynchronous Low Power Listening LPL approach also called preamble sampling to link together a sender with a duty cycling receiver The sender transmits a preamble which consists of many small packets called preamble frames These preamble frames has to be sent over a period that is at least as long as receiver s sleep period in order to wake the receiver up When the receiver wakes up the preamble will be detected and the receiver will stay awake to perform the actual transmission The short preamble and asynchronous LPL duty cycling makes X MAC more energy efficient compared to other similar techniques that uses longer preamble and synchronous LPL Contiki also offers the programmer some type of power management This feature is not provided implicitly instead it is up to the programmer to code such behavior that will result in lower power consumption One approach is to use less radio transmissions which are very power inefficient The data could instead be stored temporary within the node using Coffee an flash based file system provided by Contiki and transmitted less often in larger chunks The
56. ion http tools ietf org html rfc791 Accessed 2011 01 24 Information Sciences Institute University of Southern California 1981 Transmission Control Protocol DARPA Internet Program Protocol Specification http www ietf org rfc rfc793 txt Accessed 2011 01 24 Kozierok C M 2010 The TCP IP Guide http www tcpipguide com Accessed 2011 01 24 Postel J 1980 User Datagram Protocol http tools ietf org html rfc0768 Accessed 2011 01 24 49 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 Fielding R 1999 Hypertext Transfer Protocol HTTP 1 1 http www w3 org Protocols rfc2616 rfc2616 html Accessed 2011 01 24 Fielding R T 2000 Architectural Styles and the Design of Network based Software Architecture Modbus Organization 2006 The Modbus Organization http www modbus org Accessed 2011 01 24 Modbus Organization 2006 Modbus Application Protocol Specification V1 1b http www modbus org docs Modbus_ Application Protocol V1 1b pdf Accessed 2011 01 24 Modbus Organization 2006 Modbus over Serial Line Specification and Implementation Guide V1 02 http www modbus org docs Modbus_over_ serial line V1 02 pdf Accessed 2011 01 24 SICS The Contiki Operating System http www sics se contiki Accessed 2011 01 24 IETF Internet Engineering Task Force http www ietf org Accessed 2011
57. kground Sensors much like most other electronic components are becoming smaller and less power consuming with each year In then makes more and more sense to allow these device to become wireless about a decade ago this effort started to draw a lot of research The vision then was smart dust Sensor nodes of such small size that they were comparable with dust particles The current trend is to integrate Wireless Sensor Networks WSN into the nternet of Things 5 The Internet is usually divided into the core and the fringe Internet The core Internet consists of the backbone routers and servers The fringe Internet consists of regular Personal Computers PCs The number of hosts in the core Internet are counted in the millions whereas the number of hosts in the fringe Internet are counted in the billions The Internet of Things is a new emerging sector which consists of smart objects Smart objects are generally embedded devices which require machine to machine communication The number of hosts in the Internet of Things is expected to reach trillions Here lies the main reason for choosing 6LoWPAN to support the large number of hosts IPv6 is required which is provided by 6LoWPAN 6 1 2 Purpose The purpose is to evaluate 6LoWPAN as a viable alternative for a SenseAir WSN implementation The system has two major tasks The first task data collection is to fetch the sensor data from each sensor and aggregate it at a specific location The
58. lso used to build and run the software as well as uploading software to the JBoss AS 6 server A large number of plugins were used together with Eclipse most of them are available from the Eclipse repository and are therefore not listed here phpMyAdmin phpMyAdmin is a database management tool It was used to create maintain and examine the database 47 Wireshark Wireshark is a network protocol analyzer it was used to inspect and debug network traffic 52 52 Appendix B Node Manual Soldering This manuals purpose is to show how the AVR Raven and K30 are connected There are a number of IO interfaces available on Raven hardware guide The J202 interface marked in figure 24 is used to communicate with the K30 sensor PCB connections J202 1 and J202 2 are positioned at the top of the J202 header and will not be connected externally These two port pins are used for the internal communication between the two MCUs on Raven 1284P and 3290P The next two PCB connections J202 3 and J202 4 are used for external communication with the K30 sensor The port pin to the left is PD2 which functions as Rx and is marked in the figure as 1284P RX The port pin to the right is PD3 which functions as Tx and is marked in the figure as 284P TX 1284Ps Rx pin is connected to K30s Tx marked in the figure as K30 TX The Tx pin of 1284P is connected to the Rx pin of K30 marked as K30 RX PCB connection J202 9 positioned in the lower lef
59. lumn has the constraint unique that is this column also uniquely identifies each row Hence the ip address could be used as primary key in which case the id column is redundant However as the primary key in the sensor table is also a foreign key to the datas table sensorid a primary key of type int is preferable to one of type varchar 255 due to performance reasons The offset marks in server time when the sensor started transmitting data see section 6 3 3 The datas table holds the data for all sensors The sensorid column indicates to which sensor the data belongs As stated the sensorid is a foreign key as such the sensorid value must exist in the sensors table Timestamp indicates at which time the data points in this row were collected on the node Due to Java measuring time in milliseconds since the epoch this is of type bigint The sensorid and timestamp columns together form a compound primary key for the datas table That is each row is uniquely identified by each unique combination of sensorid and timestamp The remaining three columns are data points co2concentration is measured in ppm temperature in C and humidity in When the sensor does not have the capability to measure humidity this field is used for debugging the network and will then measure number of soft resets see section 4 3 3 34 sensorid int timestamp bigint co2concentration short temperature short humidit short id int name varchar 255 ip
60. m clock SOFT_RESET The SOFT_RESET state is triggered when the reset_timer expires This state is mainly a safe state that will prevent deadlock and restart the network process if no successful transmission have been reported for a while This state also handles offset transmission with the reset_timer reduced to five seconds The reason for this is to have a small error margin for the offset mark and still keep the transmit_timer synchronization Reaching the SOFT RESET state during offset mark 22 transmission means the offset mark has not been successfully transmitted within the five second period The network process will be restarted and another attempt to transmit the offset mark is performed This part of the state will be executed until the offset mark has been successfully transmitted to the data collection server When that happens the offset_sent flag will be set which will change the functionality of this state and also set the reset_timer to 25 seconds During normal transmissions this state functions as a soft reset Each time the reset_timer expires there is still 5 seconds before the transmit_timer triggers another sensor request The soft reset counter is increased which counts amount of unsuccessful transmissions Soft reset counter is set to allow three consecutive unsuccessful transmission before a soft reset is performed Should the soft reset counter reach the maximum value it will indicate that the network process is st
61. m developed by SenseAir figure 6 The main characteristics for both the S8 sensor and the ZigBit module is their compact size which can be seen in table 6 15 Figure 6 S8 sensor 4 2 1 AVR Raven board The AVR Raven board consist of two AVR microcontrollers 1284P and 3290P and one radio transceiver AT86RF230 32 An Universal Synchronous and Asynchronous serial Receiver and Transceiver USART is used for internal communication between the two microcontrollers The board also contains a Liquid Crystal Display LCD Aside from theses hardware parts the AVR Raven board includes some features like the 32 kHz clock crystal that is connected to both microcontroller s asynchronous timer interfaces Another feature is the voltage regulator that allows the board to be powered by either two 1 5V LR44 battery cells or by an external 5 12V DC power supply Atmega 3290P The secondary microcontroller ATmega 3290P is used to handle the LCD display on the board ATmega 3290P is an 8 bit AVR microcontroller with 32 kB flash memory 1 kB EEPROM and 2 kB SRAM 34 AT86RF230 AT86RF230 is a low power 2 4 GHz transceiver designed for low cost IEEE 802 15 4 35 The transceiver is designed for low power consumption and is connected to the Atmega 1284P 4 2 2 K30 Sensor The K30 is a sensor platform developed by SenseAir and is used for CO measurement 1 Its measurement range is between 0 and 5000 parts per million by volume ppmv The e
62. ming UDP segments For each packet a PacketHandler thread is spawned to process it The payload uses the same format as TCP collection PacketHandler will therefore determine whether the packet is an offset or data packet in the same fashion as is done in TCP collection and take the same actions as TCP collection Incoming UDP packets are received on port 20001 response packets are sent to port 20002 on the node 40 6 3 4 Data presentation SenseNet Add all sensors Remove all sensors Transient Co2 mar O 0000 Km co2 Kaes Senn 2011 04 04 A Figure 20 Web page screenshot Data presentation is performed through a single web page shown in figure 20 In the left pane there is a menu where the user can choose which sensor and what kind of data CO temperature or humidity to show The user can also set a date range In the right pane there is a chart which presents the selected data 41 ChartBean EE dbBean DBLocal serialVersionUID long sensorBean SensorBean dbBean DBLocal series List lt XyDataList gt sensor Sensor minx int sensors List lt Sensor gt maxx int sensorsOptions List lt Selectitem gt chartData FlotChartRendererData chartTypesOptions List Selectitem clickedString String dateStart Date clickedDataPointLabel String dateEnd Date clickedDataSeriesindex Integer chartType String clickedDataPoint XYDataPoint log Logger lt lt create gt gt Sens
63. nformation regarding the message e Empty line e Message content Table 2 lists the most common requests a client can perform Headers can contain information about the message and the communicating parties Common headers include date server or client names Only one header field is mandatory in HTTP 1 1 the host field which is the latest version of HTTP The host field contains the domain name of the server it is used to differentiate between multiple host names on a single IP address A sample HTTP communication is shown in figure 2 Source Destination Protocol Info bbbb 11 22ff fe33 4422 aaab 20f feff fe3c 4ca3 cap gt http alt SYN Seq 0 Win 1220 Len 0 MSS 1220 bbbb 11 22ff fe33 4422 aaab 20f feff fe3c 4ca3 TCP TCP segment of a reassembled PDU aaab 20f feff fe3c 4ca3 bbbb 11 22ff fe33 4422 TCP http alt gt cap ACK Seq 1 Ack 45 Win 4880 Len 0 bbbb 11 22ff fe33 4422 aaab 20f feff fe3c 4ca3 TCP TCP segment of a reassembled PDU aaab 20f feff fe3c 4ca3 bbbb 11 22ff fe33 4422 TCP http alt gt cap ACK Seq 1 Ack 89 Win 4880 Len 0 aaab 20f feff fe3c 4ca3 bbbb 11 22ff fe33 4422 TCP http alt gt cap ACK Seq 1 Ack 91 Win 4880 Len 0 bbbb 11 22ff fe33 4422 aaab 20f feff fe3c 4ca3 TCP cap gt http alt ACK Seq 92 Ack 131 Win 1220 Len 0 Figure 2 HTTP traffic Representational State Transfer REST is an design pattern for machine to machine communication 19 A HTTP implemented RESTful service commonly uses
64. ng CO and temperature are placed consecutively in the RAM which allows them to be fetched by a single request Therefore the request chain contains a single sensor request although more requests can be implemented The state is triggered by the SENSOR_ DATA event which is posted either from the main process itself or by an input handler function which processes the fetched sensor data The main process triggers this event when a new transmission is scheduled to take place From the input handler function the event is posted every time a sensor response has been properly processed but can also be posted if something went wrong with the sensor communication Based on the request pointer the state will issue either the next sensor request in the request chain or a transmission of the fetched sensor data The request pointer points at the sensor request that is currently handled However would something be wrong with the sensor communication the same sensor request will be issued again After each sensor request is sent to the sensor this state is exited and the main process will block awaiting another event to happen When all sensor requests within the request chain are issued and all sensor data is successfully fetched an event will be posted to the network process clearing it to transmit the received sensor data to the data collection server The data will also be sent to the 3290P MCU using a custom serial line protocol which will display t
65. ns a connection must first be established by the protocol A three way handshake is used to set up the connection after which data can be transmitted TCP offers reliability through retransmissions and acknowledgments Each TCP segment sent must be acknowledged by the receiving party Should a segment fail to be acknowledged within a certain time frame it will be retransmitted 2 2 6 User Datagram Protocol User Datagram Protocol UDP is a transport layer connection less protocol UDP like IP is a best effort protocol as such it offers no guarantee of packet delivery 17 This allows it to be even more lightweight than TCP UDP adds checksumming and multiplexing by port over the functionality IP provides 2 2 7 HTTP amp RESTful services The Hypertext Transfer Protocol HTTP is an application layer protocol designed to transfer Hypertext Markup Language HTML pages from a web server to a client 18 It lays the foundation for the World Wide Web WWW HTTP defines a number of action clients can take and the respective actions servers should take Client actions are called requests and server actions responses Requests are made on resources on the server identified by an Uniform Resource Identifier URI URI addresses always start with http or https the latter indicating a secure connection The format of a request message is as follows e Request indicating type of request and location of resource by URI e Headers meta i
66. onfiguration With the hardware properly installed the PC has access to the LAN by default Initially the Ethernet NIC is configured only with an link local address for routing purposes it must be assigned a global address The convention used for assigning global addresses was to use the link local address as template and replace the prefix 1702 which is the link local prefix with a suitable global prefix The chosen prefix was aaab The global address derived from this is used by the web server as its interface To bring the wireless network online some configuration is necessary The first task 1s to configure the PC as a router on the wireless network For this the application radvd is used radvd broadcasts router advertisements onto a network 39 The broadcasted prefix is used in the stateless auto configuration process of IPv6 A sample configuration file for radvd is available on the Contiki website Settings in this file govern aspects such as when and with which interval router advertisements should be broadcasted and which prefix should be used on the network The modified configuration file used in this project uses the prefix bbbb Initially the Jackdaw is only configured with a link local IPv6 address For routing purposes the Jackdaw must be assigned a global address which matches the network prefix By default the address is bbbb 1 In addition to configuring the PC certain modifications were also made to the code running on th
67. orBean log Logger getSensors List lt Sensor gt THRESHOLD HOURS lon init void THRESHOLD_DAYS lon QUERY LIMIT int changeSensor event ValueChangeEvent void setSensor sensor Sensor void lt create gt gt ChartBean getSensor Sensor init void setSensorsOptions sensorsOptions List lt Selectitem gt void initRandom void getSensorsOptions List Selectitem gt fetchDatas void getDateStart Date addData dataList XYDataList datas List lt Object gt void setDateStart dateStart Date void formatData datas List lt Object gt Map lt Long Tuple lt Float Integer gt gt getDateEnd Date roundToHour date Calendar Calendar setDateEnd dateEnd Date void roundToDay date Calendar Calendar setChartTypesOptions chartTypesOptions List lt Selectitem gt void getChartSeries XYDataSetCollection getChartTypesOptions List lt Selectitem gt getChartData FlotChartRendererData setChartType chartType String void setChartData chartData FlotChartRendererData void getChartType String getClickedString String setClickedString clickedString String void getClickedDataPoint XYDataPoint setClickedDataPoint clickedDataPoint XYDataPoint void Tuple getClickedDataPointLabel String STEET key X setClickedDataPointLabel clickedDataPointLabel String void Sensorview value Y ch
68. ows this link to be two way That is when the form is submitted the active value of the drop down will be stored to the instance variable of the managed SensorBean object when the form is created the value will be read from the same variable This removes a lot of so called boiler plate code which simply moves data from front end to back end The valueChangeListener attribute refers to a Java function which is triggered when the value of the dropdown is changed this link is not two way as the target is a function The enclosed tag f selectItems sets what options should be listed in the drop down The value attribute here functions much like the value attribute in the selectOneMenu tag difference being here it takes only an instance variable which is a list The se ectItems tag will iterate the list to fill the drop down with options Hence JSF is used to define the content of the page and process it to define the layout of the page Cascading Style Sheets CSS are used When a node comes online it has no knowledge of what ip address the server has this is provided to the node by means of Service Discovery However there is no clear implementation of Service Discovery in 6LoWPAN yet this expired draft seems to be the most recent development 50 A stopgap solution is to broadcast the servers ipaddress when the network is started or on demand when a node is added to the network This functionality is handled by SensorView When the Broadcast link is
69. power wireless devices It carries SICSlowpan as its own implementation of the 6LOWPAN standard Contiki proved to be a very advanced and capable operating system Developing in Contiki is significantly simplified by Cooja Cooja is a network simulator where code can be tested before it is deployed to the target hardware on which it is often much harder to debug Another notable advantage is the programming language code for Contiki is written in standard C Some of the comparable operating system require code to be written in a custom dialect or language Finally it is presently the only operating system supporting the TCP protocol which is required by some implementations in this thesis Sammanfattning Under det senaste rtiondet har det forskats mycket i tr dl sa sensorn tverk Detta resulterade 1 en m ngd propriet ra n tverksteknologier den mest framg ngsrika av dessa ar ZigBee Men med ett kande antal teknologier kom ocks ett behov av standardisering Dessutom har p senare tid ocks kravet att st dja storskaliga n tverk tillkommit Svaret p detta var IETF arbetsgruppen 6LOWPAN Deras standarder till ter IPv6 att anv ndas p str msn la n tverk IPv6 som r en v lk nd standard f r storskaliga n tverk Ett enkelt men fullst ndigt n tverk d r noderna levererar data till en central server kommer implementeras i denna tes Operativ systemet Contiki anv nds som grundsten i nodmjukvaran Utvecklat av SICS Contiki
70. protocols 2 2 2 6LOWPAN The IPv6 over Low Power Wireless Personal Area Network 6LoWPAN standard defines an adaption layer which allows IPv6 packets to be transmitted over low power networks 4 13 The standard was developed in 2007 by the Internet Engineering Task Force IETF 60 WPAN working group The IETF is a organisation with the aim to improve the Internet by providing technical documents that will aid users and designers of Internet The standard is positioned in the network layer of the OSI model The Maximum Transmission Unit MTU of IPv6 packets The MTU refers to the size of the largest Protocol Data Unit PDU that a network protocol can transmit The default MTU of an IPv6 packet is 1280 bytes which means an IPv6 packet can be as large as 1280 bytes However most of the low power networks have a much smaller frame size 127 bytes for the IEEE 802 15 4 see section 2 2 1 and thus can not support such a large packet To cope with these large IPv6 packets 6LOWPAN offers fragmentation The large IPv6 packet will be split up into smaller frames that can be transmitted over low power networks This is the main reason why 6LoWPAN is required The second functionality of 6LoWPAN is header compression Low power networks often have very low bandwidth thus sending the entire Pv6 address is very wasteful In a single network with the same prefix only the last part of the IPv6 address is needed to identify a host One feature of head
71. r Faces http www oracle com technetwork java javaee javaserverfaces 139869 html Accessed 2011 01 24 Kim K et al 2009 Simple Service Location Protocol SSLP for 6LoWPAN http tools ietf org html draft daniel 6lowpan sslp 02 Accessed 2011 01 24 Free Software Foundation Inc AVR Downloader UploaDEr http savannah nongnu org projects avrdude Accessed 2011 01 24 Wireshark Foundation Wireshark http www wireshark org Accessed 2011 01 24 SICS Tutorial Running Contiki with ulPv6 and SICSlowpan Support on the Atmel Raven http www sics se contiki tutorials tutorial running contiki with uipv6 and sicslowpan support on the atmel raven html Accessed 2011 03 08 51 Appendix A Software Tools This section lists all software tools used in the project Cooja Cooja is an advanced Java based simulation environment for Contiki operating system It was used to examine Contiki and test the application code 23 AVR Studio 4 AVR Studio 4 is an Integrated Development Environment IDE that is used to build and debug applications for 8 bit AVR microcontrollers 29 AVRDude AVR Downloader UploaDER is a Linux tool for downloading uploading firmware and fuses to AVR boards 51 It was used to program the Ravens and the usb stick Eclipse Eclipse is an Integrated Development Environment which supports a wide range of languages 45 In this project it is used for programming in both for C and Java In Java it is a
72. rable number this should be unique for each node The IP address will be created from this MAC address Connect the JTAGICE mkII to a USB port on the PC Connect the JTAG of the JTAGICE mkII to the 1284P MCUs JTAG interface on the Raven as shown in figure 25 The location of JTAG interface of 1284P is shown in figure 24 Use a 9V DC power source to power the node Turn on the JTAGICE mkII Open a terminal on the PC and navigate to the location where the application code is located in the TCP folder Remember that the contiki folder MUST be located at the same location as the implementation folder This command line will delete all the old compilation files make clean This command will compile the application code and the Contiki operating system located in the contiki folder make This command line will split the compilation output file TCP elf into TCP elf eep and TCP elf hex The eep and ber files are used to program the Raven board avr split TCP elf This command line will program the 1284P with the newly compiled application code with correct fuse bits 53 avrdude pm1284p cjtag2 Pusb u Uflash w TCP elf hex a 55 Ueeprom w TCP elf eep a Ulfuse w 0xE2 m Uhfuse w 0x99 m Uefuse w 0xFF m F igure 25 Programming a node LCD 3290P 1 pA 3 Extract the lcd folder from cd tar gz to the desired location Connect the JTAGICE mkII to a USB port on the PC Connect the JTAG of the JTAGICE mkII to the
73. rces prod_documents doc2562 pdf Accessed 2011 01 24 50 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 Canonical Ltd Ubuntu http www ubuntu com Accessed 2011 01 24 SICS Jackdaw RNDIS RPL border router http www sics se contiki wiki index php Jackdaw_RNDIS_ RPL border router Accessed 2011 04 08 Litech Systems Design Linux IPv6 Router Advertisement Daemon http www litech org radvd Accessed 2011 01 24 The PHP Group PHP Hypertext Processor http www php net Accessed 2011 01 24 Oracle Java EE at a Glance http www oracle com technetwork ava javaee overview index html Accessed 2011 01 24 The Computer Language Benchmarks Game http shootout alioth debian org u32 benchmark php test all amp lang java amp lang2 csha Accessed 2011 01 24 Oracle Glassfish Server http www oracle com us products middleware application server oracle glassfish server index html Accessed 2011 01 24 JBoss Community JBoss Application Server http www jboss org jbossas Accessed 2011 01 24 Eclipse Foundation Eclipse http eclipse org Accessed 2011 01 24 Oracle MySQL The worlds most popular open source database http www mysql com Accessed 2011 01 24 phpMyAdmin phpMyAdmin http www phpmyadmin net Accessed 2011 01 24 Sun Microsystems Inc 2009 JAX RS Java API for RESTful Web Services v1 1 Oracle Java Serve
74. rk Etudes be dca Shs rada od 3 DES 7 GE 3 222G LOWPAN ese ie A A AA AS 4 LIS BR A A A A AO Aita 5 2 2 4 AM E PEOLOC Ol 246 493 geht 5 2 2 5 Transmission Control Protocol loa 6 2 2 6 User Eeer ee A dels a Ma 6 22 EE Ee RESTO SERVICES ia it 6 LS IO AAA AAA oe Race ats 8 O a A A Nuders a k ns RONNE ee ENDE 9 Ge EE 10 e Ee Ee DE 10 O 11 412 TINY N O Mah et cats 12 E DEE KEE IN 13 4 1 4 Operating system COMA evial reine akc snavalatepe mache boi axe ence rss rn rer rn rerna 13 BD Node Hart ls anes 14 42I CNW ARS Raven DOAN EE 16 Afmesa 3290P Ed 16 ALSORE23 RE 16 IA SS OM enren vas ten da A A AN 16 4 23 STAG IGE MR AA Ai 17 RR A A A A A A EAS A AA A 17 43 Node e Te EE 17 A A eise 17 A A O aeons 18 Main PLE is 20 SENSOR REQUEST ces 21 TRANSMIT PERO ia das 21 TEP REENEN 22 SOFT RESP a gl 22 NetWork PETER o 23 RL TR EE 23 4 3 3 Pp NO O A e O atic 24 RES PAM CONECHON ds ST ALT n 24 TER COME A A a S 27 NA A oot ume a a ANS ski NASN 28 SE EE 30 5 2 E 30 KS CONO abr 32 EE 33 A ts Slat vice id 33 6 2 SOL Ware TECOS a RA E 33 6 2 1 Application E ins 33 6 22 DLI BASE A iat esse sag Band A A Mae ircamcautsauyes 34 Gs BD OM WAI EE 34 E DR ds 34 63 2 Database AV CMs a SAA R NAN SRA FAR AS Loved wen Cote 35 E ER ER Te E 37 Kukt A A A del 38 TEP CEM EEN 39 UDP Collect iS 40 GC Fick Da pr EE 41 O O RN 44 Oaa LITO a EES S E E A rama ARR FARAN ENA 46 STL RESTful colirio 46 8 2 H E CON RE A A AA AA at cll 47 5
75. rocess enters its simple state where it only can be triggered by the DATA AVAILABLE event Each time the network process is triggered an UDP segment will be sent which contains the sensor data after which the network process returns to its blocking state again to await another DATA AVAILABLE event 28 Network process No Set an offset timer to handle offset a Las Yes Offset flag set mark transmission Transmit offset mark 7 LZ Received offset mark confirmation t lt gt Yes Offset timer expired Wait for an event TRANSMIT OFFSET Wait for an event TRANSMIT DATA Transm sensor data Figure 9 UDP network process state diagram 29 5 Edge Router The edge router s main task is receiving packets on the 6LoWPAN network and forward them onto the LAN This device should be kept as simple as possible ideally 1t should not perform any task other than above described The reason for this is to uphold the end to end principle of the TCP IP stack 5 1 PC The basis of the edge router consisted of a regular PC fitted with a Network Interface Card NIC and a 802 4 15 wireless NIC The PC was supplied by SenseAir as such no major design decisions were made on this hardware The only consideration was that the PC should be able to run a modern operating system The specifications for the PC were as shown by table 11 The wireless NIC however had to be researched and procured see section 5 2
76. sidered for the project AVR Raven and Zolertia Z1 29 30 Raven is an Atmel product with an 8 bit microcontroller and Z1 is a design from Zolertia with a 16 bit microcontroller Z1 is based on an older platform called Telosb Tmote Contiki has been ported to and well tested on the Telosb platform however the platform was no longer available on the market A Contiki port for Z1 platform was planned to be released at the start of this project but was postponed Contiki port for AVR Raven already existed A comparison of the two platforms can be seen in table 5 14 Radio Transceiver AT86RF230 2 4GHz at CC2420 2 4GHz at AT86RF230 RF 250kbps 250kbps Transceiver at250kbps Table 5 Hardware platform characteristics Dimensions Height x Width x Length 2 0mm x 13 5mm x 18 8mm 8mm x 33mm x 20mm 14mm x 57mm x 51mm Table 6 Platform dimensions The characteristics for both platforms were similar the main difference being the microcontroller Z1 had a 16 bit microcontroller compared to AVR Raven s 8 bit However due to the delayed porting of Contiki for Z1 platform the Raven platform felt like a safer option Another advantage with Raven was the architecture similarities to ZigBit ZigBit is a very compact 802 15 4 ZigBee Atmel module with almost the same features as the Raven platform see table 5 31 This would give the possibility to integrate ZigBit modules with SenseAir s S8 sensors 1 S8 sensor is the newest sensor platfor
77. stall or if the sensenet application was explicitly removed from the server The server will retain the application between reboots hence this step is not necessary between simple reboots Next the TCP server must be started Open a new terminal and run tcpstart sh Wait for the server to report it has started This should take only a few seconds This step will fail if the web server has not started properly or has not finished booting Connect all nodes to power Open a web browser on the PC and navigate to http 192 168 2 131 8080 sensenet This web page should be available from other computers as well assuming there is a functional IPv6 network connecting them At http 192 168 2 131 8080 sensenet faces auto html one can find a page which auto refreshes itself though on this page the date interval is locked 62
78. t Daemon Random Access Memory Representational State Transfer Routing over Low power and Lossy networks Read Only Memory IPv6 Routing Protocol for Low Power and lossy networks Recommended Standard 232 Real Time Operating System Remote Terminal Unit Swedish Institute of Computer Science Stateless Address Autoconfiguration Static Random Access Memory Standard Query Language Transmission Control Protocol Universal Asynchronous Receiver Transmitter User Datagram Protocol Uniform Resource Identifier Universal Synchronous Asynchronous Receiver Transmitter Wireless Local Area Network Wireless Sensor Network World Wide Web 4 Introduction SenseAir AB is a world leader in infra red gas sensor manufacturing 1 They mainly develop and produce reliable low power carbon dioxide sensors Currently there exists a wired network infrastructure though it is very costly and rigid to setup A wireless network would be much more flexible as well as cheaper to install SenseAir would therefore like to produce a prototype wireless infrastructure A previous Master thesis at SenseAir studied different radio network technologies which resulted in a suggestion to use ZigBee 2 3 ZigBee being the predominant network technology for low power wireless networks Lately a new standard 6LoWPAN has started to gain momentum 4 SenseAir would like to investigate the possibilities to use this network technology for networking their sensors 1 1 Bac
79. t corner of the J202 interface is connected to internal ground OV This port pin named 7284P GO in the figure is connected to the ground pin on K30 K30 G0 Both the Raven and K30 are powered by an external 9V power source The J401 interface on the Raven is used to connect the board to an external power source The port pin positioned to the left J401 1 is connected to external 9V The next pin J401 2 is connected to ground K30 is connected to the same 9V power source as shown in the figure 53 ASA AAA AAA AVR NOB Raven ER AMEL 1284P CO gt gt Ne Exter OC al power supply OVE gt EAN K30 G0 Figure 24 Node soldering map 54 Programming Application 1284P This programming manual explains the procedures required to program an AVR Raven board with TCP collection code To program a node a JTAGICE mkII and a PC running Ubuntu is required 36 37 AVRdude has to be installed on Ubuntu as well 51 1 10 11 12 Copy usr bin avr split from the project s software directory to the usr bin folder of Ubuntu If necessary modify permissions to allow for execution Extract the contiki folder from contiki tar gz to the desired location Extract the implementation folder TCP from TCP tar gz to the same location as contiki folder Navigate to following folder contiki platform avr raven Open the file contiki raven main c Atrow 117 change the last byte of the mac_ address to a desi
80. ta www data opt jboss 6 0 0 10 Add your user to the group www data This is done easiest through the OS GUI consult Ubuntu documentation 11 Grant full access to jboss 6 0 0 to the group www data by running sudo chmod g rwx opt jboss 6 0 0 12 Copy the contents of home senseair sas found in the project s software directory to home user sas on the server where user is the home folder of the user 13 Edit if necessary home user sas jndi properties to the IPv4 address of the web server Operation This user manual assumes access to the Raven cards and the PC edge router used in the project The Ravens are preprogrammed with the TCP implementation as such only the TCP version can easily be run Before attempting to start the server ensure that the edge router is up and running 61 Boot the PC and log on to the Ubuntu operating system with user password sensealr sensepass First the web server must be started In the same terminal run webstart sh Wait for the server to report it has started This process might take several minutes Ifthe sensenet application has not previously been loaded on to the server do so now by navigating to the administration console http 192 168 2 131 8080 admin console Login using admin admin as user pass Browse to Web Application WAR s choose Add resource and follow the guide sensenet war is the file to be uploaded This step is only necessary if it s a fresh server in
81. that user has entered the options menu Pressing left within the options menu will return to the cycling mode Up and down sticks are used to navigate the different options Right stick within options menu will choose an option Presently there are five options available e CO2 enters the settings menu for CO o ON turns on the CO and returns back to cycling mode o OFF turns off the CO and returns back to cycling mode s TEMP enters the settings menu for temperature o ON turns on the temperature and returns back to cycling mode 57 o OFF turns off the temperature and returns back to cycling mode e HUM enters the settings menu for humidity o ON humidity is not used presently thus no changes will be made by this setting Returns back to the cycling mode o OFF returns back to cycling mode s ID shows the node id on the LCD display can be seen in figure 26 RESET resets all the settings to default and returns back to cycling mode although no data will be shown until next sensor data is fetched by 1284P Should the node have contact with the server an antenna symbol will be turned on which indicates this When the node is not in range to the server or if contact with the server is lost the antenna symbol will be turned off Should something be wrong with the communication between 1284P and the sensor the cycling mode will stop Instead OFFLINE will be shown on the display indicating that something probably
82. the first four requests listed in table 2 These four requests are usually mapped to a Create Read Update Delete CRUD pattern also indicated in table 2 The CRUD pattern refers to operations on the database A GET request would fetch a row from the database and present it to the client a POST request would typically create a new row in the database GET READ Fetches the content of a resource POST CREATE Posts a message to the resource PUT UPDATE Puts a message to the resource functionality similar to POST DELETE DELETE Deletes a resource HEAD Fetches only the headers of a resource Table 2 Common HTTP requests 2 2 8 Modbus The Modbus protocol was developed by Modicon in 1979 20 Modbus is a de facto industry standard serial communication protocols for devices connected on different type of buses The Modbus Application protocol is positioned at the application layer of the OSI model 21 The application protocol defines a Protocol Data Unit PDU which allows client server communication between devices A request is performed by building a PDU which consists of function code and additional information regarding the request data field see figure 3 The reply will also be a PDU containing function code and additional data response information Modbus Serial Line protocol is a master slave protocol positioned at the data link layer of the OSI model 22 The device requesting the information is called
83. the three implementations on the node side will be described RESTful collection When a node is powered on both main process and network process are started simultaneously The network process creates an ulPv6 address from the hard coded server address before reaching its initial blocking state TRANSMIT The main process calls the function usart_initialize at start up This function initializes the USART that is used to communicate with the K30 sensor A Contiki defined function is used to configure the USART with correct settings There are two USARTs for the ATmega 1284P USARTO is used internally between the two MCUs and USARTI1 can be used for external communication In this case USART1 is used to communicate with K30 at a baud rate of 9600 bps This baud rate is default for most of the sensor models at SenseAir The USART configuration is set to correspond to the K30 Modbus communication protocol settings Also during the initialization an input handler sensor_input_handler is set for USART1 that will manage the incoming sensor data After initialization of the USART is complete two event timer are set transmit_timer and reset_timer The transmit_timer is used to keep the transmitting interval synchronized The reset_timer will be used for soft reset functionality and as a transmitting interval timer for the offset mark The transmit_timer is set to 30 seconds and the reset_timer to 5 seconds The first attempt to communicate with the ser
84. uck somewhere or the server is unreachable The network process is then killed and restarted again By shutting down the network process the connection is also aborted which allows for a new connection to be established If the counter has not reached the soft reset value an ABORT event is posted to the network process This event will instruct the network process to abort the ongoing connection and reach its initial blocking state before another request is initiated by the transmit_timer Network process The functionality of the network process is to establish a stable connection with the data collection server and transmit the sampled sensor data All processes in Contiki contain some kind of blocking macros and the network process is no exception TRANSMIT The network process has only one main state TRANSMIT which will be triggered by the DATA_AVAILABLE event The process will block until the event is posted instructing the process to transmit new sensor data to the server Inside this main state there are also two other necessary TCP events used to perform the transmission to the server These two TCP states both block until they receive a TCP event from the uIPv6 stack or the ABORT event from the main process When the ABORT event is received the network process simply returns back to its main blocking state awaiting another DATA AVAILABLE event The first TCP state will block until a connection with the server is established which will b
85. unication is a slightly more complex task With two way communication a node would act both as client and server which would allow it to receive requests from the web server With this feature the nodes could be remotely reconfigured while up and running A desirable request could be to change the transmitting interval Another request could be to fetch other sensor data besides from those already being periodically transmitted Time synchronization is done with the offset mark packet when the node is powered on From that point no more time synchronization will take place unless there has been a hard reset This has proven to be a problem as the node system clock tend to drift due to configuration issues in Contiki After three days of running time each node s system clock was about three minutes ahead of the sever clock During longer periods for example years the time difference would be in range of hours A more frequent time synchronization would be recommended functionality to implement in the future 48 References 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 SenseAir Maintenance free Gas Sensors http senseair com Accessed 2011 01 24 Shu X 2010 Wireless CO Sensors ZigBee Alliance ZigBee Alliance http www zigbee org Accessed 2011 01 24 Montenegro G et al 2007 Transmission of IPv6 Packets over IEEE 802 15 4 Networks http www ietf org rfc
86. ut in contrast to X MAC uses an extended preamble TinyOS offers an Application Programming Interface API for power management which can be used to manage both radio and processor The programmer can allow the processor to sleep when there are no tasks to be run But it is still up to the programmer to implement this feature in the application Application code is written in nesC programming language which is a dialect of the standard C 4 1 3 FreeRTOS FreeRTOS is an open source Real Time Operating System RTOS 27 The operating system was originally designed by Richard Berry at Wittenstein High Integrity Systems in Bristol but has further been developed by the FreeRTOS team a group of developers and users worldwide FreeRTOS is based on a mini real time kernel which means that tasks are scheduled in real time in contrast to Contiki and TinyOS FreeRTOS does not have a native 6LoWPAN implementation in contrast to Contiki and TinyOS However it does support NanoStack which is a 6LoWPAN implementation developed by Sensinode 28 The footprint of FreeRTOS is slightly larger than for Contiki and TinyOS FreeRTOS contains an implementation of the X MAC The application code is written in C 4 1 4 Operating system comparison As shown in the table 3 all three operating systems include or supports an implementation of the 6LOWPAN standard The communication stack implementations differentiates from each other but this was not a crit
87. ver is made now by posting the DATA AVAILABLE event to the network process This is done just before the main process reaches its default blocking state The network process receives the DATA AVAILABE event which is the only event that triggers its initial blocking state The network process then tries to establish a connection with the server by calling the Contiki function tcp_connect attaching the server IP address and port number 24 8080 Then the network process blocks again until a tcpip_event is posted to the process from the uIPv6 stack If the received event indicates the connection was accepted the network process will take one step further to complete the transmission Should the ulPv6 stack post any other event at this state the network process will start over again requesting a new TCP connection When an connection is established the network process will initiate a protosocket which handles the TCP connection By calling the protosocket function send_data an attempt is made to transmit the fetched sensor data Even here the network process blocks until it receives a releasing event either from the uIPv6 stack regarding the connection or from the main process aborting the connection The function send data is called within the network process and is used to transmit data to the server This is a protosocket function which will send the sensor data over TCP using HTTP as application level protocol The data is sent as HTTP requests
88. work A node without enclosure is shown in figure 5 A node consists of an AVR Raven connected to a K30 sensor provided by SenseAir The Raven boards are running Contiki operating system AA UNUA L NR AOB Raven Figure 5 Node without enclosure 4 1 Node Operating System For this project the task was to implement a 6LoWPAN wireless sensor network With that in mind abstracting away most of the low level aspects proved to be a necessity These low level aspects can be provided by an operating system Furthermore an operating system can offer features like power management memory management scheduling polices multitasking and networking capability However traditional operating systems are not designed for devices with stringent resource constraints such as power consumption available bandwidth and memory 10 There are a number of operating systems that are specifically designed for low power and resource constrained devices They are less complex than general operating systems and most of them require merely a few kilobytes of Read Only Memory ROM and a few hundred bytes of Random Access Memory RAM The lightweight footprint make these operating systems suitable for memory constrained devices However not all operating systems contain an IP communication stack especially a 6LoWPAN implementation which is the primary functionality needed for this project The requirement of 6LoWPAN made it possible to narrow down th
89. xpression ppm is used to describe the concentration of one substance in another in this case it refers to 16 CO concentration The sensor can be powered by a 4 5 to 14V Direct Current DC source and has a baud rate of 9600 bps For external communication there is an Universal Asynchronous Receiver Transmitter UART serial interface with TxD and RxD lines where Modbus communication protocol is used Though this sensor platform does not support measurement of temperature and humidity there are other SenseAir s sensor models that include these features Because the same Modbus communication protocol is used for all sensors developed by SenseAir the sensor model can be replaced without any modification to the application software The K30 sensor platform was provided by SenseAir The sensor is connected to the AVR Raven board with 3 wire RS 232 4 2 3 JTAG ICE mkil JTAG ICE mkII is a development tool for Atmel 8 bit and 32 bit devices 36 JTAG ICE is used to program and debug the AVR boards 4 2 4 Power supply As the power was not an issue in this project an external 9V power supply is used to power both the Raven board and the sensor The sensor is not powered via the Raven board nor the other way around both are connected directly to the external power source 4 3 Node Application All AVR Raven boards are running Contiki operating system The application was developed as a Contiki program written in standard C with Contiki specif
90. ys Because the offset_sent flag has been set at this point the reset_timer will be restarted the request pointer reset and SENSOR_DATA event posted to the main process itself The event will trigger the SENSOR REQUEST which will initiate the sensor request to the K30 sensor by calling the sendframe function 25 The sendframe function takes an array containing a sensor value request The sensor requests are hard coded arrays of raw hex values Currently one request is implement which fetches both CO and temperature values More requests can be implemented though the SENSOR REQUEST state need to be slightly modified to handle those requests The current CO and temperature request is implemented as an 8 bit array The Modbus communication protocol is used between the sensor and the Raven board and hence the requests are implemented as frames with Modbus specific function codes A detailed description of the CO and temperature request frame can be seen in table 8 This request is gathered from sensor s RAM with the user defined function code 0x44 read from RAM field code Starting address of Bytes Table 8 CO2 and temperature request The Modbus protocol also requires a 16 bit CRC value to be calculated on the payload contents The CRC has to be appended as the last filed to the request as two 8 bit values with the low order byte first The CRC calculation is performed by the calc_crc function which will return a 16 bit calculated C

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