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Tap chi Khoa h(»c va Cong ngh? 102 (2014) 022-026 Using RPL Routmg protocol for Virtualization of Wireless Sensor Networks Sii dung giao thiic RPL cho ao hoa mang cam bi^n khong day Thu Ngo-Quynh School of Information and Communication Technology Hanoi University ofScience and Technology No 1, Dai Co Viet Str., Hai Ba Trung, Ha Noi, Viet Nam Received: November 01, 2013; accepted: August 25, 2014 Abstract Virtualization of Wireless Sensor Wefivorics (WSN) is a new concept that can provide a common platfomi upon which new federated sensor network architectures can be built, expenmented and evaluated A Virtualized Sensor Network (VSN) is formed by a subset of sensor nodes of a physical WSN that is dedicated to a certain task or an application at a given time In this paper, we investigate the requirements that virtualization imposes on the routing procedure of the involved WSNs and propose to implement RPL routing protocol for this virtualization purpose In addition, we consider a special application case of virtualization and investigate the operation of RPL in this case for establishing different instances per application We also present how different QoS levels can be offered by adjusting routing metncs of RPL scheme Our approach is validated using computer simulations Keywords: Virtualization, Routing protocol, Wireless sensor nehvorks Tom tat Ao hda mang cam bien la mot phuang ph^p tiip c$n m&i cho phep cac t$p htyp cac niit cim biin kit hqp vdi di thi/c hi$n mot nhiem VLI nhSt dinh mot khoing thd-i gian nhit dinh Di cd the lam duac diiu niy, vin di quan hien la thiSt ke giao thirc dinh tuyin phu hop viri Ccic ySu ciu ciia ao hoa nhw kha nang m& rang, tinh di dong, tiit kiem nang iwqmg Hien nay, IETF dang nghi&n ciru vi ph^t triin giao thirc RPL - IPv6 Routing Protocol For Low Power and Lossy Network, cho ph^p truyen IPv6 tren bo cam biin va cd nhieu tinh nang thich hap V6J ao hoa mang cam bien khong day Trong ph^m vi bai bao nay, chung tot thir nghiem vi$c ao hoa bkng each thiit lap cac instances khac cho cac img dicing khac cua RPL, ddng th&i thay doi cac thong so cOa RPL di cung cap cac mire chat luang diet) vij khic cho cac img dung ciia ao hoa Introduction Nowaday, WSN is working as isolated islands and most of the sensed data is not shared among different administrative domains Reasons for using dedicated sensor networks include the limited sensing, processing and communication abilities of the nodes, severe power constraints and most of all, the lack of algorithms, protocols and techniques for deploying complex sensor networks Under a wide vanety of conditions (large scale network of thousands nodes, crowded urban area or difficult terrains), independent sensor networks dedicated to a specific task may not be the best or the most practical deployment technique That is why it is necessary to deploy a WSN that is capable of sharing their physical resources or exchanging information over geographically isolated areas This concept is called Virtual Sensor Networking [I] In principle, a Virtual Sensor Network (VSN) consists of sensor nodes providing the ability to be leveraged by a multitude of different administrative Corresponding Author, Tel- (+84) 912,528.824 E-mail: thunq@soict hust.edu domains, platforms, communication protocols and services In a virtualized sensor networks, new applications can be served without requiring installing new sensors but just reusing existing ones For this important purpose of VSN, the most objective of VSN is tbe resource virtualization In other words, network and node resources play a very significant role for virtualization of WSN Given dial the VSN system will consist of heterogeneous devices with different capabilities anil communication resources, resource virtualization missions are: Communication resources/connectivity: As the heterogeneous devices of the system may also differ in their communication capabilities, to optitmse the overall network performance, routing can take advantage of the heterogeneous neighbours capabilities Thus, the sensor transmission range or the supported wireless interface will be considered as an attribute taken into account when routing decisions are made - Dynamic resource control: The (heterogeneous) devices included in a VSN may be battery or mains Tap chi Khoa hoc va Cong nghe 102 (2014) 022-026 powered As the energy consumption depends on a nmnber of operational parameters, these may be tuned dynamically to prolong the network lifetime, - Hardware node resources: affect the complexity of the routing protocol that can be executed For example, given that security is one of the key requirements, the implementation of trust logic can be distributed among nodes in a proportional to hardware resources manner - Security services virtualization: Different security levels have to be supported to improve tbe probability of reaching tbe destination for special purpose messages These messages may include alarm-related messages, service discovery messages which are of higher priority (more vital) in some applications than regular messages carrying sensed data - Energy level/node status: To improve the network reliability, in the requirements of VSN, the ability of nodes to report their status and energy level is included This information is also valuable for the routing protocol, since taking into account the neighbor's energy levels significant reduction in the energy consumption rate can be achieved The fact that it is a requirement to exchange such information in VSN, can and will be exploited also at the routing layer to prolong the network lifetime Scalability and mobility: To benefit from the virtualization of the wireless sensor nodes and network, all the nodes involved in the VSN have to cooperate for trust building and routing purposes Although virtualization targets the reduction of the number of devices installed in an area by exploiting already installed sensors, m this imcontrolled environment, the number of nodes in the neighbourhood can fluctuate Thus, it is mandatory for the relevant protocols to support both scalability and mobility From this point of view, virtualization of WSN aims at exploiting the dynamic symbiotic relationships of application and virtualization requirements that will produce a carefully crafted platform of sensor nodes [2] [3], In other words, a complex and heterogeneous large scale VSN imposes requirement of energy efficiency, seamless connectivity, operational reliability and security [4] [5] In order to satisfy this requirements, virtualization process will influence the design support of layer (routing) of the protocol stack significanfly In addition, when designed appropriately, VSN routing protocol can affects achieved quality of service (QoS) for different applications Furthermore, we realize that over a same WSN infrastructure, different applications require different QoS levels but satisfymg this is not always a straightforward task In order to overcome this problem, we can think about choosing appropriate routing metrics of the routing protocol for handling traffic of these applications differently A routing protocol satisfying the above requirements of virtualization is IPv6 Routing Protocol for LLNs (RPL) [6], RPL constructs Directed Acyclic Graphs (DAG) and defines the rules based on which every node selects a neighbor as its parent in the DAG, thus forming a tree To cover the diverse requirements imposed by different applications, ROLL has specified in [7] a set of link and node routing metrics and constraints (which can be static or dynamic) suitable to Low Power and Lossy link Networks to be used in RPL, The RPL protocol offers an additional feature which is very crucial for supporting virtual networks over LLNs: it supports the construction of multiple routing trees with the same or different destination (root) node based on different routing metrics, which form the socalled routing instances In other words, different routing paths firom the sensor nodes towards the sink node can be constructed to service different applications optimizing a different performance aspect each time For example, for e-health application, high reliability and low latency are required while for temperature and condition control applications, extended network lifetime is far more important than reliability For this reason, we anticipate that the adoption of RPL protocol brings important benefits when Wireless Sensor Network virtualization comes into the scene Routing design plays an important role for VSN but to the best of our knowledge, the research of impact of virtualization on routing, especially on RPL protocol is rarely investigated recently In addition, there is also no research study that proposes a virtualized routing solution based on RPL that can provide different QoS for different applications in VSN In this paper, we consider a special case of virtualization and investigate the operation of RPL in this case for establishing different instances per application We also present how different QoS levels can be offered by adjusting routing metrics of RPL scheme Our approach is validated using computer simulations The rest of the paper is organized as follows: in section I! we describe the steps that need to be carried out for virtualization purpose of an application that monitors the crossing of animal and sliding of rock In section III we provide simulation results to show how the different adopted metrics can lead to different performance aspect optimization over the same sensor network Finally, conclusions are dra-wn in section IV Tap chi Khoa h^c va Cdng nghe 102 (2014) 022-026 RPL Protocol their ranks are set up equal to received rank plus In this paper, we consider here a geographical application case of two VSNs for monitoring the crossing of animal (VSNi) and sliding of rock (VSN2), where virtualization requires an efficient use of resources Based on this information, nodes can select their parents, siblings and prefer-parent Fig Rock sliding and animal crossing [8] Step Root broadcasts DIG message in order to create second instance Sinular to the first step, root continues to broadcast DIO message to all its neighbors in both VSNi and VSN2 for establishing second instance with the following information: Fig Operation of 2"'' step More concretely, we will examine how RPL operates in order lo establish two instances for these two applications: one instance for rock sliding and one instance for animal crossing over a same physical sensor infrastructure In order to accomplish this mission, RPL needs to perform foilowmg steps: Rankld=! Instanceld=2 andDAGId=l This step is similar to tbe step when establishing the first instance Step 1: Root broadcasts DIO message in order to establish DAG for the first instance In this step, instanceld^l the DIO message contains Rankld^I and DAGId=l and only nodes belong to VSNi can receive this DIO message All nodes that receive this message will join to instance numbered 1, set up root as their preferparent and also set up their ranks according to the following equation: Rankld^Rankld of root + / Fig Operation of 3"* step Step Nodes continue to broadcast DIO message of the second instance in order to select parents, siblings and prefer-parent Fig Operation of P ' step These nodes continue to broadcast DIO message to their neighbors with the same instanceld and DAGId but the value of Rankid changed to their ranks Fig Operation of * step Step Nodes continue to broadcast message for the first instance DIO When their neighbors receive DIO message, Step This step helps to transmit data to the root When received DATA message, root will check all links that connect root to its neighbors If all these Tap chi Khoa hoc va Cong nghf 102 (2014) 022-026 links are dead, the simulation is terminated If no, nodes will continue lo transmit data lo the root In the following figure, instance is presented by black line while instance is presented by orange line More concretely, instance consists only nodes belong to VSNi while instance consists nodes belong to both VSNi and VSN2 3.1 Scenario The first scenario will contain only one instance that covers nodes of both VSNi and VSN2, but the routing metrics for this instance is hop count or node energy We evaluate the network lifetime of this scenario in these two cases in order to know which routing metric can provide better network lifetime The following figure plots the number of dead nodes in two cases Fig Operation of 5* step Step This step is for updating rank, parents, sibling and prefer-parent Periodically, nodes need to update information relating rank, parents, sibling and prefer-parent by sending DIO message Fig Operation of 6"" step Fig Number of dead nodes From this figure, we realize that using hop count as routing metric provides higher number of dead nodes than energy It can be explained easily because when using hop count, routing decision of RPL does not pay attention at residual energy of sensors The foilowmg figure presents network lifetime of the second case when using node energy for routing metric of RPL Clearly, the first node dead parameter of case using node energy is 188 rounds, and much more better than the first node dead parameter of case using hop c o u n t - 61 rounds Performance evaluation In this section, we consider two routing metrics: hop count and residual energy and evaluate network lifetime of VSNs when setting these metrics for object fimclions of RPL Finally, we examine a topology, where RPL needs to provide different quality of service levels for these sliding rock and crossing animal applications by using the above routing metrics (hop-count and residual energy) From the case descnbed m the above section, we realize that VSNi contains nodes that are distributed in a mountainous area in order to monitor the animal crossing while VSN2 monitor the sliding of rock in a more dangerous area Because of different geographical conditions of these two VSNs, it is easier to remove or change the sensors of VSNj than the sensors of VSN2 or it is more important to maintain the network lifetime of VSN2 than VSNi This problem can be resolved by providing different object fimctions for RPL Tbe above steps of RPL scheme were implemented in OMNET++ simulator We simulate here two VSNs, each has hundred nodes that are distributed randomly in an area of JJ Fig Network lifetime of P ' scenario 3.2 Scenario The purpose of this scenario is to provide different QoS levels for two applications: rock sliding and animal crossing through virtualization From the previous scenario, we realize that for providing VSN2 better network lifetime, we can select node energy as routing metric for RPL, while VSNi can use hop count for object function of RPL In this scenario, instance numbered is transmitted within VSN| only while instance numbered is transmitted within both V S N I and VSN2 We calculate number of dead nodes of two VSNs and present in the following figure: Tap chi Khoa hoc v^ Cong nghf 102 (2014) 022-026 J Fig 10 Number of dead nodes of 2'"' scenario J Fig 11 Network Hfetime of 2""* scenano From the above figiu-e, we realize that the number of dead nodes VSN? is smaller than VSNi More concretely, the network lifetime of two VSNs are presented in the following figure by two metrics, first node dead and total live round Total live round is the network operation time until all nodes are out of energy and this metric is calculated by number of rounds First node dead is the number of round when first node in the network runs out of energy The first node dead of VSNi is after 60 rounds, while for VSN2 it is after 114 rounds The total live round of VSNi is only 174 rounds while the total live roimds of VSN2 is 322 Obviously, the network lifetime of VSN2 is better than VSN| or the quality of service of VSN2 is better than VSNi This feature can be explained because instance I of VSNi utilizes hop count as routing metric for RPL object fimction, while instance of VSN2 covers nodes of both VSNs and utilizes node energy for RPL object fimction That is why it is possible to use routing metrics of RPL for providing different quality of service levels for different applications in case of virtualization Conclusion In this paper, we investigate the impact of virtualization on routing procedure of WSN We also analyze different QoS requirements of application in geographical context and provide this QoS differentiation by setting object fiinctions for the RPL protocol Via simulation, the QoS requirements are satisfied by using hop count and node energy for object function of RPL protocol References [I] Islam, M.M,; Hassan, M.M.; Lee, G.-W.; Huh, E.-N A Survey on Virtuahzahon of Wueless Sensor Networks Sensors, 12(2012)2175-2207 [2] M M Islam, M M Hassan, and E, N Huh, "Virtualization in wireless sensor network: challenges and opportunities," in Proceedings of the 13th International Conference on Computer and Information Technology (ICCIT '10), Dhaka, Bangladesh, December 2010 [3] S Kabadayi, A Pridgen, and C Julien, "Virtual sensors: abstracting data from physical sensors," in Proceedings of the International Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM '06), Buffalo-Niagara Falls, NY, USA, June 2006, pp, 587-592, [4] S Kabadayi, A, Pridgen, and C Julien, "Virtual sensors: abstracting data from physical sensors," in Proceedings of the International Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM '06), Buffalo-Niagara Falls, NY, USA, June 2006, pp, 587-592 [5] J H Shin and D, Park, "A virtual infi:astructure for large-scale wireless sensor networks," Computet CoramunicaUons, 30 (2007) 2853-2866 [6] IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and Goals, https,//datatracker.ietf.org/doc/draft-ietf-6lo-wpanproblem/ [7] RPL: IPv6 Routing Protocol for Low power and Lossy Networks, http.//tools.ietforg/hmil/draft-ietf-roll-rpl-l9 [8] Md Motaharul Islam, Eui-Nam Huh, "Virtualization in Wireless Sensor Network: Challenges and Oppominities", Joumal of Networks, (2012) 412-418, ... metric for RPL object fimction, while instance of VSN2 covers nodes of both VSNs and utilizes node energy for RPL object fimction That is why it is possible to use routing metrics of RPL for providing... (which can be static or dynamic) suitable to Low Power and Lossy link Networks to be used in RPL, The RPL protocol offers an additional feature which is very crucial for supporting virtual networks... routing, especially on RPL protocol is rarely investigated recently In addition, there is also no research study that proposes a virtualized routing solution based on RPL that can provide different
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