http://www.diva-portal.org This is the published version of a paper presented at 11th Swedish National Computer Networking Workshop (SNCNW 2015) Karlstad, May 28-29, 2015. Citation for the original published paper: Jacobsson, M., Orfanidis, C. (2015) Using software-defined networking principles for wireless sensor networks. In: Proc. 11th Swedish National Computer Networking Workshop N.B. When citing this work, cite the original published paper. Permanent link to this version: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-254172 Using Software-defined Networking Principles for Wireless Sensor Networks Martin Jacobsson and Charalampos Orfanidis Uppsala University Department of Information Technology Email:fmartin.jacobsson, [email protected] Abstract—In this paper, we propose an architecture based on This extra functionality enables a much higher degree of software-defined networking (SDN) for wireless sensor networks. tailoring, but also more advanced in-network processing. The Ideas of how to design and make use of the flexibility that latter also provides shorter communication paths between SDN offers are presented. We discuss how SDN principles can lead to the use of commodity hardware in a wider range of sensors, actuators, and the data processing. This also leads WSN deployments and then tailor the software only to meet the to more robustness due to less dependence on far away nodes, requirements of the specific deployments and their applications. as well as lower delays and less energy consumption due to A few examples are introduced that demonstrate how the the minimized communication paths. architecture can be used for networking, in-network processing, In this paper, we discuss how SDN concepts can lead to the and performance predictions. use of commodity hardware in a wider range of IoT and WSN I. INTRODUCTION applications and then tailor-making using software to meet the More and more physical objects are becoming smart and requirements of the specific deployments. connected using ICT. A key concept for this is wireless sensor The remainder of this paper is organised as follows. Sec- networks (WSN), which connects smart objects with each tion II introduces the SDN-based architecture for WSNs. other in a local area using low power wireless communi- In Section III, we discuss the networking aspects of the cations. WSN is an important building block for the future architecture, while in Section IV, we give some example Internet of Things (IoT) vision. SDN applications. Section V contains the related work and WSNs may be used for many different types of applications Section VI concludes the paper. and in many different types of environments, such as in residential homes, apartment buildings, large office buildings, II. AN SDN ARCHITECTURE FOR WSN industrial plants, outdoor in urban environments as well as SDN is a concept developed to meet the demands of rural areas. Applications may be delay-tolerant collection of more flexibility in the networking implementations on Internet sensor readings, responsive smart home applications, tracking routers. In SDN, there is a decoupling defined between the of mobile objects or persons, and time- and mission-critical control plane and the data plane with OpenFlow [3] being the operation of industrial plants, to name a few. currently most successful standard. New network control and For the IoT vision to become true, it is important to keep management solutions can easily be deployed by replacing the the costs low and this is mainly achieved through economy control plane functionality. of scale in both hardware and software. This means both OpenFlow is based on TCP, which means that the control standardized hardware and software. At the same time, appli- function could run locally on the router or somewhere else, cation requirements may force us to tailor every single WSN such as at a central server. Through the interface, the controller deployment individually and this can only be achieved by a application can configure the forwarding tables of the router high degree of reconfiguration capabilities, something that can (or network switch). The task of the controller is to provide be realised by using concepts and ideas from software-defined a coherent image of the entire network and provide it as networking (SDN) [1]. one single entity towards the SDN applications. Typical SDN The developments in hardware have made reconfiguration applications could be routing, but also other functions, such as possible. The TelosB WSN node platform [2], which is the access control and software-based traffic analysis, are possible. most commonly used experimention platform in the research The aim of this paper is to propose a flexible architecture for community, is now 10 years old. Today, for example, ARM WSN and IoT systems based on ideas from SDN and where and its partners have released new energy-efficient micro- in-network processing is a natural part. We have to mention controllers, such as the ARM Cortex M-series, which are suit- that an SDN architecture for WSNs includes challenges. The able for WSN nodes. Some of these have a 32-bit architecture WSNs have constrained resources and most of the times are and much more program and code memory as well as faster battery operated, which means that the available energy should processing capabilities than TelosB. Also the wireless chips be managed efficiently. One of the basic functions in a SDN have been updated. All this enables much more functions in architecture is the communication between the control and software. data plane and an increase in the communication will increase SDN Layers Back-End Server or Gateway SW Topology Application VM1 VM2 VM.. VM Optimization Simulation Control Specification Application Layer Application Central Execution Environment Controller r e l l Control Layer l a o r c t VM o n L o Routing & Forwarding C Local Local Local Controller Controller Controller Infrastructure Layer m r VM o f WSN Node WSN Node WSN Node t a l P e HW d Fig. 1. Overall SDN architecture for a WSN o MAC N N Reconfigurable S PHY W the energy consumption. Hence, the energy efficiency is one factor that should be considered during the design of a WSN Fig. 2. The architecture of the WSN node with SDN support architecture based on SDN. Figure 1 shows the overall architecture of our proposal with the SDN layers indicated. Each WSN node is equipped with a the WSN nodes, it also becomes possible to distribute the local controller, whose functionality can be as simple as just controller function. I.e., it is no longer required to run the receiving and executing the commands from the central con- controller on a central node. Furthermore, hybrid controller troller. The central controller communicates over the network versions can be defined. with either the used routing protocol if it is running or simple In homogenous networks, native binaries and dynamic link- networking principles, such as network-wide flooding [4]. On ing can be used, while massively heterogenous networks may top of this, message formats between the controller and the benefit from using byte code and VM technology designed WSN nodes must be defined. for embedded systems. Contiki OS has good support for On top of the central controller, there are one or more SDN dynamic loading as well as over the air programming, which applications. These applications can be related purely to the can be used if all run the same software and micro-controller networking of the WSN, such as topology control and routing. architecture. If various hardware and software systems exist In this architecture, some SDN applications may be directed in the same network, VMs may be a better choice. Some towards the network operator staff with a user interface, while researchers have proposed to put a virtual machine (VM) on others are completely automated. SDN applications may use WSN nodes. In this way, one single byte code binary can optimization solvers, simulators, specifically made algorithms, be distributed and executed on any node. Examples of VMs or a combination. developed for WSN nodes include EmbedVM, TakaTuka [6], Figure 2 shows the functionality on the WSN Nodes. Ev- and Darjeeling [7]. The latter two are Java VMs. A third erything, except potentially some parts of the local controller option is using something similar to the command chains of resides in the infrastructure layer. The main task of the local snapMac [8], i.e., a domain-specific VM-like engine with a controller is to setup, reconfigure, and monitor the parts of the small set of pre-defined commands that can be executed by software that can be reconfigured. It can do so in two ways. a very simple byte code interpreter. A fourth option is to use Either it changes parameters in the different functions, such as very simple scripting languages. Whatever choice is made, it the central frequency of the radio, the retransmission limit in is also important to have a good run-time monitoring system the MAC layer, modifying entries in the forwarding table, etc., that, for instance, can deal with application processes running or it installs new code in the different functions that changes out of hand or debugging. VMs and scripting languages may the behavior. The latter can be done by virtual machines (VM), be better in offering that functionality. but can also be done with native code and dynamically linked library functions. In this way, not only routing and MAC can III. RECONFIGURABLE NETWORKING be modified by the controller, but there is also flexibility for With SDN, we have the option to centralize all or some parts the neighbour and topology discovery functionality as well as of the networking at a more powerful node. For robustness other functions.