Abstract— Congestion has an utterly detrimental influence in the performance of Wireless Sensor Networks (WSNs). Many of the causes of congestion in WSNs are different than the causes of congestion in wired networks. Hence, new research has to be developed for the avoidance and control of congestion in WSNs. This article proposes a scheme which aims to both forecast imminent congestion and prevent its further diffusion in WSNs. The prediction of forthcoming congestion is based on the computation of a suitably built cost function, which considers a set of metrics related with the popularity of the alternate nodes and routing paths. The prevention of congestion diffusion is carried out through multi hop/path routing, by utilizing nodes and routes which are less probable to be congested. Simulation tests performed evaluate the efficacy of the proposed scheme. Index Terms— congestion avoidance, congestion control, multi hop/path routing, wireless sensor networks. I. INTRODUCTION SNs typically consist of a set of many sensor nodes which are deployed over wide areas and transmit their data to a sink node, referred as the base station. Since the distance between a source node and another destination sensor node or the base station may exceed the range of the transmission ability of the sender, then relaying is required via intermediary sensor nodes. Therefore, a sensor node apart from gathering, processing and transmitting the data it senses, it may also have to forward data it receives from other sensor nodes [1-3]. Thus, the operation of a WSN is interdependently correlated with the transmission of great quantities of data. One of the most common problems that the management of the data traffic within a WSN faces is that of congestion. Congestion occurs when current traffic load exceeds D. Kandris is with the Department of Electronics, Technological Educational Institute (T.E.I.) of Athens, 12210, Athens, Greece (phone: +306972256162; e-mail: dkandris@teiath.gr). D. J. Vergados is with the School of Electrical and Computer Engineering, National Technical University of Athens, 15773, Athens, Greece (email: djvergad@telecom.ntua.gr). D. D. Vergados is with the Department of Informatics, University of Piraeus, 18534, Piraeus, Greece (email: vergados@unipi.gr). A. Tzes is with the Department of Electrical and Computer Engineering, University of Patras, 26500, Rio, Greece (email:tzes@ece.upatras.gr). available transmission ability at any point in the network. Congestion, similarly to what happens to wired networks, has an absolutely harmful influence in the performance of WSNs too. However, many of the causes of congestion in WSNs are different than the causes of congestion in wired networks. Consequently, new research work has to be carried out. This article proposes a scheme which aims to both predict upcoming congestion and prevent its further diffusion. The forecast of imminent congestion is based on the calculation of an appropriately built cost function, which takes into consideration a set of metrics related with the popularity of the alternate nodes and routing paths. The prevention of congestion diffusion is performed through multi hop/path routing, by utilizing nodes and routes which are less probable to be congested. The remainder of this article is organized as follows. In Section II, the reader is introduced to the causes and effects of congestion in WSNs. In Section III, an overview of existing congestion control and congestion avoidance schemes is presented. In Section IV, the proposed congestion handling scheme is described. The performance evaluation of the proposed scheme takes place in Section V, through the description of simulation results. Finally, section VI concludes the article. II. CONGESTION IN WSNS The data traffic in a WSN may be sorted out in two types. The first of them is the so called downstream traffic, which is a one-to-many multicast communication, directed from the sink to the sensor nodes. The other kind of traffic is the so called upstream traffic, which is a many-to-one communication from sensor nodes to the sink. Due to the convergent nature of upstream traffic, congestion is more probable to appear in the upstream direction [4]. Actually, in WSN applications, the volume of traffic load in upstream traffic may have significant fluctuations caused by the existing demands. More precisely, the traffic may range from simple periodical or query-based reports to sudden outbursts of event-based data flow triggered in response to sensed incidents. In most cases, such event- based increases of traffic load amplify the probability of congestion occurrence. A Routing Scheme for Congestion Avoidance in Wireless Sensor Networks Dionisis Kandris, Dimitrios J. Vergados, Dimitrios D. Vergados, and Anthony Tzes W 6th annual IEEE Conference on Automation Science and Engineering Marriott Eaton Centre Hotel Toronto, Ontario, Canada, August 21-24, 2010 MoB3.2 978-1-4244-5448-8/10/$26.00 ©2010 IEEE 497