## 1 Introduction  
Cabinet environmental monitoring represents a typical application for wireless sensor networks [1,2]. From data center to substation, there are many cabinets and dedicated containers. These cabinets usually contain computers, high voltage switches, or other electronic equipments. Cabinet environmental monitoring is a technology that provides real-time recording of environment parameters in the interior of cabinets, such as temperature, humidity, smoking, noise, and so on. Depending on these data, operators can estimate the health and running status of the equipment in the cabinets. For example, a thermal alarm means a danger of potential hot spots. Operators need to identify the problem and make intelligent decisions on facility management.  
A data center or substation can have several rooms. Each room can have dozens of cabinets. And every cabinet may have several racks. Operators need real-time monitoring of the equipment on each rack. In a substation, there are hundreds of cabinets which contain many kinds of electronic equipment, therefore huge numbers of points need to be monitored. Traditional solutions for cabinet environmental monitoring involve the use of wired sensors, connected through Ethernet interfaces [3]. However, those approaches suffer from high installation and configuration costs. Furthermore, sensor deployment is constrained by the availability of Ethernet connections.  
Wireless sensor network (WSN) [4] is an ideal candidate for cabinet environmental monitoring because it is low cost and unattended technology. It can provide wide and dense coverage, and can be easily reprogrammed. Wireless sensors do not require network facility infrastructure in data centers or substations which is already a complicated environment with large amounts of equipment.  
Cabinet monitoring introduces new challenges to wireless sensor networks. The network framework must have good scalability to support new equipment. Commands have to be reliably disseminated throughout the entire system so that all parts of the network can follow the commands to change their states. Sensed data must be reliably collected, e.g. temperature alarm information is too valuable to be lost due to communication errors or collisions. For battery powered wireless sensor networks, the network lifetime is a critical factor because replacing batteries for sensor nodes is a laborious task.  
In this paper, we present CENet (Cabinet Environmental sensing Network). Focusing on network lifetime and reliability of data transmission, CENet provides two main contributions:  
* CENet implements a data-aided routing protocol. Instead of using periodic beaconing to estimate link quality and maintain network routing topology, CENet uses transmitted data to continuously estimate link quality and its routing maintenance is triggered when poor link quality is detected. Therefore the energy dissipation due to beacons can be diminished. Compared to MintRoute's fixed 1 minute beacon interval [5], CENet sends 85% fewer beacons. It can also achieve a packets delivery ratio of more than 93%.
* CENet contains two kinds of nodes: master nodes and slave nodes. In order to prolong the network life time, we propose a scheduling scheme based on B-MAC [6] for slave nodes, which reduces unnecessary message snooping and channel listening, _i.e._, a slave node keeps sleeping until it is time for sensing the environment or it has data for transmission. Using CENet, slave nodes consume about 65% less energy compared to using B-MAC, where the sample interval is 5 minutes.  
The remainder of this paper is organized as follows. Section 2 gives the system architecture of cabinet environmental monitoring. Section 3 presents the design of routing protocol. Section 4 describes the scheduling scheme. Section 5 evaluates the performance of CENet by simulations and experiments. Section 6 describes related works. Finally, Section 7 gives a brief conclusion.