## 1 Introduction  
Wireless sensor networks (WSNs) have very broad application prospects in military disaster monitoring, environmental and ecological monitoring, earthquake, fire emergencies, medical systems, urban transportation and security monitoring [1]. In most of the applications, especially in emergent situations, real-time and fault tolerance characteristics are highly required. Nodes in WSN are prone to failure due to energy depletion, hardware failure, communication link errors, malicious attack, _etc_. [2]. Fault-tolerance is the ability of a system to deliver a desired level of functionality in the presence of faults. Extensive work has been done on fault tolerance and it has been one of the most important research topics in WSNs. Fault tolerance in a WSN system may exist at hardware layer, software layer, network communication layer, and application layer [2]. In this paper, we focus on the fault tolerance in real-time routing protocol level. To guarantee the real time performance of the nodes, each data packet is constrained in a time interval in which it must be sent to the destination node. If time expires, the data packet has to be discarded. Once node failure or congestion occurs, large amounts of data packets will be discarded, which may cause disastrous consequences. Consequently, it is more significant and challenging to provide both real-time and fault tolerance characteristics in WSN routing protocol.  
Existing real-time fault tolerant WSN routing protocols adopt hop-by-hop transmission mode [3-5], where the next hop node is selected based on the transmission time estimation or the relations of the distance among the current node, neighbor node and sink node. Failure nodes are treated as an empty area (VOID), and data packets are sent to the sink node _via_ bypass. However, these methods do not predict network congestion in advance [1], and the remaining transmission time of the data packet is only used for checking the validity of the data packets. When a data packet cannot be transmitted to the next hop node, it will be automatically discarded at once, which wastes the transmission energy. Moreover, the upper stream node cannot receive the feedback information from the current node and thus affect the subsequent transmission.  
In this paper, a dynamical jumping real-time fault-tolerant routing protocol is proposed, namely DMRF. Each node utilizes the remaining transmission time of the data packets and the state of the forwarding candidate node set to dynamically select the next hop. Once node failure, network congestion or void region occurs, the transmission mode will switch to jumping mode, which aims at reducing the transmission time delay and ensuring the data packets to be sent to the destination node within the specified time limit. According to the feedback information from the downstream node, each node dynamically adjusts the jumping probabilities to increase the ratio of successful transmission.  
The remainder of this paper is organized as follows. Section 2 introduces related work. Section 3 provides the application scenario of DMRF protocol. Section 4 presents the DMRF protocol in detail. Section 5 provides the feasibility proof and performance analysis of DMRF. The performance of DMRF is evaluated in Section 6. Section 7 concludes the paper and outlines some future work.