## 2 Related Work  
In [10], a reliable query approach was proposed with the goal of having an efficient discovery and recovery of query packets. The approach lets a sensor node that discovers a query packet loss send out a NACK message to the sink. The sink recovers this loss by delivering the query message to the node again. To detect the loss of a query packet, sensor nodes adopt the NACK mechanism based on utilizing a query sequence at the sink node. The success of this approach depends on the condition of continuous queries and the approach is difficult to be used for on-demand queries from various users. The delays of query discovery and recovery may be large when the interval between two continuous queries is large.  
Directed diffusion discussed about the basic operation of data queries in sensor networks [5]. A naming mechanism for query and sensing data is presented. The proposed approach finds reliable routes for data delivery based on the route's confidence degrees. In that work, query broadcast is assumed to be ideal, _i.e_., each sensor node always successfully receives every query message from the sink node.  
There are approaches that have been proposed to enable the sensor-to-sink reliability in sensor networks, such as Event-to-Sink Reliable Transport (ESRP) [11] and Pump Slowly Fetch Quickly (PSFQ) [12]. However, most of these approaches focus only on the reliable data delivery in sensor networks from sensor to sink and the broadcast of data queries is generally assumed to be successfully performed or not discussed.  
Many approaches of local route recovery have been proposed also in application to mobile ad hoc networks [13, 14]. A basic idea of local route recovery is utilizing alternative relay nodes to build a new connection to the destination. However, these approaches are especially proposed for end-to-end unicast routing, which does not require specific detection processes for a route failure, since a node can know that it encounters a route failure when it cannot deliver a packet to the next hop node in its routing table.  
In [7], a reliable tree-based broadcast is proposed. The target is to reduce the significant overhead of packet broadcast in sensor networks. Their basic idea is to construct a spanning tree among sensor nodes in the network rooted at the source of broadcast. Their proposed approach reduces redundant packet transmissions. By neighbor requirement and packet ordering, reliable broadcast is realized for tree-based broadcast. The local repair of node failure is a parent-child based interaction. The paper does not discuss the cost of tree formation from various roots of sinks, which will lead to a large overhead for constructing the tree.  
Active query forwarding has an aim of energy efficient and localized query dissemination and then reduces the redundancy in flooding based query [15]. The basic idea is that it allows each node that carries the query message to get knowledge of the topology of its \(k\)-hop neighbors. Therefore, each node enables a trajectory forwarding of query messages to the related nodes. The proposed approach ACQUIRE highly reduces the flooding redundancy. On the other hand, the requirement of \(k\)-hop neighbor information leads to a large traffic of information updating, especially when sensor nodes that correspond to a query have been sparsely deployed.