# Movable Platform-Based Topology Detection for a Geographic Routing Wireless Sensor Network
## 2 Background  
Monitoring on WSN can be categorized into active monitoring and passive monitoring. For active monitoring, a monitoring protocol module that obtains the specific network operation data is entailed on wireless nodes, but as monitoring flow and data flow are mixed when this method is used, higher requirements are made for the network protocol design, deployment and upgrade of the target WSN. Tools used for active monitoring in WSN include Sympathy [6], Memento [7] and Emstar [8]. There are also tools designed specifically for TinyOS [9], such as SpyGlass [10], MoteView [11], NetTopo [12], WiseObserver [13] and Octopus [14]. However, these tools will bring problems like occupation of network bandwidth, powder, information transport capacity by monitoring data, and lengthening of the transport time delay of data packets. A passive monitoring method requires a monitoring network that is deployed outside the target network, and therefore less interferes with the monitored network, as network monitoring consumes no resource of the target network. [PERSON] et al. [15] put forward a framework of the passive monitoring system of WLAN which deploys many monitoring nodes to capture data packets in WLAN and combine all data packets into one complete network for the purpose of tracking. [PERSON] [16] and [PERSON] [17] improved the Yeo framework and put forward a method to track and combine, track and reason, and track the failure events of large-scale enterprise wireless network. LiveNet [18] is a passive monitoring system in WSN that tracks, combines and reasons the information lost in the rebuilding of multi-hop sensor network routing path. SNIF (Sensor Network Inspection Framework) [19] system monitors sensor networkutilizing deployed support network (DSN). SNTS (Sensor Network Troubleshooting Suite) [20] brought up one kind of statistical and data mining technology to analyze and diagnose network failure events. Pimoto [21] is similar to SNIF but their difference is that Pimoto uses Bluetooth to transfer the captured data to the gateway. The gateway is a computer that marks the data packet with a time stamp and forwards it to a central server for analysis via TCP/IP. Pimoto can also work on several sensor networks simultaneously. Its author creates a plug-in for Wireshark, a traffic analysis tool to visualize and analyze the captured data. DSN(Deployment-support networks) [22] is a toolkit for testing and monitoring WSN applications and contains a set of nodes connected to sensor nodes, all of which are connected to the server via Bluetooth. The DSN node records the events transmitted by the node application program through one of its serial interfaces and sends the information to the DSN server. In addition, they can be used as infrastructure for remote programming, command transmission and dynamic monitoring configuration. SNDS (Sensor Network Distributed Sniffer) [23] works in a way similar to SNIF or Pimoto, but it connects via Ethernet instead of Bluetooth. In NSSN [24], the sniffer node can detect the working frequency of the target WSN to be observed automatically. Via a wireless link, the collected data are sent to the monitoring server which parses, preprocesses and stores the data in the database. The information stored in the server can be visited remotely by the client which can either observe or analyze it. EPMOSt (Energy-efficient Passive Monitoring SysTem) [25] uses SNMP (Simple Network Management Protocol) proxy to collect information from the sniffer and transfer it to the server. The passive monitoring method, which requires designing and setting up an extra monitoring network at the same scale for the target network, is poorly universal and therefore cannot be applied on a large scale.