280 Chapter 11 sensor may perform only simple computation and can communicate with sensors and other nodes within a short range. The life spans of sensors are also limited by the power supply. Wireless sensor networks can be self-organizing, since sensors can be randomly deployed in some inaccessible areas. The randomly deployed sensors can cooperate with other sensors within their range to implement the task of monitoring or observing the target scene or the target phenomenon and to communicate with the base station that collects data from all sensor nodes. The cooperation might involve finding a route to transmit data to a specific destination, relaying data from one neighbor to another neighbor when the two neighbors are not within reach of each other, and so on. Mesh Networks One of the emerging technologies of wireless network is wireless mesh networks (WMNs). Nodes in a WMN include mesh routers and mesh clients. Each node in a WMN works as a router as well as a host. When it's a router, each node needs to perform routing and to forward packets for other nodes when necessary, such as when two nodes are not within direct reach of each other and when a route to a specific destination for packet delivery is required to be discovered. Mesh routers may be equipped with multiple wireless interfaces, built on either the same or different wireless technologies, and are capable of bridging different networks. Mesh routers can also be classified as access mesh routers, backbone mesh routers, or gateway mesh routers. Access mesh routers provide mesh clients with access to mesh networks; backbone mesh routers form the backbone of a mesh network; and a gateway mesh router connects the backbone to an external network. Each mesh client normally has only one network interface that provides network connectivity with other nodes. Mesh clients are not usually capable of bridging different networks, which is different from mesh routers. Similar to other ad hoc networks, a wireless mesh network can be self-organizing. Thus nodes can establish and maintain connectivity with other nodes automatically, without human intervention. Wireless mesh networks can divided into backbone mesh networks and access mesh networks. 3. Security Protocols Wired Equivalent Privacy (WEP) was defined by the IEEE 802.11 standard [2]. WEP is designed to protect linkage-level data for wireless transmission by providing confidentiality, access control, and data integrity, to provide secure communication between a mobile device and an access point in a 802.11 wireless LAN. www.syngress.com