Wireless Network Security 279 behave in accordance with the allocation decision made by the base station. With the centralized medium access control, it is possible to provide quality-of-service guarantees because the base station can control on the allocation of bandwidth to a specific node to meet the quality requirements. 2. Wireless Ad Hoc Networks Wireless ad hoc networks are distributed networks that work without fixed infrastructures and in which each network node is willing to forward network packets for other network nodes. The main characteristics of wireless ad hoc networks are as follows. · Wireless ad hoc networks are distributed networks that do not require fixed infrastructures to work. Network nodes in a wireless ad hoc network can be randomly deployed to form the wireless ad hoc network. Network nodes will forward network packets for other network nodes. Network nodes in a wireless ad hoc network directly communicate with other nodes within their ranges. When these networks communicate with network nodes outside their ranges, network packets will be forwarded by the nearby network nodes and other nodes that are on the ·