Lớp vận tải bao gồm các cao cấp của LM và chồng lên Host Controller Interface (HCI). Lớp giao thông vận tải chịu trách nhiệm về độ tin cậy và ghép kênh truyền dữ liệu trên mạng đến cấp độ được cung cấp bởi ứng dụng. Lớp phiên bao gồm điều khiển liên kết logic và thích ứng | ON-DEMAND ROUTING PROTOCOLS 175 the source broadcasts a route request packet. The neighbors in turn broadcast the packet to their neighbors till it reaches an intermediate node that has a recent route information about the destination or till it reaches the destination. A node discards a route request packet that it has already seen. The route request packet uses sequence numbers to ensure that the routes are loop-free and to make sure that if the intermediate nodes reply to route requests they reply with the latest information only. When a node forwards a route request packet to its neighbors it also records in its tables the node from which the first copy of the request came. This information is used to construct the reverse path for the route reply packet. AODV uses only symmetric links because the route reply packet follows the reverse path of route request packet. As the route reply packet traverses back to the source the nodes along the path enter the forward route into their tables. If the source moves then it can reinitiate route discovery to the destination. If one of the intermediate nodes move then the moved nodes neighbor realizes the link failure and sends a link failure notification to its upstream neighbors and so on till it reaches the source upon which the source can reinitiate route discovery if needed. AODV routing is essentially a combination of both DSRP and DSDV. It borrows the basic on-demand mechanism of route discovery and route maintenance from DSRP plus the use of hop-by-hop routing sequence numbers and periodic update packets from DSDV. The main benefit of AODV over DSRP is that the source route does not need to be included with each packet. This results in a reduction of routing protocol overhead. AODV requires periodic updates that based on simulations by Broch consume more bandwidth than is saved from not including source route information in the packets. Signal stability-based adaptive routing Signal Stability-Based Adaptive .
