Abstract. The development and widespread use of real-time constrained multi-media application in MANET has resulted in the need to optimize or update current routing mechanisms. This paper proposed a QoS routing mechanism for multi-media transmission under real-time constraint in MANET, named ad-hoc on-demand distance vector routing based on location information and linkstability evaluation (LL-AODV). The mechanism abstracts the routing problems into the shortest path problem of an undirected weighted graph in which the weights of the paths are determined by the duration time of links, the residual battery and energy consumption of nodes, and utilizes the shortest path algorithm to determine a feasible transport path. We use a prediction model of the duration time of links to predict the probable time the link may maintain, and that improves the deficiency of the AODV routing mechanism, which only uses hop counts as the transport path metric. Furthermore, it adopts periodical maintenance and rescue maintenance to ensure an alternative path can be found in time to transmit data, and thus improves the reliability of multimedia data transmission under real-time constraint. Simulation and the experimental results showed that the mechanism could provide a better QoS route for the multi-media transmission under realtime constraint in MANET. Ⅰ. IntroductionMobile ad hoc network (MANET) [1][2] is a subset of wireless and mobile network. It is a multihop temporary autonomous system without fixed infrastructures, and it employs distributed protocols to maintain the network connection. All nodes in MANET are equal and mobile, and there is no central control node. Each node can communicate with an access point with its wireless transmitters and receivers. MANET has the properties of high networking speed and high survivability [3], which make it widely used in military, civil and other fields.In recent years, with the development of multimedia and MANET technology, there is a great require of the real-time communication of multimedia data in MANET, such as real-time audio and video communication, etc. However, because of the characteristics in the MANETs, such as limited channel bandwidth, highly dynamic network topology, imprecise link state information, limited power at the nodes, etc.[4], the paths connection between source nodes and destination nodes may be very unstable and will go down at any time. It makes communication over MANET difficult and is hardly to assure the reliability of data transmission, much less could the protocol provide a better quality of service (QoS). To overcome these issues, appropriate cross-layer cooperation is required. QoS schemes provide QoS information by factoring the impacts of node mobility and lower-layer link parameters into QoS performance. But in the real-time multimedia transmission scenarios where the high rate and severe delay constraints are required, the above issues become more severe. Therefore, a new QoS routing mechanism performed well at the end-to-end real-time communica...