This paper proposes a cross-layer design to enhance the security of a set of buffered legitimate source nodes wishing to communicate with a common destination node using a time-division multiple-access scheme with probabilistic time slot assignment. The users’ assignment probabilities to the time slots are optimized to satisfy a certain quality-of-service (QoS) requirement for each of the legitimate source nodes. To further improve the system security, we propose beamforming-based cooperative jamming schemes subject to the availability of the channel state information (CSI) at the legitimate nodes. We assume that if a source node is not selected for data transmission, it is a cooperative jamming node.We impose an average transmit power constraint (averaged across time slots) on each source node. Hence, the source nodes should efficiently distribute their average transmit powers throughout the network operation between data and AN transmissions to satisfy the QoS requirements. We investigate the two cases where a global CSI is assumed at the legitimate nodes and where there is no eavesdropper’s CSI. The case where there is no CSI at the jamming nodes is also investigated and a new scheme is proposed.We derive closed-form expressions for the instantaneous secrecy rate for each scheme as well as the secrecy outage probability. Moreover, we derive the secrecy stable-throughput and delay-requirement regions of the network. Our proposed jamming schemes achieve significant increases in the secure throughput over existing schemes from the literature and over the no-jamming scheme.