Wireless mesh sensor networks (WMSNs) have recently gained a lot of interest due to their communication capability to support various applications with different Quality of Service (QoS) requirements. The most challenging issue is providing a tradeoff between the resource efficiency and the multiconstrained QoS support. For this purpose, we propose a cross-layer algorithm JSAR (Joint duty cycle Scheduling, resource Allocation and multi-constrained QoS Routing algorithm) for WMSNs on based multi-channel multi-time slot MAC. To our best knowledge, JSAR is the first algorithm which simultaneously combines, a duty cycle scheduling scheme for energy saving, a resource allocation scheme for efficient use of frequency channels and time slots, and an heuristic for multi-constrained routing protocol. The performance of JSAR has been evaluated, showing that it is suitable for on-line implementation.