• Implement a new software-based multi-hop TDMA MAC protocol with microsecond synchronization using a novel system interface for development of 802.11 overlay TDMA MAC protocols. • SySI-MAC provides a kernel independent message based interface for scheduling transmissions and sending and receiving 802.11 packets. • The key feature of SySI-MAC is that it provides near deterministic timers and transmission times, which allows for implementation of highly synchronized TDMA MAC protocols. • Building on SySI-MAC’s predictable transmission times we implement Soft-TDMAC, software based 802.11 overlay multi-hop TDMA MAC protocol. • Soft-TDMAC has a synchronization mechanism, which synchronizes all pairs of network clocks to within microseconds of each other. • Building on pair wise synchronization, Soft-TDMAC achieves tight network-wide synchronization. • Network-wide synchronization independent of data transmissions, Soft-TDMAC can schedule arbitrary TDMA transmission patterns. • Soft-TDMAC allows schedules that decrease end-to-end delay and take end-to-end rate demands into account. In summarize hundreds of hours of testing Soft-TDMAC on a multi-hop test-bed, showing the synchronization capabilities of the protocol and the benefits of flexible scheduling