Demonstration of Schedule and Latency Control in S-MAC

S-MAC is a medium-access control (MAC) protocol designed for wireless sensor networks. It is dieren t from traditional wireless MACs such as IEEE 802.11 in several ways: energy conservation and self-conguration are primary goals, while per-node fairness and latency are less important. S-MAC uses a few novel techniques to reduce energy consumption and support self-conguration . It enables low-duty-cycle operation in a multi-hop network. Nodes form virtual clusters based on common sleep schedules to reduce control overhead and enable trac-adaptiv e wake-up. S-MAC uses in-channel signaling to avoid overhearing unnecessary trac. Finally, SMAC applies message passing to reduce contention latency for applications that require in-network data processing. Although S-MAC has been designed for sensor-network applications, its principles are applicable to any application where battery lifetime dominates other design goals. S-MAC has been previously described in two papers [1, 2]. S-MAC’s peer-to-peer sleep/wakeup schedule is one of its most novel elements. While TDMA- and cluster-based sleep schedules are well understood, to our knowledge S-MAC is the rst MAC protocol where individual nodes can select their own sleep schedules independently. This demonstration will examine schedule and latency control in S-MAC with Berkeley Motes [3]. The rst part of the demonstration shows how S-MAC manages schedules in a multi-hop network. The rst and simplest case is in a single-hop network, where all nodes can hear each other. We will demonstrate that S-MAC attempts to synchronize all nodes on the same schedule. The second case is in a large, multi-hop network, where nodes form dieren t clusters by following dieren t schedules. We will present that dieren t nodes automatically congure their schedules and the network as a whole can support multiple schedules. In the last case, we will apply a new algorithm to allow nodes in multiple clusters to incrementally switch to one global schedule. The second part of the demonstration shows the latency in data transmission in a multi-hop network. We will rst demonstrate the transmission delay due to sleep schedules, and how S-MAC’s adaptive listen technique reduces the delay by waking up the next-hop node in anticipation of message forwarding. Then we will demonstrate how specically controlled sleep schedules aect latency. Data transfer in any network with sleep schedules can incur additional delay when a schedule slot is missed. A unique characteristic of a peer-to-peer network such as S-MAC is that we can select and control sleep schedules to obtain dieren t eects. In fact, sleep schedules can be skewed to allow rapid data forwarding in one direction, and slow forwarding in the opposite direction. We will place nodes in a line and congure their schedules to allow rapid propagation in one direction and slow propagation in the opposite.