In Network Processing and Data Aggregation in

Proposes a bottom (physical layer)–up (application layer) approach in thedevelopment of a protocol for a wireless sensor network. Application, MAC and physicallayers have to be tightly integrated with the hardware of the sensor node. For example theenergy penalties of switching states or the consumed power at each state of a transceiver,might determine the policy of the MAC layer scheme or even affect the network layerrouting algorithm. Multiple access schemes (Time Division Multiple Access, FrequencyDivision Multiple Access) are compared and the same is also done for modulationschemes (binary, M-ary modulation). It is found that a hybrid TDMA-FDMA scheme andthe M-ary modulation scheme achieve significant power savings. Another energyexpensive factor is the frequent turning on/off of the transceiver of a node because thecontrol input spends not negligible time on setting the right voltage to the transceiver(start-up energy). All the previous notes show that layer-1 has not to be considered as ablack box when designing an upper level protocol or even an application for a WSN.2.2 Data Link Layer (MAC)2.2.1 Medium Access Control (MAC) functionalityAbove the Physical Layer (Layer-1) resides the Data Link Layer (Layer-2). Havingonly the tools that are provided by the layer 1 in means of services, the link layer isresponsible for the transmission of data packets between two communicating nodes. Thecommunication pattern may be point-to-point or even point-to-multipoint. Nevertheless,this function is not as simple as it sounds. There are several services that the link layermay offer to the upper layers like:• medium access,• packet encapsulation in link-layer frames and data frame detection,• flow control,• error detection/correction,• data stream multiplexing and• reliable communication mode.