Скачать с ютуб Time-Division Multiple Access (TDMA) в хорошем качестве

Time-Division Multiple Access (TDMA)

Is TDMA better than CSMA for wireless networks or vice versa? We don’t know the answer to that question as it is an ill-posed question. We are biased to claim that TDMA has a unique place in the MAC protocol design space for wireless networks, particularly where most of nodes can be assumed to be stationary such as wireless mesh networks and sensor networks. The pros and cons of TDMA have been discussed in earlier papers. Let us sum up some of these arguments. TDMA uses topology information as a basis for access scheduling and this topology information comes in the form of neighboring and interference relations among nodes. TDMA can deliver very good performance especially under high contention. Unfortunately, wireless networks do not make it easy to maintain this accuracy. First, it is very difficult to precisely capture this interference relation because of interference range irregularity. Second, channel conditions may change interference relations among nodes over time. Third, clocks can drift and tight synchronization may incur too much overhead. On the other hand, CSMA does not use any topology or clock information. Thus it is highly robust to any change in the network. But in wireless networks, some of this information, although in a less accurate or reliable manner, is available to the nodes at little cost. But since CSMA does not make use of this information, contention among neigh- boring nodes muse be resolved for every data transmission. Thus its performance under high contention suffers because of high overhead in resolving contention and collision