  Our objective is to provide guaranteed packet delivery service in time
constrained sensor networks. The wireless network is a highly variable
environment, where available link bandwidth may vary with network load. Since
multimedia applications require higher bandwidth so we use FSO links for their
transmission. The main advantage of FSO links is that they offer higher
bandwidth and security, while RF links offer more reliability. The routing in
this multitier network is based on directional geographic routing protocol, in
which sensors route their data via multihop paths, to a powerful base station,
through a cluster head. Some modifications have also been incorporated in the
MAC layer to improve the QoS of such systems.
