Network of IoT devices enables a connected future and brings many benefits to human society in saving of time/money and better comfort. The devices are heterogeneous with various processing and energy capabilities. Most of the IoT devices are portable and powered by batteries. Energy in these devices must be optimally used to prolong the lifetime of the IoT network. Many attempts have been made in area of lifetime improvement of IoT networks, but still there are many gaps need to be addressed for further energy optimizations and lifetime improvement. The typical challenges in energy optimization cannot be met with solution focused on a single OSI layer alone and thus a cross layer solution is needed. This work proposes a cross layer approach for optimization of energy in IoT network with goal of increasing the lifetime of the network.