In the light of the proliferation of the Internet of Things (IoT), the device-to-device (D2D) communication is becoming a promising technology and a key enabler for enhancing the energy efficiency of the wireless network environment and reducing the traffic latency between user equipments (UEs) within their communication range. This papers considers an analytical framework for modeling a communication offloading scenario within the D2D communications underlaying cellular network, where a UE generates a session toward another UE in the same cell. The designed analytical model aims to improve the system capacity and energy-efficiency by offloading cellular traffic onto D2D communications when the source and destination UEs are proximate enough to satisfy their QoS requirements.