During an off-peak hour of a day, a Mobile Terminal (MT) can stay in idle mode for long time as there is no incoming or outgoing packet. An idle MT can move from one location to another and the wireless access network keeps tracking the idle MT. Idle MTs need to assist the wireless access network for location update; so that, on call arrival the network can route the call successfully. Mean while, Voice over IP (VoIP) got wide acceptance. To provide VoIP service in mobile environment or any IP packet based service, Mobile IP is very important protocol undeniably. However, Proxy Mobile IP was developed by IETF without considering the idle mode condition of MTs. Consequently, an idle MT needs to conduct Mobile IP binding (Layer 3 location update) whenever it moves to new area of a Foreign Agent although it does not have any incoming or outgoing packets during idle period. This phenomenon unnecessarily increases location update signaling cost. Here in this paper, based on optical wireless integrated access network we propose a mechanism that allows only Layer 2 location update when an MT is in idle mode and the Layer 3 location update is conducted after call arrives for an idle MT. Our numerical results show that proposed mechanism out performs than the existing solutions