Abstract: With technological advances in the telecommunications sector, everyone around the world would like to be connected seamlessly anytime anywhere through the best network. Making a transition from one network to another and moving between heterogeneous networks is not the only problem that worried specialists, scientific and mobile operators; the concern of QoS is as important as the handoff, The requirements like capability of the network, network conditions, handoff latency, power consumption, network cost, and user preferences must be taken into consideration during vertical handoff. Importance of inter working between architecture requires adaptive approaches to implement the vertical handoff mechanism in 4G wireless networks and produce an effective service for the user by considering handover parameters.

In this paper, we analyzed the main approaches for vertical handoff to offer a systematic comparison for new researchers. The survey revealed the need for new approach which satisfy the most important requirements and reduce the HO failure probability and the number of unnecessary handover.

Keywords: Wireless networks; 4G; vertical handoff, horizontal handoff, QOS (Quality of Service), Next Generation Network (NGN).