Day by day the telecommunications are developing and everyone is striving for best quality and service. Quality of service (QoS) is one of the most important factors in the world of telecommunications. QoS plays important role in handover. There are different handovers. The thesis describes vertical handovers. If you want seamless handover the network should provide better Quality of service. My purpose is to examine different seamless vertical handovers and help the user to choose the better network for seamless and advantageous handover.