4G will be the certain path to the future radio and mobile communication system. This paper discussed some core technologies of 4G mobile system included security strategy, hybrid network and adaptive network in 4G. This paper also compare 3G and 4G from network structure, core network mobile terminal and the core thechonolgoy,. Moreover, the paper introduced the research status in quo. It is significant to research and construct 4G to a certain extent

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Future internet works will include large numbers of portable devices moving among small, wireless cells. In order to support real-time applications, users demand seamless mobility and Quality-of-Service (QoS) provisioning.  The handover technology is one of the most important technologies for the quality of real-time operation which guarantee the QoS of mobile Internet. Mobility management issues are solved by separating macro-mobility (inter-domain) generally using Mobile IP and micro-mobility (intra-domain).  In recent years, many enhancements for macro-mobility protocols have been proposed, designed and implemented in Mobile IPv6. Hierarchical Mobile IPv6 (HMIPv6) is one of them that is designed to reduce the amount of signaling required and to improve handover speed for mobile connections. This paper presents a comparative study of the Hierarchical Mobility IPv6 and Mobile IPv6 protocols. The architecture and operation of each protocol is studied and are evaluated based on the QoS parameter: handover latency. The simulation was carried out by using the Network Simulator-2.  The first simulation results show that, HMIPv6 performs best under macro-domain mobility compared to MIPv6. The MIPv6 suffers large handover latency. The second simulation results show that the proposed scheme can get better performance in terms of packet loss and handoff dela

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