| Internet is developing to service diversity and mobility. Both non real-time applications and real-time applications are supported by the Internet. More and more real time services are applied, which stimulate the economic development of Internet. On the other hand, with the development of mobile communication technology and microelectronics technology, the performance of the mobile terminal has been greatly improved. It makes the Internet move to mobilization and people more and more rely on the mobile communication. How to support multi-services of network applications, especially the real-time services in the mobile environment, is becoming an important and urgent task.Some current mobility management proposals are defective. Pure link layer mobile management proposal cannot support macro-mobility. Mobile IPv4 faces some problems, such as triangular routing, address waste, tunneling encapsulation, low transport efficiency, high handoff delay, hard deployment, bottlenecks problem of the home agent and foreign agent, unefficient support to real-time application and so on. Though Mobile IPv6 (MIPv6) takes advantage of IPv6 extension header and Binding Cache to achieve routing optimization and end-to-end mobility. The problems of low transport efficiency, high handoff delay and home agent bottlenecks still exist. Transport layer mobile management proposal is not common enough and is hard to deploy. Pure SIP mobile management proposal can only support UDP connection, and fail to support the application based on TCP. The handoff delay is also quite long. So, a mobile management solution that accords with current network development feature and satisfies consumer's demand is required.This paper presents the mobility management solution which combines with the SIP and Network Mobility Agent, abbreviated as SIP/NMA. This solution decomposes the IP mobility into two subproblems, one is the locationmanagement and the other is mobile handoff management. A software model to seperate roaming registration and mobile handoff is proposed. Location management is aimed to solve the problem of how the network can detect the access point of the mobile host and call it. The mobile handoff management is aimed to maintain the connection when the mobile host changes network access point in the process of communication.This function is implemented by SIP entities. The solution adopts SIP-URI as host's identity. The idea is different from Mobile IP, which uses IP address as host's identity and location identification. This idea avoid waste IP address and easy to remenber and using. Mobile host's SIP-URI is binding wieh current location information. When the mobile host changes network access point, the register process will update the locationinformation. So, the mobile host and correspond host can establish communication directly and avoid triangle routing and data encapsulation problems. By establishment mathmatics model and emulation we can see, SIP/NMA decrease network cost, improve the network transport efficiency, shorten the session establishment time and decrease the network redundant traffic.Because location management of SIP/NMA adopt real-time location update, mobile host just start handoff management when it changes network access point in the process of communication. Handoff management should be implemente in the kernel space, work in end-to-end mode and cooperate with terminal. Comparing with current mobile management solution, SIP/NMA use NMA but not a fix home agent. When the mobile host changes network access point, NMA is in charge of rebuilding routing and packet transfer in order to maintain data connection. Because the handoff singalling transfer between host and NMA of near subnetwork, the transfer distance and delay is decreased. Furthermore, the solution adopts link layer trigger as mobile detection and decreases handoff delay. By establishment mathmatics model and emulation we can see, the solution decreases handoff delay and support real-time service effectively.The prototype system is implemented. SIP/NMA, Mobile IPv6 and MobileSIP is implemented and tested in a platform. Test result proved, the delay of SIP/NMA is shorter than Mobile IPv6 and Mobile SIP.To realize the solution, we only need modify the software of the mobile terminal in the network and add the network unit of NMA, instead of any modification on the router and Correspondent Node of present Internet. The solution has strong compatibility with the current system and the characteristic of simple network structure, easy extension and deployment. SIP/NMA can support not only data services, but also all kinds of real-time multimedia services. With the wide application of SIP protocol in the future, the application scope of this proposal will also be enlarged. SIP is the core control protocol in next generation network. The idea of using SIP accompanied with other protocols exploits a new solution to improve the network mobility and accustomed to the characteristic of the future network development has great expectation of application.
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