The Research On The Delay Optimization Issues Of SIP-Based VoWLAN Roaming

With devleopment of mobile communication technologies and mobile devices, the mobile business get rapid progress and its value get a lot of recognition by human society. VoIP is the most typical and the most brilliance foreground application on Internet. The integratation of VoIP with mobile communication technologies make people can use Internet telephone and other applications quite easy. It's core protocol, SIP, as a sinaling protocol, when intergrated with mobile communication technologies, provides the infrastructural of NGN. In this situation, voice call, video communication, game and the other multimedia applications could be fulfilled on the internet with mobile devices. Nowadays, there are a lot of telephone software applications emerging.When WLAN as a typical wireless access network, the SIP-based VoIP over mobile communication technologies can't provide enough mobility. Although the protocol standard of WLAN—IEEE 802.11f/n improved the support of mobility, and other institutes proposed Mobile IP solutions for solving SIP roaming problems, the real transparence is still a problem. The SIP-based VoWLAN has some problems, such as long roaming delay and high roaming lost rate. Aimed the above problems, the paper proposed a new solution to reduce the roam delay, increase the roam success rate and thereby impove the performance of VoWLAN.Our research works could be listed below.(1) Firstly, the paper analyzed the roaming process of based pure-SIP roaming solutions which is the groundwork. In fact, nowadays, most SIP application softwares take the pure-SIP roaming solution.(2) The roaming process is divided into the channel detect, resource pre-request, SIP pre-roaming, IEEE 802.11 handoff, network layer roaming and application layer roaming. We proposed a network cross-layer approach.(3) Based the history of roaming, our approach predicted the roaming direction, which is aimed to reduce channel detect cost. With the new approach, we need to pre-request the resource, include pre-requesting IP address, sending it to the communication peer, notifying the communication peer of informing the new AP and the old AP at the same time. It then reduced the SIP layer roaming delay. All the roaming process is controlled by a third-part TPRCS (Roaming Controll Server) to lessen the burden of the whole network architecture.(4) The paper proposed a new experiment approach which is composed by two parts. Firstly, we build a minitype SIP-based VoWLAN and record a mobile device's roaming action. Secondly, we simulate the performance SIP-based VoWLAN on the distributed system and input the data which recorded from the minitype network. Then, according to the data from the experiment model, we compare irs performance with the perfomance of other pure-SIP roaming solutions. We can draw the conclusions that the new roaming solution shortens the roaming delay while the network is idle and the new roaming solution decreases the roaming delay and increases the roaming success rate while the network is busy.