Research On IP Transport For GSM Evolution

The development of GSM (Global System for Mobile Communication) wireless network makes the operator's network performance requirement increasing. Although the traditional TDM (Time Division Multiple) network can provide stable and secure realtime service, it still can't meet the market requirement due to high transmission cost and low bandwidth. Considered as a convenient communication technology, IP can provide more bandwidth and less transmission cost, so it will be taken as the evolutional target for GSM wireless network.The design of mixed mode network model can make the evolution from TDM to IP better. Based on protecting the investment of network operator, it raises that the reasonable technology should support the traditional TDM equipments and new IP equipments to work together. Furthermore, this technology which is called smooth evolutional technology should not impact the basic function of the network. Under mixed mode network, TDM and IP BTS (Base Transceiver Station) can access the network together. So operator can change BTS mode gradually, which leads to easier deployment and better service quality. The model also changes interface protocol, which makes more stable and reliable interactions between equipments.Taking the mixed mode model and customer requirement into account, the smooth evolutional technology is designed and implemented. Firstly, from the view of architecture, a new application layer protocol which is called as TC signalling link is designed between BSC (Base Station Controller) and TC (TransCoder) based on TCP/IP. Through this protocol, it will be easier for BSC to do resource management and maintenance work upon TC. It's the foundation for all the basic function in mixed mode network. Secondly, from the functional view, a new call control and handover control mechanism is designed. The call control mechanism can make BSC to differentiate different call request from TDM BTS and IP BTS, while the handover mechanism can make the handover between TDM and IP BTS possible.During the simulative testing, it proves that the smooth evolutional technology can ensure TDM and IP equipments work together. It also validates that the calls and handovers are running very well. Network bandwidth is increased, together with decreasing network congestion rate.