iTDTS: A SIP-based Telephone System for Train Dispatching

Train Dispatching Telephone System(TDTS) is a telephone system works for communication among train, railway station and railway dispatching center. The traditional TDTS works on 400MHz mode for voice analog, making it difficult to realize end-to-end communication. With the application of wireless access networks in railway, VoIP-based TDTS is tending to be a reality. Different from ordinary VoIP system, clients in TDTS have multi-level precedence. Client with high level precedence can disconnect or join in an existing session consisting of low level clients. For example, when emergency happens, the dispatcher, which has the highest precedence, can deliver the dispatching command to a busy station or a busy train driver through force-insert or force-disconnect. The call flow of force-insert and force-disconnect are also different from the call flow of the ordinary call. Therefore, this paper firstly gives a formalized system model to describe the relationship among different roles, different precedence and multiple call patterns. Based on the system model, this paper focuses on the analysis and design of the call flows of precedence based force-disconnect call and force-insert call. Although the three kinds of roles(train, station, and dispatcher) in TDTS have different precedence, they have almost the same service logic, namely, signaling processing, media processing. So we design a MVC(Model-View-Control) based GUI framework for the roles. Each kind of roles can be easily developed and maintained under such GUI framework. Utilizing session initiation protocol (SIP), we design and develop the whole system iTDTS. The performance of iTDTS is finally evaluated in a real railway line over IEEE 802.16. Our efforts show that iTDTS works well over IEEE 802.16 networks.