The Research Of Safety-Critical Communication Protocol In Cbtc System

The implementation of communication in Communication-Based Train Control,"CBTC" for short, is completed by Data Communication System,"DCS" for short. High real-time and high security level is inseperable from DCS. DCS system can only guarantee the safety in transport layer and all layers below it, can not ensure the handling safety between transport layer and application.With the development of CBTC techniques, the safety issue of data communication and handling attracts wide attention. The protocol adopted in transport layer in CBTC is UDP, which is linkless and unsafe, thus the handling safety between transport layer and application layer is hard to guarantee, also often facing the threat of message repetition, loss, insertion sequence confusion, errors, transfer timeout and so on. Secure communication protocol is most directly related to a secure communication in the CBTC system. With the protection of DCS, referring to RSSP-Ⅰ of railway signaling protocol for secure communication issued, design the protocol used in CBTC system. The protocol uses the techniques such as serial number, time stamp, overtime, destination and source address identification, feedback message, double check and other measures, meanwhile secure communication protocol uses a linear feedback shift algorithm and cyclic redundancy algorithm to ensure secure transmission of user data packets by dual channel encryption computing. RSSP-Ⅰ protocol is used in most of the existing railway system, in this paper it is applied to the field of urban rail transit via adding the function of address information verification and safe link management.In order to verify the correctness of secure communication protocol design, in accordance with the secure communication protocol design, developed a software simulation system that can simulate the ATS (Automatic Train Supervision, referred ATS) server, zone controller and car controller three types of equipment in CBTC system.Domestic research on secure communications protocols mostly focus on network simulation and formal verification of mathematics, few experiment is taken based DCS system. Experiment verification can overcome the disadvantage of lacking confidence in network simulation, also can verify the protection function flexible.To make the design of the entire secure communication protocol more convincing semi-physical simulation takes place in the Southwest Jiaotong University DCS system. Southwest Jiaotong University DCS system uses sophisticated commercial equipment, its design has been applied in existing urban rail transit lines, keeping high consistence with the devices in use. Several measurements are relised with the Southwest Jiaotong University DCS system and referring to requirements for network delay in IEEE1474.1standard, the results show that after the encryption processing in DCS systems, IPSec protection for wireless network, and the processing of secure communication algorithms, the time delay and the link time of whole system meet the requirement of daily operations in CBTC system well. The result of testing software simulation shows that software achieves a good functional safety communication protocol and can ensure safety in the event of failure.