The Subway CCTV system comprises two levels: one for platforms, subway trains, parking lots and the other for control 

center. The Subway police CCTV system consists of three levels including platforms, subway trains, parking lots, 

subordinate police service centers and superior police service center. Structured by end-to-end NGN, the system realizes 

the following functions: optimized network flow by real-time video stream multicasting with no repeated occupying of 

bandwidth when recalled by many users; enhanced emergency respond speed by direct data storing to IP SAN with no 

file packaging, the reliability is higher with fast searching within a second and immediate playback; 

N + M storage backup structure for specialized CCTV foreign domains' backup with high performance-price ratio; 

dual-streams direct storing for Public Security Department with two copies of the backup of important surveillance sites. 

Till now, DSD has provided more than 20 specialized or public security CCTV systems in several cities with complete 

solutions. In return, DSD received plenty of recognitions from the owners of metro because of stable running and friendly 

interfaces of systems.