Research And Implementation Of PIS Information Multicast Technology

Passenger Information System(PIS) is an important component of urban rail transit.Nowdays,the research and application about it has just started in China.There are some common defects in the most widely adopted schemas of PIS information multicast in domestic.The first is the high cost of the software-hardware in video capture,compression and editing;the second is that the cost of the mode of download the video completely before play tends to be high,and the real-time or quasi real-time playing can not be implemented;the third is information unit cannot be retrieved,captured and adjusted easily;the last is the lacking of play control function at different layers.Aiming at these problems,the thesis targets the research at the schema of PIS information multicast and related technologies,which is networking,intelligentized,easy to be operated,reliable,and cost adaptable.A new information multicast schema of PIS is presented in this thesis.The schema uses network playing mode,which results in decrement of program acquisitioning and editing cost,with the real-time or quasi real-time playing realized as well.Based on the different types of multimedia resources characteristics,this schema adopts multi-type mode in the first phase of information multicast,including the application layer multicast for video,the request-response multicast for graphics-text,and the parsing,collation,distribution layer by layer for operation information.According to View Compose and Multicast Proxy(VCMP) of multicast domain(IPMLAN),the playing task scheduling of normal program or real-time inserting program,all types of information's view synthesis and the IP multicast for program video are implemented.This schema maintains the independence of the information entity,which meets the requirement of the information unit being captured and adjusted Furthermore,it has strong application scalability and adaptability,and is convenient for the implementation of the play control.Based on the architecture of typical PIS and the proposed schema,a multi-layer PIS information multicast system architecture,which is composed of center,line center and IPMLAN,is constructed.Through the layer-based design of information management and play control function, the architecture achieves highly cohesive in business.Furthermore,it makes every layer keep balance between the ability of control and the load by the data exchange among layers and the play control scheduling of different layer-based granularity.XML is choosed as a data exchange method for play control scheduling,and XML Schema is used to design the data exchange pattern.Time synchronization of PIS information multicast system is deeply researched and a solution is proposed.This thesis designs HPALM,a model of application layer multicast, suitable for PIS video multicast.PIS video multicast has small scale, requirement of good performance and high stability,and lower requirement of flexibility.The model adopts centralized algorithm in order to construct multicast forward topology,realizes multicast forward through application layer gateway,realizes fault-tolerant routing by using proactive algorithms as well.In the situation like PIS video multicast, which has stable multicast layer structure and high clustering receive nodes on the physical network topology,HPALM has a better relative delay penalty and physical link stress.Based on the schema proposed,this paper establishes a PIS information multicast prototype system,which offers an implementation method to make the urban rail transit passenger information multicast to be networking,intelligentized,easy to be operated,reliable,and cost adaptable.