Wednesday, December 15, 2010

Weak School】 【】 video on demand technology..

<br> <BR> With the multimedia technology, communication technology and hardware development of storage technology, people no longer meet the previous single, passive access to information, but to actively participate in programs being. .VOD (Video on Demand, VOD) is an interactive business community caused by cable television and communications industry's attention. .Interactive VOD system consists of front-end processing systems, broadband switching network, the user access network, customer premises equipment (set-top box plus add a TV or computer), and several other components. .VOD system can be used to focus on the structure, it can be centrally managed, distributed processing approach; and flexibility to use HFC, FTTB, FTTCADSL, VDSL and other access methods, users need to use set-top box can match with the access mode .interface, through the TV, PC machine for video / audio / data display and communication. .First, the user terminal through their own VOD, VOD service access to the nearest eight-sponsored the first communications call, requires the use of VOD service, the VOD service uplink channel (such as computer networks, telecommunications networks, cable TV, etc.) to the frequency of the server is .request; system to respond quickly in the user's television screen a single demand, and user information are reviewed to determine user identity; the user to choose one based on demand, play a program requirement, the system is based on the audit findings, determine whether .provide appropriate services. .Within a short time interval required for the specified device playback program, and stands ready to respond to new requests. .First, the front-end processing system front-end processing system in general by the video servers, disk arrays, program database, Broadcasting System and other accessories. .Video server's high-speed data transmission capabilities ensure that the user of a large number of films, video programs, games, business information and other services in near real-time access. .Its prominent advantages are a number of users starting from a different time watching the same program, to avoid the wonderful program exclusively by one user or a user broadcast point, other users can only passively follow, and this requires the user demand .the relative concentration of the field will be particularly suitable. .VOD video server stores compressed image a large number of programs and through the network to provide users with copies of the desired program can also include real-time encoder to access MFEG live. .Program database is a filing system, saving a lot of compression in the form of film programs, can be downloaded in batches to the video server. .VOD video server and the users through direct, real-time two-way interaction to control the broadcast, including the choice of programs, the start and end during playback, playback speed control and dynamic switching between different programs, etc., VOD video server must .running the appropriate software to coordinate action; while providing a friendly user interface. .It should have the following characteristics: (1) can store hundreds of hours at least the image shows. .(2) If a user of the VOD server, the dynamic random access procedure is called a session, then the VOD server must be able to support thousands of simultaneous but separate "session" process. .(3) has a set of encryption and user access control mechanisms to prevent unauthorized users access. .Core of the system as on-demand, VOD video server directly determines the performance of overall system performance. .In order to respond to multiple users at the same time service requirements, video server scheduling algorithms generally use the time slice. .Video server to be able to adapt to real-time, continuous and stable video stream, and its larger storage capacity, data rates must be high, and should have admission control, request processing, data retrieval, by streaming and other features to ensure that the user requests in the system .resources and effective service. .SCSI interface to storage devices should be used to ensure high-speed, parallel, multiple I / O bus capabilities. .ATM-based VOD system, using multi-channel video server is based on self-routing switch (MPSR) as the center of the broadband video server. .This structure of the server can provide real-time interactive video on demand (InteractiveVOD with Instaneous access, IVOD-i) and interactive video-on-demand delay (Interactive VOD with delayed access IVOD-d) two ways. .Demand a large number of users simultaneously, the server's transmission rate is high; also asked other related equipment can support this high data rate, it is difficult to achieve. .This can be at the network edge (such as the ATM network switch at the front) to set the video buffer pool, high-demand programs to copy to the buffer pool, so some users can only access the buffer pool, the pool is not to be on demand .programs, can go to access the server, which reduces the burden on the server, and can increase as the user pool. .Loading buffer pool available 150Mb / S rate, while the transfer from the buffer pool to the user program is 2Mb / S rate, which a server can support multiple users. .Second, the control management system control and management system is a signaling transport network, for managing the user's connection to the VOD video server. .Since actual VOD VOD system can have multiple video servers, therefore, control and management system uses two gateway management, the first stage in the digital broadband switching systems and transmission systems to realize the selection of different channels; second stage completed .In a VOD video server on a specific program choices. .VOD signaling and data flow of the concrete road as follows: (1) signaling through the pre-connected set-top box and access the population of equipment; that is connected to S3, VOD system will be the list of services to the user from the Population Division; (2) according to user requirements, population .associated with the selected video server, that is connected to S4, and provide services factors cited; (3) S4 initialization completed by the set-top box or a video server; routing information provided by the service population, program list provided by the server; (4) .Users select the program from the program and a single video server signaling to pass; (5) through the network operations will be presented by the video server sends to the set-top box, that is connected P1, if necessary, can be loaded into the program from the video library is the frequency server; that .connected P; (6) other signaling pathways S5, S6, S7 are service operations center monitoring and recording. .Third, ATM switching system with digital set management, point-exchangeable interactive VOD system, its servers, networks, access equipment, customer premise equipment, and so can run on many types of video compression modes and different bandwidth requirements .environment. .Video server according to user-demand requirements of the program the user removed from the video library, and transmitted to the user through the ATM network. .Generally use the MPEG standard video information coding, loaded ATM cell, transmission in ATM networks. .The same network may have multiple information providers, so you can have multiple video servers, deployed by the network operations center services to use. .Service function of the population are mainly based on services required by the user with the appropriate server, the user is connected to a network can have multiple service population, the population can also be a service to connect multiple users. .Services to the population as a separate network components can also be integrated into existing server or ATM switching center frequency, and other parts. .Service Operations Center is a service provider to manage and distribute information resources and provide related services for the operation of the components. .If the large number of service providers, the service can be used as a stand-alone operations center components; if a small number of service providers, the general frequency of its integration into existing server. .Video library function is stored in the form of information coding documents, access device provides the connection between the network and users, it is generally located in the network and user equipment (CPE) between equipment components. .CPE, including televisions and video recorders, set-top box and remote control. .ATM network interconnecting the network components, including the "signaling" and "program data flow", which shows data flow should meet the requirements of the user rate of demand, the connection can be point to point or multipoint. .Fourth, the transmission system transmission system transmission system from the trunk and distribution system components, the role will come from the VOD video server and other sources of information sent to the user and send the user back to the reverse information. .Trunk transmission systems can be fiber, coaxial cable and wireless transmission methods to choose from; distribution systems have fiber (FITL), copper (ADSL, etc.), hybrid fiber coaxial (HFC) and wireless (LMDS) and other implementations. .The general practice of Posts and Telecommunications companies use ADSL / HDSL / VDSL technology transfer programs in the PSTN; and radio and television departments generally use the HFC technology, broadcast programs in the CATV system. .From the transmission rate, real time, interactive, and other economic considerations, 3 common to the network as a VOD system users can only access network PSTN and CATV systems. .However, PSTN and CATV systems are required to be improved, PSTN need to raise rates, CATV system, you need to increase two-way communication capabilities. .Fifth, the user equipment is currently two main types of user equipment structure. .The first structure of a network terminal (NT) separated from the set-top boxes, multi-use E1/V24 the interface between the two can provide 2Mb / S downlink connections and two-way control connection. .In the future there will be so-called standard digital home network (DHN), a number of set-top box to allow connection and to re-use of existing twisted pair or coaxial cable to provide tens of megabits per second bandwidth. .The second structure will be integrated into the NT set-top box, STB's basic function is to decode the MPEG signal with the normal TV interface. .There are man-machine interfaces, conditional access (code), password control, smart card and credit card readers and other features. .Set-top box also has low, high-end two types of products. .The former from the current pay-TV set-top box decoder with evolved, less expensive, but only a limited user interface and processing capabilities. .The latter from the current workstation / PC machines evolved, with a high-performance processing platform, including at least 4 MB of storage capacity, providing a graphical user interface, voice recognition, animation and games. .Sixth, the network structure of VOD programs to achieve structural balance HFC coaxial cable current status of the existing building to support existing and emerging narrowband and broadband services. .The signal from the VOD video server (155Mb / s) and other traditional media such as CATV signal is fed into the center (HUb) modulation, while the HUb VOD network is digital / analog conversion interface; prior to the channel receiver .VOD digital signals and other multimedia signals to be sent to all nodes via optical fiber (NOde). .Back-channel receiver control signals from the client, to be treated, be sent to the ATM switch and VOD video server. .Node Hub via optical fiber lines to receive from the forward RF signal; be processed through the linear amplifier, sent through the coaxial cable distribution network to the user; Node must also be filtered out of the reverse RF signals from the user, and put it through .laser driver back to the HUb. .ADSL technology can also be used in fiber optic nodes and users to install ADSL equipment to achieve VOD Swiss business and other broadband services. .ATM switch and broadband VOD service subscriber loop is the key technology development. .VOD system using ATM technology, both good service to users, the network bandwidth requirements but also the smallest. .Currently, ATM switches have been commercialized, and the user is the broadband network to carry out VOD and other broadband services is one the biggest problem. .Fiber subscriber loop (FTTH, FTTC, FTTB, etc.) with its frequency bandwidth, high-speed data transmission can be even high-definition television, can adapt to B-ISDN and the information highway development, etc., is the future development of broadband high-speed subscriber loop direction .. .But because of its large investment, the user unbearable. .The near future should make full use HFC, ADSL and HDSL technology, explore the potential development of VOD and other broadband services. .<BR>.

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