1 Introduction
With the rapid development of digital technology and network communication technology in recent years, radio and television are also undergoing a tremendous transformation from analog signals to digital signals. The sharp increase in clarity, interactivity, and rich multimedia information are the intuitive feelings brought by digital signal TV. Digital high-definition television (HDTV), digital video broadcasting (DVB), and digital audio broadcasting (DAB) have slowly approached our lives.
In this transformation, some value-added technologies derived from digital TV have also attracted more and more attention. High-speed multimedia data broadcasting is one of the most important ones. It uses the existing cable TV network resources to provide broadcast services for files, data, audio, video, and integrated services; the receiving terminal is a PC card, and the system is compatible with DVB series standards; it can be transmitted through IP packets based on MPEG-1, MPEG- 2 or MPEG-4 format video data stream, so that users can enjoy high-quality video live images, fully embodies the technical advantages of broadband.
At the same time, the popularity of the Internet and the rapid advancement of today's broadband communication network (hereinafter referred to as broadband network) technologies have also made us more inclined to choose interactive information. Broadband network technology is diverse, including xDSL technology based on PSTN network, Cable Modem technology based on cable TV network, community-based broadband integrated wiring technology based on LAN, and FTTH technology that will become the mainstream in the future. These are all for our interaction. The application laid a solid network foundation.
Nowadays, the boundaries between voice communication networks, data communication networks and television networks are becoming more and more blurred, and the trend of triple play is becoming more and more obvious.
2 The concept of cable TV network multimedia data broadcasting
High-speed multimedia data broadcasting is the fourth-generation broadcasting method that integrates audio, video, and text after audio and video broadcasting. Data broadcasting is divided into two types: reverse data broadcasting (also called teletext) and forward data broadcasting (also called high-speed multimedia data broadcasting).
Cable TV network multimedia data broadcasting uses digital signals loaded by TV signals to transmit digitized information from one point to multiple points at high speed. It uses the cable TV network as a transmission medium, giving full play to the advantages of cable TV network coverage, low price, broadband high speed, stable and reliable home access, and provides TV programs, digital audio, distance education, Internet website broadcasting, finance And securities information, electronic newspapers and periodicals subscription, high-speed on-demand download and Internet tour services.
Like the cable television network, high-speed data broadcasting is also a one-way transmission mechanism from top to bottom. Because it uses digital signals, the user terminal can selectively receive broadcast data by using some powerful software, and store, browse, and analyze the information according to its own needs; its interactive mode is a virtual interaction In fact, the PC first stores the data to the local hard disk, and then the user selects the required content from the local. If the demand information submitted by the user is not in the broadcast content, the information will not be available.
3 The concept of broadband communication network
Broadband communication network refers to a high-speed digital communication network with a rate above 1.544Mbps and a waiting time within tens of milliseconds. It is a computer communication network based on IP protocol. In just 10 years, the user access rate has grown from the early 9.6kbps to the current 1Mbps, 10 / 100Mbps, an increase of thousands of times, and the access methods are also diverse, such as xDSL, WLAN, Cable Mode, WLAN, FTTH, etc.
Power line access (PLC) is currently the main access technology. The user side is mainly PC, and most of the operating systems use Microsoft Windows platform, which can carry out video and audio on demand and download, remote education online games, instant messaging, web browsing and other interactive services, and the number of various websites Even in hundreds of millions, there is almost no information that cannot be found. With such rich content, the network has become an indispensable tool for people's life, work, and study. Its outstanding features are bidirectionality, real-timeness, and interactivity. This is also lacking in high-speed multimedia data broadcasting, and currently multimedia content is in broadband The transmission on the Internet is not perfect, for example, IPTV users' access bandwidth requirements reach 3Mbps-4Mbps (using MPEG-2 encoding) or 2Mbps (using MPEG-4 or higher compression ratio encoding), some high-definition videos The demand for program bandwidth is greater and the broadband network is difficult to meet. This is the characteristic of high-speed multimedia data broadcasting. Therefore, the application of integrating multimedia data broadcasting and broadband network has certain complementarity and inevitability.
4 The composition and function of the cable TV network multimedia data broadcasting system
The cable TV network multimedia data broadcasting system is mainly composed of data broadcasting subsystem, user subsystem, external interaction subsystem, video live broadcasting subsystem and satellite receiving subsystem. The functions of each part are described as follows.
4.1 Data Playout Subsystem
The data broadcasting subsystem is a core part of the broadband multimedia data broadcasting system. Its main function is to effectively organize various information resources, and convert the resource data into information that can be broadcast on the cable TV network through specific broadcasting equipment and software. , And send the information to the cable TV broadcast equipment, at the same time, monitor the data broadcast and manage the system users. The main equipment of the data broadcast subsystem includes: data broadcast management network, playback server and front-end modulator of multimedia data broadcast system.
4.2 User subsystem
In order to receive multimedia data broadcast data or use broadband network for Internet access, users need to be equipped with corresponding hardware equipment and application software. These hardware and software constitute the user subsystem.
4.3 External interaction subsystem
The main function of the external interaction subsystem is to realize the two-way access service for the system, which is an important extension based on the one-way data broadcasting service. The main components of the external interaction subsystem include: convergence layer switches, backbone routers and network management servers of the metropolitan area network.
4.4 Video Live Subsystem
The main function of the video live broadcast subsystem is to collect video signals in real time through the video acquisition module and send them to the broadcast system, thereby realizing the real-time relay or live broadcast of the video signals in the data broadcasting system.
4.5 Satellite receiving subsystem
The satellite receiving subsystem is mainly used to receive various information resources from the satellite channel, and send the received data to the data broadcast management network storage or directly broadcast to the cable TV network through the broadcast server.
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