Label: IPTV IP Multicast
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1. Broadband network Digital TV, also known as IPTV or BTV, is an interactive network TV. It is a kind of interactive service that provides broadband TV, multimedia and other technologies to provide home users with digital TV. New technology. It can adapt well to the rapid development of today's networks and fully utilize existing broadband network resources.
In the current commercial broadband network, users can enjoy IPTV services in two ways at home:
(1) Computer: In this way, users can listen to radio programs or listen to music while surfing the Internet through a computer, or watch TV or movies directly on the computer.
(2) Network set-top box (STB) + ordinary TV set. The user adds a new network set-top box (STB) in the home, and the set-top box provides an AV interface, which is directly connected to the ordinary television set, and the user selects to watch the broadband network television program by controlling the set-top box.
Users can enjoy traditional INTERNET data services and online games through PCs, as well as wide-band video programs such as TVs and movies on ordinary TVs through a dedicated conversion device STB.
2. Key technologies in IPTV
The essence of IPTV application is the transmission and distribution of streaming media over broadband networks. Therefore, the application and development of IPTV are the result of simultaneous application of the following key technologies.
(1) Broadband access technology: The rapidly developing broadband access technology provides a path for media stream transmission.
Among the broadband access technologies currently used, DSL is a technology capable of providing broadband data services over ordinary telephone lines. The commonly used ADSL (Asymmetrical Digital Subscriber Line) technology can provide downlink 8M bandwidth. The ITU-T G.992.1 standard for ADSL has been defined in detail. With the rapid development of technology, ITU-T launched two new generation ADSL standards in June 2002 and January 2003 respectively: ADSL2 (G.992.3) and ADSL2+ (G.992.5). ADSL2 supports a maximum uplink and downlink rate of 1.3M/15M, while ADSL2+ supports a maximum uplink and downlink rate of 1.3M/24M. Higher bandwidth makes it possible to transfer large amounts of streaming media.
(2) IP multicast routing technology: powerful support for streaming media distribution.
IP multicast routing technology enables efficient data transmission from point to multipoint in IP networks. It can effectively save network bandwidth and reduce network load. Multicast is a network technology that allows one or more senders (multicast sources) to simultaneously send the same data packet to multiple recipients. It is a kind of network that can double the load without increasing the backbone network. An effective solution to increase the number of business users has become the preferred solution for current high-traffic video services. In the application of IPTV, IP multicast routing technology can effectively distribute media streams and reduce network traffic. Currently, the access device implements the on-demand joining and leaving functions of the user through the IGMP Proxy function, thus realizing the on-demand distribution of the media stream. It also reduces the transition of multicast to bandwidth. With the application of IP multicast technology on integrated access devices, most devices support IGMP Snooping and IGMP Proxy.
IGMPsnooping is a basic solution to the problem of IP multicast flooding on Layer 2 network devices. The device obtains the user list information of the multicast service by using the IGMP protocol message between the user and the multicast routing device on the Layer 2 network device, and forwards the multicast data according to the current user information, thereby suppressing Layer 2 multicast. The purpose of flooding.
IGMPproxy provides a complete solution for the multicast service of Layer 2 devices through the proxy mechanism. The Layer 2 network device of the IGMP proxy is implemented. The user side assumes the role of the server and periodically queries the user information. The network routing side assumes the role of the client and sends the current user information to the network when needed. Not only can it achieve the purpose of suppressing the flooding of Layer 2 multicast, but it can be more effectively acquired and controlled.
User information is also played a role in reducing network side protocol messages to reduce network load.
(3) Digital coding technology: technical support for transmission reliability.
The transmission of multimedia information such as audio/video over the network involves reliable real-time transmission of streaming media. Therefore, digital codec technology is one of the key technologies of IPTV. At present, the coding standards applicable in the broadband network environment are: MPEG-4, AC-1, and H.264. MPEG-4 is an ISO/IEC standard, developed by MPEG, currently used by MPEG-4 Part2; H.264 is a video coding standard developed by ITU-T's VCEG and ISO/IEC MPEG joint video group JVT, which is both ITU- T's H.264 is also ISO/IEC MPEG-4 Part 10; AC-1 is Microsoft's video coding standard, which is the name of the coding standard used by WMV9 after submitting data to the codec standard organization.
The continuous improvement of network bandwidth, such as the application of ADSL2 or ADSL2+ technology, can increase the user's uplink and downlink rates to 1.3M/24M. If the media stream is encoded by ITU-T H.264 or WMV9, the 800K code rate can provide close to DVD quality quality, which fully meets the requirements of current users. Therefore, the combination of the two guarantees the transmission reliability of the IPTV media stream. Although there is no corresponding national standard for digital coding technology adopted by IPTV, both MPEG-4, H.264, and WMV9 coding technologies have met the requirements of IPTV applications. With the new broadband access technology, any encoded streaming video program can be transmitted in real time.
3, summary
The emergence of IPTV as a new application is not simply an application on a broadband network. It is produced by the development of network transmission technology, IP multicast routing technology and streaming media coding technology. It is the result of powerful combination of these key technologies.
IPTV will inject new life into broadband operators and program providers. In addition to providing users with communication and information services, broadband operators can also provide users with rich and personalized TV programs through IPTV, which is of great help to attract users and improve user satisfaction.
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