Expert analysis: Operational IPTV technology (1)

IPTV is a display terminal that uses a home TV or PC to provide rich multimedia services including TV programs over the Internet. IPTV has a distinctive feature that enables interaction between media service providers and consumers. It can provide a wide range of multimedia service functions based on user selection, including VOD, Web browsing, email, entertainment, education, and business. IPTV is the integration of new technologies for computing, communication, multimedia, and home appliances. It brings new interactive video content to users, while increasing value to ISP network services and entering a virtuous circle. As an important part of the network operator, system provider, consumer electronic product manufacturer, and ICP industry chain, ISP naturally needs to be concerned with the related technologies that promote the development of IPTV services and their current application status, focus on the relationship between this technology and the in-service network, and the future development trend of IPTV technology.

Transmission of streaming media signals over IP Networks

(1) IP network playback Mode

IPTV video streams have two receiving modes in the opinion of end users: on-demand video streaming and broadcasting. On-demand video streams are personalized, And the received content and time depend on users' preferences and have real-time interaction characteristics; in the user's view, broadcast receiving is passive. the user's choice of content is limited to the provided channels and is not hierarchical. However, in terms of the effectiveness of video stream transmission, the two video streams are transmitted on the IP network in different technical categories. The broadcast receiving method requires the Multicast function (Multicast) on the IP network; the VOD receiving method requires that the IP network be able to effectively push video streams to the User Access Network (VDN/CDN ).

Multicast Transmission: multicast is a network technology that allows one or more senders (Multicast sources) to send a single packet to multiple receivers at the same time. The Multicast Source sends data packets to a specific multicast group, and only the addresses belonging to the multicast group can receive data packets. In IPTV, there is often only one Multicast Source. Even if the number of users doubles, the backbone bandwidth does not need to be increased, because no matter how many target addresses there are, only a single video stream is transmitted on any trunk link of the network, that is, "one-time transmission, intra-group broadcast ". Multicast improves data transmission efficiency and reduces the possibility of congestion on the backbone network.

Video distribution network: the basic principle of VDN/CDN is to copy and distribute the user-selected streaming media content with a high compression rate from the initial Streaming Media Server to the Cache Server closest to the end user, when an end user requests a video service, the service is provided by the Cache Server closest to the request terminal. Obviously, VDN/CDN is linked between the initial server and the cache server, and the bandwidth usage is much less than the non-VDN/CDN environment in which the user accesses the central streaming media server in a centralized manner, it effectively solves the congestion caused by high access traffic and unbalanced Server distribution on the backbone network, improves the scope and response speed of user access to streaming media content, and is a very effective networking mode in the video-on-demand business.

(2) VDN/CDN Construction Pattern

VDN/CDN features centralized management and distributed storage strategy. It consists of four parts: distributed storage, Server Load balancer, network request redirection, and content management, content management and global network traffic management are the core of VDN/CDN. Based on the principle of nearby access and Server Load balancer, ensure that streaming media content provides services for user requests in an extremely efficient manner. Of course, in the streaming media application service, content management also includes service authentication and billing.

VDN/CDN has many applications in China. The system also covers man and Wan in China. The former is mostly due to regional business competition of operators, especially competition for entertainment market share. The system has a strong support function for streaming media distribution services. The latter has a wide coverage area, the consideration is not only the smooth network, but also the brand awareness of the operator's network services to attract more excellent ICPs to join their own Internet platforms. Therefore, the system's distribution content is often comprehensive, including Web content and streaming media services.

Whether it is an IPTV service or a VDN/CDN network that supports PCVOD, they should have the following general requirements:

1. The management center, distribution center, and cache service points are in a hierarchical network structure. Load Balancing and backup are performed between multiple distributed nodes to facilitate performance and function expansion;

2. Complete service authentication and billing systems, including system management, user management, configuration management, monitoring statistics, content management, ICP management, and activation management;

3. Based on the application layer solution, the application layer redirection Based on MMS, RTSP, and HTTP protocols is supported to direct users to edge nodes, and streaming media services are provided to users through the media service system of remote nodes;

4. NAT deployment for cross-Network Address Translation solves the problem that global Load Balancing cannot switch from NAT to private network;

5. The system has good scalability and compatibility.

(3) Trend of multicast and distribution network applications

According to the characteristics of the above multicast and distribution networks that support streaming media, the two applications have certain differences: first, compared with the traditional TV and multicast receiving modes, apsaravideo for VOD is more in line with people's preference for interactive watching programs. If the content of the programs is rich, the on-demand receiving mode will soon be recognized by the market. In this way, the construction of the video distribution network will be valued by ISPs. Second, although single businesses such as IPTV or small-scale Multicast can be implemented, multicast for a wide range of comprehensive businesses is still difficult to implement because Multicast technology involves network security and complex network heterogeneity issues, in addition, the multicast receiving mode has poor interactivity, so its development prospects are not optimistic. Finally, the technical problems encountered when the distribution network is built are far from the complexity of multicast, although there are also issues such as security, real-time and player compatibility, these issues are almost irrelevant to the second and third-layer network devices. It is suitable for both man and Wan deployment. Therefore, the business model and technical features of the distribution network are more conducive to the development of IPTV services.