I. Background of IPTV
The development of internet technology, network and commerce has changed people's study, work and life style in all aspects, bringing great convenience to people. Internet has become an indispensable part of people's lives. However, the rapid development of the Internet has not brought corresponding returns to Internet operators. Following the widely recognized applications such as Web services and e-mail, people in the industry are looking for killer applications that will bring great benefits to network operators. At the end of the 20th century, people regarded distance education and e-commerce as killer applications in the future, and placed high hopes on them. But a few years later, people in the IT industry did not get the expected benefits except the bitter wine brought by the network bubble. After entering the 2 1 century, with the continuous improvement of streaming media technology, internet network technology and network bandwidth, people began to pay attention to using IP protocol to provide TV services similar to those welcomed by many users at present, that is, IPTV services, and regarded it as a killer application on broadband Internet in the future. However, at present or for a period of time, will IPTV service become an application that provides huge profits for operators and is welcomed by users as expected, or will it be used by users all the time like e-commerce and distance education services, but it has not achieved the expected profits.
Second, the feasibility analysis of IPTV technical characteristics
1.IPTV related technologies and standards
(1)IPTV related technologies. IPTV is the abbreviation of Internetprotocoltelevision, which refers to providing video services to users in the form of on-demand or multicast on the network based on IP protocol. The provision of IPTV services benefits from the development of information processing technology and content distribution technology. It mainly includes video image coding technology and streaming media technology, such as MPEG-4/H.264 coding technology, MPEG-7 and MPEG-2 1 metadata technology, content distribution technology (including CDN and peertopeer topeer content distribution technology, multicast technology, access technology, etc. ) and DRM (Digital Rights Management) technology.
(2) Video image coding and streaming technology and standards. Audio and video image compression coding standards are mainly formulated by ITU-T and MPEG. ITU-T protocols H.26 1, H.262, H.263, H.264, MPEG- 1, MPEG-2, MPEG-4 and so on have been released. At present, H.264 and MPEG-4 are considered as the most suitable standards for streaming media systems. At present, AVS organizations in China are also developing and formulating image compression coding standards with independent intellectual property rights in China.
(3) Metadata technology. Metadata is structured information that describes, explains, locates or makes it easier to search, use or manage information resources.
(4) Content distribution technology. Including CDN technology and multicast technology.
(IPTV-related standardization organizations. Standardization organizations related to IPTV mainly include ITU, Streaming Media Alliance ISMA, Open Mobile Alliance OMA, Digital Audio/Video Alliance (DAVIC), ISO, Interactive Television Alliance (ITV), DSL Alliance, Broadband Service Alliance and IETF.
2.2 Advantages and possible problems. IPTV service
(1) Advantages of IPTV service
Compared with traditional TV services, IPTV services have some advantages: IPTV services provide interactive communication channels for users; Users can choose to use the content provided by IPTV service according to their personal preferences; Users can watch the played video programs or existing content information at any time; From the characteristics of technology and service itself, IPTV service can provide users with infinitely different information and provide convenience for users to provide personalized information; IPTV service providers can provide services to users connected to all networks covered by IP-based networks.
(2) Problems existing in the provision of IPTV services by telecom operators
As for the content problem, telecom operators mainly operate networks and have no experience in providing content services. Content plays a very important role in the successful provision of IPTV services. Although content providers can find new content distribution channels through IPTV service platform, due to the current problems of digital rights management, only content protection can be realized. At present, if there is no price acceptable to users, then the degree of protection is acceptable to content providers. It will be difficult for telecom operators to obtain continuous content from content providers.
As for the quality of service, IPTV services currently under discussion mainly include multicast video services and video-on-demand services. Opening video broadcast/multicast on the current IP network will inevitably lead to network congestion and the quality of service is difficult to guarantee. For VOD service, due to the limitation of content distribution and the number of VOD users, when the number of VOD users exceeds a certain number, the network bandwidth and the processing capacity of the server will affect the service quality of the service.
The business model, from the name of IPTV itself, will allow users to compare with the currently accepted TV services when deciding whether to use the service, including price, service quality and ease of use. At present, radio and television mainly rely on advertising revenue to supplement the shortage of expenditure. Whether IPTV should also rely on charging advertising fees to supplement the lack of services.
Content retrieval, IPTV will provide interactive transmission of video information, how users can find what they want from massive information, and how service providers can classify content information is also a question of whether services can develop healthily.
Policies and regulations, the provision of IPTV services will break the geographical restrictions of content information. For some countries, the content that can be played locally is not allowed to be played beyond its prescribed scope, and some information outside the local area is not allowed to be played within the local scope. At the same time, TV services in some countries are operated by designated departments, and it is not clear whether IPTV services are open to telecom operators.
Thirdly, IPTV multicast solution.
Technically, IPTV has strong requirements for multicast, bandwidth, QoS and network security. Generally speaking, IPTV services suggest that the user bandwidth should not be less than 2M. In order to save the network bandwidth from the access layer to convergence layer, Ethernet switches should at least support the Layer 2 multicast protocol IGMPsnooping. At the same time, the access layer equipment that cannot support multicast needs to be replaced step by step according to the service development. The uplink and downlink bandwidth of convergence layer equipment is expanded and upgraded, and the downlink bandwidth is upgraded according to the upgrade of access layer equipment, and the uplink bandwidth is designed as N×GE. Because of the real-time and continuity of video stream in IPTV service, the bearer network needs to provide QoS guarantee, and the service is sensitive to the delay, packet loss and jitter of the bearer network. Among them, live video services such as live TV require higher QoS than video-on-demand services such as video-on-demand. Game service is a two-way interactive data service, and its service characteristics, such as the sensitivity of operation commands, determine that the transmission delay of data packets is particularly high.
According to the requirements of IPTV for switches in multicast, according to the different multicast replication/control points, there are roughly three multicast schemes for access networks.
1. multicast replication mode based on BRAS
User set-top boxes use PPPOE or IPOE mode to access, and establish PPPOE or IPOE channels with BRAS. BRAS terminates the IGMP message of STB, and BRAS is responsible for multicast replication of user STB, and copies multicast message to PPPOE or IPOE channel corresponding to STB. The specific implementation method is shown in figure 1.
Figure 1 multicast replication mode based on BRAS
This implementation method is suitable for all kinds of access modes, PC is connected through PPPOE, STB is connected through PPPOE or IPOE, and PC and STB can use a PVC/VLAN or be configured separately. This implementation method does not need to make much transformation to the existing network, and is suitable for the networking situation of "integrated mode", and only needs to make a few changes to the broadband billing background. However, in this implementation, BRAS replicates IPTV multicast service for user STB, and the user-oriented multicast replication point is BRAS. That is to say, from BRAS to each user, the content requested by each user is a separate data stream, which requires high downlink bandwidth of BRAS and is not suitable for large-scale IPTV networking. Generally used in the initial stage of IPTV service development.
2. Multicast replication mode based on aggregation switch (multicast switch)
The user STB (set-top box) in this implementation can adopt multiple access modes, namely PPPOE or IPOE. However, when using PPPOE access, the set-top box must support dual-stack, and can send IGMP messages based on IPOE encapsulation. The convergence switch will terminate the IGMP messages of the set-top box and be responsible for replicating the IPTV live broadcast service of multicast M-VLAN to users across VLANs. Fig. 2 shows the specific implementation in the case of unilateral service access.
Figure 2 Multicast Replication Mode Based on Aggregation Switch (Multicast Switch)
This implementation is suitable for all access modes, but when the set-top box uses PPPOE access, the set-top box must support dual stack and be able to send IGMP messages based on IPOE encapsulation. The live broadcast service between the aggregation switch and IPTV service control point is carried by multicast M-VLAN, and the aggregation switch has IGMPProxy function, so the IPTV multicast service can be delivered to the aggregation switch by active static pull-down or dynamic pull-down through multicast M-VLAN, and then copied to users across VLANs as required. The so-called active static pull-down means that the convergence switch actively sends multicast join messages to the uplink for drainage regardless of whether there are users who need multicast traffic; The so-called dynamic pull-down means that only the first user joins the multicast, and subsequent users will not be drained. When all users leave the multicast, the aggregation switch sends a multicast leave message to cut off the multicast traffic, so as to achieve the purpose of "on-demand drainage, one-time drainage and multi-user application".
This implementation method has little change to the existing network, supports all access methods, and relieves the access pressure of BRAS. However, the bandwidth pressure based on BRAS multicast replication between the corresponding convergence switch and DSLAM/ layer 2 switch has not improved, and the problem of controlling user multicast access should be considered, which is suitable for the transitional stage of IPTV service development.
3. Multicast replication mode based on layer 2 switches.
In this implementation, the user's set-top box can adopt multiple access modes, PPPOE or IPOE, but when PPPOE is used for access, the set-top box must support dual stack and can send IGMP messages based on IPOE encapsulation, and the IGMP messages of the set-top box will be terminated in layer 2 switches. Fig. 3 shows the specific implementation in the case of unilateral service access.
Fig. 3 Multicast replication mode based on layer 2 switches.
This implementation is suitable for all access methods, but when the set-top box uses PPPOE access, the set-top box must support dual stack and be able to send IGMP messages based on IPOE encapsulation. The live broadcast service between layer 2 switches and IPTV service control point is carried by multicast M-VLAN, and the switch has IGMPProxy function. IPTV multicast service can be delivered to aggregation switch by active static pull-down or dynamic pull-down through multicast M-VLAN, and then copied to users across VLAN as required. This implementation has greatly improved the existing network. layer 2 switches that does not support multicast needs to be completely replaced, and all access modes are supported, which reduces the pressure of multicast replication above layer 2 switches, but the problem of controlling user multicast access should also be considered. In the large-scale IPTV numbering stage, layer 2 switches is the best choice for multicast replication/control point.