The Progress of P2P IPTV

Abstract:The development of IPTV is restricted by the bottleneck of I/O of the client/server mode. On the other hand, the development of P2P Internet TV has achieved great progress in China. P2P TV means to develop IPTV based on the P2P Internet TV concept and technology. P2P IPTV is expected to be the top layer innovation and lead the development trend in the world.

1 Limitation of IPTV System with Client/Server Architecture
IPTV services generally refer to the audio/video contents transmitted through IP networks and received by TV. At present, telecom operators use the manageable IP networks supporting multicast to offer IPTV services, including Live TV, Time-shifted TV, Video on Demand (VOD) and interactive data services.

      IPTV systems in China are adopting the client/server architecture to offer unicast and on-demand (includes VoD and Time-shifted TV) services. With the restriction of I/O bandwidth, a server can only support limited concurrent streams (with the order of magnitude of thousand). Therefore, both a large number of servers and an extremely broad network bandwidth are required to ensure that thousands and millions of viewers enjoy IPTV services at the same time. Currently there are two solutions. One is to adopt multicast technologies to broadcast, and the other is to use Content Delivery Network (CDN) technologies to put servers as close to clients as possible in order to lessen the burden on the network. However, existing networks need reconstruction in order to support multicast, which will directly lead to increased cost and lead to a loss of ubiquity of Internet access. Therefore, IPTV can only provide broadcast services in local reconstructed networks. The present client/server architecture is not able to support IPTV services well.

      Therefore, the client/server architecture has become the bottleneck of IPTV development, and changing the system architecture to P2P is the solution to this problem.

2 Evolution of P2P Content Distribution Technology
The development of computer networks has been swinging from centralized mode to  distributed. Previously, numerous users shared large computers until the introduction of personal computers, with the centralized usage mode changed into distributed. The Internet is going through the same process from the early client/server mode using centralized servers to the mode using distributed servers.

      With P2P technology, a large number of users use one network, sharing bandwidth and processing data in the network together. Different from the traditional client/server mode, each client terminal is both a client and a server in the P2P architecture. Taking shared downloading as an example, each of the clients downloading the same file needs only download one section of the file, then exchanges the sections with each other, and finally gets the complete file.
The first step to fulfill P2P is to search on the Internet to find the node addresses having required content and computing ability. The second step is to implement P2P connection through the Internet. In order to keep ubiquity of Internet access, the Internet protocols don磘 allow any changes. Therefore, the only solution is to deploy a P2P overlay network on the basic Internet.

      P2P overlay networks can be divided into the unstructured, structured and hybrid P2P overlay networks. The unstructured P2P overlay networks have widely been used on the Internet as for Bit Torrent (BT) downloading. The structured P2P overlay networks like Tapestry, Chord, Pastry and Content Addressable Network (CAN) are still under research. New-generation P2P applications including multicast and network storage need fulfilling on such structured P2P overlay networks. Some practical systems start to use the hybrid architecture.

      The unstructured P2P overlay network has evolved for several generations. The first generation adopts centralized topology. The early software Napster adopts such architecture. The second generation adopts decentralized topology, which is applicable to applications on an Ad hoc network?for instance the instant messaging. The third generation adopts a hybrid network architecture, which combines the advantages of both the first and the second generation networks. It replaces a centralized directory server with distributed super nodes, and speeds up retrieval by further utilizing the Distributed Hash Table (DHT) of the structured network.

      There are two methods for distributing broadcasting and movie files: one is to download before watching, called Podcast, and the other is watching while downloading by streaming media technology. P2P technologies support both methods.

      People are rather familiar with P2P shared downloading. The popular P2P software BT belongs to the
third-generation hybrid unstructured network. Everyday tens of millions of netizens worldwide use BT to download movies, MP3 and large-scale software. The BT data traffic constitutes more than 70% of overall traffic on the Internet. It is the same situation in China, and most traffic is used for P2P applications on broadband networks. However, the development of P2P downloading is beset by copyrights. Fortunately, some Podcast websites with legal copyrights are growing healthily.

      P2P streaming media have been developing recently. They are growing well in China, and more than ten websites are using their own software to offer P2P video services on the Internet, with 2.5 million registered users.

3 Development of P2P Streaming Media Live Broadcast Technology
The Webcast system, emerging in 1998, fulfilled on-demand and live broadcast of large-scale streaming media by P2P technologies. Thereafter streaming media live broadcast services developed rapidly due to its simplicity. End System Multicast (ESM), the prototype of P2P video live broadcast system, emerged in 2000. It transported multimedia content among users in real time with the method of making the optimal media data multicast tree by interconnecting mesh networks of the users. Restricted by algorithm, the ESM system could only be extended to supporting thousands of users on line at the same time. However, it marked the stage of system development for P2P streaming media live broadcast system.

      Thereafter, all kinds of prototype systems and highly scalable application-layer multicast protocols emerged in great quantities. Among the prototype systems, Peercast system from Standford University and P2P Radio system from Germany are typical ones for audio broadcast. Both systems adopt open source codes. Application-layer multicast protocols include Microsoft磗 Coopnet/Splitstream, Cisco磗 Overcast, NICE from the University of Maryland and Gossip from the University of Berkeley. Though these systems and protocols are not applicable yet, they are the solid theory foundation for P2P streaming media live broadcast.

      In May 2004, the CoolStreaming prototype system developed by Dr. Zhang Xinyan from the Hong Kong University of Science and Technology made a success of its trial operation on the Planetlab. This system uses the Gossip protocol for transmission of control signaling between users, and a multipoint-to-multipoint data transport protocol similar to BT for transporting medium data packets. The CoolStreaming system is the first solution to apply the highly-scalable and highly-reliable mesh multicast protocol into P2P streaming live broadcast system, which makes the stage of commercial-operation-to-be of P2P live broadcast technology. Encouraged by the success of CoolStreaming, the technology and business of streaming media live broadcast has developed rapidly in China. There have been more than ten websites using their own software to offer P2P streaming media live broadcast services in China, out of which the Synacast system developed by PPLive has the largest number of users. The core of Synacast is a complete online video transmission and operation support service platform. The functions such as program collection, broadcasting, authentication and statistics analysis can be easily fulfilled on this platform.

      With hybrid P2P networking, Synacast enables both the efficiency of P2P networks and the stability of client/server architecture. It can automatically sense the network situations at the user磗 end, dynamically adjust transmission policy, and ensure to the highest degree the reliability of end-to-end transmission. Unlike BT, Synacast adopts DHT-based hybrid P2P network topology, which supports self-evolution and partial adjustment of network topology. The topology centralizes the connections of clients of an Internet Service Provider (ISP), which not only decreases the outlet traffic of the ISP, but also increases the play quality at the client磗 end. With regard to network connection, Synacast can traverse most firewalls and Network Address Translation (NAT) gateways. Therefore, both internal and external users of the network can receive service with the same quality. Moreover, Synacast can automatically monitor the changes in network bandwidth, dynamically adjust the P2P algorithm and transmission policy, and ensure consistent reliability of network transmission.

      The multi-layer architecture makes the system easily scalable. In addition, with both Windows Media and Real player coding and decoding systems, the system can easily interoperate with other streaming media management systems.

      The PPLive network consists of two kinds of host nodes: the streaming media distribution server (the source) and the client terminal (the P2P point). The program at the source encapsulates the original streaming media data according to Synacast protocol, and distributes it to the network in the P2P mode. Each TV channel corresponds to one program at the source. The program at the client end will automatically log on the corresponding streaming media distribution network after starting, search and connect to multiple P2P nodes, and conduct uploading and downloading of data according to resource and network conditions. One server can support several TV programs.
Due to the adoption of P2P technology for the distribution of streaming media content, the Synacast system minimally taxes the servers. Under normal situations, each source distribution program only takes about 5% of CPU load, 20 MB memory and 10 Mb/s of network bandwidth. Take PPLive as an example. The PPLive website originally used the conventional Windows Media servers, and one 100 Mb/s server could at most support 200-300 users at the same time when it provides live broadcast of one program by unicast broadcasting. However, using Synacast technology, an ordinary PC server connected to the Internet at 100 Mb/s can provide live broadcast of  5-10 programs, each of which can be viewed by millions of users at the same time.

      At present, P2P streaming media live broadcast has these performance.

      (1) The rate of TV programs broadcast is 3-500 kb/s. Some channels have started to offer 800 kb/s code rate with picture quality better than that of VCD.

      (2) Data buffering can be completed within 20 s-1 min before playing program. Stable and clear TV programs are enabled without pauses playing under normal conditions.

      (3) With functionality of traversing the internal network, P2P streaming media live broadcast can be used by users of the internal network.

      (4) Servers with 5-10 Mb/s outlet bandwidth are used to enable millions of users online at the same time.

      (5) The authentication and accounting platform is available.

      Now computer terminals are used for P2P streaming media TV live broadcast, with only minutes of contents stored in the client磗 computer. The hard disc is unnecessarily used. Cheap set top boxes are under development.

4 Development of P2P Streaming Media On-demand Broadcast Technology
P2P technology develops rather slowly in the field of streaming media on-demand broadcasting compared with that in live broadcasting. The main reason is the demand for high interactivity in on-demand broadcasting, which makes the implementation of P2P technology complex. In addition, the copyrights issue blocks the application of P2P
on-demand technology. In 2000, Purdue University in the USA developed the first P2P on-demand broadcasting system named GnuStream which was based on the Gnutella network. This system also adopts the mesh multicast policy. Due to the copyrights issue, this system wasn磘 put into large-scale application. After 2000, P2P on-demand technology made great improvements in application-layer transmission protocols, bottom coding technology and digital copyright technology. The P2Cast protocol proposed in 2002 and the CollectCast protocol (for PROMISE system) in 2003 are important application-layer transmission protocols. Currently practical P2P on-demand systems are under development and entering the commercial application stage.

      AOL is cooperating with Warner Brothers to develop In2TV service on the Internet by using P2P VoD system from Kontiki Company. In2TV is a TV series on-demand service, offering 6 categories of TV series with DVD quality. Moreover, In2TV offers all kinds of interactive services such as games.

      Unlike P2P streaming media live broadcast, P2P streaming media on-demand broadcast requires terminals with hard discs. Therefore, its terminal costs more than the live broadcast one.

5 Development and Problems of P2P Internet TV
In 2004 websites using P2P streaming media technology to offer live TV broadcast services on the Internet emerged in China. At present there are more than ten websites offering P2P streaming media live broadcast services. A wave of P2P Internet TV has been set off in China, and the main internet TV systems include the following:

• PPLive network (using Synacast software)
• ppStream network
• QQ live broadcast network (bonded with new version of QQ)
• Cat Eye network TV (mop.com)
• TVKoo network
• Rox.com
  

      Telecom operators in China are actively preparing for entry into this business. For example, the Guizhou branch of China Network Communications Corporation is doing a trial P2P Internet TV operation using SNS techonology. The Shannghai branch of China Telecom is also conducting trials for P2P Internet TV.

      P2P streaming media not only increase the accessibility of TV, but also enable a lower threshold of telecast.
China Central Television (CCTV) offered broadcast services worldwide through the client/server mode at its website in the past. However, the viewing screen was small and the number of viewers online at the same time limited. Now cctv.com adopts the P2P Internet TV. It can support far more viewers at the same time with a high quality of playing, besides maintaining the accessibility of the Internet and worldwide coverage. P2P streaming media also enable a lower threshold of TV broadcast by using a simple server to fulfill streaming media broadcast on the Internet. Moreover, P2P shared downloading decreases the requirements for content distribution.

      The CCTV website used P2P and CDN technologies to live broadcast its Spring Festival Gala 2006 held on 28th January, 2006. CCTV not only deployed CDN worldwide and used the client/server mode to offer live broadcasting, but also implemented P2P streaming media live TV broadcasting through the Gridmedia system of Tsinghua University and UUSee.com. From 16:00 on the 28th of January to 1:00 of the 29th of January 2006, the click rate of the CCTV website reached 296 million, and its webpage counted up to 47.92 million visits.

      4.1 million people watched the Spring Festival Gala through the live video broadcasting, with 890 thousand from overseas. The maximum number of people concurrently visiting the website was 467 000 with 75 000 from overseas. The maximum bandwidth exceeded 5.38 Gb/s, including the maximum international bandwidth of 4.9 Gb/s.

      The final of Super Girl 2005, a game show held by Hu Nan Satellite TV of China, was broadcast live on PPLive, and attracted 500 000 people. Moreover, at the night of the 31st of December 2005, the number of people using PPLive to watch the "2005-2006 Super Girl Singing Show" exceeded 1 000 000, with 30% from overseas.
99bill.com, cooperating with eeMedia.com, has launched an online payment platform based on E-mail and mobile phone numbers. This platform is the first system in China to apply the P2P content copyright protection technology to network live broadcasting. It requires users to get free tickets for network live broadcasting.

      China has started live broadcasting of news by P2P streaming media. For instance, Chinese leading portals including Sohu, Sina and Netease all used P2P streaming media technology to broadcast the launch and return of the Shenzhou VI manned spacecraft live.

      Cooperating with Roxbeam Media Network Corporation who owns the internationally advanced streaming media technology, sdnews.com.cn, one of the top three news websites in Shandong province of China, successfully opened its online news video. Sohu has launched its P2P network TV station for the singing contest My Show in 2006.

      The fast development of P2P streaming media technology and business has caught the attention and favor of capital markets. For instance, Softbank has invested in CoolStreaming Corporation, established Roxbeam, operated on rox.com, and offered P2P streaming media technology to Yahoo BB. Besides, UUsee, Mysee, PPLIve, PPstream and thousand Oak all received investment from Venture Capital (VC) firms.

      P2P Internet TV has developed fast in the past year, with 2 500 000 subscribers by the end of 2005. It has shown a great potential, but also faces many difficulties and problems.

      Firstly, P2P internet TV lacks a profitable operation model and industry chain for sustainable development. At present, the P2P internet TV services are offered free in order to increase the click rate, and further, to obtain investment from VC. This model fails to get video contents legally through a healthy industry chain. It can only broadcast available games from TV channels or get some contents by grey ways.

      Secondly, the threshold for entering the business is rather low. Therefore, many newly established companies have joined the competition and make it fiercer. Besides, most of the entrepreneurs in this field have technical backgrounds and are not familiar with the media industry. Moreover, their capital investment is not enough to create a scale effect, which only leads to low-level competition.

      Thirdly, the development of P2P Internet TV is causing a series of legal problems. Conventional TV offers local services, under the supervision of a series of laws and regulations. It is infeasible to simply transplant the laws and regulations on conventional TV services to the Internet. Currently the European Communities (EC) have started to set up new regulations for Internet TV.

      Finally, P2P Internet TV may cause the problem of interests distribution. In China, there have been rumors of Chinese telecom operators trying to prohibit BT and Skype software. In USA, some telecom operators presented a proposal for 2-class services, which has lead to an argument on whether Congress should legislate maintaining the neutral property of networks.

6 P2P IPTV
At present, IPTV and P2P Internet TV are following two routes to develop independently in China. They are facing different obstacles in development. However, it is possible to create a favorable new picture of the evolution of network media by integrating IPTV and P2P Internet TV , using the resources and force for developing IPTV to develop P2P Internet TV, or in other words, using the concept and technologies of P2P Internet TV to develop IPTV. This is the concept of P2P IPTV.

      China is constructing an innovation-oriented country, and developing P2P-based IPTV is a historical opportunity for China to innovate on a world-class level. At present, China is in the lead position with respect to the technology and application of P2P Internet TV, and has advanced network infrastructure and competitive telecom and network equipment vendors. Moreover, China磗 telecom industry has a strong demand for and a good preparation for developing broadband services. Therefore, China can support the innovation.

      P2P IPTV system operates on the public Internet, builds a P2P overlay network, establishes its operation platform, has the authentication, authorization and accounting system, and enables ubiquity of Internet access. It can support the smooth evolution to new network media.

      P2P IPTV is still facing problems in technique, operation models, industry chain and legal issues. Solution to these problems is the opportunity for technical innovation. The development of P2P IPTV is helpful to balance the interests of every party and to establish the industry chain with sustainable development.

7 Conclusions
The development of IPTV faces the limitation of the client/server mode. China has made great achievements in P2P Internet TV. P2P IPTV hence arises as a new idea to develop IPTV with the concept and technologies of P2P Internet TV. P2P IPTV is expected to be a world-class technical innovation from China.

References
[1] Hou Ziqiang. Issues of IPTV磗 location and development[C]//The IPTV World Forum 2006. Mar 06-08, 2006, London, UK.
[2] ???. ??IPTV?????????[J]. ????, 2006, 19(2): 30-32.
[3] ???. ?CNGI IPv6????????P2P?????????[J]. ??????, 2005, 11(3): 21-24.

Manuscript received:2006-03-12

Author Introduce:

  Hou Ziqiang is a researcher of DSP Engineering Center of Institute of Acoustics, Chinese Academy of Sciences. He is also a member of Communications Technology Commission of Ministry of Information Industry (MII) of China, and the independent director of CNC (Hong Kong). He was the former secretary-general of the Chinese Academy of Sciences, and the former president of the Institute of Acoustics.