Technical Requirements and System Architecture of IPTV Services

Abstract:Delivering IPTV services entails a complex integration of a variety of industries as well as the support of network, computer, and image processing technologies. That is to say, the IPTV architecture should carry a myriad of services and technologies. In light of current telecom/TV status, the IPTV architecture can be set up on the convergence of the three networks to deliver comprehensive services and make Live TV, TV on Demand (TVOD), and Time-shifted TV services accessible on one platform. It also supports local and cross-regional user and service certification, provides EPG and smooth TV images and guarantees secured content as well.

      Delivering the IPTV service in China requires integrating the communication security of telecommunications networks, the content of broadcast and television networks, and the network features of Internet. Yet the IPTV is totally different from the following 3 points:

      (1) Traditional telecommunications feature person to person interactions while in IPTV we see a new pattern of person to machine communication from service initiation through termination.

      (2) The IPTV allowing subscribers to customize their individual TV programmes, view them regardless the time and location. It is possible to control the speed of the program (fast forward or backward) that is not a feature of the traditional TV where viewers only can accept what prepared for them.

      (3) IPTV has different business pattern and search technology from Internet services.

      To sum up, IPTV is a content-based new service endowed with multimedia features. The "newcomer" service of IPTV is now taking hard steps forward. Industry barriers, content shortage, defective delivery chain and immature business pattern are standing in its way. However, it磗 still driven forward by market demands of not only telecom operators, but also the content providers and consumers.

1 Technical Requirements of IPTV Services
The IPTV, as a brand-new service, features a much longer and more complex industrial chain than traditional service patterns. On the chain, the main nodes are the content providers, the service network carrier and the end user, in which the service network carrier is the main body of the service. The service network is made up of the IPTV service network and the service bearer network. The service bearer network can be the existing transmission access network that is carrying telecommunications or broadcast and television services. The service network carrier can then set up the IPTV service network over the telecommunications or broadcast and television infrastructure, collect programs from the content provider, and finally deliver applications and services to end users. The content provider is responsible for offering attractive content to pull the users in the network. This is critical as the IPTV is a content-based service and the end user is the revenue source on the chain that determines whether the IPTV service is capable of going further or not. The 3 factors on the chain pose different requirements on the IPTV service network and they as a whole determine the technical orientation of IPTV service.

      While the Internet services developed these years, conventional telecom services have been shrinking and it now seems the Average Revenue Per User (ARPU) for the fixed network can never straighten up again. Telecom operators have to turn to new services for fresh growth poles. Then it comes the IPTV service, by whose rosy prospect and market potential the telecom operators are attracted. Most telecommunications operators abroad have had IPTV deployed to provide Triple Play services that integrate voice, video and data to boost ARPU. Two fixed network operators in China are also conducting experimentation of IPTV services on their networks in a bid to work out optimum network architecture and business pattern.

      Content providers have to "market" their products in this developing market economy of China. The simple mode of content publishing seems just outdated and it often ends up in stickers. The IPTV is just such a new platform for content providers to showcase and revitalize their products. As an upstream node on the IPTV industrial chain, content providers are especially concerned with copyright protection issues and revenues that content resources can bring through specific business pattern.

      During the past few years, broadband users in China have multiplied in response to the advancement of broadband network infrastructure and network access technologies. While progresses are being made in the Internet, computer and multimedia technologies, more and more broadband users are expecting multimedia services to be delivered in addition to existing text and data transmission over IP network. Nowadays the IPTV emerges as the most needed solution to the broadband user磗 demand. End users of IPTV services are interested in whether the services are worth the cost or not. They expect more colorful content than traditional movie/TV programs, better feature and quality than cable TV, and easy use such as remote control. They would like to customize individual programs and enjoy it at any given time and place.

      Business exists where the customers are. As in the case of IPTV, its service network should involve network, computer and image technologies. To deliver IPTV services, issues of old business patterns, network integration, and security mechanisms have to be addressed first. Listed below are the technical requirements of IPTV services:

      (1) Quality of Service (QoS)
      The IPTV is a content-based real-time service that is expected to entertain the customers, which makes high QoS an essential piece in service delivering.

      (2) Source Codec
      The IPTV service network has to select high quality source codec and network transmission technologies to provide high quality images.

      (3) Service Performance
      The service should come with clear program guide and navigation functions, as well as great-information search and governance technology, content storage, and distribution technology.

      (4) Business Pattern
      Proper business pattern should be designed to optimize customer experience in an economical way.

      (5) Digital Security 
      To protect content providers? content resources, security management and copyright protection measures should be taken in the service system. Unified certification should be employed to suit customer磗 nomadic feature.

      (6) Network Quality
      The service bearer network and the access network should be able to deliver high-quality service, and the network resources should be knowable and controllable.

      Generally, the IPTV service requires technologies that comprise information security, QoS, business pattern, content provisioning, service governance, network capability, source codec, and customer roaming. Every technical requirement is implemented with the support of corresponding technologies. In constructing the IPTV service architecture, it磗 better to keep an eye on the future especially for those immature techniques adopted while supporting as many technical requirements as possible. The IPTV service network is to be designed as the new generation multimedia application platform that is open and secure and fully use the advantages of the current network and technology.

2 IPTV Service Architecture
The architecture of the content-based IPTV service should first allow for comprehensive services. It provides live TV, TV on Demand (TVOD), and time-shifted TV on one platform. The architecture is open and it supports local and cross-regional user and service certification. Next, it should have good service performance and security mechanisms and able to provide clear Electronic Program Guide (EPG) and smooth TV images. The IPTV architecture breaks into three parts: the service network layer, the bearer network layer, and the service terminal, as shown in Figure 1.

2.1 Structure and Function of the Service Network Layer
The service network layer implements the service control of IPTV and is a foundation to expand service applications. Figure 2 shows the structure of the service network layer, which comprises functionality of content operation, operation and maintenance, portal navigation, service management, media delivery, security management, and accounting and settlement respectively. Each functionality has several function sets.

      The content operation system is included in the IPTV architecture because of the business pattern of IPTV. They are direct sales mode, distribution mode, package purchase mode or QoS-based subscription mode. The TV program providers and operators are the main source for current IPTV contents. Most present IPTV trial networks are providing contents through direct sales mode. That is, the user registers for certification on the IPTV platform to set up connection with the content operators; the content operators will then provide programs to the user.

      The operation and maintenance system that also referred to as the management system of the service network is responsible in monitoring and governing the components of the IPTV structure. It is equipped with efficient QoS detection and fault detection tools to make sure of smooth rollout of IPTV services. The system is engaged in remote management of terminals, online version upgrade, and remote fault detection.

      The portal navigation system provides users with the interface for service access, live TV forecast, EPG and search of programs, movie/TV previews, and navigation/connection functions for other services.

      The service management system is core to the service network layer. It works in the following aspects:
      (1) User information management, including user accounts, service subscription, and user status.

      (2) User certification management, mainly in authenticating uses? licenses.
     

      (3) Program index management, that is, receiving the metadata, previews, contents, and price list provided by the content operators.

      (4) Charging management, that is, keeping track of service status (duration and traffic volume) and generating bills needed by the accounting system.

      (5) Service customization management, managing content source, multicast channel status, package plan services, and price policies.

      (6) Content provider/operator management, managing qualifications of content providers and operators, as well as the lifetime of content they provide.

      The media delivery system delivers IPTV programs including storing and distributing programs. Once a user selects a program, the system transfers it to the user terminal. It controls the dispatching process and the streaming service.

      The security management system is responsible for content security and broadcasting security. The former refers but not limited to copyright protection, cryptography, and conditional access measures. The latter is applied in the process of playing that illegal plug-ins and interceptions are screened off.

      The accounting and settlement system does account settlement with the service operators, content operators, and network operators. It receives charging information from the service management system and generates bills for end users.

2.2 Structure and Functions of the Bearer Network Layer
The bearer network layer of IPTV includes the transfer network and the access network. As IPTV integrates the services of telecom, TV and Internet, the telecommunications IP network and the TV Hybrid Fiber/Coaxial Cable (HFC) network are able to transfer IPTV services. Nevertheless, none of the two networks is good enough.

      However, the 3 basic services available in current IPTV system are posing different requirements on the networks.
      (1) The live TV service needs 
      end-to-end bandwidth for distribution. Live TV is quite the same as digital TV in user experience. They are homogeneous services. This requires that the live TV have the same or preferably better image quality than the old TV program and the capability to switch from channel to channel quickly.

      (2) TVOD is a service obtained from searching and it requires fast information exchange and multiple location across the network.

      (3) Time-shifted service is stored first and retrieved later, it features replay of old programs, and fast forwarding of programs that磗 being played. It requires capabilities of storage, channel identification, and network switchover.
The IP network and the HFC network are essentially different. The IP network features bi-directional communication and switching. It also an assembling network in using resource. It has large bandwidth at the core network. The band becomes smaller toward the network edge and leaves very little at the user access point. This is reasonable for traditional telecommunications switched services but is not suitable for live TV of IPTV. First, the access bandwidth of IP network doesn磘 support live TV ? users who cannot accept the slow response to channel switching would give up the service. Second, the current IP network is not able to support global multicast unless additional investment is put in to reform the current network devices. The IP network would make an optimum solution for TVOD services instead. This is because its bi-directional features support the search, selection, and control operations.

      The HFC network, a tree-structure distribution network, is a typical unidirectional transmission network and its bandwidth doesn磘 change. This feature is good for live TV services. The signal bandwidth of TV programs keeps the same all the way from the TV station to the user terminal. With the large bandwidth of the user terminal, TV signals can encapsulate plenty of information with the coding and transmission methods that have low compression rate. All channel information can be transmitted to TV set along with TV signals. Channel switching can be done locally and quickly. The large bandwidth of user terminals ensures a high image quality. However, as the HFC network allows one-way transmission only, TVOD services would be hard to implement unless additional investment is put in to make the transmission bi-directional. Moreover, a bi-directional HFC network should face a new problem of reverse link noise.

      As the IP network and the HFC network support totally different services, the IPTV bearer network need make use of their respective advantages to integrate the bi-directional interaction and the end-to-end bandwidth capabilities on a layered basis.

      At the service network layer, 3 basic services use the unified management and service platform but different networks of bearer access. Those services are the IP network for TVOD services and time-shifted services, the HFC network for media distribution of live TV services and the IP network for switching, certification and authentication of live TV services. The IP networks and HFC networks transfer information to user terminals. Set-top box integrates services as a final step in the service flow. Figure 3 shows the live TV service flow on the IP network in conjunction with the HFC network.

      The HFC network can provide live TV channels but then it磗 difficult to differentiate it for users. As the HFC network has broadcast-distribution capabilities, it磗 unable to provide multicast that is similar to the IP multicast service. Yet, this defect can be offset through properly planned service structure together with user磗 service management authentication, TV program navigation, and channel encryption technologies. Free channels are open to all users and need no authentication. Pay channels are open to authenticated users only. The paid program is provided to users in the following process. The user is provided with free EPG, introductions and previews. The user uses the EPG to select pay channels just as he does with the free channels, while subscription information is shown to the user. The channel is made accessible to the user for one day after subscription. The user has to subscribe to the channel over again if he still wants it for another day. Once a user subscribes to a pay channel, the security management system in the IPTV network sends a key to the user for accessing the channel on that day. The user cannot view the program even if he can receive signals from the pay channel, unless he gets the key. The chargeable live TV has its key changed everyday by the IPTV media delivery system of IPTV system. At a fixed time everyday, the media delivery system gets the key for the day from the security management system and the key works for the program on that very day. The service management system handles user subscription and the accounting system handles the bills. In this process, the HFC network is responsible for the media delivery while the IP network for the EPG preview, channel selection, subscription, and key acquisition.

      As to TVOD services, it磗 uneconomical to send media streaming on HFC networks. For a single demand needs one streaming as one channel, HFC networks can磘 afford that many channels. Therefore, TVOD services should be realized in IP networks.

2.3 Service Terminals
The integration of networks and services is finally showed in terminals, which need adequately embody the characteristics of IPTV services. The IPTV service terminals may be personal PC, set top box + TV set or mobile phone. Set top box +TV set is expected to take the leading position. The set top box is kernel to the terminal as it manages information of the user and terminal such as account name, account number, and service certificate which can be stored in an intelligent card. Besides, some control functions, the set top box can also encode/decode video/audio signals and output audio/video information. Better still, it will be able to support dual modes, that is, IP and DVB protocols, and will be improved with the development of IPTV services.

3 Conclusion
Delivering IPTV services in China entails complex industrial relations. Problems in social values, copyright protection and network integration baffle the IPTV deployment. The ultimate objective of IPTV is to realize the integration of 3 networks to be a new generation telecom service[1-2].

References
[1] ITU-T F.700 Framework recommendation for multimedia services[S], 2000.
[2] ITU-T F.741 Service description and requirements for audiovisual on demand services[S]. 2005.

Manuscript received: 2006-03-11

Author Introduce:

  Jin Wei  graduated from Beijing University of Posts and Telecommunications and is now a senior engineer with the Institute of Communications Standards Research, CATR, MII. She has long years of research experience in the field of data communication technology. Her recent study includes IP and multimedia services. She is the winner of the first prize of science from Ministry of Posts and Telecommunications and the second prize for scientific progress of Beijing. She has published over 10 technological papers.