China Unicom´s Experience in Network Evolution towards NGN

The development of Next Generation Network (NGN) is a process of gradual evolution, not a sudden change or a total revolution. For operators, the coordinated development of network and services is a key point in transiting their existing networks towards NGN, which can ensure a timely and sufficient investment return and keep the network evolution in a stable and healthy way. The construction and operation of China Unicom´s IP-based network for data and fixed services has made a good example of this evolution process.

1 Constructing Network Architecture Aiming

   at Telecom-Level Integrated Services
From the very beginning, China Unicom has abandoned the idea of pure IP networking. In stead, they worked out a system architecture with regards to service applications and market demands. This applied network model has well reflected their objective of "building up a network with perfect overall performance". In the model, the routing exchange layer and the service layer were designed with particular attention.

  Under the circumstance that integration of different services were not well solved at that time, China Unicom designed a new network solution to realize the service integration on the bearer layer, which is also the theoretical basis for establishing a unified data network platform. Such a platform can reduce the costs of network construction, operation and maintenance, and improve the utilization of network resources and speed up the deployment of new services. In a word, China Unicom´s main objective was to provide telecom-level integrated services. Other demands were supposed to be satisfied under the main target.

  In the new system architecture, the ATM+IP layer is very important, which functions as a unified data network platform. It can make up for the insecurity of IP technology, unguaranteed QoS and weak management. It can also provide flexible bandwidth control, reduce costs of network construction and maintenance and quickly setup various service networks. Furthermore, it can easily provide unified network management and customized services and guaranteed QoS.

  In the new system, the Multiprotocol Label Switching (MPLS) technology is used to effectively integrate ATM and IP. As a matured technology, the QoS mechanism of low-layer ATM/FR is used to ensure the network service quality. The combined ATM+IP layer supports virtual private networks for different services. In respect of service bearing networks, the IP-phone service, public video exchange and other networks were constructed based on IP technologies.

2 Selecting Service Network System on  Principle

   of Quick Service Deployment
As to packet service technologies, in recent years, a series of signaling control protocols such as H.323, SIP and H.248/MGCP have been formulated. In face of various technologies, China Unicom considered that it is impossible to begin a network construction after its relevant key technologies become fully matured or rashly construct a new network regardless of the maturity of existing network architecture. It needs correct judgment, and the fundamental principle of setting up a new network is that the network should be able to offer relatively perfect services in a short period of time. Besides that, operator´s actual situation is another important factor. Different from some other operators, at that time China Unicom didn´t have a large scale Public Switched Telephone Network (PSTN), so it should find a new way to construct the IP-based data and fixed services network and provide differentiated services.

  China Unicom´s integrated service network consists of the bearer layer, medium processing layer, signaling control layer and operational supporting layer from bottom to top. The bearer layer makes use of China Unicom´s unified data network platform and the metropolitan area bearer network to provide a QoS guaranteed service transmission platform. The bearer network can meet different requirements of different services for the quality of service.

  China Unicom´s first service network was a VoIP network, which adopted
ITU-T´s H.323 protocols. In 1999, VoIP was a relatively matured packet service network technology. But there also existed many problems with the technology, especially in the respect of establishing a large network. China Unicom made joint efforts with equipment manufactures and put forward a multi-level gatekeeper networking solution, which successfully solved the "large network" problem.

3 Building up Multi-Level  Metropolitan Area Networks

   (MAN) and Access Networks
China Unicom aimed at building up MANs and access networks to support integrated services. But these networks faced the same problems in QoS, security and management as the backbone network did. Especially, the access network should realize the user management and service calling management functions.

  In practice, China Unicom divided a MAN into a bearer network and an integrated service network, and set up networks of different sizes at different cities. For super metropolises, the MAN consists of the backbone Point-of-Presence (POP) layer, convergence POP layer and POP access points; for big cities, the MAN consists of the backbone POP layer and POP access points; for middle cities, the MAN consists of the backbone POP points and POP access points. For access networks, it was emphasized that all the services were accessible via one line, i.e. the Unione service.

  Recently, China Unicom urged equipment manufactures, software developers and system integration providers to develop special equipment and software to meet the specific demands of China Unicom´s metropolitan area integrated service network. Through the construction of such a network, China Unicom aims at providing end users with diversified backbone services along with local voice and video exchange services.

4 Improving Network Performance to Provide 

   Perfect Services
Though China Unicom´s newly constructed IP-based data and fixed services network was well designed and strictly tested, there still exist some problems, such as the inadaptability of some technologies to the large network, unstableness of some new functions, failure to support some service flow and incomplete service networks, and so on. However, it is certain that, the network will develop towards packet network; the service layer should adopt the IP-based system, the bearer layer should adopt QoS-guaranteed technologies and the packet services will be gradually deployed on the end networks.

  The problem associated with the ATM-based MPLS at Layer 3 for a large network has not been thoroughly solved in a worldwide scope. With great efforts, China Unicom eventually solved the problem by modifying software programs, contributing to a stable operation and improved performance of the exchange at Lay 3. In addition, problems associated with faxing, supplementary services and some intelligent services were also successively solved with joint efforts of China Unicom and some equipment manufacturers.

  In a word, the construction of China Unicom´s IP-based data and fixed services network is a process of continuous innovation. Correct guidelines made by relevant departments of the government, practical networking schemes for carrier-level services and deep analysis on diversified technologies are the key factors that have assured the success of the project.

Manuscript received: 2004-02-23