On Construction of R99/R4 Network

The 3G license has become a hot topic as 3G technology advances and matures. The most important issue for mobile network operators is how to effectively construct and operate networks to reduce investment and achieve maximum return.

1 Operators’ Considerations on  Network Construction

Existing mobile network operators have abundant mobile network resources, network operation experiences, good marketing and maintenance teams and infrastructures of the mobile network and the Internet. They focus on how to protect existing GSM/GPRS network resources as far as possible, especially to protect the gradually-added investments later on for network upgrade. In other words, these investments should ensure the existing networks can evolve to the future All-IP networks smoothly and successfully. At the same time, when the WCDMA network is introduced, the influence on the operation of existing GSM/GPRS networks, the end users and the complexity of network upgrade should be minimal.

Future mobile operators will have powerful PSTN network resources, ample data network resources, and a good subscriber base. They are more concerned about how to follow the development  trend  and  construct  a  cover-all and brand new network that can be unified into future network architecture, how to make full use of existing resources and reduce investment cost at the initial stage of network construction, and how to control the investment in wireless access products that account for approximately 80% of the total investment.

It is obvious that the key to the smooth transition from the present to the future is to make maximum use of existing resources without adding new non-effective investment. Joint efforts of manufacturers and operators are needed to a great extent to achieve this goal.

2 Technical and Market Analysis of R99/R4

2.1 R99

Backward compatibility of existing products is fully considered in R99. In this system the circuit switched domain and packet-switched domain independently perform transport and control, and they are respectively connected to PSTN and the public data network. Therefore the realizability of the technology in existing networks is thoroughly guaranteed. And from the perspective of market incubation, R99 is widely supported by various manufacturers and a multi-vendor environment has been created. The interworking between systems and between network element equipment has tended to reach the ideal.

At the same time it should be noticed that R99 is a transitional architecture in the process of the network development. For the sake of backward compatibility and rapid and convenient network construction, some inherent defects have been created. The problems related to the follow-up development of networks have never been thoroughly resolved. Consequently it has caused new waste investment.

For example, core networks still use time division multiplexing （TDM） technology and the utilization rate of transmission resources is low. The parallel architectures of the packet- switched domain and circuit switched domain makes the network management system complicated and the maintenance cost high. The point-by-point upgrade is badly needed for the implementation of new services and its procedure is also complicated.

Currently each manufacturer is endeavoring to implement smooth upgrade from R99 product series to R4 product series and reduce further investment during this period of time in order to simplify the transitional process.

2.2 R4

The most significant difference between R4 and R99 is that the R4 core network reflects the concept of NGN architecture. The circuit switched domain of R4 evolves from TDM central node switching to typical distributed architecture of packet voice and its service logic is separated from its lower-layer bearer. R4’s layered network architecture increases the flexibility of service extension, and the flattened network architecture also reduces the bottleneck of the transmission process and thoroughly clears away obstacles in the process of follow-up network evolution. It is very likely that the full-blown applications of R4 will bring a forward leap to the operation of existing networks.

It can be considered that R4 technology is fully developed at present. But its commercial pilot operation is carried out on a relatively small scale. Operators and manufacturers still need a period of time to accumulate experience in the new network operation, and address new problems that are likely to arise, such as the security problem of the IP network and QoS problems. In addition, a longer time is required to complete the interworking between various manufacturers’ network element equipment and discover ways to use this equipment to optimize network architecture.

3 Discussion on Schemes of  WCDMA Network Construction

How to construct the WCDMA network, especially the core network of 3G is a topic that both equipment manufacturers and operators are actively discussing. The schemes can be summarized as follows:

(1)Use R4 based on IP bearer.

(2)Use R4 based on TDM bearer.

(3)Use R99.

R99 can be directly developed to R5 in the future. And with the development of network construction, the interactive multimedia server (IMS) will gradually replace the TDM circuit switched domain.

From the perspective of technology, the IP-based R4 technology fully reflects the All-IP network-oriented development trend and its own advantages of the network architecture. However, since the current IP network itself is not mature enough, problems such as network security, QoS and limited IP address resource hinder the large-scale commercial application of R4 technology in the near future.

However, ample domestic TDM resources meet the needs for full use of the existing equipment and reduction of mass investment during the initial stage of network construction, and also avoid the insecurity of the IP network. Thus, the scheme of R4 based on TDM bearer is incubated. It should be admitted that though the scheme of R4 based on TDM bearer itself inherits TDM interfaces of R99 in the wireless access side, its core network still employs the mobile switching center (MSC) server and media gateway (MGW) architecture. Therefore the WCDMA network still cannot avoid the risk that an IP network has. At the same time, compared with the R99 network, currently the R4 network doesn’t have obvious advantages in providing fixed network services though its service ability is enhanced to a certain extent.

On the other hand, from the point of view of the development of fixed network voice services, Softswitch as the core technology of NGN is being successfully applied currently. Its advantages in service and other aspects will be gradually presented as the network develops. But it will not influence the long time presence of the PSTN network. As the Softswitch network is fully developed, the existing PSTN can be gradually replaced by Softswitch or degraded to access layer. It can be used as a reference in the construction of a mobile network. It is obvious that the circuit-switched domain using TDM can also exist for a long time and will be slowly replaced as the multimedia domain IMS of R5 gradually develops and matures.

Based on the analysis of the current network status in mainland China, ZTE Corporation makes some suggestions:

In the next 1-2 years, the matured R99 or TDM R4 technology will be employed and attention should be concentrated on network stability and reliability as well as network operability. As the IP network develops and matures, the evolution to R5 can take priority. The gradual evolution to ATM/IP R4 is not recommended. During the actual application, the TDM circuit switched domain of R99/TDM R4 will coexist with R5 for a long period of time and will be gradually replaced by R5 IMS. Consequently a real All-IP network architecture will be implemented.

4 ZTE´s Achievements

ZTE has powerful R&D strength and sophisticated technological experience in the mobile communications area. Since 1998, ZTE has been following the trends and doing research on WCDMA. Currently ZTE has developed the whole system of R99 and R4, and provided solutions with its own characteristics.

ZTE Communication has currently launched WCDMA product series (ZXWN). ZXWN was developed on the basis of the core technologies of R4. Equipment in the circuit-switched domain can provide various networking modes such as ATM/IP/TDM R4 and support the open H.248 protocol. It can also provide TDM interface on user’s request and be forward compatible with R99 equipment. The design and development of multimedia domain IMS of R5 are completed on the R4 platform. ZXWN can be smoothly upgraded to work on All-IP networks.

The circuit-switched domain and packet-switched domain of the whole core network equipment of ZXWN have been developed on the same platform. This contributes to the reduction of platforms needed for operators to construct networks and at the same time improves the system stability and reliability. MSC Server and MGW are also based on the exactly same hardware platform and can implement the interchange at the single board level, which may significantly save maintenance cost at the initial stage of network construction. The system is highly integrated and its circuit-switched domain can serve 2 million subscribers with 4 machine frames. It supports a number of key technologies, such as tandem-free operation (TFO), transcoder free operation (TrFO) and MSC server dualhoming.

In addition, ZTE has given much thought to the development of the whole network for operators:

(1)In the field of fixed NGN, at the initial stage of the system development, ZTE considered the convergence and development of mobile NGN and fixed NGN. Now ZTE’s Softswitch product has become the No.1 brand on the Chinese market and is the only Softswitch equipment used by all telecom operators in China. It has also been put into use in Romania and other countries. ZTE is on the same level as other world famous companies in the study of Softswitch technology.

(2)Provide convergence schemes of WLAN and WCDMA. They can complement each other and provide integrated user authentication and accounting management.

(3)Provide access solutions for the existing personal handy-phone system (PHS) to protect operator’s existing investment.

It is certain that ZTE will make more contributions to the Chinese and world communication industry with advanced technologies and high-quality products and services.