China's Highways of Light

Notwithstanding the economic and political challenges facing China, investment in the country's telecommunications infrastructure is robust. Optical networking gear is already a key feature of this investment, and the country is poised to expand its optical platform with new technology.

By: Sando Anoff, Lucent Technologies

Contents
•China's optical network today
•Historical development
•Evolving to DWDM
•Network evolution

With a GNP growth rate near 10% and a population of more than 1.2 billion, China has embarked on what is perhaps the most ambitious telecommunications build-up in history. By the year 2020, the country plans to have increased its telephone density from 100 million phone lines (or nine telephone lines per 100 people) to 1,000 million lines—a 10-fold increase.

Demand for communications services in China is rising not only for voice, but also for data services, such as the Internet. Voice traffic still dominates network traffic by a wide margin, but according to China Internet Network Information Center (CNNIC), the number of Internet subscribers in China increased from some 620,000 in October 1997 to nearly 2.1 million in December 1998. In video networks, China's cable TV operators are installing some of the world's most modern optical-video transmission systems in a market that is increasing by almost 10% annually.

Growth in demand for communications services in China has led to an enormous growth in network capacity requirements. China's total investment in post and telecom fixed assets increased from less than $1 billion in 1990 to approximately 15 billion in 1997, according to IGI. This financial commitment indicates that China regards a modern and reliable telecommunications infrastructure as critical to the country's economic and technological growth.

China's optical network today
At the core of China's information superhighway is a rapidly expanding optical network consisting of the latest synchronous digital hierarchy (SDH) technologies and, more recently, dense wavelength division multiplexing (DWDM) equipment. SDH, the international optical transmission standard, was first installed in China's networks in 1994.

Since 1994, most of China's optical networks have been converted to SDH. Deployment of the technology in China comprises the most extensive SDH networks in the world, according to Insight Research Corp. Approximately 2 million km of single-mode fiber had been installed by mid-1997. This number is expected to reach 3.4 million by 2000.

Historical development
Network planners in China were quick to recognize the benefits of SDH and embrace its flexibility, protection, and centralized network management advantages compared with the plesiochronous digital hierarchy (PDH) optical transmission standard that existed before it.

Once international trade restrictions were lifted, rural and urban SDH networks started popping up all over China, as did provincial backbone networks and a central, high-capacity national backbone network. Lucent Technologies installed the first 2.5 Gb/s high-capacity backbone between Hong Kong and the Guangzhou in 1994. The result of the development is a unified, centrally-managed infrastructure that allows a considerable amount of regional autonomy.

It was not only the Ministry of Posts and Telecommunications (MPT) that used SDH. The Ministry of Railways (MOR), for instance, set up its own SDH network—a single layer network for communications transport along the railway lines. Transmission capacities reach beyond 2.5 Gb/s.

China's optical networks now use the latest technologies. Most of the China's optical transmission networks are SDH-based and continue to expand, using the latest add/drop multiplexers and cross-connects. Sophisticated protection mechanisms such as multiplex section shared protection ring (MS-SPRing) were introduced at a very early stage, and China Telecom now has one of the most advanced optical network management systems in existence.

Most of the cities and regional networks in China and a large percentage of the national backbone use a Lucent management cross-domain management system that manages both the cross-connects and multiplexers. The platform allows end-to-end fault management, path management, and provisioning—all the way down to the 2-Mb/s level. The system also allows geographic partitioning of the management system—a desirable feature in light of the regional management required in China.

China's cable TV operators also are advancing their infrastructures with SDH. Hubei Cable TV Network has announced what will be the world's largest digital video network using Lucent's fiber-based digital video system. The MPEG-II codec system supports simultaneous real-time compression and multiplexing of multiple program services into a single STM-1 or 34Mb/s stream.

Evolving to DWDM
With the introduction of DWDM, China has already taken the next step in the evolution of optical networks. China is one of the first countries outside the United States to launch massive DWDM deployment. The first commercial DWDM system in China was installed between Xi'An and Wuhan, covering a distance of about 1,400 km. Lucent has signed DWDM contracts in China for networks covering nearly 12,000 km.

DWDM first will be used in the backbone networks, multiplying capacity up to 16-fold (in the near future, up to 80-fold), but DWDM is also expected to appear in China's regional and metropolitan networks. The capacities provided by these systems will enable cost-effective multiservice networks.

As high-speed multimedia services begin to appear on China's networks, ATM switches—widely deployed in the region—will likely route this kind of traffic. Where the ATM switches have a variety of interfaces (34Mb/s and above), it will be possible to connect them directly to a multi-wavelength metropolitan DWDM system, resulting in considerable cost savings for China's service providers. DWDM networks will also accommodate China's IP traffic growth.

Network evolution
Optical networks will continue to evolve at an incredible pace in China. Its basic 8x8 national backbone grid, completed in 1998, will continue to expand. The provincial and city networks are also growing, as are wireless networks and increased applications in the access network.

Within the SDH networks, new equipment will integrate several SDH multiplexing layers (STM-1, STM-4, and STM-16) into one system. The digital cross-connects will handle as many as 1 million simultaneous telephone conversations each (one million phone calls is equivalent to the capacity of 512 STM-1s, with non-blocking switching at the 2-Mb/s level). In cable TV networks, combining SDH with ATM for video transmission will provide flexibility, digital quality, high compression ratios, statistical multiplexing, and evolution to HDTV.

As China's transmission networks continue to evolve, network management challenges will require more advanced systems. Apart from the need to jointly manage DWDM and SDH equipment as efficiently as possible, the increasing size of the overall network, the higher capacity of the individual network elements, and the convergence of such protocols as IP, SDH, and ATM pose challenges.

As DWDM evolves into a technology that will profoundly change networks of the future, it will play a pivotal role in shaping China's rapidly changing telecommunications infrastructure. DWDM will be based on such additional functions as add/drop and cross connects, which will be realized in the optical plane. Present networks will migrate gracefully to meet the demands of the future; the interworking of SDH technology with DWDM will provide highly reliable and manageable networks in China. IP and ATM will continue to be a part of the network, but the reliable, high-speed optical transport core will be SDH and DWDM based, at least in the near and medium term.

While the optical network in China faces many challenges, fueled by growing traffic and the demand for an increasing variety of services, emerging technologies will enable China's service providers to serve their customers with the most advanced voice, data, and video applications.

About the author…
Sando Anoff is a Technical Marketing Manger for Lucent Technologies' Optical Networking Group, Holmdel, NJ.