Current Status and Development Trend of High Quality Optical Cable Transmission

The high-capacity fiber optic cable trunk has become the "information national highway" of China. Among the eight vertical and eight horizontal fiber optic cables of China Telecom, Beijing Long Distance Bureau plays a pivotal role as the capital bureau and the leading business bureau. The establishment of a high-capacity, high-quality optical cable transmission network has laid the foundation for the development of digital, integrated, broadband, intelligent and personalized communication services. In the face of rapid changes, using and managing the advanced optical cable transmission network well is an important guarantee for the development of high level networks such as business networks, support networks, and management networks, etc. We would like to introduce the status and development of the transmission network of Beijing Long Distance Telephone Bureau. Overview of the optical cable transmission network Since the opening of the overhead optical cable trunk in October 1993, there are seven optical cable trunks in Beijing, covering most of China, with the longest trunk of more than 3,000 kilometers and the shortest of 1,700 kilometers, which are Beijing-Shenzhen-Ha, Beijing-Qiha, Beijing-Shanghai, Beijing-Han-Guang, Beijing-Kuang, Beijing-Taizhou-West, and Beijing-Hu-Yinlan. At present, the network is running PDH, SDH equipment. With the increasing maturity of DWDM technology, the Bureau has six optical cable trunk lines with DWDM equipment, using 4×2.5Gbit/s and 8×2.5Gbit/s systems. With the completion and use of these optical cable trunks, the capacity of the Bureau's optical cable transmission has reached 1.3 million channels. The optical cable transmission network consists of four levels of network, mainly using SDH equipment, as shown in Figure 1. The SDH development of the inter-provincial trunk network adopts the priority of line system, combined with network expansion, and then SDXC is installed at the nodes to provide a wide range of flexible VC connections. The network structure is a lattice network (mesh network) with a small number of linear networks. Currently, most of the nodes are TM, and a few routes use ADM, such as a 622Mbit/s line on the Beijing-Kowloon Expressway, which is being built in some provinces and cities. The provincial trunk network uses mesh network in a few provinces with large business volume, many nodes and routes, while most provinces use ring network due to few nodes and routes. The trunk network is a ring network with a small number of lines in general cities, and a ring network with SDXC in large cities. Establishing optical cable relay between long-distance telecommunication hubs With the large-scale construction and transformation of long-haul networks and the continuous development of new services, the original two long-haul hub bureaus in Beijing can no longer meet the requirements of growing communication services and communication security. For the construction of long distance hubs, Beijing Telecom has proposed a plan with the Beijing Long Distance Building as the center and four communication bureaus such as Wangjing Bureau as the support point, distributing the fiber optic cable trunks concentrated in the Long Distance Building to four bureau sites. At the same time, domestic long-distance switches will be installed at the new bureaus. In order to solve the problems of long-distance transfer, long-distance exchange service relay, international exchange service relay and service protection in each hub building, the International Long-distance Second Hub Bureau will expand the capacity of the original long-distance inter-hub optical cable network and adopt a 2.5Gbit/s two-fiber two-way multiplexed segment protection ring. Optical cable trunk network management The optical cable trunk network management is an important guarantee for the normal operation of the national optical cable trunk. The three sub-network management centers of the national PDH centralized network management are located in Beijing Longtalk Building. The Bureau has explored the scientific management of large networks, and has formulated "sub-network management and maintenance rules" in terms of network management contents and maintenance methods, which plays an important role in regulating the management of the entire network. The network management of our 7 optical cable trunk lines is managed in the direction of trunk lines, and each trunk line has its own network management system for PDH, SDH and DWDM equipment, so there are more than 20 monitoring systems for management respectively. Beijing Bureau can monitor and test the whole equipment from the monitoring equipment, and use the performance management, fault management and security management of the monitoring system for daily maintenance and management. The Beijing Bureau, as the leading national business bureau, can make reasonable network adjustment and work plan arrangement through the network management system, especially it can reflect the operation status of all trunk routes in real time; it can apply the network management to direct each station along the route to carry out daily maintenance and emergency circuit adjustment, so that the obstacle time can be compressed to the shortest. The Beijing Bureau, as the capital bureau, often undertakes various important communication tasks, and each time a key communication task comes, the key circuit is set up on the network management platform to monitor the operation status in real time. Development and Outlook In the future, the fiber optic cable trunk network will be organized in such a way that the two transmission levels of the primary trunk network and secondary trunk network in Figure 1 will be combined into one level, and the relay network and subscriber network will be combined into one level to realize unified planning and design, unified investment and construction, unified scheduling and management, unified protection and recovery, and unified maintenance and management, which will eventually constitute a non-hierarchical and integrated long-distance communication trunk network. Due to the application of WDM, there will be a breakthrough in transmission network capacity, with a transmission capacity of 320 Gbit/s (2×16×10 Gbit/s) and 100 Gbit/s (40×2.5 Gbit/s). However, only WDM links without eliminating node bottlenecks are unable to realize network broadbanding. Therefore, the introduction of optical transmission network characterized by optical split multiplexer and optical cross-connector node is the ultimate solution for network broadbanding. For the safety and reliability of network operation, with the expansion and transformation, the protection of long-distance optical cable trunks should be protected by 1+1 multiplexing section and MS-SPRING self-healing ring according to the status of investment and local site. In order to improve the network management capability, realize the centralized maintenance and centralized monitoring of multiple long-distance hub bureaus, and establish a technical support system with the technical backbone of the transmission center as the core, Beijing Long-distance Telephone Bureau will carry out the development of the "Integrated Management System for Long-distance Transmission Maintenance Service", the system structure of which is shown in Figure 2. The completion of the system will enable the management of long-distance transmission maintenance work to a new level, providing strong technical support for the safe and efficient operation of the trunk transmission network. At the same time, it will also drive the improvement of the maintenance management level of the bureaus along the route and truly realize the status of the leading business bureau.