Optical Distribution Network (ODN) is an FTTH fiber optic network based on PON devices. It is the part of the optical access network that provides optical transmission from the optical line terminal (OLT) to the optical network unit (ONU) and in the opposite direction. It is used to allocate optical signal power and provide a physical channel for optical signal transmission.
Sometimes ODN can also be understood as Optical Distribution Node, which is an optical distribution node. Refers to the fiber optic nodes of analog fibers in HFC (Hybrid Fiber Coax), used to connect analog fibers.
The construction cost of ODN network is relatively high, up to 50% to 70% of the total investment, which is the focus of FTTx investment. At the same time, it is also a difficult point in FTTx management. Compared to the simple P2P structure of copper wire, ODN mostly adopts P2MP topology, with many connecting nodes in the network and complex network management. Fiber optic is more sensitive than copper wire and is more susceptible to damage. Therefore, efficient construction, operation, and maintenance of ODN are crucial, requiring an intelligent and accurate management solution to ensure that the ODN network is fully utilized and effectively protect long-term investments.
Just like when we see barcodes on food and other products in supermarkets, electronic labels can be added to the fiber optic head to effectively manage the fiber optic, which we call EODN; At present, this technology has become the focus of discussion and attention among major operators and standard organizations such as ITU-T.
The construction of ODN needs to meet the needs of growth and smooth evolution of next-generation PON technology, which is the foundation for the long-term development of telecommunications in the future.
The leader of ODN construction has surpassed the main equipment and terminals, and the construction period is long, which has a significant impact on the business and requires forward-looking comprehensive consideration
Australia, Singapore and other countries have established national broadband projects to be responsible for the construction of fiber optic infrastructure networks, and ODN construction has become a national strategy.
ODN can be divided into four parts from the office end to the user end: feeder cable subsystem, distribution cable subsystem, drop cable subsystem, and fiber optic terminal subsystem.
The feeder section from the ODF (optic distribution frame) in the data center to the fiber optic distribution point serves as the backbone cable, long-distance coverage; The distribution section from the fiber optic cable distribution point to the user access point is used to allocate fiber optic cables to nearby user areas along the feeder cable route; The drop section from the user access point to the terminal enables fiber optic access to the home.
From the perspective of network structure, the optical distribution network consists of feeder fibers, optical splitters, and drop cable, which are respectively composed of different passive optical devices. The main passive optical devices are:
Fiber optic cables: urban fiber optic cables, indoor distribution fiber optic cables,ftth drop cables, etc
Fiber optic distribution equipment: ODF, MODF, OCC, splice closure, splitter box, etc
Fiber optic connectors: movable connectors, mechanical splicer, fiber optic field fast connectors, etc
There are mainly 3 types of solutions for ODN splitting, each have their own advantages and disadvantages, and can be selected based on user distribution and number distribution; The on-demand/on-chip construction mode and various spectral modes can be combined arbitrarily according to the specific user distribution characteristics.
[Solution]: Concentrated splitter, 1:32 or 1:64 ABS module splitter installed on large capacity ODF/FDT. The number of splitters can be increased according to the expansion needs, and FAT can be set up in the corridor to cover multiple floors. FAT can choose direct fusion or wiring products according to the characteristics of the network.
[Solution]: Primary splitter 1:32 or 1:64 box splitter installed in small ODF/FDT or FAT. The number of splitters can be increased according to the expansion needs of the available FAT in the corridor, covering users on multiple floors.
[Solution]: Secondary splitting, combined into 32 or 64, with a ratio of 1:8+1:8 or 1:16+1:4. The primary splitting is in the community data center/FDT, while the secondary splitting is in the weak current room of the building or the FAT in the hallway. By adjusting the splitting ratio, the ODN network remains unchanged while meeting the increase in user penetration rate.
Through the analysis of PON’s technical implementation, configuration operation, and maintenance management, it is found that the main difficulties faced by PON in fault handling and network maintenance are the presence of a large number of optical fibers and passive components in the network, which precisely become blind spots in the monitoring and fault handling process of PON network management systems.
Since 2008, with the development of a large number of FTTx construction and renovation projects in the current network and the large-scale deployment of services, the workload of network maintenance has significantly increased. The faults of FTTx PON are mainly distributed in the backbone fiber optic cable section and user access section, as shown in Table 1. According to statistics, the number of ODN faults such as backbone fiber optic cable segment faults and user access segment faults is on the rise. It is urgent to adopt fault detection and diagnosis technologies to effectively monitor ODN, in order to reduce the difficulty of network maintenance personnel in fault handling and improve network maintenance efficiency.
The main issues with the scale deployment of FTTH ODN are as follows:
How can planning and design capabilities support large-scale deployment? | How to enter households with FTTH fiber optics; ODN site acquisition; How to deploy ODN in different scenarios. |
ODN product selection is difficult to evaluate, how to ensure product quality? | High requirements for infrastructure and product lifecycle; There are significant differences in usage environments and no system standards; Multiple product types, high reliability requirements, and difficult selection and testing operations. |
Difficulty in fiber access home, how to perform high efficiency indoor wiring? | Insufficient space for wiring ducts in old building shafts; The wiring resources inside the building are complex, and there are significant differences among different buildings; How to achieve a one-time entry into the station due to difficulties in coordination and low efficiency when entering the building or household |
How to efficiently manage massive amounts of optical fibers? | Passive network, unable to automatically manage; Static resource management, fully manual maintenance, high error rate, frequent rework of engineering maintenance |
In response to the unprecedented difficulties faced by PON in actual maintenance and line fault handling, with the increasing scale and number of users worldwide, operators and mainstream equipment manufacturers around the world are actively conducting research to achieve monitoring and fault diagnosis of PON, especially ODN. Currently, there are three main technologies applied to ODN monitoring and fault diagnosis:
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