Contributed Article
The optical distribution network (ODN) is a point-to-multipoint passive optical network (PON), as shown in FIG. 2-1. The ODN is an optical transmission channel from an optical line terminal (OLT) in a central office (CO) to multiple optical network units (ONUs) on the user side.
In traditional ODN construction, the feeder optical cables, distribution optical cables, and drop cables are stripped or terminated onsite for fiber connection. In both OSP and ISP scenarios, cable distribution boxes need to be opened before optical cable installation and connection.
It is difficult to monitor the traditional ODN resources in real time because the ODN is passive. Currently, the traditional ODN resources are managed mainly by means of manual onsite recording with paper labels. Therefore, problems such as difficult fault locating and delayed update of maintenance information exist in the data entry and resource maintenance phases, causing heavy workloads and low efficiency. Even faults and errors caused by data information deviation may occur. As the scale of the broadband access network increases, the traditional ODNs face a series of challenges in applications.
In the traditional ODN, the connection status of optical ports in the cable distribution box is usually labeled on patch cords and recorded in a chart attached to the box. The installation and maintenance personnel manually record the connection status on site and enter the information into the system afterwards. After long-term O&M, the paper labels may fall off or severely fade, causing disordered port scheduling and failing to sort out the connections with the patch cords. According to survey statistics, the accuracy of optical port information manually recorded by some carriers outside China is lower than 70%.
In addition, because the optical ports of the conventional ODN distribution box are not associated with the ONUs/ONTs of users, after the users apply for network exit, information indicating release of the optical ports cannot be fed back to the resource management system in a timely manner. As a result, the cables are still connected but the user devices have been removed. The resource silence rate of some carriers outside China reaches up to 10% to 20%, wasting the initial construction investment. Even some feeder and distribution optical cables also need to be reconstructed after resource silence, reducing the efficiency of the investment in the optical network construction.
Inaccurate ODN connection information has always been a major challenge for carriers. The traditional O&M depends on manual operations and has many problems. Therefore, strict processes and specifications are required to improve the resource management accuracy.
How to resolve the bottleneck of the traditional ODNs will be the focus of research on digital and intelligent ODNs. Therefore, to address the challenges faced by the traditional ODN construction and health management, digital and intelligent management is required for the next-generation ODNs.
As the fiber infrastructure, the ODN is the most complex and costly part of fiber to the home (FTTH) construction. How to reduce the construction and O&M difficulties has been a continuous research topic in the industry. Based on the industry consensus, three generations are defined for different evolution phases of the digital and intelligent ODN solution, as shown in the following figure.
A digital and intelligent ODN system connects the OLT and ONUs through digital and intelligent ODN hardware, and connects to the carriers’ operation support system (OSS, including the resource management system and fault management system) in the upstream direction, to collect optical path information from the ODN network, restore the optical path topology, and demarcate and locate faults. The following figure shows the position of the digital and intelligent ODN system on the network.
The digital and intelligent ODN system consists of the physical label, digital and intelligent ODN device, intelligent optical path sensing device, intelligent management terminal, intelligent management system, and dumb resource collection and control module. It supports interconnection with the third-party OSS system. The following figure shows the reference model of the digital and intelligent ODN.
The construction of the digital and intelligent ODN includes reconstruction of the traditional ODN and new deployments. The following figure shows the functional entity model in the traditional ODN reconstruction scenario.
The following figure shows the functional entity model in the new deployment scenario.
Currently, the commercial digital and intelligent ODN technologies belong to ODN 2.0, and the ODN 3.0 technology is still in the R&D phase. The following describes the ODN 2.0 solution and its applications. The digital and intelligent ODN is a passive ODN network that is highly automated and intelligent in terms of precise resource management and fast service provisioning by introducing new technologies such as digitalization and artificial intelligence (AI) throughout its lifecycle, including planning, construction, acceptance, O&M, and maintenance. It improves the O&M efficiency and quality. The following figure shows the requirements for network digitalization throughout the ODN lifecycle.
In traditional networking of digital and intelligent ODNs, an intelligent optical path sensing device, optical path switching device (OSW), and optical coupler are deployed on the OLT side, and an intelligent digital optical splitter with the split ratio of 1:4 or 1:8 is installed in the level-1 FDT.
In new deployment scenarios of QuickConnect ODNs, each link consists of a Hub Box, multiple Sub Boxes, and one End Box (all of them have a built-in intelligent digital optical splitter). The onsite construction procedure is the same as that of traditional QuickConnect devices, without additional processes or requirements. In this way, intelligent O&M can be implemented in coordination with the intelligent optical path sensing device and OSW device on the OLT side, to support remote acceptance and fault demarcation and locating, as shown in the following figure.
In the reconstruction scenarios for QuickConnect ODN networking, because the shell of the QuickConnect product cannot be opened, external intelligent digital optical cables or fiber adapters can be used to upgrade the optical splitters on the live network so that the optical splitters have digital-intelligent capabilities to support intelligent O&M, remote acceptance, and fault demarcation and locating, thereby implementing live network reconstruction, as shown in the following figure.
The following figure shows the CO migration for OLT upgrade when the intelligent optical path sensing device and optical path switch unit are installed in the OLT subrack.
The ODN is an important part of a fiber bandwidth network. The traditional ODN cannot meet the requirements of high-quality development of fiber broadband networks due to long construction period, high deployment cost, difficult fiber management, and slow troubleshooting. Therefore, the digital and intelligent ODN has become the ODN evolution direction due to cost-effective deployment, efficient management and O&M, and simplified connections.
Based on the technologies such as identification of branch optical lines, QuickConnect, and uneven optical splitting of optical splitters, the digital and intelligent ODN features automatic setup of network topology, real-time monitoring of the line status, flexible scalability, easy construction and maintenance, and precise resource management, thereby implementing visualized management of access network resources throughout the lifecycle.
