Graphical illustration of a fiber optic communication system (iii)

“Via this concept and figure, it is easy to describe the functions and procedures as well as the requirements for specifying network requirements.”

Fiber access network
  An optical access network (OAN) is an access network that uses optical fibers as a transmission medium and uses optical waves as optical carriers to transmit signals. It refers to local switches or remote switching modules and users. A system that uses fiber optic communication or partially fiber optic communication. The basic configuration of the fiber access network system is shown in the figure below. The most important feature of the fiber is that it can transmit high-speed digital signals with large capacity; and can use wavelength division multiplexing, frequency division multiplexing, time division multiplexing, space division multiplexing (SDM), and Subcarrier Multiplexing (SCM) so on optical multiplexing technologies to further improve the utilization of optical fibers.

FOT Blog: Basic configuration of fiber access PON network system

Interface & Functions of fiber access PON network system

  As can be seen from the above figure, the sum of transmission means from a given network interface (V interface) to a single user interface (T interface) is called an access link. Via this concept, it is easy to describe the functions and procedures as well as the requirements for specifying network requirements. Generally, the user side and the network side of the access link are different and thus asymmetric. Optical access transmission can be seen as a specific implementation method using optical fibers to support access links. The optical access network can be defined as: a series of access links that share the same network side interface and are supported by the optical access transmission system, and are provided by an optical line terminal (OLT, Optical Line Terminal), an optical distribution network/optical wiring terminal. (ODN/ODT, Optical Distributing Network/Optical Distributing Terminal), Optical Network Unit (ONU), and related adaptation function (AF, Adaptation Function) devices, and may also include several ODNs connected to the same OLT.

Role of the OLT

  The role of the OLT is to provide an interface between the network side and the local switch for the optical access network, and to communicate with the ONU on the user side through one or more ODNs. The relationship between the OLT and the ONU is the master-slave communication relationship. The OLT can separate the switched and non-switched services, manage the signaling and monitoring information from the ONU, and provide maintenance and assignment functions for the ONU and itself. The OLT can be physically separate or integrated with other functions in one device.

ODN Introduction

  The ODN provides optical transmission between the OLT and the ONU. Its main function is to complete the task of assigning optical signals. ODN is a pure passive optical distribution network composed of passive optical components (such as optical cables, optical connectors, optical splitters, etc.) in a tree-like branch structure. The role of ODT is the same as that of ODN. The main difference is that ODT is composed of optical active devices.

Role of the ONU

  The role of the ONU is to provide a direct or remote user-side interface for the optical access network, which is on the user side of the ODN. The main function of the ONU is to terminate the fiber from the ODN, process the optical signal, and provide service interfaces for multiple small business users and residential users. The network side of the ONU is an optical interface, and the user side is an electrical interface. Therefore, the ONU needs to have optical/electrical and electrical/optical conversion functions, as well as digital-to-analog and analog-to-digital conversion, multiplexed signaling processing, and maintenance management functions for voice signals. The location of the ONU is very flexible and can be set either at the user’s home or at the DP (wiring point) or even at the FP (flexible point).
  The AF provides an adaptation function for the ONU and the user equipment. The specific physical implementation can be included in the ONU or completely independent. Taking Fiber to The Curb (FTTC) as an example, the ONU is physically separated from the basic rate NT 1 (Network Termination 1, equivalent to AF). When the ONU is independent of the AF, the AF also provides the service delivery function on the last segment of the incoming line.

The most typical of fiber access PON network

  As information transmission transitions to full digitalization, optical access methods will inevitably become the ultimate solution for broadband access networks. At present, there are two main ways to “fiberize” the user network: one is based on the existing telephone copper cable users, the introduction of optical fiber and optical access transmission system into an optical access network; the second is based on cable television (CATV) coaxial cable network, introduced The fiber and optical transmission system was transformed into a fiber-optic/coaxial hybrid (HFC) network. Access methods used in fiber access networks include: FTTH (Fiber To The Home), Fiber to The Building (FTTB, Fiber To The Building), Fiber to The Curb (FTTC), Fiber Optics To the office (FTTO, Fiber To The Office), Fiber to the Zone (FTTZ, Fiber To The Zone) and Fiber to The Node (FTTN). The main difference between the different access methods is that the ONUs are placed in different locations, the most typical of which are FTTB, FTTC and FTTH.

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