1. Basic principles of PON system
PON (passive optical network) refers to an optical access network in which the ODN (optical distribution network) between the OLT (optical line terminal) and the ONU (optical network unit) all adopts passive equipment.PON is a point-to-multipoint (P2MP) optical access system, which can save optical fiber resources, ODN does not require power supply, user access is convenient, and supports multi-service access. It is a broadband optical fiber access technology that operators are currently vigorously promoting , There are mainly two technologies, EPON and GPON.The PON system is mainly composed of three parts: OLT, ODN and ONU. ODN does not contain active equipment. The OLT to ONU is connected through an optical splitter to form a P2MP (point-to-multipoint) structure.
2.The basic components of the PON system
● Optical line terminal (OLT) equipment at the central office
● ODN refers to the optical distribution network used to connect the central office OLT equipment and the remote ONU equipment. ODN only contains passive components or facilities
● Optical Network Unit (ONU/ONT)
3.OLT equipment introduction
The OLT is the core functional module of the PON, and the OLT is generally physically presented in the form of a rack. Rack-mounted OLT (large) adopts a plug-in board structure, which has complex functions, large capacity and high difficulty in realization. Including the following boards,
● Interface board (or called line card)
● Main Switch Board
● Main control board (main control and main switch board may be combined in one board)
● Uplink board (GE/10GE)
Box OLT (small), 1U high integrated small equipment: 2-4 PON ports, 1-2 uplink GE ports. Simple function, small capacity, easy to implement
4.ONU equipment introduction
The ONU is located between the user terminal and the ODN and provides user interface and multi-service access. The ONU uplink port (PON port) is an optical port, and the user-side interfaces include,
● Ethernet interface (FE GE)
● POTS interface (RJ11)
● E1 interface
● CATV interface
The PON interface module is the core part, the voice processing module provides voice services in the form of VoIP, and the CPU is responsible for the control and management of the entire ONU (including communication with the OLT and network management).
5.FTTH ONU equipment classification
ONU equipment can be divided into the following types according to the different application modes of the client,
● SFU (Single Household Unit) ONU: Mainly used for single household users, only supporting broadband access terminal functions, with 1 or 4 Ethernet interfaces, providing Ethernet/IP services, and supporting VoIP services (built-in IAD) ) Or CATV business, mainly used in FTTH occasions (it can be used in conjunction with home gateways to provide stronger business capabilities).
● HGU (Home Gateway Unit) ONU: Mainly used for single home users, with home gateway function, equivalent to a home gateway with EPON uplink interface, with 4 Ethernet interfaces, 1 WLAN interface and at least 1 USB interface provides Ethernet/IP service, can support VoIP service (built-in IAD) or CATV service, and supports TR-069 remote management. Mainly used in FTTH occasions.
● SBU (Single Merchant Unit) ONU: It is mainly used for individual enterprise users and individual offices in the enterprise, supports broadband access terminal functions, has an Ethernet interface and an E1 interface, and provides Ethernet/IP services and TDM services. Mainly used in FTTO occasions.
6.Introduction to ODN
ODN is located between ONU and OLT, provides optical transmission means for OLT and ONU, and completes optical signal transmission and power distribution tasks.ODN usually has a tree-like branch structure, mainly including the following equipment:
● Central office wiring facilities: optical distribution frames, etc.
● Optical distribution point facilities: optical distribution frame, optical transfer box, optical branch box, optical splitter, optical branch joint box, etc.
● Optical user access point facilities: optical splitter, optical branch box, optical branch connector box, etc.
● User termination facilities: user intelligent terminal box, optical fiber information panel
● Other basic equipment: optical cables, optical connectors, pigtails, etc.
Tags : PON System , OLT , ONU , ODN , FTTx
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