A friend mentioned the principle of fiber-to-the-home and what parts it consists of. Today we will learn about it together.
FTTH fiber to the home, PON is the technology used in FTTH.
First, the basic principle of PON system
PON (Passive Optical Network) refers to an optical access network in which all ODN (Optical Distribution Network) between OLT (Optical Line Terminal) and ONU (Optical Network Unit) use passive devices.
PON is a point-to-multipoint (P2MP) optical access system, which can save fiber resources, ODN does not need power supply, user access is convenient, and supports multi-service access. It is a broadband fiber access technology that operators are currently vigorously promoting. , There are mainly two technologies, EPON and GPON.
The PON system adopts WDM (Dense Wavelength Division Multiplexing) technology to realize single-fiber bidirectional transmission.
In order to separate the incoming and outgoing signals of multiple users on the same fiber, the following two multiplexing techniques are used:
The PON system is mainly composed of three parts: OLT, ODN and ONU. The ODN does not contain active equipment. The OLT and ONU are connected through optical splitters to form a P2MP (point-to-multipoint) structure.
Upstream direction is TDMA mode
The upstream data of each ONU is sent in time-sharing, and the sending time and length of each ONU are centrally controlled by the OLT
The downstream direction is broadcast mode
Downlink data broadcast transmission, each ONU receives its own data according to the identification information of the downlink data, and discards the data of other users
The basic components of a PON system are:
ODN, refers to the optical distribution network used to connect the central office OLT equipment and the remote ONU equipment, ODN only includes passive devices or facilities
The OLT is the core functional module of the PON, and the OLT is generally presented in the form of a rack physically. The rack-mounted OLT (large) adopts a plug-in structure, which has complex functions and large capacity, and is difficult to implement. Includes the following boards:
Box OLT (small): 1U high integrated small equipment: 2-4 PON ports, 1-2 uplink GE ports. Simple function, small capacity, easy to implement
The ONU is located between the user terminal and the ODN, and provides user interfaces and multi-service access. The ONU uplink port (PON port) is an optical port, and the user-side interfaces include:
The block diagram of the ONU is shown in the figure, in which 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).
ONU devices can be divided into the following types according to different application methods of the client:
(1) SFU (Single Residential Unit) type ONU: mainly used for single household users, only supports broadband access terminal function, has 1 or 4 Ethernet interfaces, provides Ethernet/IP services, and can support VoIP services (built-in IAD) ) or CATV business, mainly used in FTTH occasions (can be used in conjunction with home gateways to provide stronger business capabilities).
(2) HGU (Home Gateway Unit) type ONU: mainly used for individual 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 services, can support VoIP services (built-in IAD) or CATV services, and supports TR-069 remote management. Mainly used in FTTH occasions.
(3) SBU (Single Merchant Unit) ONU: It is mainly used for individual enterprise users and a single office in the enterprise. It supports broadband access terminal functions, has Ethernet interface and E1 interface, and provides Ethernet/IP services and TDM services. Mainly used in FTTO occasions.
The ODN is located between the ONU and the OLT, providing optical transmission means for the OLT and the ONU to complete the tasks of optical signal transmission and power distribution.
ODN usually has a tree branch structure, mainly including the following devices:
Optical distribution point facilities: optical distribution frame, optical transfer box, optical distribution box, optical splitter, optical branch joint box, etc.
Optical user access point facilities: optical splitter, optical splitter box, optical branch connector box, etc.
Fourth, the realization of FTTH in PON
Depending on where the fiber reaches the user side, the application modes (construction modes) of the broadband optical access network include the following, which are collectively referred to as FTTx and mainly include:
(1) FTTN: Fiber To The Node, fiber to the node
(2) FTTZ: Fiber To The Zone, fiber to the cell
(3) FTTCab: Fiber To The Cabinet
(4) FTTC: Fiber To The Curb, fiber to the curb
(5) FTTB: Fiber To The Building
(6) FTTP: Fiber To The Premise, fiber to the customer premises
(7) FTTH: Fiber To The Home, fiber to the home
(8) FTTO: Fiber To The Office
Among them, the main application methods are FTTH, FTTB/C, FTTCab, FTTH, FTTO, FTTP realize the access of end users in the way of full fiber, which is the most ideal broadband fiber access method
Five, FTTH typical network structure
The typical networking structure of FTTH is shown in the figure. According to the different business needs of users and the situation of home wiring, the home network can adopt different home networking methods, either wired or wired + wireless AP access. Convenient and flexible access to voice, broadband data, IPTV, WLAN and other services
Six, EPON and GPON technology comparison
Comparison of main technical indicators of GPON and EPON
IEEE 802.3av specifies 10Gb/s downlink, 1Gb/s uplink asymmetric mode (10/1GBASE-PRX) and 10Gb/s uplink and downlink symmetrical mode (10GBASE-PR) two rate modes
10G-EPON working wavelength
1Gb/s uplink: 1260～1360nm (1310nm)
Coexistence of Different Rate Signals (Physical Layer)
Downlink: 10G and 1G signals coexist in WDM mode
Multipoint Control Protocol Supplement (Data Link Layer)
Eight, FTTH line requirements and transmission indicators
The ONU can work normally only when the optical power on the receiving side of the ONU is less than the minimum receiving optical power of the ONU.
When the transmission distance is less than or equal to 5 kilometers, the fiber redundancy is not less than 1dB;
When the transmission distance is less than or equal to 10 kilometers, the fiber redundancy is not less than 2dB;
When the transmission distance is more than 10 kilometers, the fiber redundancy is not less than 3dB.
The above figure is used as an example to calculate the optical power of the full path path. The red point represents the flange, the total length of the optical channel is 3KM, and the optical cable has a total of 4 fusion splices.
It is packaged in a small box, and different pigtails such as SCFCLC can be drawn out according to requirements.