Introduction
FTTH (FiberToTheHome)-Fiber to the home is the best mode for full-service, high-bandwidth access requirements so far.
The development of FTTH mainly has two paths-active optical network and passive optical network.
The active optical network has the characteristics of long transmission distance, but the equipment has a large degree of specialization, which is not suitable for areas with dense users, and the port price is relatively high. In addition, the active characteristics also make the installation of equipment very difficult. It is largely limited and easily affected by electromagnetic interference in the surrounding environment, which increases the failure points of the network and leads to higher maintenance costs.
Because the passive optical network is a pure medium network, it has a natural ability to resist the influence of electromagnetic interference, reduces the failure points of the access network, and has high system reliability and low maintenance cost. At the same time, the FTTH of the passive optical network mode has good transparency, can support the application of multiple standards, and is more suitable for large-scale development of users. Passive optical networks have gradually become the mainstream development direction of FTTH.
The physical layer of FTTH uses optical fiber, and the use of optical network provides a good basic guarantee for high-bandwidth service transmission capabilities. But only the physical layer is not enough. To realize the transmission of information, it is more important to control the second layer. Therefore, the development of FTTH has experienced a revolution on the second layer of the network-the development process from ATM to Ethernet, corresponding to the two series of APON and E/GPON respectively.
Main business
FTTH is a comprehensive access solution for all services. Although the main driving force of FTTH is future broadband video services, FTTH must be able to support various existing narrowband and broadband services, as well as new services that may appear in the future. The FTTH system must be able to provide comprehensive access so that users can enjoy multiple services at the same time. The main services that FTTH should support include:
Video: HDTV, using MPEG-2 standard compression, original image pixels from 1080×1920 to 4320×7680, using Dolby Digital 5.1 channel decoder system Multi-channel high-fidelity sound; standard DTV, compressed by MPEG-2 standard, the original image pixel is about 640×720, ordinary mono or stereo; various statics using MPEG-1 and MPEG-4 and other compression technologies Image business and low-resolution surveillance image business.
Data: Data services of various code rates, ranging from a few Kbps to tens of megabytes.
Voice: Including traditional POTS phone and digital phone services, multiple high-fidelity voices.
Multimedia: a variety of mixed data, voice, and image services with different qualities.
Networking principle
Similar to the "handover wiring method" of all-plastic telephone cables for communications, fiber to the home (FTTH) optical distribution network (ODN) is divided into backbone optical cables Subsystem, distribution fiber optic cable subsystem and household fiber optic cable terminal subsystem.
(1) Trunk optical cable subsystem
This refers to the optical cable between the central office optical distribution rack ODF connected to the optical fiber access equipment OLT, and the optical cable connected to the user optical cable transfer box Distribution system. In the optical fiber distribution equipment at the two ends, the optical cables are terminated by heat fusion, and the optical fiber pigtails are used for jumper connection between each other.
(2) Distribution fiber optic cable subsystem
This refers to the fiber optic cable from the optical junction box to the "optical fiber integrated distribution box" in the user's building. This is an optical distribution panel that directly connects the input optical cable and the output optical cable "back-to-back". Usually, the optical splitter device is also placed in it.
(3) Optical splitter (OBD)
The optical splitter is a "optical fiber multiplexing device" that "multiplexes" the channels of a single-core optical cable into multiple channels. The ratio is 1:16; 1:32 and 1:64. In the FTTH system of EPON mode, because the transmission rate is 1.2Gb/s, in order to ensure that the user bandwidth reaches more than 30Mb/s, the most commonly used splitting ratio (also known as "splitting ratio") is 1:32.
Optical splitter (OBD) can consider different types of splitters according to the placement position, mainly including "box-type fiber splitter", "tray-type splitter" and "plug-in end There are three types of "type optical splitters"; the models of the fiber optic cable pigtail plugs are all SC type "square head" fiber optic plugs.
Advantages
The advantages of FTTH are mainly in five points: First, it is a passive network, from the central office to the user, the middle can basically be passive; second , Its bandwidth is relatively wide, and the long distance is just in line with the large-scale use of operators; third, because it is a service carried on optical fiber, there is no problem; fourth, because its bandwidth is relatively wide, The supported protocols are more flexible; fifth, with the development of technology, more complete functions have been developed including point-to-point, 1.25G and FTTH methods.
In the optical access family, there are FTTB (FibreToTheBuilding) fiber to the building, FTTC (FibreToTheCurb) fiber to the roadside, FTTSA (FibreToTheServiceArea) fiber to the service area and so on.
Connect the optical fiber directly to the user’s home. There are no restrictions on its bandwidth, wavelength, and transmission technology. It is suitable for introducing various new services. It is the most ideal service transparent network and the ultimate goal of the development of the access network. Way.
Although the mobile communication is developing at an amazing speed, due to its limited bandwidth, the size of the terminal is unlikely to be too large, and the display screen is limited, people still pursue fixed terminals with relatively superior performance, that is, they hope to achieve fiber optics. To home. The charm of fiber-to-the-home is that it has a huge bandwidth, and it is the best solution to the bottleneck phenomenon of the "last mile" from the Internet backbone to the user's desktop.