Views: 90 Author: Site Editor Publish Time: 2020-04-15 Origin: Site
Fiber optical communication is the main transmission method of modern communication networks. Its development history is only one or two decades. It has experienced three generations: short-wavelength multi-mode fiber, long-wavelength multi-mode fiber and long-wavelength single-mode fiber. The use of optical fiber communication is a major change in the history of communications. More than 20 countries such as the United States, Japan, Britain, and France have announced that they will no longer build cable communication lines and are committed to developing optical fiber communications. China's optical fiber communication has entered the practical stage.
The birth and development of optical fiber communication is an important revolution in the history of telecommunications, ranked with satellite communications and mobile communications as technologies in the 1990s. After entering the 21st century, due to the rapid development of Internet services and the growth of audio, video, data, and multimedia applications, there is a more urgent need for large-capacity (ultra high speed and ultra long distance) light wave transmission systems and networks. Optical fiber communication is the latest communication technology that uses light waves as a carrier to transmit information, and optical fiber as a transmission medium to achieve information transmission to achieve the purpose of communication.
The development process of communication is the process of continuously increasing the carrier frequency to expand the communication capacity. The optical frequency has reached the upper limit of the communication carrier as the carrier frequency, because light is an extremely high frequency electromagnetic wave. Therefore, using light as a carrier for communication has a huge capacity, which is thousands of times that of the previous communication methods, and has great appeal. Optical communication is a long-cherished goal and an inevitable direction for the development of communication.
Challenges:
The widely used ADSL technology has certain advantages in providing broadband services. Compared with FTTH: A. The price is cheap; B. The original copper wire network is used to make the project construction simple; C. For the transmission of 1Mbps-500kbps film and television programs, it can meet the demand. Therefore, the promotion of FTTH is restricted.
For broadband services to be developed in the near future, such as: online education, online office, conference TV, online games, remote diagnosis and treatment and other two-way services and HDTV high-definition digital TV, ADSL is difficult to meet the requirement. Especially HDTV, after compression, its transmission rate still needs 19.2Mbps. It is being developed with H.264 technology, which can be compressed to 5-6Mbps. It is generally believed that the highest transmission speed of ADSL guaranteed to QOS is 2Mbps, and it is still difficult to transmit HDTV. It can be considered that HDTV is the main driving force of FTTH. That is, when the HDTV service arrives, FTTH is absolutely necessary.
Solutions:
There are usually two types of P2P （point-to-point ）and PON （passive optical networks）.
1)P2P solution
Advantages: Each user transmits independently without affecting each other, the system changes flexibly. Cheap low-speed optoelectronic modules can be used, and the transmission distance is long.
Disadvantages: In order to reduce the fiber and pipeline directly from the user to the office, an active node that aggregates users needs to be placed in the user area.
2) PON solution
Advantages: Passive network maintenance is simple.
Disadvantages: It needs to use expensive high-speed optoelectronic modules and use different electronic modules to distinguish the user distance to avoid the uplink signals conflict of each user. The transmission distance is shortened by the PON ratio. The downlink bandwidth of each user occupies each other, if users’ bandwidth cannot be guaranteed, not only network expansion is required, but also PON and user modules need to be replaced.
For now, FTTH using fiber optical is mainly to solve the downlink transmission of HDTV broadband video. Of course, some downlink data can also be included when needed. This forms a "fiber to home + wireless access" (FTTH + wireless access) home network. FTTH + wireless access is the future development trend.
