Fiber Closure as a Transmission Medium Is Very Necessary for the Trunk Line. Fiber closure is not easy to branch because it transmits optical signals, so it is generally used for point-to-point connections. Fiber closures are produced in this situation. The experimental multipoint system for the fiber bus topology has been built, but the price is still too expensive. Due to the small power loss and attenuation of the optical fiber, there is a greater bandwidth potential. Therefore, the number of taps that an fiber closure can support is much greater than that of a twisted pair or coaxial cable. The current low-cost, reliable transmitter is a 0.85um wavelength LED that can support 100Mbps transmission rates and LANs in the range of 1.5 to 2KM. An LED detector PIN operating at a wavelength of 0.85um is also a low-cost receiver. Avalanche photodiodes have a higher signal gain than PIN, but they require a 20 to 50V supply, while the PIN detector requires only 5V. If you want to reach more distant distances and higher rates, you can use a 1.3um wavelength system, which attenuates very little but is more expensive than the 0.85um wavelength system. In addition, it is also very important that the fiber closure connector is matched with it. The connection loss of each connector is required to be less than 25dB, which is easy to install and the price is low. The larger the core and the aperture of the optical fiber, the more light received from the light emitting diode LED, the better its performance. An fiber closure with a core diameter of 100 μm and a cladding diameter of 140 μm can provide very good performance. The light energy it receives is 4dB more than 62.5/125um fiber and 8.5dB more than 50/125um fiber. The attenuation of the fiber closure operating at the wavelength of 0.8um is 6dB/Km, and the attenuation of the fiber closure operating at the wavelength of 1.3um is 4dB/Km. The 0.8um fiber bandwidth is 150MHz/Km, and the 1.3um fiber bandwidth is 500MHz/Km. In the integrated cabling system, the use of fiber closures as a transmission medium is very suitable and necessary for the trunk line.