There are many types of services in the tunnel and the locations are densely packed, and the distance from the tunnel wall to the management sub-center is long. ReviewOptical fiber project for vehicle monitoring system in highway tunnel in a provinceIn the networking process, what is worth pondering is how to group services and how many layers to cascade.

Business grouping is determined based on the impact of the fault

If one point in the same group is wrong, it will affect the entire group, so they should not be put together. The groups within the cave are usually divided as follows:

• The image categories are grouped according to the hole side and station number interval, and one group covers several adjacent cameras;
• Control signals such as vehicle detectors and variable information boards are grouped separately to avoid being involved in image traffic;
• The fan and lighting control take independent data channels and are transmitted on the same cable as the video but via separate fibers.

After the control signal is independent, the start and stop actions of the jet fan will not be linked to the image channel, and conversely, image return congestion will not slow down the control response; low-speed control signals are used2-way bidirectional RS485 data optical terminalCan be carried in pairs.

The number of cascade layers generally does not exceed two levels

In long caverns, multiple nodes may be strung together and reused step by step. With each additional level, the optical power at the receiving end becomes less and there are more fault points. The method is to first calculate the link budget: the attenuation of the optical cable segment plus the loss of splicing and connectors, and then compare it with the minimum sensitivity of the model used, usually leaving a margin of about 3dB. When the budget is already tight, or there are too many channels connected to one layer of nodes, causing the impact of power failure on any node to be too great, it should be changed to an independent end-back distribution center instead of continuing to add layers.

Requirements for equipment in the cave environment

Moisture and dust make the chassis and interfaces more prone to problems than indicators. Use armored jumpers on the lower section of the cave wall and leave a sufficient bending radius. The connector box should be sealed and the equipment in the electromechanical box should be sealed.Security video surveillance fiber optic transmission solutionCheck the protective methods for outdoor items. EB-LINK recommends keeping light records of each core by cave during the operation period, so that the interval can be directly located when the fiber is broken.

Once the grouping and level are determined, the quantity of equipment and the ratio of spare parts will naturally become stable.