Advanced internal structure Easy to re-enter, it never requires re-entry kits. Fiber optic splice tray is designed in SLIDE-IN-LOCK and its opening angle is above 90. Therefore it is easy and fast to increase and reduce FOST. The housing of FOSC is spacious in particular, while straight-through fiber cable is for branching application, fibers not cut off are for straight-through after being fixed and winded, fibers cut off are for branching after fusion splicing with fibers of other branching fiber cable. All of the above features make it easy and convenient for installation, maintenance and reuse. If required, the earthing deriving device can be installed on the housing of FOSC for deriving metallic parts of fiber cable for earthing connection. Pressure testing valve can be installed as well for pressure testing and sealing testing after injecting air.