An assembly for installing an optical access network includes at least one in-line optical cable and a drop cable. The assembly includes a duct suitable for housing the at least one in-line optical cable and an optical transition box for snaking an optical connection between the at least one in-line optical cable and the drop cable. The duct has a window. The optical transition box has a base with two sidewalls. Each of the two sidewalls has a first opening allowing the in-line optical cable to enter and exit the base. The base is suitable for being partially inserted in the duct through the window in such a way that, when the base is partially inserted in the duct, the first opening is contained within the duct.