Both outside plant and in-building communications cable are often placed in conduit or duct. The conduit provides protection from both physical and environmental abuse. In underground installation, conduit protects cable from shifting rocks, aggressive rodents, and/or damage from hand shovels. Underground cable that is in conduit is easy to replace or upgrade. The old cable can be pulled out of the conduit and the new pulled in without extensive and expensive digging.
Cable installation contractors making the transition from underground pulling to fiber optic cable blowing can find the process to be both interesting and challenging. Cable blowing equipment employ high-volume air flow to force the delicate fiber cable through a duct or innerduct. An air missile can be attached to the front of the cable to assist the cable's movement along with the air flow. Therefore, air pressure can either drag the cable by itself or push a missile as the missile pulls the cable behind it.