it cools. At the completion of the process, all of the fibers in the optical cable must be tested to ensure that no damage has occurred. Cable pulling A common cable installation technique for fiber cables remains cable pulling. After the duct is placed, a high-strength pull line is blown into the duct (if one has not already been pre-installed by the duct manufacturer). The pull line is attached to one end of the cable and is used to pull the cable through the duct. Cable blowing Traditional cable pulling methods are very sensitive to the condition of the duct and to the number of bends and undulations throughout the duct route. Therefore, for microducts, air-blown cable installation techniques are expected to be the most useful. Air-blown cable installation requires the use of a device that injects a high volume of air into the duct, at pressures as high as 20-25 psi. The viscous drag forces generated by the rushing air along the length of the cable act to reduce or overcome the friction between the cable and the duct. Traditional duct installation For telecommunications, cables can be installed in water, in air or underground. In the latter case, the cables might be direct buried or installed in ducts. The first is more common for copper balanced cables; the latter for fibre optic cables. The ducts in which the fibre optic cables are installed are usually made of polyethylene. They have a size ranging from typically 25 mm to 100 mm. Sometimes they are installed as subducts in larger ducts. These larger ducts can also consist of other materials, like concrete. The installation of fibre optic cables in ducts can be done by pulling or by cable jetting. Problems with fibre optic cables It is more difficult to make branching fibre optic networks in the access network than it is for copper balanced cables. Splicing optical fibres is much more difficult than connecting copper wires. In Fibre to the Home (FTTH), where multiple branches are present in the network, an Optical Distribution Network is used to branch the cables from a roadside cabinet or pit that contains optical equipment and is fed from the Central Office Microduct cabling With microduct cabling, bundles of small microducts may be installed in larger protective duct (e.g., PVC conduit). This can be done by jetting for example. Bundles of microducts can also be factory