It’s not brittle,but it’s not tough or strong either.It’s thin and it’s subjected to breakage which is known as fibre cut in technical terms.They are used in communication process to transmit signals over long distances in form of light with less attenuation(loss). . To avoid them from breakage,they are coated with a buffer which is a shock absorbing material along with a synthetic coating called jacket.It provides the fibre some sort of durability,but they are still vulnerable to twists ,shocks and impacts. They are installed by two means. 1.By underground cables 2.By overhead wires. In underground the strands of optical fibres which come in 6F,12F,60F,120F(the number gives the number of optical fibre strands in each unit) are bunched together and coated with another protective cover and laid. In over head systems they are just hung from one pole to another and that’s not a wise idea in communication engineering with respect to design and afety parameters.Moreover, it gives a very ugly look to the surroundings.