Cables are required to carry many telephone channels. Early cables bundled multiple pairs of insulated copper wires. Some of these were huge and repairs were very time-consuming. Later cables incorporated fewer co-axial cables, each of which could carry several multiplexed telephone signals. All these cables were large, heavy and used expensive Copper material.
Optical Fibre Cables
Each single optical fibre is capable of carrying almost unimaginable numbers of phone channels or very high bit rates. Different scenarios require different protection. Inshore undersea cables need heavy armouring, while fibres used in aircraft must be protected bt light-weight.