Complex sentence: For example, telephone trunklines that carry phone calls between switching centers are made of modern optical fiber, but the last mile is typically twisted pair wires, a technology which has essentially remained unchanged for over a century since the original laying of copper phone cables.
Split into simpler sentences: For example, telephone trunklines that carry phone calls between switching centers are made of modern optical fiber, but the last mile is typically twisted pair. Telephone wiring that provides service to customers' premises has essentially remained unchanged for over a century since the original laying of copper phone cables.