Communication Basics #23 Worked Example: Twisted Pair Infrastructure Cost

Instructor: Dr. Süleyman Burak ÇELİK

Fifth midterm preparation video in the Communication Basics series. We work through the classic twisted pair infrastructure cost problem step by step in light mode. There are about 2 billion telephone subscribers in the world. Each subscriber is connected to the local exchange with twisted pair copper cable, with an average distance of 4 km. The cost of the twisted pair cable is 0.5 YTL per meter. We compute the total infrastructure value, then use that result to compare the feasibility of fiber replacement vs DSL upgrade. We solve two parts and add real-world scale: first we compute the total cable length (8 billion km — about 200,000 trips around Earth, or 53 times the Earth-Sun distance), then multiply by cost to get 4 trillion YTL ≈ 3 trillion USD (2011 conversion). Finally, we look at fiber replacement vs DSL upgrade — keep the existing copper, drop in a DSLAM at the exchange and a modem at the home, and VDSL gives you up to 52 Mbps over the same 4 km of copper for ~30× less cost. Cost comparison: $3 trillion fiber rollout vs ~