Theoretical line rate and actual data rates are different most of the time. Real data rate is less due to use of packet overhead. With development of new technologies with higher data rates, upgrade process starts from core of the network and continues in the edge direction. It happens over time while component cost decrease and availability increase. When designing network it is necessary to make it future-proof, so future upgrades could be made with minimal hardware changes and close to none network disruptions. If the hardware upgrade is necessary for the network, due to its original design for high latency signal, this network would not be scalable in cost-effective manner.