Consider a transmission system using frequency division multiplexing What Cost factors are involved in adding one more pair of stations to the system?

In many cases, the cost of the transmission medium is large compared to the cost of a single transmitter/receiver pair or a modulator/demodulator pair. If there is spare bandwidth, then the incremental cost of the transmission can be negligible. The new station pair is simply added to an unused sub channel. If there is no unused sub channel it may be possible to re divide the existing sub channels creating more sub channels with less bandwidth. If, on the other hand a new pair causes a complete new line to be added then the incremental cost if large indeed.