Transmission Time - Propagation Delay

Propagation Delay

The transmission time should not be confused with the propagation delay, which is the time after full message has been sent from the sender, until it has reached the receiving node. The propagation speed depends on the physical medium of the link (that is, fiber optics, twisted-pair copper wire, etc.) and is in the range of meters/sec for copper wires and for wireless communication, which is equal to the speed of light. The propagation delay of a physical link can be calculated by dividing the distance (the length of the medium) in meter by its propagation speed in m/s.

Propagation time = Distance / propagation speed

Example: Ethernet communicaiton over a UTP copper cable with maximum distance of 100 meter between computer and switching node results in:

Maximum link propagation delay ≈ 100 m / (200 000 000 m/s) = 0.5 μs