How to understand the High-speed network link increase the data transmission rate only reduces the data transmission delay? I am reading a document: > 1.Transmission delay: (the time required for the host or router to send data frames, formula: transmission delay = data frame length / transmission rate). > > 2.Propagation delay: (The time it takes for electromagnetic waves to propagate a certain distance in the channel, formula: propagation delay: channel length / propagation rate of electromagnetic waves on the channel). > > **High-speed network link** : The increase is the data transmission rate rather than the bit propagation rate on the link. Increasing the data transmission rate only reduces the data transmission delay. I can not understand the High-speed network link increasing the data transmission rate only reduces the **data transmission delay**. in the 1 and 2 definition, the reduces should be **Propagation delay**.

"Bit propagation rate" is a bit misleading here as it jumbles up the different aspects.

When the data rate is increased, a transmitting interface can pump out the data faster and a data packet of a given size finishes outgoing transmission earlier.

The electromagnetic wave carrying the information travels (propagates) always at the same speed, depending on the medium but independent from the data rate. For most media (copper wire, fiber), this is roughly 2/3 of the speed of light c0. A medium's _velocity factor_ tells you the fraction of c0 that is achieved. Of course, wireless communication through air is almost at 1.0; in a vacuum it's exactly 1.0.

The effective total delay is the transmission delay (also _serialization delay_ ) plus the propagation delay. The beginning of transmission overlaps with propagation, so it only counts once.