From the wikipedia:
Propagation delay – time for a signal to reach its destination
and from the slideplayer.com I found the image:
there seems the Propagation delay represent the signal transport on the chain and
into the other router(whether this is mean
signal into the cache queue contained in the propagation delay), there do not make it clear the whether the propagation delay contains the
signal into the cache queue.
So, I want to make it clear in this professional networking site.