From the wikipedia:

Propagation delay – time for a signal to reach its destination

and from the slideplayer.com I found the image:

enter image description here

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.

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1 Answer 1


The propagation delay does not include processing overhead like queueing/unqueueing. It's purely medium-in to medium-out. Neither egress nor ingress queueing, nor serialization ("transmission delay" in your diagram) is part of the propagation delay.

  • but how about the duration of signal into the cache queue? it belongs to which delay?
    – aircraft
    Aug 19, 2020 at 8:43
  • The send queue is no cache, and no, that's processing overhead and it doesn't count as propagation.
    – Zac67
    Aug 19, 2020 at 22:14

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