שאלה | How is propagation time defined in the context of network communication?

How is propagation time defined in the context of network communication?

		The time elapsed between the reception of a packet and its forwarding to the next hop in the network.
		The period between the transmission of a packet and the acknowledgment of its receipt by the destination.
		The time taken for routers to analyze packet headers and determine routing paths.
		The time it takes for a signal to travel from the source to the destination over the network medium.