שאלה | Why might the link layer sometimes implement reliable data transfer (RDT) mechanisms, even if the network layer above it already provides RDT?

Why might the link layer sometimes implement reliable data transfer (RDT) mechanisms, even if the network layer above it already provides RDT?

		RDT is only required at the network layer, and is unnecessary at the link layer.
		The link layer always needs to provide RDT, regardless of what the network layer does.
		Implementing RDT at multiple layers is redundant and wasteful.
		To handle the specific error characteristics of the local communication link, which may have long propagation delays or high error rates.