TCP/IP Link Layer (Data Link Plus Physical)
The TCP/IP model’s original link layer defines the protocols and hardware required to deliver data across some physical network. The term link refers to the physical connections, or links, between two devices and the protocols used to control those links.
Just like every layer in any networking model, the TCP/IP link layer provides services to the layer above it in the model. When a host’s or router’s IP process chooses to send an IP packet to another router or host, that host or router then uses link-layer details to send that packet to the next host/router.
Because each layer provides a service to the layer above it, take a moment to think about the IP logic related to Figure 1-10. In that example, ...
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