Defines protocols and hardware that is required for data transfer in physical networks. Link refers to the physical cable links between 2 devices. The 5 layer TCP & IP model simply splits the link layer into its 2 functions of data transfer and physical media within the TCP & IP Data Layer and TCP & IP Physical Layer.
Like all layers, the link layer provides services to the layer above it. Higher level layers like if the network layer wants to send something to another IP, it is the ethernet that manages how the packet maneuvers.
Networking diagrams often represent Ethernet as lines. Just simple lines.
Ethernet Forwarding
ethernet forwarding can be broken down into 4 steps::
- Our own computer Encapsulation the packet inside an Ethernet Frame
- The packet is physically transmitted through electricity over Ethernet cabling
- Router physically receives the electrical signal and re-creates the encapsulated packet through decoding the electrical signals
- Router decapsulates the packet from the Ethernet Frame
Certain tasks in those 4 mentioned above within the 5 layer model are split between TCP & IP Data Layer and the TCP & IP Physical Layer. For example, Encapsulation and Addressing is a uniquely TCP & IP Data Layer procedure. Likewise, Bit transmission is special to the TCP & IP Physical Layer. The link layer includes a large number of protocols and standards. For example: Ethernet protocols with other LAN standards like WAN.