Link Layer

What
The link layer is a protocol layer in a protocol stack that is responsible for moving the datagrams from the network layer to the node that the network specified.

Examples of Link Layer Protocols

 * WiFi
 * Ethernet
 * Point-to-Point

Services that Link Layer Protocols Provide

 * Framing - Almost all link layer protocols put the network layer datagram into a frame and send it out that way
 * Link Access - There exists a Medium Access Control (MAC Protocol) that governs which nodes are allowed to transmit on a link at a time. For point to point connections, this is pretty simple.
 * Reliable Delivery - A Link Layer Protocol that implements reliable delivery makes sure that frames get across links without errors
 * Flow Control - Flow control limits the amount of frames that are on the fly at once because each side of the connection can only have a certain amount of buffering capacity
 * Error Detection - checks for bit level errors using hardware
 * Error Correction - Corrects for bit level errors in the header
 * Half Duplex and Full Duplex - half duplex is when the link can only handle one sending connection at once, but full duplex is when frames can come both to and from.

How
Link layer protocols are installed on multiple end users and they can send the datagrams as frames.