In the TCP/ IP world, the link layer is the lowest layer of the TCP/IP protocol stack. The link layer is where procedures and protocols reside that operate exclusively on the links between hosts. The links are formed by physical and logical network components that bind the hosts or nodes to the network.
Compared to the layer designation of the OSI reference model, the link layer of the TCP/IP protocol suite can be viewed as a combination of the link layer and the physical layer. However, the layers of the TCP/IP protocol architecture describe the operation-specific applications such as a host-to-host connection or a network link, and do not represent mandatory regulations for the transmission procedures, the data structures or network technologies.
Link layer protocols include Address Resolution Protocol( ARP), routing algorithms such as Open Shortest Path First( OSPF) or Neighbor Discovery Protocol( NDP), tunneling with Layer 2 Tunneling Protocol( L2TP), or Point-to-Polint Protocol ( PPP). Medium Access Control( MAC) is where the well-known transmission technologies are located, such as Ethernet, ISDN and xDSL technologies.