ABSTRACT
The IEEE splits the data-link layer in half because the layer has two jobs to do. The first is to coordinate the physical transfer of data. The second is to manage access to the physical medium. Dividing the layer allows for more modularity and therefore more flexibility. The type of medium access control has more to do with the physical requirements of the network than the actual management of data transfer. In other words, the MAC layer is closer to the physical layer than the LLC layer. By dividing the layer, a number of MAC layers can be created, each corresponding to a different physical layer, but just one LLC layer can handle them all. This increases flexibility and gives the LLC an important role in providing an interface between the various MAC layers and the higher-layer protocols. The role of the data-link's upper layer is so crucial, the IEEE gave it a standard of its own: 802.2 LLC.
