Physical Layer (Layer 1)
The physical layer of the OSI model identifies the physical characteristics of the network, including the following specifications:
Hardware The type of media used on the network such as type of cable, type of connector, and pinout format for cables.
Topology The physical layer identifies the topology to be used in the network. Common topologies include ring, mesh, star, and bus.
In addition to these, the physical layer also defines the voltage used on a given media and the frequency at which the signals that carry the data move from one state to another. These characteristics dictate the speed and bandwidth of a given media as well as the maximum distance over which a certain media type can be used.
Data-link Layer (Layer 2)
The data-link layer is responsible for getting data to the physical layer so that it can be transmitted over the network. The data-link layer is also responsible for error detection, error correction, and hardware addressing. The term frame is used to describe the logical grouping of data at the data-link layer.
The data-link layer has two distinct sublayers the Media Access Control (MAC) sublayer and the Logical Link Control (LLC) sublayer.
MAC layer The MAC address is defined at this layer. The MAC address is the physical or hardware address burned into each NIC. The MAC sublayer also controls access to network media. The MAC layer specification is included in the IEEE802.1 standard.
LLC layer The LLC layer is responsible for the error and flow-control mechanisms of the data-link layer. The LLC layer is specified in the 802.2 standard.