The Physical Layer
Physical layer is concerned with transmitting raw bits over a communication channel. The design issues here largely deal with mechanical,electrical & timing interfaces and physical transmission medium.
2.The Data Link Layer
This layer transform a raw transmission facility into a line that appears free of undetected transmission errors to the network layer.In the data link layer a fast transmitter from drowning a slow receiver in data.Frequently, this flow regulation and error handling are integrated. In the data link layer, in broadcast n/w how to control access to the shared channel. A special sublayer of the data link layer, medium Access control sublayer, deals with this problem.