The simulation of the flight following system i6 primarily chosen in the interest of Ethiopian Airlines need to implement the system to replace the currently used flight following system which is based on verbal communication between aircraft and ground control people. The first section of this paper discusses the components of data communication system, aspects and objective of data communication system. The second section laid the emphasis on the fundamental communication concepts parallel transmission, serial transmission and the different types of serial transmission. The theory behind the simulation is basically based on the different types of transmission modes. The third section build the foundation for the characteristics of data transmission, direction of information flow: simplex, half-duplex and full duplex and finally rate of transmiesion effect on data transmission. In section 4 the different coding technology and structures are presented. A unique feature of the paper is section 5 protocol. There are sections on identifying and defining a problem in data communication specially for good understanding between a sender and a receiver.