We need to resend those frames that have been destroyed during the transmission. Thus there is the only frame that is frame 1.1 from station 1 that survives. Among these 8 frames, there are some frames that collide with each other. The above figure shows that there are 4 stations and each station sends two frames, thus there is a total of 8 frames on the shared medium. Let us now take a look at the frames in a pure ALOHA network: The main idea behind this protocol is that each station sends a frame whenever it has a frame to send.Īs we have already told you that the medium is shared among different stations, thus there is a possibility of collision between frames from the different stations. This protocol is very simple but elegant at the same time. Original ALOHA is simply termed as "Pure ALOHA". Thus the data from the two stations collide. The earliest method used for random access was ALOHA and it was developed at the University of Hawaii in early 1970.ALOHA was mainly designed for radio/Wireless LAN but it can also be used for shared mediums.Īs the medium is shared between the stations, when a station sends the data then the other station may attempt to do so at the same time. Given below are the protocols that lie under the category of Random Access Protocols: In case if there are two or more stations that try to send the data, there occurs a conflict in the access and it is referred to as Collision. Thus these methods are also referred to as Contention methods. There are no rules regarding which station should send the data next, all stations compete with one another in order to access the medium.
There is no time scheduled for any station in order to transmit the data, the transmission is random among all stations that is why these methods are called random access. It simply means that there is no station that permits another station to send.Ī station that has the data to send mainly makes the use of a procedure that is defined by the protocol in order to make a decision whether to send or not to send the data.Īnd the decision mainly depends upon the state of the medium as a medium can either be idle or it can be busy. In Random Access methods, there is no station that is superior to another station and none is assigned control over the other. In this tutorial, we will be covering the Random access protocols in the data link layer in Computer Networks. Difference between OSI and TCP/IP Model.TCP/IP REFERENCE MODELCOMPUTER NETWORKS.Connection Oriented and Connectionless Services.