This applet illustrates the media access control protocol, used by the Ethernet local area network. That media access protocol is called Carrier Sense Multiple Access / Collision Detection (CSMA/CD).
Place a station on the link by entering the station's location in the Station Position text field and then clicking the Add Station button. A rectangle representing the station will then appear on the link in the proper place. Click on the station's rectangle to cause that station to start attempting to transmit a frame. The applet shows graphically the sequence of states the station goes through in the process of transmitting a frame.
Additional stations (up to a maximum of four stations) can be added in a similar manner. Click on several station rectangles in close succession to cause more than one station to be attempting to transmit at the same time. This will cause frame collisions that may or may not be detected by the stations involved. The applet shows graphically how the stations, in following the media access control protocol, eventually successfully transmit their frames. During this process there may be collisions between frames of different stations as well as backoffs by stations that detect collisions.
Click the Clear button to reset the simulation so that there are neither any stations nor any frames in transmission. Click the Suspend button to suspend the animation and click the Resume button to resume the animation. Click the Help button for a short explanatory message. Remember that new parameter values do not take effect until the Enter key is pressed.
The link is characterized by its bandwidth, frame size, and length. Default values for these characteristics have been provided. However, you can change those values. To change one of these values, edit the text field labeled by that characteristic. If you press the Enter key after editing one of these text fields, the change will immediately take effect (this is visible in the case of a bandwidth change or a link length change because parts of the animation area change). However, in any case, when you click on a station, the current values for these text fields will be read and the change will take place at that time.
What concepts is this applet illustrating?
Acknowledgements and Developer Information
Current Version: February 2004
Copyright (C) Mark A. Holliday. All rights reserved.