Transmission Encodings Simulation
written by Teresa Carrigan
- What is it?
- How it works
- How to use it
- Things to notice
- Things to try
- Extending the model
- NetLogo features
- Related models
- Credits and References
- For more information
- Download the model
WHAT IS IT?This model demonstrates various data transmission encodings: Unipolar, NRZ, NRZI, Manchester, RZ, AMI, PM, FM, MFM.
HOW IT WORKSA random 16-digit bit pattern is generated. For each bit sent, both a synchronization clock pulse and the transmission waveform are displayed. The transmission waveform will differ depending on the encoding chosen.
HOW TO USE ITThe setup button generates a random bit pattern, and initializes variables for the chosen encoding.
The random button selects a random encoding scheme, and then sets up a random bit pattern.
The slow-motion slider is an easy way to adjust the speed of the display. Set it to zero if you want to show the final result as quickly as possible. 0.3 is a good setting for most purposes.
The step button processes the next bit of the message to be sent. It then stops so you can take notes. This is useful when you are first learning an encoding method.
The go button processes the remaining bits, at a speed determined by the slow-motion slider. This is useful when you do not need to take notes between each step, or do not wish to press the step button sixteen times to get an answer. If you want to pause the demonstration, simply click the go button a second time and it will stop after it finishes the current step. You may then click go a third time to resume.
The change encoding button resets the screen without changing the bit pattern. This allows you to select a different encoding scheme for the same bit pattern.
The encoding choice box allows you to select the encoding scheme to be demonstrated. Refer to a textbook or lecture notes for details on the various encoding schemes.
THINGS TO NOTICESome encoding schemes are prone to loss of synchronization. That is, some bit patterns will produce an encoding where the signal stays at the same voltage level for multiple time slices. Which encoding schemes might have this problem? Which never do?
If the average voltage is not zero, then there is a DC component to the signal. This can cause signal distortion and possibly even damage equipment. Which encoding schemes might have this problem? Which never do?
Which encoding schemes use the fewest number of transitions? Which use the greatest?
THINGS TO TRYSet slow-motion to 0.3, click random, and then click go.
Set the encoding choice box to the type of encoding you want to drill, then click setup. Attempt one bit at a time on paper, and then click the step button to check that you did that bit correctly.
EXTENDING THE MODELAllow the user to input a starting bit pattern.
Add more encodings: Differential Manchester, BnZS, 2B1Q, MLT-3, 8B/10B, 8B/6T.
Modify so that the signal is generated first, and then translated into bits.
NETLOGO FEATURESexplain-encoding and send-bit use the NetLogo run command combined with an integer variable to run the appropriate procedures, without needing nested ifelse blocks.
The go procedure uses "forever" on the button, and an ifelse in the procedure instead of a while loop. When the while loop would have finished, the else branch is executed: "stop", which halts the forever execution of "go".
CREDITS AND REFERENCESThis model was written by Teresa W. Carrigan, 2004.
Permission to use, modify or redistribute this model is hereby granted, provided that both of the following requirements are followed:
Contact Teresa Carrigan for appropriate licenses for redistribution for profit.
- this copyright notice is included.
- this model will not be redistributed for profit without permission from Teresa Carrigan.
To refer to this model in academic publications, please use: Carrigan, T. (2004). Transmission Encodings Simulation model. Blackburn College, Carlinville, IL.
In other publications, please use: Copyright 2004 by Teresa W. Carrigan. All rights reserved.
FOR MORE INFORMATIONFor more information on Transmission Encodings, see one of the following textbooks:
- Null, L. and Lobur, J. Essentials of Computer Organization and Architecture, First Edition, Jones and Bartlett, pages 67-73.
- Forouzan, B. Data Communications and Networking, Third Edition, McGrawHill, pages 89-94.
Applets on this website were written by Teresa Carrigan in 2004, for use in computer science courses at Blackburn College, with the exception of the Fireworks applet. The applets made with NetLogo require Java 1.4.1 or higher to run. The applets made with NetBeans require Java 1.4.2 or higher to run. Applets might not run on Windows 95 or Mac OS 8 or 9. You may obtain the latest Java plugin from Sun's Java site.