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by Steve Taylor and Joanie Wexler

Communications from the ground up

Opinion
Mar 09, 20042 mins
Networking

* All about code sets

A Network World Fusion Convergence newsletter last week noted that another code was recently added to Morse Code to represent the “@” sign.  The reason was that ham radio operators needed a more efficient mechanism for sharing e-mail addresses. 

As our needs for communicating more complex information have grown, so has code-set complexity.  For example, an early code set used in the WAN – made famous by Paul Revere – was about as simple as you can get. 

In this case, the “one if by land, two if by sea” code set referred to the encryption scheme used by Revere during the American Revolution. It was based on the number of lanterns he lit in the belfry of Old North Church to pass along information as to how the enemy was approaching. 

As illustrated by Revere’s simple encoding, a fundamental agreement for code sets must be present: the entity sending the code and the entity receiving the code must agree on what the code set means.

But there are other important characteristics.  Because the codes used in modern WAN communications are processed digitally, code sets all contain the same number of bits.  (Morse Code does not meet this characteristic.  There are various numbers of “dots” and “dashes” for different letters.)  And here we get to a fundamental trade-off.  The more bits, the more complex the code set.  And the more bandwidth it takes to transmit a given symbol such as a letter or a number.

So for a code set to be useful in WAN communications, the following rules must apply:

1) The code set must consist of a fixed number of bits.

2) The sender and the receiver must agree on what the bits represent.

For compatibility with the digital processors that must analyze these codes in communications equipment, essentially all communications protocols today are built around 8-bit bytes for transferring information.  Next time, we’ll take a look how these code sets developed over the years.