TRANSMISSION CODES in Telecom

All data communication codes are based on the binary system (1s and 0s). A message can be encoded into a meaningful string of 1s and 0s that can be transmitted along a data line and decoded by a receiver. The string of 1s and 0s is meaningful because it is defined by a code that is known to both the source and the receiver. Code is limited by the number of bits (binary digits) it contains, e.g. one-bit code means that we can have 2 characters so that we can encode the letter A by '0' and B by '1'. Similarly, a 2 bit code will enable us to handle 4 characters. Thus, a n-bit code enables us to handle 2ⁿ characters. 

Some commonly used codes are :

1.             Baudot code

2.             ASCII code

3.             BCDIC code

4.             EBCDIC Code

ASCII Code (American Standard Code for Information Interchange)

It is an eight-bit code which consists of seven information bits and one bit for parity checking. This is most widely used data code. Seven information bits gives us 128 combinations, which allows us to encode a full keyboard of the computer.

-          52 alphabets (capital and small).

-          0-9 (10 numbers).

-          Punctuation marks

-          Additional graphic and control characters.

BCDIC (Binary Code Decimal Interchange Code)

It is a six-bit code that is used as an internal code by some computers. With 6 information bits, we can have 2⁶ = 64 possible code combinations. For data transmission, code is implemented as 7-bit code containing 6 information bits and one parity bit.

EBCDIC (Extended Binary Coded Decimal Interchange Code)

It is a 8-bit code in which all the 8-bits are used for information (unlike ASCII), giving 256 possible code combinations. EBCDIC is used as an internal machine code in some of the computers.