tion Interchange (ASCII) is nearly universally used worldwide. Figure 10.1 illustrates ASCII. It will be noted in the figure that there are more than 30 special bit sequences such as SOH, NAK, EOT, and SO on. These are/were used for data circuit control. For a full explanation of these symbols, refer to Ref. 3. Another, yet richer code was developed by IBM. It is the EBCDIC (extended binary coded decimal interchange code) code that uses eight information bits per character. Therefore it has 28 = 256 character possibilities. This code is illustrated in Figure 10.2. It should be noted that a number of the character positions are unassigned. 10.5 ERRORS IN DATA TRANSMISSION 10.5.1 Introduction In data transmission, one of the most important design goals is to minimize error rate. Error rate may be defined as the ratio of the number of bits incorrectly received to the total number of bits transmitted or to a familiar number such as 1000, 1,000,000, and SO on. CCITT holds with a design objective of better than one error in one million (bits transmitted). This is expressed as 1 X 10-6. Many circuits in industrialized nations provide error performance two or more orders of magnitude better than this. ITU-T has revised their G.821 recommendation (Ref. 28) to reflect considerably better performance. Error performance is stated in terms of ESR (errored second ratio) and SESR (severely errored second ratio) with a recommended measurement period of one month. We should expect an ESR of <0.08 and an SESR of <0.002. One method for minimizing the error rate would be to provide a "perfect" transmission channel, one that will introduce no errors in the transmitted information at the output of the receiver. However, that perfect channel can never be achieved. Besides improvement of the channel transmission parameters themselves, error rate can be reduced by forms of a systematic redundancy. In old-time Morse code, words on a bad circuit were often sent twice; this is redundancy in its simplest form. Of course, it took twice as lon