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Framing Zero Insertion Without Deletion

IP.com Disclosure Number: IPCOM000077791D
Original Publication Date: 1972-Sep-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

West, LP: AUTHOR

Abstract

Present telecommunications and data processing systems, having a central station and numerous remote stations, call for the maintenance of coded character synchronization in the transmission medium by the use of a unique framing character, such as a sequence of ones or zeros. These framing characters are used to obtain synchronization and to set the data text apart from other coded transmissions. In order to prevent confusion, it is necessary to assure that whatever framing sequence of bits is used, it does not occur in a normal text.

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Framing Zero Insertion Without Deletion

Present telecommunications and data processing systems, having a central station and numerous remote stations, call for the maintenance of coded character synchronization in the transmission medium by the use of a unique framing character, such as a sequence of ones or zeros. These framing characters are used to obtain synchronization and to set the data text apart from other coded transmissions. In order to prevent confusion, it is necessary to assure that whatever framing sequence of bits is used, it does not occur in a normal text.

In normal use, the character check polynomial (CRC) is generated by having all transmitted bits flow through a character check generator at the transmitter side, and through a character check receiver on the receiving end. When the block of data transmission is complete, the CRC character is transmitted as a continuous string of bits and, when this string of bits is received and has passed fully through the receiver character checking hardware, the result should be all zeros in the character check registers unless an error is detected. For an eight- bit character, a fourteen-bit CRC character is transmitted with a leading zero ahead of the first eight bits and a leading zero ahead of the second eight bits. The receiving terminal must then count and delete the second zero, which requires counting and deletion hardware to be included at the receiver end.

Fig. 1 illustrates an apparatus which assures that the CRC character will not contain a framing sequence and in which no zero deletion hardware or method is required. The apparatus assures that when the CRC polynomial is developed, it contains an internal zero which will be sufficiently centered in the character so that a framing sequence will not be formed. In this example, a framing sequence consists of a sequence of nine ones and the CRC is a fourteen-bit sequence. After the last message character of nine bits (eight character bits and a parity bit) is sent, the central station sends a three-bit sequence with...