Ref0_DataLink - Ref0_T Data transparency Halsal 3.8 Data...

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[ Ref0_T ] Data transparency [ Halsal 3.8] Data Transparency : This is the term used to indicate that the frame synchronization method associated with the transmission control scheme transparent to the contents of the frame being transmitted. This is particularly important when the frame contents are pure binary data. With pure binary data, the frame contents may then contain a bit pattern which is the same as that used to signal the end of a frame. Data transparency using Character stuffing Character stuffing: With a character-oriented transmission control scheme, the start and end of each frame is signaled by the use of special control characters. If pure binary data are to be transmitted then steps have to be taken to ensure that the frame does not contain a bit sequence which is equal to the end-of-frame character. This is achieved firstly by preceding each control character (eg. STX and ETX) by a special control character called data link escape ( DLE ) and by inserting (stuffing) an extra DLE character into the transmitted character sequence whenever a DLE character is detected in the frame contents. Data transparency using Zero bit insertion Zero bit insertion: With a bit oriented transmission control scheme, the end and start of each frame is signaled by the use of a flag, special bit sequence –01111110. To ensure the frame contents does not contain a bit sequence corresponding to the flag, the transmitter automatically inserts an additional binary 0 into the transmitted bit sequence whenever it detects five continuous binary 1 bits. The receiver, after detecting the opening flag of a frame, monitors the incoming bit stream and whenever it detects a binary 0 after five continuous binary 1’s, removes it from the stream. Assume a terminal is connected to a computer and data entry through the keyboard to the computer. Techniques used to achieve error control and flow control Error control : Parity check – As each key is pressed on the keyboard, the resultant character is transmitted to the remote computer with parity bit set. If correct parity is received with the character, the character is accepted otherwise it will be discarded. Echo
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This note was uploaded on 02/26/2011 for the course EE 3016 taught by Professor Chau during the Spring '11 term at City University of Hong Kong.

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Ref0_DataLink - Ref0_T Data transparency Halsal 3.8 Data...

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