H - Electricity – 04 – N
Patent
H - Electricity
04
N
350/34, 340/75
H04N 7/08 (2006.01) H04L 1/00 (2006.01)
Patent
CA 1301309
ABSTRACT OF THE DISCLOSURE A system or scheme for automatic detection of and recovery from transmission errors in the asynchro- nous communication mode at the data link level with complete transparency at the higher levels is dis- closed wherein the transmissions are in the form of a sequence of data packets, and an improved combination of end-of-text (ETX) bytes along with checksums is used in each data packet to detect errors. The ETX character is dynamically selected for each packet after the data comprising the packet has been assembled. This character is coded differently from the remaining character codes in its respective packet and is made the second byte thereof following the start-of-text byte (STX). The third byte in each packet is made the comple- ment of the preceding ETX byte, the latter of which is also made the last byte in the packet. Thus, the second and last bytes in each packet are iden- tical, and different from all the other bytes, and the third byte is their complement. Other bytes m each packet include: one byte indicating the lo- cation of the packet in a set in a given trans- mission sequence; a byte distinguishing the Y0985-005 packet's set from other transmission sequences: two bytes indicative of the number of data bytes in the packet; one byte operating as a control character indicating the functional nature of the packet; data bytes; and, two checksum bytes which precede the last ETX byte. Among the advantages of trans- missions using packets containing the foregoing improved combination of bytes, is the fact that all transmission errors will be detected and upon de- tection of an error in a packet, the transmitter is immediately notified and retransmission is car- ried out only from the erroneous packet rather than from the beginning of the entire sequence as in the prior art. Y0985-005
524577
Braudaway Gordon W.
Burket Thomas Gerard
Kannan Krishnamurthi
Kruesi Deborah Jean
Meltzer Clifford Bennett
International Business Machines Corporation
Rosen Arnold
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