EP0229353A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Method and system for handling transmission errors
Assignee: International Business Machines Corp
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Filing: 1986-12-18
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Granted: —
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Expires: 2006-12-18
Abstract
Abstract Automatic detection of and recovery from errors of transmissions in the form of a sequence of data packets is described as well as an improved combination of end-of-text (ETX) bytes along with checksums in each data packet to detect errors. The ETX character (12) 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 (3) in each packet is made the complement of the preceding ETX byte, the latter of which is also made the last byte in the packet. Other bytes in each packet indude: one byte (4) indicating the location of the packet in a set in a given transmission sequence; a byte (7) distinguishing the packet's set from other transmission sequences; two bytes (5,6) indicative of the number of data bytes in the packet; one byte (8) operating as a control character indicating the functional nature of the packet; data bytes; and two checksum bytes (9,10+m) which precede the last ETX byte. Upon detection of an error in a packet, the transmitter is immediately notified and retransmission is carried out only from the erroneous packet rather than from the beginning of the entire sequence as in the prior art.
Inventors
- 👤 Clifford Bennett Meltzer
- 👤 Krishnamurthi Kannan
- 👤 Thomas Gerard Burket
- 👤 Deborah Jean Kruesi
- 👤 Gordon Wesley Braudaway
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-04 23:15
CPC Classifications
H; H04; H04L; H04L1/00; H04L1/0078; H04L1/0083
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
189 words
A method for detection of and recovery from transmission errors over asynchronous communication lines between transmitting and receiving stations, comprising the steps of: producing the transmissions in packets containing n bytes, with the first byte in each packet being coded as a start-of-transmission character STX; selecting an end-of-transmission character ETX for each packet after the data tu be transmitted in the packet has been assembled, which ETX character is different from the remaining character codes in its respective packet and is made the second byte thereof; making the third byte in each packet the complement of the ETX character selected for the respective packet; making the bytes preceding the last three bytes in each packet data bytes; making the next-to-last two bytes in each packet, checksum bytes; and . making the last byte in each packet the same as the ETX character of the second byte to indicate the end of each packet, whereby the ETX character bytes are distinguishable from data bytes, and errors in either instance thereof are respectively checked by the third and second bytes in the packet, while data errors are checked by the checksums.
Claim 2
Independent Claim
189 words
A method for detection of and recovery from transmission errors over asynchronous communication lines between transmitting and receiving stations, comprising the steps of: producing the transmissions in packets containing n bytes, with the first byte in each packet being coded as a start-of-transmission character STX; selecting an end-of-transmission character ETX for each packet after the data tu be transmitted in the packet has been assembled, which ETX character is different from the remaining character codes in its respective packet and is made the second byte thereof; making the third byte in each packet the complement of the ETX character selected for the respective packet; making the bytes preceding the last three bytes in each packet data bytes; making the next-to-last two bytes in each packet, checksum bytes; and . making the last byte in each packet the same as the ETX character of the second byte to indicate the end of each packet, whereby the ETX character bytes are distinguishable from data bytes, and errors in either instance thereof are respectively checked by the third and second bytes in the packet, while data errors are checked by the checksums.
Claim 3
Dependent Claim
142 words
A method as in claim 1 comprising the further steps of: making the fourth byte in each packet indicative of the location of each respective packet in a set of data packets in a given transmission sequence; making the fifth and sixth bytes in each packet indicative of the number of data bytes in the respective packet; making the seventh byte in each packet a sequence control flag distinguishing said set of data packets from another transmission sequence; making the eighth byte in each packet a control character; making all but the last three remaining bytes in each packet, data bytes; making the next to last two bytes in each packet, checksum bytes; and making the last byte in each packet the same as the ETX character of the second byte in the respective packet to indicate the end of each packet.
Claim 4
Dependent Claim
27 words
A method as in claim 1 or 2 wherein said checksum bytes are made indicative of the total number of bytes in the respective packet less four.
Claim 5
Independent Claim
15 words
A method as in one of the claims 1 - 3 wherein n equals 256.
Claim 6
Independent Claim
176 words
A method as in one of the claims 1 - 4 comprising the further steps of: a) creating a table of 2 y dividend modifiers by respectively applying the traditional bit-at-a-time CRC algorithm to each of the possible y-bit sequences and storing the results in said table at the locations indexed by the original y-bit values; b) computing the CRC remainder of any k x y message using one of the standard CRC generator polynomials by: 1) computing the CRC remainder of a k-byte message by appending 2 bytes of 0's to the low order end of the message to form a k+2 byte dividend; and 2) repeating the following steps k times: i) using the leftmost dividend byte, byte 0, as an index into the table of dividend modifiers, combining bytes 1 and 2 with the designated sixteen-bit dividend modifier using an EXLUSIVE OR; and ii) shifting the dividend left 8 positions; and c) inserting the final bytes, 0 and 1, into the two appended bytes of the augmented message to form a revised message.
Claim 7
Dependent Claim
56 words
A method as in claim 5 comprising the further steps of: d) receiving said revised message at said receiving station; e) recomputing the CRC remainder using said repeated steps; and f) after k iterations, checking bytes 0 and 1 of the dividend to determine if they are zero, whereupon the message has been received without error.
Claim 8
Independent Claim
64 words
A method as in one of the claims 1 - 6 comprising the further steps of: storing duplicates of said transmissions in a buffer at said transmitting station; transmitting a pause packet at selected intervals during a long transmission asking for an acknowledgement from said receiving station; and releasing said duplicates from said buffer upon receipt of an acknowledgement packet from said receiving station.
Claim 9
Independent Claim
28 words
A method as in one of the claims 1 - 7 wherein videotex signals are transmitted, the first byte in each packet being the ASCII character STX (X'02').
Claim 10
Independent Claim
197 words
A system for detection of and recovery from transmission errors over asynchronous communication lines between transmitting and receiving stations, comprising: means for producing the transmissions in packets containing n bytes, with the first byte in each packet being coded as a start-of-transmission character STX; means for selecting an end-of-transmission character ETX for each packet after the data to be transmitted in the packet has been assembled, which ETX character is different from the remaining character codes in its respective packet and is made the second byte thereof; means for making the third byte in each packet the complement of the ETX character selected for the respective packet; means for making the bytes preceding the last three bytes in each packet data bytes: means for making the next-to-last two bytes in each packet, checksum bytes; and means for making the last byte in each packet the same as the ETX character of the second byte to indicate the end of each packet, whereby the ETX character bytes are distinguishable from data bytes, and errors in either instance thereof are respectively checked by the third and second bytes in the packet, while data errors are checked by the checksums.
Claim 11
Independent Claim
197 words
A system for detection of and recovery from transmission errors over asynchronous communication lines between transmitting and receiving stations, comprising: means for producing the transmissions in packets containing n bytes, with the first byte in each packet being coded as a start-of-transmission character STX; means for selecting an end-of-transmission character ETX for each packet after the data to be transmitted in the packet has been assembled, which ETX character is different from the remaining character codes in its respective packet and is made the second byte thereof; means for making the third byte in each packet the complement of the ETX character selected for the respective packet; means for making the bytes preceding the last three bytes in each packet data bytes: means for making the next-to-last two bytes in each packet, checksum bytes; and means for making the last byte in each packet the same as the ETX character of the second byte to indicate the end of each packet, whereby the ETX character bytes are distinguishable from data bytes, and errors in either instance thereof are respectively checked by the third and second bytes in the packet, while data errors are checked by the checksums.
Claim 12
Dependent Claim
21 words
A system as in claim 9 comprising means to carry out the steps of one of the claims 2 - 8.
References Cited (Backward Citations)
No citation records indexed.
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