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Browse Prior Art Database

Error Recovery in Data Transmission

IP.com Disclosure Number: IPCOM000074208D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Maiwald, D: AUTHOR [+3]

Abstract

Data terminals communicating with each other or with a central computer over a transmission system verify transmitted data blocks by echo checking with data buffered at the origin terminal. At the destination terminal, data is dynamically stored in a buffer to allow for error recovery.

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Error Recovery in Data Transmission

Data terminals communicating with each other or with a central computer over a transmission system verify transmitted data blocks by echo checking with data buffered at the origin terminal. At the destination terminal, data is dynamically stored in a buffer to allow for error recovery.

Two additional bit positions in the data blocks are required. One of these bits signifies whether the currently transmitted block is a data block or an error recovery message. The second bit describes the validity of a block in the sender or receiver buffer. In the sender buffer this flag bit indicates not yet transmitted blocks, or it marks a block for retransmission. A flag bit 0 labels already transmitted blocks still in the sender buffer. In the receiver buffer, flag bit 1 denotes a correctly transmitted and received block as a valid block. Flag bit 0 indicates an invalid block which is by echo checking recognized as wrongly transmitted or received.

If the echo check by the transmitter indicates a transmission error for the last data block, the transmitter indicates an error recovery routine which marks the data block in the transmitter buffer for retransmission and which sends an error recovery ER message to the receiver. The ER message invalidates itself and specifies how many more previous messages in the receiver buffer have to be invalidated. In the case of a single error only the last data block is invalidated, in burst errors longer sequences can be e...