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Data Validation for Async File Transfers

IP.com Disclosure Number: IPCOM000062669D
Original Publication Date: 1986-Dec-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Giles, MD: AUTHOR

Abstract

This article describes a data validation method for asynchronous file transfers between a personal computer (PC) and a main frame (host) system. To ensure data validity, it is common to perform a 'check-sum' on data being sent or received through the asynchronous communication line. A check-sum is a function invoked at both ends (PC and host) which returns a number depending upon the data sent or received. This check-sum is compared. When the sums are not the same, the transmission is issued once again. An unequal check-sum value can be caused by 'noise' on the phone line; thus retransmitting the data ensures valid data. The following equation is used for the check-sum algorithm: MODULO of (Sum of each character value in record / 256) This provides an efficient data validation routine between a PC and host.

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Data Validation for Async File Transfers

This article describes a data validation method for asynchronous file transfers between a personal computer (PC) and a main frame (host) system. To ensure data validity, it is common to perform a 'check-sum' on data being sent or received through the asynchronous communication line. A check-sum is a function invoked at both ends (PC and host) which returns a number depending upon the data sent or received. This check-sum is compared. When the sums are not the same, the transmission is issued once again. An unequal check-sum value can be caused by 'noise' on the phone line; thus retransmitting the data ensures valid data. The following equation is used for the check-sum algorithm: MODULO of (Sum of each character value in record / 256) This provides an efficient data validation routine between a PC and host. However, it poses some problems. One problem is to insure that the equation yields the same results on the host and PC. A host system character set is based on EBCDIC, while the PC uses ASCII. By using the equation, the string "ABC" on the host yields 70 (MOD(193+194+195)/256)), while the string on the PC yields 198 (MOD(65+66+67)/256)). The solution is to provide a translate table on one end. In this case, the host is chosen to provide a table of the ASCII values because of the efficient use of translate tables in the System/370 assembler instruction set. The next problem is to select characters which are consistently translated from ASCII to EBCDIC and from EBCDIC to ASCII by the host's asynchronous control unit (EP or NCP/NTO). These characters are A-Z, a-z, 0-9, period, comma, open and close parenthesis, question mark and percent sign. The translate table contains the ASCII value...