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Hardware Scheme for the Support of Transmission Control Protocol and International Standards Organization Checksum Calculations

IP.com Disclosure Number: IPCOM000113957D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Branstad, MW: AUTHOR [+5]

Abstract

A hardware scheme for calculating the Transmission Control Protocol/Internet Protocol (TCP/IP) and ISO-TP4 checksums on communication protocol's data is disclosed. The hardware will read the data, calculate both the TCP/IP and ISO-TP4 checksum, and put the results in two registers.

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Hardware Scheme for the Support of Transmission Control Protocol
and International Standards Organization Checksum Calculations

      A hardware scheme for calculating the Transmission Control
Protocol/Internet Protocol (TCP/IP) and ISO-TP4 checksums on
communication protocol's data is disclosed.  The hardware will read
the data, calculate both the TCP/IP and ISO-TP4 checksum, and put the
results in two registers.

      To calculate a checksum, every bit in a data packet is read and
a non-trivial calculation is performed on each bit.

      The TCP/IP checksum is a simple sum of 16 bit quantities with
the carry-out folded back into the result.

      The ISO-TP4 checksum is more complicated.  The data is modified
such that the 8-bit sum (with end-around-carry) is equal to zero.  It
is also modified such that if each 8-bit byte is added to an
accumulator with end-around-carry that is shifted by 1 bit before
each addition, the accumulator will equal zero (either X'00'  or
X'FF').

      Two registers, one for each checksum, contain the actual
checksum values after the calculations have completed.