Browse Prior Art Database

Memory - to - Memory Data Integrity for Systems with Communications Adapters

IP.com Disclosure Number: IPCOM000113016D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Christensen, KJ: AUTHOR [+2]

Abstract

Disclosed is a method to provide memory-to-memory data integrity for systems with communications adapters. Existing methods provide only adapter-to-adapter data integrity for data transferred across a communication medium (e.g., a LAN). To insure memory-to-memory data integrity, the Frame Check Sequence (FCS) field of a frame is checked three times -- when the frame is transmitted, when the frame is received, and after the frame is stored in system memory. Thus, the disclosed method extends FCS protection to include data transfer across the system buses of both the transmitting and receiving systems.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Memory - to - Memory Data Integrity for Systems with Communications
Adapters

      Disclosed is a method to provide memory-to-memory data
integrity for systems with communications adapters.  Existing methods
provide only adapter-to-adapter data integrity for data transferred
across a communication medium (e.g., a LAN).  To insure
memory-to-memory data integrity, the Frame Check Sequence (FCS) field
of a frame is checked three times -- when the frame is transmitted,
when the frame is received, and after the frame is stored in system
memory.  Thus, the disclosed method extends FCS protection to include
data transfer across the system buses of both the transmitting and
receiving systems.

      The Figure shows a system with an attached communications
adapter.  Data transmitted or received via the communications adapter
is transferred across the system bus from or to system memory.  Data
on the communications medium is protected by an FCS field included in
every data frame.  This FCS field is generated by the transmitting
adapter and checked by the receiving adapter.  Any data errors that
occur on the medium are detectable at the receiving adapter.  Data on
the bus is protected only on a word basis (e.g., with a parity bit
for every byte).  Thus, the problem is that data words that are lost
or duplicated during the system bus data transfers cannot be
detected.

      The solution to this problem is to check the FCS value (for
each frame) three times.  The FCS value is computed when the frame
passes through the adapters (transmitting and receiving) and after
the received frame is stored in system memory.  If the checked FCS
values are not the same, data corruption has occurred and the frame
should be discarded.  A discarded frame can be recovered by
higher-layer communications protocols.  Calculating the FCS value in
software is unacceptable due to the number of system CPU cycles that
would be needed.  Therefore, a hardware solution is the desired
embodiment.

      A hardware solution consists of using the existing FCS hardware
in the transmit channel of the communications adapter.  A "channel"
is a system bus interface point for transferring data between the
adapter and bus.  T...